Showing 1–40 of 40 results for author: Chudaykin, A

One-point matter PDFs beyond TopHat filters

Authors: Anton Chudaykin, Alexander M. Kayssi, Sergey Sibiryakov

Abstract: We study the one-point probability distribution function (PDF) for matter densities averaged with an arbitrary spherically symmetric window function. The PDF is analytically modeled within the path integral framework, enabling a non-perturbative description of large-scale structure. It contains a leading order contribution controlled by the spherically symmetric gravitational collapse dynamics, as… ▽ More We study the one-point probability distribution function (PDF) for matter densities averaged with an arbitrary spherically symmetric window function. The PDF is analytically modeled within the path integral framework, enabling a non-perturbative description of large-scale structure. It contains a leading order contribution controlled by the spherically symmetric gravitational collapse dynamics, as well as an order-one factor arising from aspherical fluctuations. We develop a numerical pipeline to compute the leading spherical-collapse part of the PDF and apply it to a family of window functions interpolating between the TopHat and Gaussian filters in coordinate space, as well as to a window function with non-monotonic radial dependence. We find that the PDF weakly depends on the choice of the filter, provided the width of the filter is normalized to yield a fixed linear averaged density variance. For each filter and each value of the averaged density, our pipeline gives the most probable density profile. We find that these profiles vastly differ for different filters in the case of overdensities, but closely follow a universal curve at underdensities. We obtain a perturbative expression for the aspherical part of the PDF valid at small density contrasts. We find from it that all PDFs are equally sensitive to the effective field theory (EFT) corrections accounting for short-scale clustering, regardless of how smooth the filter's boundary is. We test our PDF model against the results of high-resolution N-body simulations. The agreement is excellent for filters with widths larger than 10 Mpc/h. Small discrepancies at a few percent level arise for narrower filters and are interpreted as higher-order perturbative corrections. △ Less

Submitted 20 August, 2026; originally announced August 2026.

Comments: 54 pages, 19 figures

Inflation, Open Universes, and Dark Energy

Authors: Anton Chudaykin, Mikhail M. Ivanov, Renata Kallosh, Andrei Linde, Oliver H. E. Philcox, Yusuke Yamada

Abstract: We study the impact of spatial curvature ($Ω_k$) and dynamical dark energy (parametrized by $w_0$ and $w_a$) on the spectral index $n_s$ using a combination of cosmic microwave background datasets (Planck, SPT, and ACT), and spectroscopic galaxy samples from DESI, including both BAO and full-shape clustering measurements. We show that a small negative curvature, $Ω_k\simeq 3\times 10^{-3}$, lowers… ▽ More We study the impact of spatial curvature ($Ω_k$) and dynamical dark energy (parametrized by $w_0$ and $w_a$) on the spectral index $n_s$ using a combination of cosmic microwave background datasets (Planck, SPT, and ACT), and spectroscopic galaxy samples from DESI, including both BAO and full-shape clustering measurements. We show that a small negative curvature, $Ω_k\simeq 3\times 10^{-3}$, lowers the value of $n_s$, bringing it closer to predictions of the Starobinsky, Higgs, and simplest $α$-attractor inflationary models. In particular, we find $n_s= 0.9667\pm0.0041$ (using Planck and DESI data) or $n_s= 0.9692\pm0.0035$ (adding ACT and SPT). Allowing for time-evolving dark energy also reduces the spectral index, leading to $n_s=0.9716\pm0.0032$ (from the combined dataset), or $n_s=0.9694\pm0.0035$ in combination with a small negative curvature. Our results demonstrate that the tension between current observational data and the Starobinsky, Higgs, and simplest $α$-attractor models holds only for $Λ$CDM, and can be mitigated in extended cosmological models. We discuss implications of these findings for inflationary models in an open universe and/or with dynamical dark energy, including scenarios with quantum tunneling and non-standard topology. Furthermore, we briefly describe a special class of $α$-attractor models, where one can make $n_s$ arbitrarily large, and we describe the $α$-attractor quintessence model. Such models may be of particular relevance when future data from DESI, as well as DESI-II, SPHEREx, Euclid, Rubin, and Roman, becomes available. △ Less

Submitted 30 July, 2026; originally announced July 2026.

Comments: 29 pages, 5 figures, 2 tables;

Report number: MIT-CTP/6076

Inflationary interpretation of the gravitational-wave signal in the European Pulsar Timing Array DR2 with constraints

Authors: Philippe Turgeon, Chiara Caprini, Anton Chudaykin, Martin Kunz, Delphine Perrodin, Ismael Cognard, Lucas Guillemot, Gilles Theureau

Abstract: The second data release of the European Pulsar Timing Array (EPTA) collaboration provides evidence for the presence of a gravitational-wave (GW) background. In this work, we explore a potential cosmological interpretation of this signal in terms of inflationary scenarios. We parametrize the tensor power spectrum in terms of the tensor-to-scalar ratio $r$, the tensor spectral index $n_t$, the rehea… ▽ More The second data release of the European Pulsar Timing Array (EPTA) collaboration provides evidence for the presence of a gravitational-wave (GW) background. In this work, we explore a potential cosmological interpretation of this signal in terms of inflationary scenarios. We parametrize the tensor power spectrum in terms of the tensor-to-scalar ratio $r$, the tensor spectral index $n_t$, the reheating temperature $T_{\text{rh}}$, and the cut-off frequency $f_{\text{end}}$. We incorporate all relevant observational constraints, including those from the Cosmic Microwave Background, Big Bang Nucleosynthesis, and LIGO-Virgo-KAGRA observations. We demonstrate that imposing these constraints consistently reduces the region of parameter space that provides a viable interpretation of the EPTA signal, to $-11.66 \lesssim \log_{10}r \lesssim -1.45$, $1.32 \lesssim n_t \lesssim 2.47$, $1.78\text{ MeV} \lesssim T_{\text{rh}} \lesssim 28.2\text{ GeV}$, and $75.86\text{ nHz} \lesssim f_{\text{end}} \lesssim 14.45\text{ Hz}$ at the 95% confidence level. This favours the scenario in which the GW spectrum in the EPTA frequency band originates from tensor modes that re-entered the Hubble radius during the radiation-dominated era, allowing for a higher $r$ and a flatter spectrum. However, $T_{\text{rh}}$ must take very low values, which are challenging to explain theoretically. △ Less

Submitted 8 June, 2026; originally announced June 2026.

Euclid preparation: Testing multi-field inflation with galaxy power spectrum and bispectrum

Authors: Euclid Collaboration, D. Linde, A. Moradinezhad Dizgah, G. Parimbelli, K. Pardede, E. Sefusatti, M. S. Cagliari, G. D'Amico, V. Desjacques, A. Eggemeier, M. Biagetti, A. Veropalumbo, B. Camacho Quevedo, A. Chudaykin, M. Crocce, L. Castiblanco, E. Castorina, A. Farina, M. Guidi, M. Karcher, A. Pezzotta, A. Pugno, B. Altieri, S. Andreon, N. Auricchio , et al. (259 additional authors not shown)

Abstract: Primordial non-Gaussianity (PNG) is a powerful probe of the origin of cosmic structure. Stage-IV surveys like \Euclid will measure galaxy $2$- and $3$-point clustering at high signal-to-noise, whose exploitation requires robust joint analysis. We prepare for Euclid's spectroscopic sample by validating a redshift-space power-spectrum and bispectrum pipeline (one-loop $P_\ell$, tree-level $B_\ell$)… ▽ More Primordial non-Gaussianity (PNG) is a powerful probe of the origin of cosmic structure. Stage-IV surveys like \Euclid will measure galaxy $2$- and $3$-point clustering at high signal-to-noise, whose exploitation requires robust joint analysis. We prepare for Euclid's spectroscopic sample by validating a redshift-space power-spectrum and bispectrum pipeline (one-loop $P_\ell$, tree-level $B_\ell$) on Euclid-like mocks from Abacus-PNG $N$-body simulations with Gaussian and local-PNG initial conditions, using a halo occupation distribution (HOD) tuned to Euclid Flagship 2. We stress-test analysis choices -- PNG-bias parametrisation, priors, and scale cuts -- and perform null tests without PNG. In a `prior-agnostic setup', detection of the dominant PNG term $\propto f_{\rm NL} \, b_φ$ in single redshift bins is difficult; nevertheless, the bispectrum provides constraints on other PNG combinations that partially lift degeneracies. We propose a physically motivated prior on $b_φ$ that yields unbiased $f_{\rm NL}$ while accounting for theory uncertainty, and determine scale cuts that give unbiased $Λ$CDM and $f_{\rm NL}$. With $V_{\rm eff}=16\,h^{-3}\,{\rm Gpc}^3$ across four snapshots ($0.8\le z\le1.7$), our likelihood analyses recover $<1σ$ bias in $f_{\rm NL}$ and $Λ$CDM. At fixed cuts, $B_\ell$ alone reduces $σ({f_{\rm NL}})$ by $\sim29$--$46\%$ relative to $P_\ell$, and joint power spectrum-bispectrum analysis tightens a further $\sim8$--$13\%$; the cumulative gain from $z=0.8$ to $1.7$ is $\sim2.3$ for the joint case. The bispectrum quadrupole is key. Our strongest results are at $z=1.7$: $1.9σ$ for $f_{\rm NL} \, b_φ$ (prior-agnostic) and $2.35σ$ for $f_{\rm NL}$ (prior-based). Joint analyses thus offer strong prospects for testing multi-field inflation, pending end-to-end validation in the full Euclid geometry with observational systematics. △ Less

Submitted 20 May, 2026; originally announced May 2026.

Late-time reconstruction of non-minimally coupled gravity with a smoothness prior

Authors: Gen Ye, Anton Chudaykin, Camille Bonvin, Martin Kunz

Abstract: We present a non-parametric, model-independent reconstruction of the cosmological background and perturbation dynamics in non-minimally coupled theories of gravity. Within the Effective Field Theory of dark energy framework, we reconstruct the time-dependent cosmological constant, $Λ(t)$, and the non-minimal coupling function, $Ω(t)$, from cosmological data. To ensure stability, we apply a correla… ▽ More We present a non-parametric, model-independent reconstruction of the cosmological background and perturbation dynamics in non-minimally coupled theories of gravity. Within the Effective Field Theory of dark energy framework, we reconstruct the time-dependent cosmological constant, $Λ(t)$, and the non-minimal coupling function, $Ω(t)$, from cosmological data. To ensure stability, we apply a correlated smoothness prior that restricts the reconstruction to the space of sufficiently smooth functions. Using CMB, DESI BAO, Type Ia supernovae, CMB-ISW lensing cross-correlations, and large-scale 3x2pt DES Year 3 data, we find a $2.8σ$ hint for a non-minimal coupling. For the dark energy equation of state, our results indicate a preference for the existence of crossing of the phantom divide, $w_{DE}=-1$, at $z<0.8$. The non-minimal coupling effect stabilizes dark energy perturbations, providing a viable physical interpretation of the phantom crossing scenario. Our work paves the way for model-agnostic searches for signatures of modified gravity in cosmological data. △ Less

Submitted 12 May, 2026; originally announced May 2026.

Comments: 15 pages, 8 figures

Euclid preparation. Galaxy power spectrum and bispectrum modelling

Authors: Euclid Collaboration, K. Pardede, A. Eggemeier, D. Alkhanishvili, E. Sefusatti, A. Moradinezhad Dizgah, L. Christoph, A. Chudaykin, M. Kärcher, D. Linde, M. Marinucci, C. Porciani, A. Veropalumbo, M. Crocce, M. S. Cagliari, B. Camacho Quevedo, L. Castiblanco, E. Castorina, G. D'Amico, V. Desjacques, A. Farina, G. Gambardella, M. Guidi, F. Janssen, J. Lesgourgues , et al. (284 additional authors not shown)

Abstract: Higher-order correlation functions of the large-scale galaxy distribution offer access to information beyond that contained in standard 2-point statistics such as the power spectrum. In this work we assess this potential for the $\textit{Euclid}$ mission using synthetic catalogues of H$α$ galaxies based on the 54 $\, h^{-3} \, {\rm Gpc}^3$ Flagship I simulation, designed to reproduce the… ▽ More Higher-order correlation functions of the large-scale galaxy distribution offer access to information beyond that contained in standard 2-point statistics such as the power spectrum. In this work we assess this potential for the $\textit{Euclid}$ mission using synthetic catalogues of H$α$ galaxies based on the 54 $\, h^{-3} \, {\rm Gpc}^3$ Flagship I simulation, designed to reproduce the $\textit{Euclid}$ spectroscopic sample. We comprehensively validate the one-loop galaxy power spectrum and tree-level bispectrum predictions from perturbation theory in both real and redshift space. Assuming scale cuts consistent with our previous power spectrum study on the same catalogues, this modelling yields unbiased cosmological constraints for the bispectrum up to $k_{\rm max} = 0.15\,\, h \, {\rm Mpc}^{-1}$ in real space and $0.08 \, (0.1)\,\, h \, {\rm Mpc}^{-1}$ at the lowest (highest) redshift, corresponding to $z=0.9$ ($z=1.8$), for the monopole and quadrupole in redshift space using statistical uncertainties corresponding to the full simulation volume. With these scale cuts, adding bispectrum information to the power spectrum improves constraints on the amplitude of scalar perturbations and the matter density by up to 30 %, increasing the overall figure of merit for key cosmological parameters by a factor of about 2.5. Similar conclusions hold when statistical uncertainties are rescaled to a $\textit{Euclid}$-like volume, highlighting the importance of the bispectrum for fully exploiting the forthcoming $\textit{Euclid}$ data. Our analysis also provides the first detailed characterisation of the nonlinear bias model of H$α$ emitters, showing that bias relations calibrated on low-resolution \textit{N}-body simulations do not adequately describe the clustering of H$α$ galaxies at low redshift, whereas excursion-set and co-evolution relations for tidal biases remain accurate. △ Less

Submitted 10 April, 2026; v1 submitted 29 March, 2026; originally announced March 2026.

Comments: 16+2 pages, 11 figures, 4+1 tables, abstract abridged for arXiv submission

Reanalyzing DESI DR1: 5. Cosmological Constraints with Simulation-Based Priors

Authors: Anton Chudaykin, Mikhail M. Ivanov, Oliver H. E. Philcox

Abstract: We analyze the public DESI full-shape clustering data using simulation-based priors (SBPs). Our priors are obtained by fitting normalizing flows to the distribution of EFT parameters measured from field-level simulations, themselves generated using tailored halo occupation distribution (HOD) models for each tracer. Incorporating SBPs in a power spectrum analysis significantly enhances $Λ$CDM cosmo… ▽ More We analyze the public DESI full-shape clustering data using simulation-based priors (SBPs). Our priors are obtained by fitting normalizing flows to the distribution of EFT parameters measured from field-level simulations, themselves generated using tailored halo occupation distribution (HOD) models for each tracer. Incorporating SBPs in a power spectrum analysis significantly enhances $Λ$CDM cosmological parameter constraints; in combination with BAO information from DESI DR2 and a BBN prior on the baryon density, we find the matter density parameter $Ω_m=0.2987\pm0.0066$, the Hubble constant $H_0=68.80\pm0.35\,\rm{km}\,\rm{s}^{-1}\rm{Mpc}^{-1}$, and the mass fluctuation amplitude $σ_8 = 0.766\pm0.015$ (or the lensing parameter $S_8=0.764\pm0.018$), which are $1\%$, $40\%$ and $50\%$ stronger than the baseline results, though with a notable downwards shift in $σ_8$, driven by the quasar HOD assumptions. The SBPs also have a significant impact in extended models, with the dark energy figure-of-merit improving by $70\%$ ($20\%$) in a $w_0w_a$CDM analysis when combining with the CMB (and supernovae). In the SBP analysis, we do not find statistically significant evidence for dynamical dark energy: the equation of state parameters are consistent with a cosmological constant within $2.2σ$ ($1.4σ$) in analyses without (with) supernovae. The neutrino mass constraints are also enhanced, with the $95\%$ limits $M_ν<0.073\,\rm{eV}$ and $M_ν<0.090\,\rm{eV}$ in $Λ$CDM and $w_0w_a$CDM respectively. The latter is the strongest constraint obtained to date and reinforces the preference for the normal neutrino mass hierarchy, regardless of the background dynamics. While our results are sensitive to HOD modeling assumptions, they clearly demonstrate that the inclusion of small-scale information can significantly sharpen cosmological parameter constraints. △ Less

Submitted 18 July, 2026; v1 submitted 20 February, 2026; originally announced February 2026.

Comments: 24+2 pages, 8+1 figures, 9+1 tables; v2: added Appendix D exploring the sensitivity of the results to quasar priors; added a comparison with previous analyses; matched the version accepted by Phys. Rev. D

Report number: MIT-CTP/6007

Euclid preparation. Galaxy power spectrum modelling in redshift space

Authors: Euclid Collaboration, B. Camacho Quevedo, M. Crocce, M. Pellejero Ibañez, R. E. Angulo, A. Pezzotta, A. Eggemeier, G. Gambardella, C. Moretti, E. Sefusatti, A. Moradinezhad Dizgah, E. Gaztanaga, M. Zennaro, M. -A. Breton, A. Chudaykin, G. D'Amico, V. Desjacques, S. de la Torre, P. Fosalba, M. Guidi, M. Kärcher, K. Pardede, C. Porciani, A. Pugno, J. Salvalaggio , et al. (270 additional authors not shown)

Abstract: Accurate modelling of redshift-space distortions (RSD) is essential for maximizing the cosmological information extracted from large galaxy redshift surveys. In preparation for the forthcoming analysis of the Euclid spectroscopic data, we investigate three approaches to modelling RSD effects on the power spectrum multipoles of mock H$α$ emission line galaxies. We focus on two one-loop perturbation… ▽ More Accurate modelling of redshift-space distortions (RSD) is essential for maximizing the cosmological information extracted from large galaxy redshift surveys. In preparation for the forthcoming analysis of the Euclid spectroscopic data, we investigate three approaches to modelling RSD effects on the power spectrum multipoles of mock H$α$ emission line galaxies. We focus on two one-loop perturbation theory models -- the effective field theory (EFT) and velocity difference generator (${\rm VDG_ \infty}$) -- which differ in their treatment of the real-to-redshift space mapping on small scales, and a third approach, the BACCO emulator, which adopts a hybrid strategy combining perturbation theory with high-resolution N-body simulations. We assess the ability of these models to recover key cosmological parameters, including the expansion rate $h$, the cold dark matter density parameter $ω_{\rm c}$, and the scalar amplitude $A_{\rm s}$, across four redshift bins spanning $0.9 \leq z \leq 1.8$. In each bin, we find that ${\rm VDG_ \infty}$ and BACCO outperform the EFT model across all scales up to $k_{max} \lesssim 0.35 h\,Mpc^{-1} $. While BACCO saturates in constraining power at intermediate scales and higher redshift, the ${\rm VDG_ \infty}$ model continues to improve parameter constraints beyond $k_{max} \gtrsim 0.30 h\,Mpc^{-1}$. The EFT model, although robust on large scales, exhibits significant parameter biases for $k_{max} \gtrsim 0.25 h\,Mpc^{-1}$, limiting its applicability to Euclid-like H$α$ samples. Among the full perturbation theory-based models, the enhanced treatment of small-scale RSD effects in ${\rm VDG_ \infty}$ improves cosmological parameter constraints by up to a factor of two. △ Less

Submitted 9 March, 2026; v1 submitted 28 January, 2026; originally announced January 2026.

Comments: 14 pages,9 figures

Reanalyzing DESI DR1: 4. Percent-Level Cosmological Constraints from Combined Probes and Robust Evidence for the Normal Neutrino Mass Hierarchy

Authors: Mikhail M. Ivanov, James M. Sullivan, Roger de Belsunce, Shi-Fan Chen, Anton Chudaykin, Mark Maus, Oliver H. E. Philcox

Abstract: We present cosmological parameter measurements from the full combination of DESI DR1 galaxy clustering data, described with large-scale structure effective field theory. By incorporating photometric galaxies and CMB lensing cross-correlations, and extending the bispectrum likelihood to smaller scales with a consistent one-loop computation, we achieve substantial gains in constraining power. Combin… ▽ More We present cosmological parameter measurements from the full combination of DESI DR1 galaxy clustering data, described with large-scale structure effective field theory. By incorporating photometric galaxies and CMB lensing cross-correlations, and extending the bispectrum likelihood to smaller scales with a consistent one-loop computation, we achieve substantial gains in constraining power. Combined with the latest DESI baryon acoustic oscillation (BAO) data and cosmic microwave background (CMB) priors on the spectral tilt and baryon density, we find, in $Λ$CDM, $H_0=69.08\pm 0.37~\mathrm{km}\,\mathrm{s}^{-1}\mathrm{Mpc}^{-1}$, $Ω_m=0.2974\pm 0.0050$, and $σ_8 = 0.838\pm 0.017$ ($S_8 = σ_8\sqrt{Ω_m/0.3} =0.834\pm 0.018$). Adding the Pantheon+ supernovae (SNe), we find a $2.2σ$ preference for the $w_0w_a$ dynamical dark energy model from low-redshift data alone, rising to $2.7σ$ when exchanging the SNe for \textit{Planck} CMB data. Combining the full-shape, BAO, CMB, and SNe likelihoods improves the dark energy figure-of-merit by $15\%$ and bounds the neutrino mass sum to $M_ν<0.049$ eV ($Λ$CDM) and $M_ν<0.077$ eV ($w_0w_a$CDM) at 95\% CL. This is the strongest $w_0w_a$CDM bound to date, $37\%$ tighter than from the background expansion data alone. The preference for the normal neutrino mass ordering thus holds regardless of the background model: the inverted hierarchy is disfavored at ${\approx}\,3.5σ$ in $Λ$CDM and ${\approx}\,2.4σ$ in $w_0w_a$CDM, with the latter constraint free of the geometric tension between CMB and BAO that is known to sharpen the $Λ$CDM bound. △ Less

Submitted 22 July, 2026; v1 submitted 22 January, 2026; originally announced January 2026.

Comments: v2: 40 pages, 4 tables, 5 figures, results improved after a minor bug fix in one-loop B2, full 3x2pt photo-z and gk-kk spec-z CMB lensing analyses added

Report number: MIT-CTP/5993

Euclid preparation. Galaxy 2-point correlation function modelling in redshift space

Authors: Euclid Collaboration, M. Kärcher, M. -A. Breton, S. de la Torre, A. Veropalumbo, A. Eggemeier, M. Crocce, E. Sefusatti, E. Sarpa, R. E. Angulo, B. Camacho Quevedo, L. Castiblanco, E. Castorina, A. Chudaykin, V. Desjacques, A. Farina, G. Gambardella, M. Guidi, D. Linde, F. Marulli, A. Moradinezhad Dizgah, M. Moresco, C. Moretti, K. Pardede, A. Pezzotta , et al. (287 additional authors not shown)

Abstract: The Euclid satellite will measure spectroscopic redshifts for tens of millions of emission-line galaxies. In the context of Stage-IV surveys, the 3-dimensional clustering of galaxies plays a key role in providing cosmological constraints. In this paper, we conduct a model comparison for the multipole moments of the galaxy 2-point correlation function (2PCF) in redshift space. We test state-of-the-… ▽ More The Euclid satellite will measure spectroscopic redshifts for tens of millions of emission-line galaxies. In the context of Stage-IV surveys, the 3-dimensional clustering of galaxies plays a key role in providing cosmological constraints. In this paper, we conduct a model comparison for the multipole moments of the galaxy 2-point correlation function (2PCF) in redshift space. We test state-of-the-art models, in particular the effective field theory of large-scale structure (EFT), one based on the velocity difference generating function (VDG$_{\infty}$), and different variants of Lagrangian perturbation theory (LPT) models, such as convolutional LPT (CLPT) and its effective-field-theory extension (CLEFT). We analyse the first three even multipoles of the 2PCF in the Flagship 1 simulation, which consists of four snapshots at $z\in\{0.9,1.2,1.5,1.8\}$. We study both template-fitting and full-shape approaches and find that with the template-fitting approach, only the VDG$_{\infty}$ model is able to reach a minimum fitting scale of $s_{\rm min}=20\,h^{-1}\,{\rm Mpc}$ at $z=0.9$ without biasing the recovered parameters. Indeed, the EFT model becomes inaccurate already at $s_{\rm min}=30\,h^{-1}\,{\rm Mpc}$. Conversely, in the full-shape analysis, the CLEFT and VDG$_{\infty}$ models perform similarly well, but only the CLEFT model can reach $s_{\rm min}=20\,h^{-1}\,{\rm Mpc}$ while the VDG$_{\infty}$ model is unbiased down to $s_{\rm min}=25\,h^{-1}\,{\rm Mpc}$ at the lowest redshift. Overall, in order to achieve the accuracy required by Euclid, non-perturbative modelling such as in the VDG$_{\infty}$ or CLEFT models should be considered. At $z=1.8$, the CLPT model is sufficient to describe the data with high figure of merit. This comparison selects baseline models that perform best in ideal conditions and sets the stage for an optimal analysis of Euclid data in configuration space. △ Less

Submitted 8 January, 2026; originally announced January 2026.

Comments: 29 pages, 13 figures, abstract abridged for arxiv submission

Reanalyzing DESI DR1: 3. Constraints on Inflation from Galaxy Power Spectra & Bispectra

Authors: Anton Chudaykin, Mikhail M. Ivanov, Oliver H. E. Philcox

Abstract: Models of cosmic inflation generically predict a weak but potentially detectable amount of primordial non-Gaussianity (PNG), which can be used to obtain insights into the degrees of freedom during inflation and their interactions. The simplest types of PNG are the local and non-local (equilateral and orthogonal) shapes of the primordial three-point correlators, which are predicted by models with m… ▽ More Models of cosmic inflation generically predict a weak but potentially detectable amount of primordial non-Gaussianity (PNG), which can be used to obtain insights into the degrees of freedom during inflation and their interactions. The simplest types of PNG are the local and non-local (equilateral and orthogonal) shapes of the primordial three-point correlators, which are predicted by models with multiple light fields and derivative interactions in single-field inflation, respectively. In this paper we place constraints on local, equilateral, and orthogonal non-Gaussianities using the power spectrum and bispectrum extracted from first public release of the Dark Energy Spectroscopic Instrument (DESI). Our analysis makes use of higher-order clustering information through a consistent effective field theory (EFT) model for both the power spectrum and bispectrum at one-loop order. Using robust scale cuts where the EFT description is valid, we find the following constraints on PNG amplitudes: $f^{\rm loc}_{\rm NL}=-0.1\pm 7.4$, $f^{\rm equil}_{\rm NL}=719\pm 390$, $f^{\rm orth}_{\rm NL}=-200\pm 100$ (at $68\%$ CL). Non-local PNG constraints can be further improved by combining high-redshift DESI with legacy BOSS data and using simulation-based priors on bias parameters, yielding the strongest large-scale structure constraints to date $f^{\rm equil}_{\rm NL}=200\pm 230$, $f^{\rm orth}_{\rm NL}=-24\pm 86$. Our constraint on $f^{\rm loc}_{\rm NL}$ is competitive with the cosmic microwave background (CMB) limit; the combination gives $f^{\rm loc}_{\rm NL}=-0.0\pm 4.1$, $18\%$ stronger than the CMB only result, which represents the strongest bound on multi-field inflation yet obtained. △ Less

Submitted 3 December, 2025; originally announced December 2025.

Comments: 15 pages, 5 figures, 1 table

Report number: MIT-CTP/5971

Reanalyzing DESI DR1: 2. Constraints on Dark Energy, Spatial Curvature, and Neutrino Masses

Authors: Anton Chudaykin, Mikhail M. Ivanov, Oliver H. E. Philcox

Abstract: We carry out an independent re-analysis of the Dark Energy Spectroscopic Instrument (DESI) public dataset, focusing on extensions to the standard cosmological model, $Λ$CDM. Utilizing the dataset and Effective Field Theory (EFT)-based pipeline described in Paper 1, we constrain cosmological models with massive neutrinos ($Λ$CDM+$M_ν$), spatial curvature ($oΛ$CDM), dynamical dark energy ($w_0w_a$CD… ▽ More We carry out an independent re-analysis of the Dark Energy Spectroscopic Instrument (DESI) public dataset, focusing on extensions to the standard cosmological model, $Λ$CDM. Utilizing the dataset and Effective Field Theory (EFT)-based pipeline described in Paper 1, we constrain cosmological models with massive neutrinos ($Λ$CDM+$M_ν$), spatial curvature ($oΛ$CDM), dynamical dark energy ($w_0w_a$CDM), and their combinations using the power spectrum and bispectrum of DESI galaxies and quasars. Our work also presents the first measurements of relevant non-minimal cosmological parameters from the combination of cosmic microwave background (CMB) and DESI full-shape (FS) data, which are made possible thanks to carefully chosen priors on EFT parameters. We find that the addition the FS likelihood to DESI's baryon acoustic oscillation (BAO) data improves the limits on the spatial curvature by a factor of two over the BAO only results, though the improvements are less significant with the CMB data. The dark energy equation of state figure-of-merit increases both with and without the supernovae data (SNe), by $\approx30\%$ and $\approx20\%$ relative to the CMB+BAO and CMB+BAO+SNe results, respectively. Our FS likelihood also yields the strongest CMB-independent constraint on the total neutrino mass $M_ν<0.32\,{\rm eV}$, with the $30\%$ improvement due to the bispectrum. In combination with the CMB, we find a $14\%$ improvement assuming the $Λ$CDM+$M_ν$ model (yielding $M_ν<0.059\,{\rm eV}$), but this increases to $22\%$ when using non-minimal backgrounds: $M_ν<0.097\,{\rm eV}$ in $oΛ$CDM+$M_ν$ and $M_ν<0.13\,{\rm eV}$ in $w_0w_a$CDM+$M_ν$. Overall, our work illustrates that robust and substantial gains in constraining power can be obtained by incorporating the FS power spectrum and bispectrum measurements in analyses of non-minimal cosmological models. △ Less

Submitted 14 April, 2026; v1 submitted 25 November, 2025; originally announced November 2025.

Comments: 19+2 pages, 6+1 figures, 10 tables; v2: added discussion of the sensitivity of full-shape observables in the extended models; included tension metrics for individual analyses; matched the version accepted by Phys. Rev. D

Report number: MIT-CTP/5960

Reanalyzing DESI DR1: 1. $Λ$CDM Constraints from the Power Spectrum and Bispectrum

Authors: Anton Chudaykin, Mikhail M. Ivanov, Oliver H. E. Philcox

Abstract: We present the first independent re-analysis of the galaxy clustering data from DESI Data Release 1, utilizing an effective field theory full-shape model. We analyze the power spectra and bispectra of the public catalogs using a custom-built pipeline based on window-deconvolved quasi-optimal estimators, accounting for a number of systematic effects. Compared to the official collaboration analysis,… ▽ More We present the first independent re-analysis of the galaxy clustering data from DESI Data Release 1, utilizing an effective field theory full-shape model. We analyze the power spectra and bispectra of the public catalogs using a custom-built pipeline based on window-deconvolved quasi-optimal estimators, accounting for a number of systematic effects. Compared to the official collaboration analysis, we add the galaxy power spectrum hexadecapole and the bispectrum monopole, and also introduce a novel stochastic estimator for fiber collisions, which facilitates robust bispectrum analyses. As a first application, we perform a full-shape analysis of the DESI power spectra and bispectra in the context of the standard cosmological model, $Λ$CDM. Using external priors on the physical baryon density and the primordial power spectrum tilt, we constrain the matter density fraction to $Ω_m=0.284\pm 0.011$, the Hubble constant to $H_0=70.7\pm 1.1$ km/s/Mpc, and the mass fluctuation amplitude to $σ_8=0.811\pm 0.030$. The bispectrum sharpens constraints on $σ_8$ and $Ω_m$ by $\approx 10\%$ and shifts $Ω_m$ by $\approx 1σ$ towards the \textit{Planck} $Λ$CDM value. Combining our full-shape likelihood with the official DESI DR2 BAO measurements, cosmological parameters shift further towards the \textit{Planck} values, with $Ω_m=0.296\pm 0.007$, $H_0=68.8\pm 0.6$ km/s/Mpc, $σ_8=0.818\pm 0.029$ (with tighter constraints obtained in joint analyses). Similar results are obtained in a joint analysis with DR1 BAO, accounting for the cross-covariance. Finally, the bispectrum data improves measurements of quadratic bias parameters, which are consistent with predictions from halo occupation distribution models. Our work highlights the importance of higher-order statistics and sets the stage for upcoming full-shape analyses of non-minimal cosmological models. △ Less

Submitted 14 January, 2026; v1 submitted 17 July, 2025; originally announced July 2025.

Comments: 38+5 pages, 13+2 figures, 6+3 tables; v2: Two appendices added. Appendix C presents a joint analysis of DESI DR1 full-shape and DR2 BAO data, approximately accounting for the full-shape-BAO cross-correlation. Appendix D introduces a joint DR1-only full-shape and BAO analysis using an analytic cross-covariance. Matched the version accepted by Phys. Rev. D

Report number: MIT-CPT/5890

One-loop kernels in scale-dependent Horndeski theory

Authors: Ziyang Zheng, Hanqiong Jia, Bilal Tüdes, Anton Chudaykin, Martin Kunz, Luca Amendola

Abstract: We investigate the nonlinear evolution of cosmological perturbations in theories with scale-dependent perturbation growth, first in general and then focusing on Horndeski gravity. Within the framework of standard perturbation theory, we derive the second- and third-order kernels and show that they are fully determined by two effective functions, \( h_1 \) and \( h_c \), which parametrize deviation… ▽ More We investigate the nonlinear evolution of cosmological perturbations in theories with scale-dependent perturbation growth, first in general and then focusing on Horndeski gravity. Within the framework of standard perturbation theory, we derive the second- and third-order kernels and show that they are fully determined by two effective functions, \( h_1 \) and \( h_c \), which parametrize deviations from general relativity. Using the Wronskian method, we obtain solutions for the nonlinear growth functions and present explicit expressions for the resulting kernels, including bias and redshift space distortions, valid in the limit in which the $k$-dependent part is subdominant. We show that the kernels are entirely dependent on the linear growing mode: once this is calculated, the kernels are analytic up to a time integral. We also include redshift-space distortions (RSD) and scale-dependent bias. Our approach provides a physically motivated framework for evaluating the one-loop galaxy power spectrum in scale-dependent theories, suitable for the forecasts and actual data analysis. △ Less

Submitted 7 November, 2025; v1 submitted 22 May, 2025; originally announced May 2025.

Comments: 40 pages, 2 figures, version 2; Version accepted for publication in JCAP

The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics

Authors: Eleonora Di Valentino, Jackson Levi Said, Adam Riess, Agnieszka Pollo, Vivian Poulin, Adrià Gómez-Valent, Amanda Weltman, Antonella Palmese, Caroline D. Huang, Carsten van de Bruck, Chandra Shekhar Saraf, Cheng-Yu Kuo, Cora Uhlemann, Daniela Grandón, Dante Paz, Dominique Eckert, Elsa M. Teixeira, Emmanuel N. Saridakis, Eoin Ó Colgáin, Florian Beutler, Florian Niedermann, Francesco Bajardi, Gabriela Barenboim, Giulia Gubitosi, Ilaria Musella , et al. (516 additional authors not shown)

Abstract: The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-t… ▽ More The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. [Abridged] △ Less

Submitted 4 August, 2025; v1 submitted 2 April, 2025; originally announced April 2025.

Comments: 416 pages, 81 figures

Journal ref: Phys. Dark Univ. 49 (2025) 101965

Modified gravity constraints with Planck ISW-lensing bispectrum

Authors: Anton Chudaykin, Martin Kunz, Julien Carron

Abstract: We present updated constraints on modified gravity by including the Integrated Sachs-Wolfe (ISW) effect from CMB lensing-CMB temperature cross-correlations, based on the latest Planck PR4 maps. Utilizing the Effective Field Theory of dark energy approach and adopting the $w_0w_a$CDM background cosmological model, we find that including the CMB ISW lensing cross-correlations tighten constraints on… ▽ More We present updated constraints on modified gravity by including the Integrated Sachs-Wolfe (ISW) effect from CMB lensing-CMB temperature cross-correlations, based on the latest Planck PR4 maps. Utilizing the Effective Field Theory of dark energy approach and adopting the $w_0w_a$CDM background cosmological model, we find that including the CMB ISW lensing cross-correlations tighten constraints on the modified gravity parameters by approximately $20\%$, reducing the viable parameter space by $40-80\%$. We derive constraints from Planck CMB, Planck and ACT CMB lensing, DESI DR1 BAO, CMB ISW-lensing, and type Ia supernovae (SN Ia) data. The constraints on the EFT parameters controlling the kinetic braiding and non-minimal coupling are consistent with General Relativity (GR) at the $95\%$ CL. In particular, we obtain a bound on the kinetic braiding parameter, $c_B < 1.2$ at $95\%$ CL. In the $w_0$-$w_a$ parameter space, our results imply a crossing of the phantom divide, $w=-1$. The modified gravity model shows a mild preference over $Λ$CDM at the $1.8σ$, $2.6σ$ and $3.2σ$ levels for the combinations with Pantheon+, Union3 and DESY5 supernova datasets. We find that using the latest $\texttt{HiLLiPoP}+\texttt{LoLLiPoP}$ likelihoods alleviates the departure of modified gravity parameters from the GR-values compared to results using {\it Planck} 2018 data. This paper underlines the importance of the ISW lensing probe in constraining late-time modifications of gravity. △ Less

Submitted 15 October, 2025; v1 submitted 12 March, 2025; originally announced March 2025.

Comments: 12+1 pages, 5 figures, 3 tables; v2: minor corrections, results unchanged; v3: matched version accepted by Phys. Rev. D

Lyman Alpha Forest - Halo Cross-Correlations in Effective Field Theory

Authors: Anton Chudaykin, Mikhail M. Ivanov

Abstract: We provide a perturbative effective field theory (EFT) description for anisotropic (redshift-space) correlations between the Lyman alpha forest and a generic biased tracer of matter, which could be represented by quasars, high-redshift galaxies, or dark matter halos. We compute one-loop EFT power spectrum predictions for the combined analysis of the Lyman alpha and biased tracers' data and test th… ▽ More We provide a perturbative effective field theory (EFT) description for anisotropic (redshift-space) correlations between the Lyman alpha forest and a generic biased tracer of matter, which could be represented by quasars, high-redshift galaxies, or dark matter halos. We compute one-loop EFT power spectrum predictions for the combined analysis of the Lyman alpha and biased tracers' data and test them on the publicly available high fidelity Sherwood simulations. We use massive and light dark matter halos at redshift $z=2.8$ as proxies for quasars and high-redshift galaxies, respectively. In both cases, we demonstrate that our EFT model can consistently describe the complete data vector consisting of the Lyman alpha forest auto spectrum, the halo auto spectrum, and the Lyman alpha -- halo cross spectrum. We show that the addition of cross-correlations significantly sharpens constraints on EFT parameters of the Lyman alpha forest and halos. In the combined analysis, our EFT model fits the simulated cross-spectra with a percent level accuracy at $k_{\rm max}= 1~h$Mpc$^{-1}$, which represents a significant improvement over previous analytical models. Thus, our work provides precision theoretical tools for full-shape analyses of Lyman alpha - quasar cross-correlations with ongoing and upcoming spectroscopic surveys. △ Less

Submitted 22 January, 2025; v1 submitted 8 January, 2025; originally announced January 2025.

Comments: 24 pages, 13 figures, 2 tables; v2: minor corrections, main results and conclusions unchanged

Report number: MIT-CTP/5825

On priors and scale cuts in EFT-based full-shape analyses

Authors: Anton Chudaykin, Mikhail M. Ivanov, Takahiro Nishimichi

Abstract: Parameter estimation from galaxy survey data from the full-shape method depends on scale cuts and priors on EFT parameters. The effects of priors, including the so-called ''prior volume'' phenomenon have been originally studied in Ivanov et al. (2019) and subsequent works. In this note, we repeat and extend these tests and also apply them to other priors used in the literature. We point out that i… ▽ More Parameter estimation from galaxy survey data from the full-shape method depends on scale cuts and priors on EFT parameters. The effects of priors, including the so-called ''prior volume'' phenomenon have been originally studied in Ivanov et al. (2019) and subsequent works. In this note, we repeat and extend these tests and also apply them to other priors used in the literature. We point out that in addition to the ''prior volume'' effect there is a more dangerous effect that is largely overlooked: a systematic bias on cosmological parameters due to overoptimistic scale cuts. Unlike the ''prior volume'' effect, this is a genuine systematic bias due to two-loop corrections that does not vanish with better priors or with larger data volumes. Our study is based on the high fidelity BOSS-like PT Challenge simulation data which offer many advantages over analyses based on synthetic data generated with fitting pipelines. We show that some analysis choices associated with the PyBird code, especially the scale cuts, significantly bias parameter recovery, overestimating $σ_8$ by over $5\%$ (equivalent to $1σ$). The bias on measured EFT parameters is even more significant. In contrast, the analysis choices associated with the CLASS-PT code lead to much smaller ($\lesssim 1\%$) shifts in cosmological parameters based on their best-fit values. △ Less

Submitted 10 December, 2025; v1 submitted 21 October, 2024; originally announced October 2024.

Comments: 14+3 pages, 3+1 figures, 2+1 tables; v2: extended discussion of EFT modeling choices, added a conclusion highlighting the main findings of our work

Modified gravity interpretation of the evolving dark energy in light of DESI data

Authors: Anton Chudaykin, Martin Kunz

Abstract: The Dark Energy Spectroscopic Instrument (DESI) collaboration has recently released measurements of baryon acoustic oscillation (BAO) from the first year of observations. A joint analysis of DESI BAO, CMB, and SN Ia probes indicates a preference for time-evolving dark energy. We evaluate the robustness of this preference by replacing the DESI distance measurements at $z<0.8$ with the SDSS BAO meas… ▽ More The Dark Energy Spectroscopic Instrument (DESI) collaboration has recently released measurements of baryon acoustic oscillation (BAO) from the first year of observations. A joint analysis of DESI BAO, CMB, and SN Ia probes indicates a preference for time-evolving dark energy. We evaluate the robustness of this preference by replacing the DESI distance measurements at $z<0.8$ with the SDSS BAO measurements in a similar redshift range. Assuming the $w_0w_a$CDM model, we find an evolution of the dark energy equation of state parameters consistent with $Λ$CDM. Our analysis of $χ^2$ statistics across various BAO datasets shows that DESI's preference for evolving dark energy is primarily driven by the two LRG samples at $z_{\rm eff}=0.51$ and $z_{\rm eff}=0.71$, with the latter having the most significant impact. Taking this preference seriously, we study a general Horndeski scalar-tensor theory, which provides a physical mechanism to safely cross the phantom divide, $w=-1$. Utilizing the Effective Field Theory of dark energy and adopting the $w_0w_a$CDM background cosmological model, we derive constraints on the parameters $w_0=-0.856\pm0.062$ and $w_a=-0.53_{-0.26}^{+0.28}$ at $68\%$ CL from Planck CMB, Planck and ACT CMB lensing, DESI BAO, and Pantheon+ datasets, showing good consistency with the standard $w_0w_a$CDM model. The modified gravity model gives results discrepant with $Λ$CDM at the $2.4σ$ level, while for $w_0w_a$CDM it is at $2.5σ$, based on the best-fit $χ^2$ values. We conclude that modified gravity offers a viable physical explanation for DESI's preference for evolving dark energy. △ Less

Submitted 28 November, 2024; v1 submitted 2 July, 2024; originally announced July 2024.

Comments: 10+1 pages, 5 figures, 3 tables; v2: model selection analyses added, matched version accepted by Phys. Rev. D

Renormalizing one-point probability distribution function for cosmological counts in cells

Authors: Anton Chudaykin, Mikhail M. Ivanov, Sergey Sibiryakov

Abstract: We study the one-point probability distribution function (PDF) for matter density averaged over spherical cells. The leading part to the PDF is defined by spherical collapse dynamics, whereas the next-to-leading part comes from the integration over fluctuations around the saddle-point solution. The latter calculation receives sizable contributions from short modes and must be renormalized. We prop… ▽ More We study the one-point probability distribution function (PDF) for matter density averaged over spherical cells. The leading part to the PDF is defined by spherical collapse dynamics, whereas the next-to-leading part comes from the integration over fluctuations around the saddle-point solution. The latter calculation receives sizable contributions from short modes and must be renormalized. We propose a new approach to renormalization by modeling the effective stress-energy tensor for short perturbations. The model contains three free parameters. Two of them are related to the counterterms in the one-loop matter power spectrum and bispectrum, one more parameterizes their redshift dependence. This relation can be used to impose priors in fitting the model to the PDF data. We confront the model with the results of high-resolution N-body simulations and find excellent agreement for cell radii $r_*\geq 10\,{\rm Mpc}/h$ at all redshifts down to $z=0$. Discrepancies at a few per cent level are detected at low redshifts for $r_*\leq 10\,{\rm Mpc}/h$ and are associated with two-loop corrections to the model. △ Less

Submitted 7 August, 2023; v1 submitted 19 December, 2022; originally announced December 2022.

Comments: v2: 39 pages main text+appendices, 25 figures, 7 tables. Structure rearranged, comparison with previous works added, main results unchanged. Accepted for publication in JCAP

Report number: INR-TH-2022-028

Cosmological constraints from the power spectrum of eBOSS quasars

Authors: Anton Chudaykin, Mikhail M. Ivanov

Abstract: We present the effective-field theory (EFT)-based cosmological full-shape analysis of the anisotropic power spectrum of eBOSS quasars at the effective redshift $z_{\rm eff}=1.48$. We perform extensive tests of our pipeline on simulations, paying a particular attention to the modeling of observational systematics, such as redshift smearing, fiber collisions, and the radial integral constraint. Assu… ▽ More We present the effective-field theory (EFT)-based cosmological full-shape analysis of the anisotropic power spectrum of eBOSS quasars at the effective redshift $z_{\rm eff}=1.48$. We perform extensive tests of our pipeline on simulations, paying a particular attention to the modeling of observational systematics, such as redshift smearing, fiber collisions, and the radial integral constraint. Assuming the minimal $Λ$CDM model, and fixing the primordial power spectrum tilt and the physical baryon density, we find the Hubble constant $H_0=(66.7\pm 3.2)~$km~s$^{-1}$Mpc$^{-1}$, the matter density fraction $Ω_m=0.32\pm 0.03$, and the late-time mass fluctuation amplitude $σ_8=0.95\pm 0.08$. These measurements are fully consistent with the Planck cosmic microwave background results. Our eBOSS quasar $S_8$ posterior, $0.98\pm0.11$, does not exhibit the so-called $S_8$ tension. Our work paves the way for systematic full-shape analyses of quasar samples from future surveys like DESI. △ Less

Submitted 6 February, 2023; v1 submitted 30 October, 2022; originally announced October 2022.

Comments: 19+2 pages, 13 figures, 6+2 tables; v2: Appendix F added, matched version accepted by Phys. Rev. D

Precision cosmology from large-scale structure of the Universe

Authors: A. Chudaykin

Abstract: Large scale structure of the Universe becomes a leading source of precision cosmological information. We present two particular tools that can be used in cosmological analyses of the redshift space galaxy clustering data: a new open-source code CLASS-PT and the theoretical error approach. CLASS-PT computes one-loop power auto- and cross-power spectra for matter fields and biased tracers in real an… ▽ More Large scale structure of the Universe becomes a leading source of precision cosmological information. We present two particular tools that can be used in cosmological analyses of the redshift space galaxy clustering data: a new open-source code CLASS-PT and the theoretical error approach. CLASS-PT computes one-loop power auto- and cross-power spectra for matter fields and biased tracers in real and redshift spaces. We show that the code meets the precision standards set by the upcoming high-precision large-scale structure surveys. The theoretical error likelihood approach allows one to analyze galaxy clustering data without having to measure the scale cut $k_{\rm max}$. This approach takes into account that theoretical uncertainties affect parameter estimation gradually, which helps optimize data analysis and ensures that all available cosmological information is extracted. △ Less

Submitted 13 April, 2022; originally announced April 2022.

Comments: 4 pages, 2 figures, 1 table. Contribution to the 2022 Cosmology session of the 56th Rencontres de Moriond

Cosmology Intertwined: A Review of the Particle Physics, Astrophysics, and Cosmology Associated with the Cosmological Tensions and Anomalies

Authors: Elcio Abdalla, Guillermo Franco Abellán, Amin Aboubrahim, Adriano Agnello, Ozgur Akarsu, Yashar Akrami, George Alestas, Daniel Aloni, Luca Amendola, Luis A. Anchordoqui, Richard I. Anderson, Nikki Arendse, Marika Asgari, Mario Ballardini, Vernon Barger, Spyros Basilakos, Ronaldo C. Batista, Elia S. Battistelli, Richard Battye, Micol Benetti, David Benisty, Asher Berlin, Paolo de Bernardis, Emanuele Berti, Bohdan Bidenko , et al. (178 additional authors not shown)

Abstract: In this paper we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant $H_0$, the $σ_8$--$S_8$ tension, and other less statistically significant anomalies. While these discordances can still be in part the result of system… ▽ More In this paper we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant $H_0$, the $σ_8$--$S_8$ tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the $5.0\,σ$ tension between the {\it Planck} CMB estimate of the Hubble constant $H_0$ and the SH0ES collaboration measurements. After showing the $H_0$ evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade's experiments will be crucial. Moreover, we focus on the tension of the {\it Planck} CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density $Ω_m$, and the amplitude or rate of the growth of structure ($σ_8,fσ_8$). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the $H_0$--$S_8$ tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals.[Abridged] △ Less

Submitted 24 April, 2022; v1 submitted 11 March, 2022; originally announced March 2022.

Comments: Contribution to Snowmass 2021. 224 pages, 27 figures. Accepted for publication in JHEAp

Journal ref: J. High En. Astrophys. 2204, 002 (2022)

Exploring $Λ$CDM extensions with SPT-3G and Planck data: 4$σ$ evidence for neutrino masses and implications of extended dark energy models for cosmological tensions

Authors: Anton Chudaykin, Dmitry Gorbunov, Nikita Nedelko

Abstract: We present new cosmological constraints in a set of motivated extensions of the $Λ$CDM model using the polarization and gravitational lensing measurements from the South Pole Telescope and the Planck CMB temperature observations at large angular scales. In all cosmological scenarios, this CMB data brings the clustering measurements into agreement with the low-redshift probes of large-scale structu… ▽ More We present new cosmological constraints in a set of motivated extensions of the $Λ$CDM model using the polarization and gravitational lensing measurements from the South Pole Telescope and the Planck CMB temperature observations at large angular scales. In all cosmological scenarios, this CMB data brings the clustering measurements into agreement with the low-redshift probes of large-scale structure. Combining the SPT-3G, SPTpol and Planck large-scale temperature data with the latest full-shape BOSS and BAO measurements, information from the weak lensing and photometric galaxy clustering, and Pantheon supernova set we find a $4σ$ evidence for nonzero neutrino mass, $\sum m_ν=0.22\pm0.06\,{\rm eV}$.Breaking the CMB degeneracies between $\sum m_ν$ and the cosmological parameters by the BOSS data is a major contribution to our neutrino mass measurement. The future CMB data would allow for investigating this measurement. Then we explore the possibility of dynamical dark energy with two model-independent approaches: one introduces a phantom crossing in dark energy equation of state, another provides with a sharp transition in the dark energy evolution. For the combination of all data considered, the both models predict $H_0\simeq68\,{\rm km\,s^{-1}Mpc^{-1}}$ being in a $\sim3σ$ tension with the SH0ES constraint. However, when the local Type Ia supernovae are calibrated by Cepheids, the late Universe scenarios suggest significantly higher values of $H_0$ consistent with SH0ES. Our work draws attention to the supernova absolute magnitude calibration as one of the issues on the way to reconcile the $H_0$ tension. △ Less

Submitted 13 April, 2023; v1 submitted 7 March, 2022; originally announced March 2022.

Comments: 39+2+24 pages, 10+8 figures, 6+11 tables. SPT-3G likelihood for montepython environment is available at http://github.com/ksardase/SPT3G-montepython. v2: minor corrections, Bayesian analysis included. v3: major revision, supernova data is included

Exploring Early Dark Energy solution to the Hubble tension with Planck and SPTPol data

Authors: Anton Chudaykin, Dmitry Gorbunov, Nikita Nedelko

Abstract: A promising idea to resolve the long standing Hubble tension is to postulate a new subdominant dark-energy-like component in the pre-recombination Universe which is traditionally termed as the Early Dark Energy (EDE). However, as shown in Refs. \cite{Hill:2020osr,Ivanov:2020ril} the cosmic microwave background (CMB) and large-scale structure (LSS) data impose tight constraints on this proposal. He… ▽ More A promising idea to resolve the long standing Hubble tension is to postulate a new subdominant dark-energy-like component in the pre-recombination Universe which is traditionally termed as the Early Dark Energy (EDE). However, as shown in Refs. \cite{Hill:2020osr,Ivanov:2020ril} the cosmic microwave background (CMB) and large-scale structure (LSS) data impose tight constraints on this proposal. Here, we revisit these strong bounds considering the Planck CMB temperature anisotropy data at large angular scales and the SPTPol polarization and lensing measurements. As advocated in Ref. \cite{Chudaykin:2020acu}, this combined data approach predicts the CMB lensing effect consistent with the $Λ$CDM expectation and allows one to efficiently probe both large and small angular scales. Combining Planck and SPTPol CMB data with the full-shape BOSS likelihood and information from photometric LSS surveys in the EDE analysis we found for the Hubble constant $H_0=69.79\pm0.99\,{\rm km\,s^{-1}Mpc^{-1}}$ and for the EDE fraction $f_{\rm EDE}<0.094\,(2σ)$. These bounds obtained without including a local distance ladder measurement of $H_0$ (SH0ES) alleviate the Hubble tension to a $2.5σ$ level. Including further the SH0ES data we obtain $H_0=71.81\pm1.19\,{\rm km\,s^{-1}Mpc^{-1}}$ and $f_{\rm EDE}=0.088\pm0.034$ in full accordance with SH0ES. We also found that a higher value of $H_0$ does not significantly deteriorate the fit to the LSS data. Overall, the EDE scenario is (though weakly) favoured over $Λ$CDM even after accounting for unconstrained directions in the cosmological parameter space. We conclude that the large-scale Planck temperature and SPTPol polarization measurements along with LSS data do not rule out the EDE model as a resolution of the Hubble tension. This paper underlines the importance of the CMB lensing effect for robust constraints on the EDE scenario. △ Less

Submitted 13 February, 2021; v1 submitted 9 November, 2020; originally announced November 2020.

Comments: 14+3 pages, 2+1 figures, 4 tables; v2: Appendix A added, matched version accepted by Phys. Rev. D

Report number: INR-TH-2020-041

Journal ref: Phys. Rev. D 103, 043529 (2021)

Optimizing large-scale structure data analysis with the theoretical error likelihood

Authors: Anton Chudaykin, Mikhail M. Ivanov, Marko Simonović

Abstract: An important aspect of large-scale structure data analysis is the presence of non-negligible theoretical uncertainties, which become increasingly important on small scales. We show how to incorporate these uncertainties in realistic power spectrum likelihoods by an appropriate change of the fitting model and the covariance matrix. The inclusion of the theoretical error has several advantages over… ▽ More An important aspect of large-scale structure data analysis is the presence of non-negligible theoretical uncertainties, which become increasingly important on small scales. We show how to incorporate these uncertainties in realistic power spectrum likelihoods by an appropriate change of the fitting model and the covariance matrix. The inclusion of the theoretical error has several advantages over the standard practice of using the sharp momentum cut $k_{\rm max}$. First, the theoretical error covariance gradually suppresses the information from the short scales as the employed theoretical model becomes less reliable. This allows one to avoid laborious measurements of $k_{\rm max}$, which is an essential part of the standard methods. Second, the theoretical error likelihood gives unbiased constrains with reliable error bars that are not artificially shrunk due to over-fitting. In realistic settings, the theoretical error likelihood yields essentially the same parameter constraints as the standard analysis with an appropriately selected $k_{\rm max}$, thereby effectively optimizing the choice of $k_{\rm max}$. We demonstrate these points using the large-volume N-body data for the clustering of matter and galaxies in real and redshift space. In passing, we validate the effective field theory description of the redshift space distortions and show that the use of the one-parameter phenomenological Gaussian damping model for fingers-of-God causes significant biases in parameter recovery. △ Less

Submitted 13 February, 2021; v1 submitted 22 September, 2020; originally announced September 2020.

Comments: 41+11 pages, 17+4 figures, 5+5 tables; v2: Appendix C added, practical realization of our approach clarified, matched version accepted by Phys. Rev. D

Report number: INR-TH-2020-040, CERN-TH-2020-154

Journal ref: Phys. Rev. D 103, 043525 (2021)

Constraints on the curvature of the Universe and dynamical dark energy from the Full-shape and BAO data

Authors: Anton Chudaykin, Konstantin Dolgikh, Mikhail M. Ivanov

Abstract: We present limits on the parameters of the o$Λ$CDM, $w_0$CDM, and $w_0 w_a$CDM models obtained from the joint analysis of the full-shape, baryon acoustic oscillations (BAO), big bang nucleosynthesis (BBN) and supernovae data. Our limits are fully independent of the data on the cosmic microwave background (CMB) anisotropies, but rival the CMB constraints in terms of parameter error bars. We find th… ▽ More We present limits on the parameters of the o$Λ$CDM, $w_0$CDM, and $w_0 w_a$CDM models obtained from the joint analysis of the full-shape, baryon acoustic oscillations (BAO), big bang nucleosynthesis (BBN) and supernovae data. Our limits are fully independent of the data on the cosmic microwave background (CMB) anisotropies, but rival the CMB constraints in terms of parameter error bars. We find the spatial curvature consistent with a flat universe $Ω_k=-0.043_{-0.036}^{+0.036}$ ($68\%$ C.L.); the dark-energy equation of state parameter $w_0$ is measured to be $w_0=-1.031_{-0.048}^{+0.052}$ ($68\%$ C.L.), consistent with a cosmological constant. This conclusion also holds for the time-varying dark energy equation of state, for which we find $w_0=-0.98_{-0.11}^{+0.099}$ and $w_a=-0.33_{-0.48}^{+0.63}$ (both at $68\%$ C.L.). The exclusion of the supernovae data from the analysis does not significantly weaken our bounds. This shows that using a single external BBN prior, the full-shape and BAO data can provide strong CMB-independent constraints on the non-minimal cosmological models. △ Less

Submitted 13 February, 2021; v1 submitted 21 September, 2020; originally announced September 2020.

Comments: 20+5 pages, 8+3 figures, 4+1 tables; v2: measurements of the sound horizon added; v3: joint analysis with Planck added (Appendix B), matched version published in Phys. Rev. D

Report number: INR-TH-2020-041

Journal ref: Phys. Rev. D 103, 023507 (2021)

Cosmology Intertwined IV: The Age of the Universe and its Curvature

Authors: Eleonora Di Valentino, Luis A. Anchordoqui, Ozgur Akarsu, Yacine Ali-Haimoud, Luca Amendola, Nikki Arendse, Marika Asgari, Mario Ballardini, Spyros Basilakos, Elia Battistelli, Micol Benetti, Simon Birrer, François R. Bouchet, Marco Bruni, Erminia Calabrese, David Camarena, Salvatore Capozziello, Angela Chen, Jens Chluba, Anton Chudaykin, Eoin Ó Colgáin, Francis-Yan Cyr-Racine, Paolo de Bernardis, Javier de Cruz Pérez, Jacques Delabrouille , et al. (66 additional authors not shown)

Abstract: A precise measurement of the curvature of the Universe is of primeval importance for cosmology since it could not only confirm the paradigm of primordial inflation but also help in discriminating between different early Universe scenarios. The recent observations, while broadly consistent with a spatially flat standard $Λ$ Cold Dark Matter ($Λ$CDM) model, are showing tensions that still allow (and… ▽ More A precise measurement of the curvature of the Universe is of primeval importance for cosmology since it could not only confirm the paradigm of primordial inflation but also help in discriminating between different early Universe scenarios. The recent observations, while broadly consistent with a spatially flat standard $Λ$ Cold Dark Matter ($Λ$CDM) model, are showing tensions that still allow (and, in some cases, even suggest) a few percent deviations from a flat universe. In particular, the Planck Cosmic Microwave Background power spectra, assuming the nominal likelihood, prefer a closed universe at more than 99\% confidence level. While new physics could be in action, this anomaly may be the result of an unresolved systematic error or just a statistical fluctuation. However, since a positive curvature allows a larger age of the Universe, an accurate determination of the age of the oldest objects provides a smoking gun in confirming or falsifying the current flat $Λ$CDM model. △ Less

Submitted 13 October, 2020; v1 submitted 25 August, 2020; originally announced August 2020.

Comments: Snowmass2021 - Letter of Interest

Journal ref: Astropart. Phys. 131, 102607 (2021)

Cosmology Intertwined III: $f σ_8$ and $S_8$

Authors: Eleonora Di Valentino, Luis A. Anchordoqui, Ozgur Akarsu, Yacine Ali-Haimoud, Luca Amendola, Nikki Arendse, Marika Asgari, Mario Ballardini, Spyros Basilakos, Elia Battistelli, Micol Benetti, Simon Birrer, François R. Bouchet, Marco Bruni, Erminia Calabrese, David Camarena, Salvatore Capozziello, Angela Chen, Jens Chluba, Anton Chudaykin, Eoin Ó Colgáin, Francis-Yan Cyr-Racine, Paolo de Bernardis, Javier de Cruz Pérez, Jacques Delabrouille , et al. (67 additional authors not shown)

Abstract: The standard $Λ$ Cold Dark Matter cosmological model provides a wonderful fit to current cosmological data, but a few tensions and anomalies became statistically significant with the latest data analyses. While these anomalies could be due to the presence of systematic errors in the experiments, they could also indicate the need for new physics beyond the standard model. In this Letter of Interest… ▽ More The standard $Λ$ Cold Dark Matter cosmological model provides a wonderful fit to current cosmological data, but a few tensions and anomalies became statistically significant with the latest data analyses. While these anomalies could be due to the presence of systematic errors in the experiments, they could also indicate the need for new physics beyond the standard model. In this Letter of Interest we focus on the tension of the Planck data with weak lensing measurements and redshift surveys, about the value of the matter energy density $Ω_m$, and the amplitude or rate of the growth of structure ($σ_8,fσ_8$). We list a few interesting models for solving this tension, and we discuss the importance of trying to fit with a single model a full array of data and not just one parameter at a time. △ Less

Submitted 13 October, 2020; v1 submitted 25 August, 2020; originally announced August 2020.

Comments: Snowmass2021 - Letter of Interest

Journal ref: Astropart. Phys. 131, 102604 (2021)

Cosmology Intertwined II: The Hubble Constant Tension

Authors: Eleonora Di Valentino, Luis A. Anchordoqui, Ozgur Akarsu, Yacine Ali-Haimoud, Luca Amendola, Nikki Arendse, Marika Asgari, Mario Ballardini, Spyros Basilakos, Elia Battistelli, Micol Benetti, Simon Birrer, François R. Bouchet, Marco Bruni, Erminia Calabrese, David Camarena, Salvatore Capozziello, Angela Chen, Jens Chluba, Anton Chudaykin, Eoin Ó Colgáin, Francis-Yan Cyr-Racine, Paolo de Bernardis, Javier de Cruz Pérez, Jacques Delabrouille , et al. (68 additional authors not shown)

Abstract: The current cosmological probes have provided a fantastic confirmation of the standard $Λ$ Cold Dark Matter cosmological model, that has been constrained with unprecedented accuracy. However, with the increase of the experimental sensitivity a few statistically significant tensions between different independent cosmological datasets emerged. While these tensions can be in portion the result of sys… ▽ More The current cosmological probes have provided a fantastic confirmation of the standard $Λ$ Cold Dark Matter cosmological model, that has been constrained with unprecedented accuracy. However, with the increase of the experimental sensitivity a few statistically significant tensions between different independent cosmological datasets emerged. While these tensions can be in portion the result of systematic errors, the persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the need for new physics. In this Letter of Interest we will focus on the $4.4σ$ tension between the Planck estimate of the Hubble constant $H_0$ and the SH0ES collaboration measurements. After showing the $H_0$ evaluations made from different teams using different methods and geometric calibrations, we will list a few interesting new physics models that could solve this tension and discuss how the next decade experiments will be crucial. △ Less

Submitted 13 October, 2020; v1 submitted 25 August, 2020; originally announced August 2020.

Comments: Snowmass2021 - Letter of Interest

Journal ref: Astropart. Phys. 131, 102605 (2021)

Cosmology Intertwined I: Perspectives for the Next Decade

Authors: Eleonora Di Valentino, Luis A. Anchordoqui, Ozgur Akarsu, Yacine Ali-Haimoud, Luca Amendola, Nikki Arendse, Marika Asgari, Mario Ballardini, Spyros Basilakos, Elia Battistelli, Micol Benetti, Simon Birrer, François R. Bouchet, Marco Bruni, Erminia Calabrese, David Camarena, Salvatore Capozziello, Angela Chen, Jens Chluba, Anton Chudaykin, Eoin Ó Colgáin, Francis-Yan Cyr-Racine, Paolo de Bernardis, Javier de Cruz Pérez, Jacques Delabrouille , et al. (67 additional authors not shown)

Abstract: The standard $Λ$ Cold Dark Matter cosmological model provides an amazing description of a wide range of astrophysical and astronomical data. However, there are a few big open questions, that make the standard model look like a first-order approximation to a more realistic scenario that still needs to be fully understood. In this Letter of Interest we will list a few important goals that need to be… ▽ More The standard $Λ$ Cold Dark Matter cosmological model provides an amazing description of a wide range of astrophysical and astronomical data. However, there are a few big open questions, that make the standard model look like a first-order approximation to a more realistic scenario that still needs to be fully understood. In this Letter of Interest we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances present between the different cosmological probes, as the Hubble constant $H_0$ value, the $σ_8 - S_8$ tension, and the anomalies present in the Planck results. Finally, we will give an overview of upgraded experiments and next-generation space-missions and facilities on Earth, that will be of crucial importance to address all these questions. △ Less

Submitted 13 October, 2020; v1 submitted 25 August, 2020; originally announced August 2020.

Comments: Snowmass2021 - Letter of Interest

Journal ref: Astropart. Phys. 131, 102606 (2021)

Combined analysis of Planck and SPTPol data favors the early dark energy models

Authors: Anton Chudaykin, Dmitry Gorbunov, Nikita Nedelko

Abstract: We study the implications of the Planck temperature power spectrum at low multipoles, $\ell<1000$, and SPTPol data. We show that this combination predicts consistent lensing-induced smoothing of acoustic peaks within $Λ$CDM cosmology and yields the robust predictions of the cosmological parameters. Combining only the Planck large-scale temperature data and the SPTPol polarization and lensing measu… ▽ More We study the implications of the Planck temperature power spectrum at low multipoles, $\ell<1000$, and SPTPol data. We show that this combination predicts consistent lensing-induced smoothing of acoustic peaks within $Λ$CDM cosmology and yields the robust predictions of the cosmological parameters. Combining only the Planck large-scale temperature data and the SPTPol polarization and lensing measurements within $Λ$CDM model we found substantially lower values of linear matter density perturbation $σ_8$ which bring the late-time parameter $S_8=σ_8\sqrt{Ω_m/0.3}=0.763\pm0.022$ into accordance with galaxy clustering and weak lensing measurements. It also raises up the Hubble constant $H_0=69.68\pm1.00{\rm \,\,km\,s^{-1}Mpc^{-1}}$ that reduces the Hubble tension to the $2.5σ$ level. We examine the residual tension in the Early Dark Energy (EDE) model which produces the brief energy injection prior to recombination. We implement both the background and perturbation evolutions of the scalar field which potential scales as $V(φ)\propto φ^{2n}$. Including cosmic shear measurements (KiDS, VIKING-450, DES) and local distance-ladder data (SH0ES) to the combined fit we found that EDE completely alleviates the Hubble tension while not degradating the fit to large-scale structure data. The EDE scenario significantly improves the goodness-of-fit by $2.9σ$ in comparison with the concordance $Λ$CDM model. The account for the intermediate-redshift data (the supernova dataset and baryon acoustic oscillation data) fits perfectly to our parameter predictions and indicates the preference of EDE over $Λ$CDM at $3σ$. △ Less

Submitted 13 July, 2020; v1 submitted 27 April, 2020; originally announced April 2020.

Comments: 28+6 pages, 6 figures, 3+3 tables. SPTPol likelihoods for montepython environment are available at https://github.com/ksardase/SPTPol-montepython. v2: major revision which includes chi2 analysis for each likelihood in LCDM and EDE fits, detailed comparison with previous works and various clarifications. The results are unchanged. v3: minor corrections, accepted in JCAP

Report number: INR-TH-2020-019

Non-linear perturbation theory extension of the Boltzmann code CLASS

Authors: Anton Chudaykin, Mikhail M. Ivanov, Oliver H. E. Philcox, Marko Simonović

Abstract: We present a new open-source code that calculates one-loop power auto- and cross-power spectra for matter fields and biased tracers in real and redshift space. These spectra incorporate all ingredients required for a direct application to data: non-linear bias, redshift-space distortions, infra-red resummation, counterterms, and the Alcock-Paczynski effect. Our code is based on the Boltzmann solve… ▽ More We present a new open-source code that calculates one-loop power auto- and cross-power spectra for matter fields and biased tracers in real and redshift space. These spectra incorporate all ingredients required for a direct application to data: non-linear bias, redshift-space distortions, infra-red resummation, counterterms, and the Alcock-Paczynski effect. Our code is based on the Boltzmann solver CLASS and inherits its advantage: user friendliness, ease of modification, high speed, and simple interface with other software. We present detailed descriptions of the theoretical model, the code structure, approximations, and accuracy tests. A typical end-to-end run for one cosmology takes $\sim 0.3$ seconds, which is sufficient for Markov Chain Monte Carlo parameter extraction. As an example, we apply the code to data from the Baryon Oscillation Spectroscopic Survey (BOSS) and infer cosmological parameters from the shape of the galaxy power spectrum. △ Less

Submitted 29 August, 2020; v1 submitted 22 April, 2020; originally announced April 2020.

Comments: v1: 48 pages, 9 figures. v2: 56 pages, 14 figures, minor edits, version to appear in PRD. The code and custom-built BOSS likelihoods are available at https://github.com/Michalychforever/CLASS-PT and https://github.com/Michalychforever/lss_montepython

Report number: INR-TH-2020-016, CERN-TH-2020-062

Journal ref: Phys. Rev. D 102, 063533 (2020)

Scalar induced resonant sterile neutrino production in the early Universe

Authors: F. Bezrukov, A. Chudaykin, D. Gorbunov

Abstract: It has been recently suggested \cite{Bezrukov:2017ike,Bezrukov:2018wvd} that a cosmic scalar field can completely change the keV-scale sterile neutrino production in the early Universe. Its effect may, for various parameter choices, either suppress sterile neutrino production and make moderate active-sterile mixing cosmologically acceptable, or increase the production and generate considerable dar… ▽ More It has been recently suggested \cite{Bezrukov:2017ike,Bezrukov:2018wvd} that a cosmic scalar field can completely change the keV-scale sterile neutrino production in the early Universe. Its effect may, for various parameter choices, either suppress sterile neutrino production and make moderate active-sterile mixing cosmologically acceptable, or increase the production and generate considerable dark matter component out of sterile neutrino with otherwise negligible mixing with SM. In this paper we provide analytic estimates complementing and providing details of the numerical calculations performed in \cite{Bezrukov:2018wvd} in the case of resonant amplification of the sterile neutrino production. We also discuss phenomenological and theoretical issues related to the successful implementation of this idea in fully realistic extensions of the Standard Model of particle physics. △ Less

Submitted 13 July, 2020; v1 submitted 19 November, 2019; originally announced November 2019.

Comments: v1: 29 pages, 6 figures. v2: a clear explanation of differences and improvements with respect to previous works is added, published version

Journal ref: Phys. Rev. D 101, 103516 (2020)

Measuring neutrino masses with large-scale structure: Euclid forecast with controlled theoretical error

Authors: Anton Chudaykin, Mikhail M. Ivanov

Abstract: We present a Markov-Chain Monte-Carlo (MCMC) forecast for the precision of neutrino mass and cosmological parameter measurements with a Euclid-like galaxy clustering survey. We use a complete perturbation theory model for the galaxy one-loop power spectrum and tree-level bispectrum, which includes bias, redshift space distortions, IR resummation for baryon acoustic oscillations and UV counterterms… ▽ More We present a Markov-Chain Monte-Carlo (MCMC) forecast for the precision of neutrino mass and cosmological parameter measurements with a Euclid-like galaxy clustering survey. We use a complete perturbation theory model for the galaxy one-loop power spectrum and tree-level bispectrum, which includes bias, redshift space distortions, IR resummation for baryon acoustic oscillations and UV counterterms. The latter encapsulate various effects of short-scale dynamics which cannot be modeled within perturbation theory. Our MCMC procedure consistently computes the non-linear power spectra and bispectra as we scan over different cosmologies. The second ingredient of our approach is the theoretical error covariance which captures uncertainties due to higher-order non-linear corrections omitted in our model. Having specified characteristics of a Euclid-like spectroscopic survey, we generate and fit mock galaxy power spectrum and bispectrum likelihoods. Our results suggest that even under very agnostic assumptions about non-linearities and short-scale physics a future Euclid-like survey will be able to measure the sum of neutrino masses with a standard deviation of 28 meV. When combined with the Planck cosmic microwave background likelihood, this uncertainty decreases to 13 meV. Over-optimistically reducing the theoretical error on the bispectrum down to the two-loop level marginally tightens this bound to 11 meV. Moreover, we show that the future large-scale structure (LSS) spectroscopic data will greatly improve constraints on the other cosmological parameters, e.g. reaching a percent (per mille) error on the Hubble constant with LSS alone (LSS + Planck). △ Less

Submitted 4 November, 2019; v1 submitted 15 July, 2019; originally announced July 2019.

Comments: v1: 50 pages, 5 figures. v2: 62 pages, 7 figures, appendices D, E and F are added, appendix C is complemented by a new analysis for the optimally reconstructed BAO

Report number: INR-TH-2019-014

Journal ref: JCAP11(2019)034

Induced resonance makes light sterile neutrino Dark Matter cool

Authors: F. Bezrukov, A. Chudaykin, D. Gorbunov

Abstract: We describe two new generation mechanisms for Dark Matter composed of sterile neutrinos with ${\cal O}(1)$ keV mass. The model contains a light scalar field which coherently oscillates in the early Universe and modulates the Majorana mass of the sterile neutrino. In a region of model parameter space, the oscillations between active and sterile neutrinos are resonantly enhanced. This mechanism allo… ▽ More We describe two new generation mechanisms for Dark Matter composed of sterile neutrinos with ${\cal O}(1)$ keV mass. The model contains a light scalar field which coherently oscillates in the early Universe and modulates the Majorana mass of the sterile neutrino. In a region of model parameter space, the oscillations between active and sterile neutrinos are resonantly enhanced. This mechanism allows us to produce sterile neutrino DM with small mixing angle with active neutrinos, thus evading the X-ray constraints. At the same time the spectrum of produced DM is much cooler, than in the case of ordinary oscillations in plasma, opening a window of lower mass DM, which is otherwise forbidden by structure formation considerations. In other regions of the model parameter space, where the resonance does not appear, another mechanism can operate: large field suppresses the active-sterile oscillations, but instead sterile neutrinos are produced by the oscillating scalar field when the effective fermion mass crosses zero. In this case DM component is cold, and even 1 keV neutrino is consistent with the cosmic structure formation. △ Less

Submitted 21 April, 2019; v1 submitted 24 September, 2018; originally announced September 2018.

Comments: 6 pages, 4 figures, PRD accepted version

Report number: INR-TH-2018-022

Journal ref: Phys. Rev. D 99, 083507 (2019)

Dark matter component decaying after recombination: Sensitivity to BAO and RSD probes

Authors: A. Chudaykin, D. Gorbunov, I. Tkachev

Abstract: It has been recently suggested~\cite{Berezhiani:2015yta} that a subdominant fraction of dark matter decaying after recombination may alleviate tension between high-redshift (CMB anisotropy) and low-redshift (Hubble constant, cluster counts) measurements. In this report, we continue our previous study~\cite{Chudaykin:2016yfk} of the decaying dark matter (DDM) model adding all available recent baryo… ▽ More It has been recently suggested~\cite{Berezhiani:2015yta} that a subdominant fraction of dark matter decaying after recombination may alleviate tension between high-redshift (CMB anisotropy) and low-redshift (Hubble constant, cluster counts) measurements. In this report, we continue our previous study~\cite{Chudaykin:2016yfk} of the decaying dark matter (DDM) model adding all available recent baryon acoustic oscillation (BAO) and redshift space distortions (RSD) measurements. We find, that the BAO/RSD measurements generically prefer the standard $Λ$CDM and combined with other cosmological measurements impose an upper limit on the DDM fraction at the level of $\sim$\,5\,\%, strengthening by a factor of 1.5 limits obtained in \cite{Chudaykin:2016yfk} mostly from CMB data. However, the numbers vary from one analysis to other based on the same Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12 (DR12) galaxy sample. Overall, the model with a few percent DDM fraction provides a better fit to the combined cosmological data as compared to the $Λ$CDM: the cluster counting and direct measurements of the Hubble parameter are responsible for that. The improvement can be as large as 1.5\,$σ$ and grows to 3.3\,$σ$ when the CMB lensing power amplitude ${\rm A_L}$ is introduced as a free fitting parameter. △ Less

Submitted 17 April, 2018; v1 submitted 17 November, 2017; originally announced November 2017.

Report number: INR-TH-2017-028

Journal ref: Phys. Rev. D 97, 083508 (2018)

Hiding an elephant: heavy sterile neutrino with large mixing angle does not contradict cosmology

Authors: F. Bezrukov, A. Chudaykin, D. Gorbunov

Abstract: We study a model of a keV-scale sterile neutrino with a relatively large mixing with the Standard Model sector. Usual considerations predict active generation of such particles in the early Universe, which leads to constraints from the total Dark Matter density and absence of X-ray signal from sterile neutrino decay. These bounds together may deem any attempt of creation of the keV scale sterile n… ▽ More We study a model of a keV-scale sterile neutrino with a relatively large mixing with the Standard Model sector. Usual considerations predict active generation of such particles in the early Universe, which leads to constraints from the total Dark Matter density and absence of X-ray signal from sterile neutrino decay. These bounds together may deem any attempt of creation of the keV scale sterile neutrino in the laboratory unfeasible. We argue that for models with a hidden sector coupled to the sterile neutrino these bounds can be evaded, opening new perspectives for the direct studies at neutrino experiments such as Troitsk $ν$-mass and KATRIN. We estimate the generation of sterile neutrinos in scenarios with the hidden sector dynamics keeping the sterile neutrinos either massless or superheavy in the early Universe. In both cases the generation by oscillations from active neutrinos in plasma is suppressed. △ Less

Submitted 3 April, 2019; v1 submitted 5 May, 2017; originally announced May 2017.

Comments: 14 pages, 5 figures, v3: corrected important typo in formula (4.3) and updated corresponding figure, without changes to the results of the paper

Report number: INR-TH-2017-013

Journal ref: JCAP 06, 051 (2017)

Dark matter component decaying after recombination: lensing constraints with Planck data

Authors: A. Chudaykin, D. Gorbunov, I. Tkachev

Abstract: It has been recently suggested~\cite{Berezhiani:2015yta} that emerging tension between cosmological parameter values derived in high-redshift (CMB anisotropy) and low-redshift (cluster counts, Hubble constant) measurements can be reconciled in a model which contains subdominant fraction of dark matter decaying after recombination. We check the model against the CMB Planck data. We find that lensin… ▽ More It has been recently suggested~\cite{Berezhiani:2015yta} that emerging tension between cosmological parameter values derived in high-redshift (CMB anisotropy) and low-redshift (cluster counts, Hubble constant) measurements can be reconciled in a model which contains subdominant fraction of dark matter decaying after recombination. We check the model against the CMB Planck data. We find that lensing of the CMB anisotropies by the large-scale structure gives strong extra constraints on this model, limiting the fraction as $F<8\%$ at 2\,$σ$ confidence level. However, investigating the combined data set of CMB and conflicting low-$z$ measurements, we obtain that the model with $F\approx2\!-\!5$\% exhibits better fit (by 1.5-3\,$σ$ depending on the lensing priors) compared to that of the concordance $Λ$CDM cosmological model. △ Less

Submitted 15 September, 2016; v1 submitted 25 February, 2016; originally announced February 2016.

Comments: 5 pages, 4 figures; v2: journal version, pages++, figures++

Report number: INR-TH/2016-006

Journal ref: Phys. Rev. D 94, 023528 (2016)

Cosmology based on $f(R)$ gravity with ${\cal O}(1)$ eV sterile neutrino

Authors: A. S. Chudaykin, D. S. Gorbunov, A. A. Starobinsky, R. A. Burenin

Abstract: We address the cosmological role of an additional ${\cal O}(1)$ eV sterile neutrino in modified gravity models. We confront the present cosmological data with predictions of the FLRW cosmological model based on a variant of $f(R)$ modified gravity proposed by one of the authors previously. This viable cosmological model which deviation from general relativity with a cosmological constant $Λ$ decre… ▽ More We address the cosmological role of an additional ${\cal O}(1)$ eV sterile neutrino in modified gravity models. We confront the present cosmological data with predictions of the FLRW cosmological model based on a variant of $f(R)$ modified gravity proposed by one of the authors previously. This viable cosmological model which deviation from general relativity with a cosmological constant $Λ$ decreases as $R^{-2n}$ for large, but not too large values of the Ricci scalar $R$ provides an alternative explanation of present dark energy and the accelerated expansion of the Universe. Various up-to-date cosmological data sets exploited include Planck CMB anisotropy, CMB lensing potential, BAO, cluster mass function and Hubble constant measurements. We find that the CMB+BAO constraints strongly the sum of neutrino masses from above. This excludes values $λ\sim 1$ for which distinctive cosmological features of the model are mostly pronounced as compared to the $Λ$CDM model, since then free streaming damping of perturbations due to neutrino rest masses is not sufficient to compensate their extra growth occurring in $f(R)$ gravity. Thus, we obtain $λ>8.2$ ($2σ$) with cluster systematics and $λ>9.4$ ($2σ$) without that. In the latter case we find for the sterile neutrino mass $0.47\,\,\rm{eV}$$\,<\,$$m_{ν,\,\rm{sterile}}$$\,<\,$$1\,\,\rm{eV}$ ($2σ$) assuming the active neutrinos are massless, not significantly larger than in the standard $Λ$CDM with the same data set: $0.45\,\,\rm{eV}$$\,<\,$$m_{ν,\,\rm{sterile}}$$\,<\,$$0.92\,\,\rm{eV}$ ($2σ$). However, a possible discovery of a sterile neutrino with the mass $m_{ν,\,\rm{sterile}} \approx 1.5\,$eV motivated by various anomalies in neutrino oscillation experiments would favor cosmology based on $f(R)$ gravity rather than the $Λ$CDM model. △ Less

Submitted 13 May, 2015; v1 submitted 16 December, 2014; originally announced December 2014.

Comments: 17 pages, 19 figures

Journal ref: JCAP 05, 004 (2015)