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Powerful Yukawas
Authors:
Timothy Cohen,
Matthew McCullough,
Neal Weiner
Abstract:
We introduce a class of models where the masses of the light Standard Model fermions are due to an Effective Field Theory operator that appears beyond dimension-4 in the power counting expansion, resulting in a `Powerful Yukawa'. The effective Yukawa coupling structure is UV-completed using a collective symmetry breaking pattern in the flavour sector, which we dub `Sprouted Symmetry Breaking.' The…
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We introduce a class of models where the masses of the light Standard Model fermions are due to an Effective Field Theory operator that appears beyond dimension-4 in the power counting expansion, resulting in a `Powerful Yukawa'. The effective Yukawa coupling structure is UV-completed using a collective symmetry breaking pattern in the flavour sector, which we dub `Sprouted Symmetry Breaking.' The irreducible signature is an enhanced Higgs coupling to the light Standard Model fermions.
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Submitted 3 December, 2025;
originally announced December 2025.
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Physics Briefing Book: Input for the 2026 update of the European Strategy for Particle Physics
Authors:
Jorge de Blas,
Monica Dunford,
Emanuele Bagnaschi,
Ayres Freitas,
Pier Paolo Giardino,
Christian Grefe,
Michele Selvaggi,
Angela Taliercio,
Falk Bartels,
Andrea Dainese,
Cristinel Diaconu,
Chiara Signorile-Signorile,
Néstor Armesto,
Roberta Arnaldi,
Andy Buckley,
David d'Enterria,
Antoine Gérardin,
Valentina Mantovani Sarti,
Sven-Olaf Moch,
Marco Pappagallo,
Raimond Snellings,
Urs Achim Wiedemann,
Gino Isidori,
Marie-Hélène Schune,
Maria Laura Piscopo
, et al. (105 additional authors not shown)
Abstract:
The European Strategy for Particle Physics (ESPP) reflects the vision and presents concrete plans of the European particle physics community for advancing human knowledge in fundamental physics. The ESPP is updated every five-to-six years through a community-driven process. It commences with the submission of specific proposals and other input from the community at large, outlining projects envisi…
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The European Strategy for Particle Physics (ESPP) reflects the vision and presents concrete plans of the European particle physics community for advancing human knowledge in fundamental physics. The ESPP is updated every five-to-six years through a community-driven process. It commences with the submission of specific proposals and other input from the community at large, outlining projects envisioned for the near-, mid-, and long-term future. All submitted contributions are evaluated by the Physics Preparatory Group (PPG), and a preliminary analysis is presented at a Symposium meant to foster a broad community discussion on the scientific value and feasibility of the various ideas proposed. The outcomes of the analysis and the deliberations at the Symposium are synthesized in the current Briefing Book, which provides an important input in the deliberations of the Strategy recommendations by the European Strategy Group (ESG).
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Submitted 5 November, 2025;
originally announced November 2025.
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The Price of a Large Electron Yukawa Modification
Authors:
Lukas Allwicher,
Matthew McCullough,
Sophie Renner,
Duncan Rocha,
Benjamin Smith
Abstract:
The theoretical implications of an electron Yukawa modification are considered in the context of a possible Higgs pole run at FCC-ee, aimed at bounding this coupling. We start from an effective field theory viewpoint, considering the impact of renormalisation group effects on related observables and also examining assumptions on the broader UV flavour structure. We then give an overview of the lan…
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The theoretical implications of an electron Yukawa modification are considered in the context of a possible Higgs pole run at FCC-ee, aimed at bounding this coupling. We start from an effective field theory viewpoint, considering the impact of renormalisation group effects on related observables and also examining assumptions on the broader UV flavour structure. We then give an overview of the landscape of simplified models, investigating phenomenological constraints arising at higher orders. A short discussion of fine-tuning is also included.
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Submitted 4 November, 2025;
originally announced November 2025.
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Flavor hierarchies with nonminimal irreducible representations
Authors:
Hannah Banks,
Graeme Crawford,
Matthew McCullough,
Dave Sutherland
Abstract:
We propose a new class of flavour models in which the spurion which breaks Standard Model flavour symmetries transforms in a non-minimal representation. Hierarchies in fermion masses, which arise from multiple insertions of this spurion, may be generated in a technically natural, accidental manner, from a handful of untuned $\mathcal{O}(1)$ elements in the UV. This relies explicitly on the non-Abe…
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We propose a new class of flavour models in which the spurion which breaks Standard Model flavour symmetries transforms in a non-minimal representation. Hierarchies in fermion masses, which arise from multiple insertions of this spurion, may be generated in a technically natural, accidental manner, from a handful of untuned $\mathcal{O}(1)$ elements in the UV. This relies explicitly on the non-Abelian nature of the symmetry, distinguishing it from standard Froggatt-Nielsen-like scenarios. The pattern of flavour violating operators at dimension-6 can radically differ from previously considered scenarios, and emphasises the need for a broad flavour programme across all generations.
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Submitted 19 May, 2026; v1 submitted 3 October, 2025;
originally announced October 2025.
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pNGB Higgs Naturalness at a Tipping Point
Authors:
Matthew McCullough,
Adriana Menkara,
Ennio Salvioni
Abstract:
In scenarios where the Higgs is viewed as a pseudo Nambu-Goldstone boson (pNGB) the question of naturalness finds itself, from a phenomenological perspective, at a tipping point between direct searches and precision. If, by the end of the High-Luminosity LHC operation, all experimental results were to remain consistent with the Standard Model, precision Higgs coupling measurements will begin to dr…
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In scenarios where the Higgs is viewed as a pseudo Nambu-Goldstone boson (pNGB) the question of naturalness finds itself, from a phenomenological perspective, at a tipping point between direct searches and precision. If, by the end of the High-Luminosity LHC operation, all experimental results were to remain consistent with the Standard Model, precision Higgs coupling measurements will begin to drive the naturalness tension. To illustrate this from a fresh perspective we construct a maximally natural `Kitchen Sink' model, throwing into the mix three approaches to symmetry-based naturalness: Supersymmetry, Twin Higgs, and pNGB Higgs models with a Gegenbauer potential. In other words, we build a `Supersymmetric Gegenbauer's Twin' model. This model not only maximises naturalness, at least from a technical perspective, but can also interpolate between all three ingredients smoothly, revealing the interplay between direct exploration and precision. Implications for FCC-ee and FCC-hh are discussed.
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Submitted 9 May, 2025;
originally announced May 2025.
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Future Circular Collider Feasibility Study Report: Volume 2, Accelerators, Technical Infrastructure and Safety
Authors:
M. Benedikt,
F. Zimmermann,
B. Auchmann,
W. Bartmann,
J. P. Burnet,
C. Carli,
A. Chancé,
P. Craievich,
M. Giovannozzi,
C. Grojean,
J. Gutleber,
K. Hanke,
A. Henriques,
P. Janot,
C. Lourenço,
M. Mangano,
T. Otto,
J. Poole,
S. Rajagopalan,
T. Raubenheimer,
E. Todesco,
L. Ulrici,
T. Watson,
G. Wilkinson,
A. Abada
, et al. (1439 additional authors not shown)
Abstract:
In response to the 2020 Update of the European Strategy for Particle Physics, the Future Circular Collider (FCC) Feasibility Study was launched as an international collaboration hosted by CERN. This report describes the FCC integrated programme, which consists of two stages: an electron-positron collider (FCC-ee) in the first phase, serving as a high-luminosity Higgs, top, and electroweak factory;…
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In response to the 2020 Update of the European Strategy for Particle Physics, the Future Circular Collider (FCC) Feasibility Study was launched as an international collaboration hosted by CERN. This report describes the FCC integrated programme, which consists of two stages: an electron-positron collider (FCC-ee) in the first phase, serving as a high-luminosity Higgs, top, and electroweak factory; followed by a proton-proton collider (FCC-hh) at the energy frontier in the second phase.
FCC-ee is designed to operate at four key centre-of-mass energies: the Z pole, the WW production threshold, the ZH production peak, and the top/anti-top production threshold - delivering the highest possible luminosities to four experiments. Over 15 years of operation, FCC-ee will produce more than 6 trillion Z bosons, 200 million WW pairs, nearly 3 million Higgs bosons, and 2 million top anti-top pairs. Precise energy calibration at the Z pole and WW threshold will be achieved through frequent resonant depolarisation of pilot bunches. The sequence of operation modes remains flexible.
FCC-hh will operate at a centre-of-mass energy of approximately 85 TeV - nearly an order of magnitude higher than the LHC - and is designed to deliver 5 to 10 times the integrated luminosity of the HL-LHC. Its mass reach for direct discovery extends to several tens of TeV. In addition to proton-proton collisions, FCC-hh is capable of supporting ion-ion, ion-proton, and lepton-hadron collision modes.
This second volume of the Feasibility Study Report presents the complete design of the FCC-ee collider, its operation and staging strategy, the full-energy booster and injector complex, required accelerator technologies, safety concepts, and technical infrastructure. It also includes the design of the FCC-hh hadron collider, development of high-field magnets, hadron injector options, and key technical systems for FCC-hh.
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Submitted 25 April, 2025;
originally announced May 2025.
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Future Circular Collider Feasibility Study Report: Volume 3, Civil Engineering, Implementation and Sustainability
Authors:
M. Benedikt,
F. Zimmermann,
B. Auchmann,
W. Bartmann,
J. P. Burnet,
C. Carli,
A. Chancé,
P. Craievich,
M. Giovannozzi,
C. Grojean,
J. Gutleber,
K. Hanke,
A. Henriques,
P. Janot,
C. Lourenço,
M. Mangano,
T. Otto,
J. Poole,
S. Rajagopalan,
T. Raubenheimer,
E. Todesco,
L. Ulrici,
T. Watson,
G. Wilkinson,
P. Azzi
, et al. (1439 additional authors not shown)
Abstract:
Volume 3 of the FCC Feasibility Report presents studies related to civil engineering, the development of a project implementation scenario, and environmental and sustainability aspects. The report details the iterative improvements made to the civil engineering concepts since 2018, taking into account subsurface conditions, accelerator and experiment requirements, and territorial considerations. I…
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Volume 3 of the FCC Feasibility Report presents studies related to civil engineering, the development of a project implementation scenario, and environmental and sustainability aspects. The report details the iterative improvements made to the civil engineering concepts since 2018, taking into account subsurface conditions, accelerator and experiment requirements, and territorial considerations. It outlines a technically feasible and economically viable civil engineering configuration that serves as the baseline for detailed subsurface investigations, construction design, cost estimation, and project implementation planning. Additionally, the report highlights ongoing subsurface investigations in key areas to support the development of an improved 3D subsurface model of the region.
The report describes development of the project scenario based on the 'avoid-reduce-compensate' iterative optimisation approach. The reference scenario balances optimal physics performance with territorial compatibility, implementation risks, and costs. Environmental field investigations covering almost 600 hectares of terrain - including numerous urban, economic, social, and technical aspects - confirmed the project's technical feasibility and contributed to the preparation of essential input documents for the formal project authorisation phase. The summary also highlights the initiation of public dialogue as part of the authorisation process. The results of a comprehensive socio-economic impact assessment, which included significant environmental effects, are presented. Even under the most conservative and stringent conditions, a positive benefit-cost ratio for the FCC-ee is obtained. Finally, the report provides a concise summary of the studies conducted to document the current state of the environment.
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Submitted 25 April, 2025;
originally announced May 2025.
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Future Circular Collider Feasibility Study Report: Volume 1, Physics, Experiments, Detectors
Authors:
M. Benedikt,
F. Zimmermann,
B. Auchmann,
W. Bartmann,
J. P. Burnet,
C. Carli,
A. Chancé,
P. Craievich,
M. Giovannozzi,
C. Grojean,
J. Gutleber,
K. Hanke,
A. Henriques,
P. Janot,
C. Lourenço,
M. Mangano,
T. Otto,
J. Poole,
S. Rajagopalan,
T. Raubenheimer,
E. Todesco,
L. Ulrici,
T. Watson,
G. Wilkinson,
P. Azzi
, et al. (1439 additional authors not shown)
Abstract:
Volume 1 of the FCC Feasibility Report presents an overview of the physics case, experimental programme, and detector concepts for the Future Circular Collider (FCC). This volume outlines how FCC would address some of the most profound open questions in particle physics, from precision studies of the Higgs and EW bosons and of the top quark, to the exploration of physics beyond the Standard Model.…
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Volume 1 of the FCC Feasibility Report presents an overview of the physics case, experimental programme, and detector concepts for the Future Circular Collider (FCC). This volume outlines how FCC would address some of the most profound open questions in particle physics, from precision studies of the Higgs and EW bosons and of the top quark, to the exploration of physics beyond the Standard Model. The report reviews the experimental opportunities offered by the staged implementation of FCC, beginning with an electron-positron collider (FCC-ee), operating at several centre-of-mass energies, followed by a hadron collider (FCC-hh). Benchmark examples are given of the expected physics performance, in terms of precision and sensitivity to new phenomena, of each collider stage. Detector requirements and conceptual designs for FCC-ee experiments are discussed, as are the specific demands that the physics programme imposes on the accelerator in the domains of the calibration of the collision energy, and the interface region between the accelerator and the detector. The report also highlights advances in detector, software and computing technologies, as well as the theoretical tools /reconstruction techniques that will enable the precision measurements and discovery potential of the FCC experimental programme. This volume reflects the outcome of a global collaborative effort involving hundreds of scientists and institutions, aided by a dedicated community-building coordination, and provides a targeted assessment of the scientific opportunities and experimental foundations of the FCC programme.
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Submitted 25 April, 2025;
originally announced May 2025.
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MATHUSLA: An External Long-Lived Particle Detector to Maximize the Discovery Potential of the HL-LHC
Authors:
Branden Aitken,
Cristiano Alpigiani,
Juan Carlos Arteaga-Velázquez,
Mitchel Baker,
Kincso Balazs,
Jared Barron,
Brian Batell,
Austin Batz,
Yan Benhammou,
Tamara Alice Bud,
Karen Salomé Caballero-Mora,
John Paul Chou,
David Curtin,
Albert de Roeck,
Miriam Diamond,
Mariia Didenko,
Keith R. Dienes,
William Dougherty,
Liam Andrew Dougherty,
Marco Drewes,
Sameer Erramilli,
Erez Etzion,
Arturo Fernández Téllez,
Grace Finlayson,
Oliver Fischer
, et al. (48 additional authors not shown)
Abstract:
We present the current status of the MATHUSLA (MAssive Timing Hodoscope for Ultra-Stable neutraL pArticles) long-lived particle (LLP) detector at the HL-LHC, covering the design, fabrication and installation at CERN Point 5. MATHUSLA40 is a 40 m-scale detector with an air-filled decay volume that is instrumented with scintillator tracking detectors, to be located near CMS. Its large size, close pr…
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We present the current status of the MATHUSLA (MAssive Timing Hodoscope for Ultra-Stable neutraL pArticles) long-lived particle (LLP) detector at the HL-LHC, covering the design, fabrication and installation at CERN Point 5. MATHUSLA40 is a 40 m-scale detector with an air-filled decay volume that is instrumented with scintillator tracking detectors, to be located near CMS. Its large size, close proximity to the CMS interaction point and about 100 m of rock shielding from LHC backgrounds allows it to detect LLP production rates and lifetimes that are one to two orders of magnitude beyond the ultimate reach of the LHC main detectors. This provides unique sensitivity to many LLP signals that are highly theoretically motivated, due to their connection to the hierarchy problem, the nature of dark matter, and baryogenesis. Data taking is projected to commence with the start of HL-LHC operations. We summarize the new 40m design for the detector that was recently presented in the MATHUSLA Conceptual Design Report, alongside new realistic background and signal simulations that demonstrate high efficiency for the main target LLP signals in a background-free HL-LHC search. We argue that MATHUSLA's uniquely robust expansion of the HL-LHC physics reach is a crucial ingredient in CERN's mission to search for new physics and characterize the Higgs boson with precision.
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Submitted 1 April, 2025;
originally announced April 2025.
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Conceptual Design Report for the MATHUSLA Long-Lived Particle Detector near CMS
Authors:
Branden Aitken,
Cristiano Alpigiani,
Juan Carlos Arteaga-Velázquez,
Mitchel Baker,
Kincso Balazs,
Jared Barron,
Brian Batell,
Austin Batz,
Yan Benhammou,
Tamara Alice Bud,
Karen Salomé Caballero-Mora,
John Paul Chou,
David Curtin,
Albert de Roeck,
Miriam Diamond,
Mariia Didenko,
Keith R. Dienes,
William Dougherty,
Liam Andrew Dougherty,
Marco Drewes,
Sameer Erramilli,
Erez Etzion,
Arturo Fernández Téllez,
Grace Finlayson,
Oliver Fischer
, et al. (48 additional authors not shown)
Abstract:
We present the Conceptual Design Report (CDR) for the MATHUSLA (MAssive Timing Hodoscope for Ultra-Stable neutraL pArticles) long-lived particle detector at the HL-LHC, covering the design, fabrication and installation at CERN Point 5. MATHUSLA is a 40 m-scale detector with an air-filled decay volume that is instrumented with scintillator tracking detectors, to be located near CMS. Its large size,…
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We present the Conceptual Design Report (CDR) for the MATHUSLA (MAssive Timing Hodoscope for Ultra-Stable neutraL pArticles) long-lived particle detector at the HL-LHC, covering the design, fabrication and installation at CERN Point 5. MATHUSLA is a 40 m-scale detector with an air-filled decay volume that is instrumented with scintillator tracking detectors, to be located near CMS. Its large size, close proximity to the CMS interaction point and about 100 m of rock shielding from HL-LHC backgrounds allows it to detect LLP production rates and lifetimes that are one to two orders of magnitude beyond the ultimate sensitivity of the HL-LHC main detectors for many highly motivated LLP signals. Data taking is projected to commence with the start of HL-LHC operations. We present a new 40m design for the detector: its individual scintillator bars and wavelength-shifting fibers, their organization into tracking layers, tracking modules, tower modules and the veto detector; define a high-level design for the supporting electronics, DAQ and trigger system, including supplying a hardware trigger signal to CMS to record the LLP production event; outline computing systems, civil engineering and safety considerations; and present preliminary cost estimates and timelines for the project. We also conduct detailed simulation studies of the important cosmic ray and HL-LHC muon backgrounds, implementing full track/vertex reconstruction and background rejection, to ultimately demonstrate high signal efficiency and $\ll 1$ background event in realistic LLP searches for the main physics targets at MATHUSLA. This sensitivity is robust with respect to detector design or background simulation details. Appendices provide various supplemental information.
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Submitted 26 March, 2025;
originally announced March 2025.
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In Pursuit of New Paradigms: TASI 2024
Authors:
Matthew McCullough
Abstract:
These lectures discuss diverse theoretical approaches, old and new, towards understanding the origin of the Higgs sector of the Standard Model and the lightness of the Higgs boson.
These lectures discuss diverse theoretical approaches, old and new, towards understanding the origin of the Higgs sector of the Standard Model and the lightness of the Higgs boson.
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Submitted 20 December, 2024;
originally announced December 2024.
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New Physics at Tera-$Z$: Precision Renormalised
Authors:
Lukas Allwicher,
Matthew McCullough,
Sophie Renner
Abstract:
We study the power of a Tera-$Z$ run at FCC-ee for indirectly detecting or constraining heavy new physics. Our main finding is that nearly every new particle which matches at tree level to dimension-six operators of the Standard Model Effective Field Theory (SMEFT) affects electroweak precision observables (EWPOs) at either tree level or via one loop renormalisation group (RG) running. This is tru…
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We study the power of a Tera-$Z$ run at FCC-ee for indirectly detecting or constraining heavy new physics. Our main finding is that nearly every new particle which matches at tree level to dimension-six operators of the Standard Model Effective Field Theory (SMEFT) affects electroweak precision observables (EWPOs) at either tree level or via one loop renormalisation group (RG) running. This is true almost regardless of the structure of couplings to the Standard Model; just a handful of exceptions are identified which can produce zeroes in the EWPO RG equations. Under simple flavour assumptions, we perform fits of each state to projected FCC-ee $Z$ pole measurements, showing that all scenarios can be tested at the TeV scale or better, with many projected exclusions reaching tens of TeV. Tera-$Z$ is argued to provide an almost inescapable probe of heavy new physics.
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Submitted 10 March, 2025; v1 submitted 7 August, 2024;
originally announced August 2024.
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A Nuclear Interferometer for Ultra-Light Dark Matter Detection
Authors:
Hannah Banks,
Elina Fuchs,
Matthew McCullough
Abstract:
We propose the nuclear interferometer - a single-photon interferometry experiment based upon the thorium-229 nuclear clock transition - as a novel detector for ultra-light dark matter. Thanks to the enhanced sensitivity of this transition to the variation of fundamental constants, we find that possible realisations of such an experiment deploying either single ions or clouds of atoms have the pote…
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We propose the nuclear interferometer - a single-photon interferometry experiment based upon the thorium-229 nuclear clock transition - as a novel detector for ultra-light dark matter. Thanks to the enhanced sensitivity of this transition to the variation of fundamental constants, we find that possible realisations of such an experiment deploying either single ions or clouds of atoms have the potential to complement advanced very-long-baseline terrestrial clock atom interferometers in the search for ultra-light dark matter with scalar couplings to photons in the future. Nuclear interferometry may also offer an unparalleled window to new physics coupling to the QCD sector via quarks or gluons, with a discovery reach that could enhance existing and proposed experiments over a range of frequencies in the direction of well-motivated parameter space.
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Submitted 29 July, 2026; v1 submitted 15 July, 2024;
originally announced July 2024.
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Boundaries of Universal Theories
Authors:
Matthew McCullough,
Lorenzo Ricci,
Marc Riembau
Abstract:
Universal theories are a broad class of well-motivated microscopic dynamics of the electroweak sector that go beyond the Standard Model description. The long distance physics is described by electroweak parameters which correspond to local operators in the Effective Field Theory. We show how unitarity and analyticity constrain the space of parameters. In particular, the $W$ and $Y$ parameters are…
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Universal theories are a broad class of well-motivated microscopic dynamics of the electroweak sector that go beyond the Standard Model description. The long distance physics is described by electroweak parameters which correspond to local operators in the Effective Field Theory. We show how unitarity and analyticity constrain the space of parameters. In particular, the $W$ and $Y$ parameters are constrained to be positive and are necessarily the leading terms in the low energy expansion. We assess the impact of unitarity on the interpretation of Drell-Yan data. In passing, we uncover an unexpected Wilson coefficient transcendental cancellation at the $\mathcal{O}(<10^{-3})$ level.
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Submitted 6 December, 2023;
originally announced December 2023.
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Broad Sterile Neutrinos & the Reactor/Gallium Tension
Authors:
Hannah Banks,
Kevin J. Kelly,
Matthew McCullough,
Tao Zhou
Abstract:
Significant evidence exists for the apparent disappearance of electron-type neutrinos in radioactive source experiments. Yet, interpreted within the standard `3+1 sterile neutrino scenario', precision short-baseline measurements of electron antineutrinos from nuclear reactors strongly disagree with these results. Recently, it has been demonstrated that allowing for a finite wavepacket size for the…
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Significant evidence exists for the apparent disappearance of electron-type neutrinos in radioactive source experiments. Yet, interpreted within the standard `3+1 sterile neutrino scenario', precision short-baseline measurements of electron antineutrinos from nuclear reactors strongly disagree with these results. Recently, it has been demonstrated that allowing for a finite wavepacket size for the reactor neutrinos can ameliorate such a tension, however the smallness of the required wavepackets is a subject of intense debate. In this work, we demonstrate that a `broad' sterile neutrino may relax this tension in much the same way. Such a phenomenological possibility can arise in plausible hidden sector scenarios, such as a clockwork-style sector, for which we provide a concrete microscopic model.
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Submitted 10 November, 2023;
originally announced November 2023.
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Phases of Pseudo-Nambu-Goldstone Bosons
Authors:
Fotis Koutroulis,
Matthew McCullough,
Marco Merchand,
Stefan Pokorski,
Kazuki Sakurai
Abstract:
We study the vacuum dynamics of pseudo-Nambu-Goldstone bosons (pNGBs) for $SO(N+1) \rightarrow SO(N)$ spontaneous and explicit symmetry breaking. We determine the magnitude of explicit symmetry breaking consistent with an EFT description of the effective potential at zero and finite temperatures. We expose and clarify novel additional vacuum transitions that can arise for generic pNGBs below the i…
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We study the vacuum dynamics of pseudo-Nambu-Goldstone bosons (pNGBs) for $SO(N+1) \rightarrow SO(N)$ spontaneous and explicit symmetry breaking. We determine the magnitude of explicit symmetry breaking consistent with an EFT description of the effective potential at zero and finite temperatures. We expose and clarify novel additional vacuum transitions that can arise for generic pNGBs below the initial scale of $SO(N+1) \rightarrow SO(N)$ spontaneous symmetry breaking, which may have phenomenological relevance. In this respect, two phenomenological scenarios are analyzed: thermal and supercooled dark sector pNGBs. In the thermal scenario the vacuum transition is first-order but very weak. For a supercooled dark sector we find that, depending on the sign of the explicit symmetry breaking, one can have a symmetry-restoring vacuum transition $SO(N-1) \rightarrow SO(N)$ which can be strongly first-order, with a detectable stochastic gravitational wave background signal.
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Submitted 27 September, 2023;
originally announced September 2023.
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Gravitational Wave Backgrounds from Colliding ECOs
Authors:
Hannah Banks,
Dorota M. Grabowska,
Matthew McCullough
Abstract:
Long baseline atom interferometers offer an exciting opportunity to explore mid-frequency gravitational waves. In this work we survey the landscape of possible contributions to the total 'gravitational wave background' in this frequency band and advocate for targeting this observable. Such an approach is complimentary to searches for resolved mergers from individual sources and may have much to re…
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Long baseline atom interferometers offer an exciting opportunity to explore mid-frequency gravitational waves. In this work we survey the landscape of possible contributions to the total 'gravitational wave background' in this frequency band and advocate for targeting this observable. Such an approach is complimentary to searches for resolved mergers from individual sources and may have much to reveal about the Universe. We find that the inspiral phases of stellar-mass compact binaries cumulatively produce a signal well within reach of the proposed AION-km and AEDGE experiments. Hypothetical populations of dark sector exotic compact objects, harbouring just a tiny fraction of the dark energy density, could also generate signatures unique to mid- and low-frequency gravitational wave detectors, providing a novel means to probe complexity in the dark sector.
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Submitted 15 February, 2023;
originally announced February 2023.
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How Broad is a Neutrino?
Authors:
Hannah Banks,
Kevin J. Kelly,
Matthew McCullough
Abstract:
Canonical neutrino oscillations arise due to the propagation of three mass eigenstates from production to detection. We aspire to capture, in one simple framework, a broad range of new physics effects on neutrino propagation beyond this canonical picture - this can be done by promoting the neutrino propagators to the general Källén-Lehmann form. In this work we demonstrate how models predicting ad…
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Canonical neutrino oscillations arise due to the propagation of three mass eigenstates from production to detection. We aspire to capture, in one simple framework, a broad range of new physics effects on neutrino propagation beyond this canonical picture - this can be done by promoting the neutrino propagators to the general Källén-Lehmann form. In this work we demonstrate how models predicting additional light propagating species of neutrino are naturally accommodated in this language and propose a simple model spectrum composed of just three `broadened' states as a flexible ansatz by which to explore the phenomenology of new physics in neutrino propagation. Reinterpreting existing neutrino oscillation measurements, we illustrate how this framework provides the capacity to probe deviations from the standard three-neutrino scenario systematically and generally. Whilst current data allows for relatively strong constraints on broadened neutrinos, we find the upcoming JUNO experiment will yield significant improvements, particularly for the heaviest neutrino, paving the way to a clearer understanding of how neutrinos propagate in vacuum.
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Submitted 22 September, 2022;
originally announced September 2022.
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Charting the Higgs self-coupling boundaries
Authors:
Gauthier Durieux,
Matthew McCullough,
Ennio Salvioni
Abstract:
Could new physics first manifest itself in Higgs self-coupling measurements? In other words, how large could deviations in the Higgs self-coupling be, if other Higgs and electroweak measurements are compatible with Standard Model predictions? Using theoretical arguments supported by concrete models we derive a bound on the ratio of self-coupling to single-Higgs coupling deviations in ultraviolet c…
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Could new physics first manifest itself in Higgs self-coupling measurements? In other words, how large could deviations in the Higgs self-coupling be, if other Higgs and electroweak measurements are compatible with Standard Model predictions? Using theoretical arguments supported by concrete models we derive a bound on the ratio of self-coupling to single-Higgs coupling deviations in ultraviolet completions of the Standard Model where parameters are not fine-tuned. Broadly speaking, a one-loop hierarchy is allowed. We thus stress that self-coupling measurements at the LHC and future colliders probe uncharted parameter space, presenting discovery potential even in the absence of emerging hints in single-Higgs coupling measurements. For instance, if other observables show less than two-sigma deviations by the end of the LHC programme, the Higgs self-coupling deviations could still exceed 200% in the models discussed, without introducing fine-tuning of ultraviolet parameters.
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Submitted 29 December, 2022; v1 submitted 1 September, 2022;
originally announced September 2022.
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dE/dx from boosted long-lived particles
Authors:
Gian F. Giudice,
Matthew McCullough,
Daniele Teresi
Abstract:
At colliders massive long-lived charged particles could be revealed through their anomalously large ionisation energy loss $dE/dx$. In this paper we explore a class of scenarios in which the LLPs are particularly boosted, owing to production from the decay of a heavy parent resonance. Such scenarios give rise to unique signatures as compared to traditionally considered $dE/dx$ new-physics benchmar…
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At colliders massive long-lived charged particles could be revealed through their anomalously large ionisation energy loss $dE/dx$. In this paper we explore a class of scenarios in which the LLPs are particularly boosted, owing to production from the decay of a heavy parent resonance. Such scenarios give rise to unique signatures as compared to traditionally considered $dE/dx$ new-physics benchmarks. We demonstrate that this class of models, unlike traditional new-physics theories, can explain the recently reported excess of events in the $dE/dx$ search by the ATLAS collaboration without conflicting with the determination of $β$ from ionisation and time-of-flight measurements.
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Submitted 20 July, 2022; v1 submitted 9 May, 2022;
originally announced May 2022.
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The dark side of the proton
Authors:
Matthew McCullough,
James Moore,
Maria Ubiali
Abstract:
We study the sensitivity of the High-Luminosity LHC to a light baryonic dark photon B, primarily coupled to quarks, as a constituent of the proton. This is achieved by allowing for a dark photon parton distribution function (PDF) in the PDF evolution equations. Depending on the mass and coupling of the dark photon, the evolution of standard quark and gluon PDFs is distorted to varying degrees. By…
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We study the sensitivity of the High-Luminosity LHC to a light baryonic dark photon B, primarily coupled to quarks, as a constituent of the proton. This is achieved by allowing for a dark photon parton distribution function (PDF) in the PDF evolution equations. Depending on the mass and coupling of the dark photon, the evolution of standard quark and gluon PDFs is distorted to varying degrees. By analysing the effect of the dark photon on the tails of Drell-Yan invariant mass distributions, we demonstrate the potential of the LHC in determining competitive bounds on dark photon parameter space.
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Submitted 23 March, 2022;
originally announced March 2022.
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Recent Progress and Next Steps for the MATHUSLA LLP Detector
Authors:
Cristiano Alpigiani,
Juan Carlos Arteaga-Velázquez,
Austin Ball,
Liron Barak,
Jared Barron,
Brian Batell,
James Beacham,
Yan Benhammo,
Benjamin Brau,
Karen Salomé Caballero-Mora,
Paolo Camarri,
Roberto Cardarelli,
John Paul Chou,
Wentao Cui,
David Curtin,
Miriam Diamond,
Keith R. Dienes,
Liam Andrew Dougherty,
William Dougherty,
Marco Drewes,
Sameer Erramilli,
Rouven Essig,
Erez Etzion,
Jared Evans,
Arturo Fernández Téllez
, et al. (71 additional authors not shown)
Abstract:
We report on recent progress and next steps in the design of the proposed MATHUSLA Long Lived Particle (LLP) detector for the HL-LHC as part of the Snowmass 2021 process. Our understanding of backgrounds has greatly improved, aided by detailed simulation studies, and significant R&D has been performed on designing the scintillator detectors and understanding their performance. The collaboration is…
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We report on recent progress and next steps in the design of the proposed MATHUSLA Long Lived Particle (LLP) detector for the HL-LHC as part of the Snowmass 2021 process. Our understanding of backgrounds has greatly improved, aided by detailed simulation studies, and significant R&D has been performed on designing the scintillator detectors and understanding their performance. The collaboration is on track to complete a Technical Design Report, and there are many opportunities for interested new members to contribute towards the goal of designing and constructing MATHUSLA in time for HL-LHC collisions, which would increase the sensitivity to a large variety of highly motivated LLP signals by orders of magnitude.
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Submitted 30 March, 2023; v1 submitted 15 March, 2022;
originally announced March 2022.
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Gegenbauer's Twin
Authors:
Gauthier Durieux,
Matthew McCullough,
Ennio Salvioni
Abstract:
In Twin Higgs models the dominant source of fine-tuning is the cancellation of order $v^2/f^2$ required to obtain a Standard Model-like Higgs, where $v$ and $f$ are the electroweak and new physics scales, respectively. Recently proposed Gegenbauer Goldstone models naturally realise $v^2/f^2 \ll 1$ and hence remove this source of fine-tuning. By combining the two into `Gegenbauer's Twin', we obtain…
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In Twin Higgs models the dominant source of fine-tuning is the cancellation of order $v^2/f^2$ required to obtain a Standard Model-like Higgs, where $v$ and $f$ are the electroweak and new physics scales, respectively. Recently proposed Gegenbauer Goldstone models naturally realise $v^2/f^2 \ll 1$ and hence remove this source of fine-tuning. By combining the two into `Gegenbauer's Twin', we obtain a symmetry-based model for Higgs sector naturalness consistent with current collider measurements without fine-tuning of parameters. Single-Higgs coupling deviations of a few percent and trilinear self-coupling deviations of order one are irreducible in the natural parameter space. Thus, notably, the fingerprints of Gegenbauer's Twin could emerge first through di-Higgs measurements at the High-Luminosity LHC.
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Submitted 24 May, 2022; v1 submitted 2 February, 2022;
originally announced February 2022.
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Gegenbauer Goldstones
Authors:
Gauthier Durieux,
Matthew McCullough,
Ennio Salvioni
Abstract:
We investigate radiatively stable classes of pseudo-Nambu-Goldstone boson (pNGB) potentials for approximate spontaneously broken $\mathrm{SO}(N+1)\to\mathrm{SO}(N)$. Using both the one-loop effective action and symmetry, it is shown that a Gegenbauer polynomial potential is radiatively stable, being effectively an `eigenfunction' from a radiative perspective. In Gegenbauer pNGB models, one natural…
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We investigate radiatively stable classes of pseudo-Nambu-Goldstone boson (pNGB) potentials for approximate spontaneously broken $\mathrm{SO}(N+1)\to\mathrm{SO}(N)$. Using both the one-loop effective action and symmetry, it is shown that a Gegenbauer polynomial potential is radiatively stable, being effectively an `eigenfunction' from a radiative perspective. In Gegenbauer pNGB models, one naturally and automatically obtains $v \propto f/n$, where $n\in 2\mathbb{Z}$ is the order of the Gegenbauer polynomial. For a Gegenbauer Higgs boson, this breaks the usual correlation between Higgs coupling corrections and `$v/f$' tuning. Based on this, we argue that to conclusively determine whether or not the Higgs is a composite pNGB in scenarios with up to $\mathcal{O}(10\%)$ fine-tuning will require going beyond both the Higgs coupling precision and heavy resonance mass reach of the High-Luminosity LHC.
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Submitted 20 January, 2022; v1 submitted 13 October, 2021;
originally announced October 2021.
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Self-Organised Localisation
Authors:
Gian F. Giudice,
Matthew McCullough,
Tevong You
Abstract:
We describe a new phenomenon in quantum cosmology: self-organised localisation. When the fundamental parameters of a theory are functions of a scalar field subject to large fluctuations during inflation, quantum phase transitions can act as dynamical attractors. As a result, the theory parameters are probabilistically localised around the critical value and the Universe finds itself at the edge of…
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We describe a new phenomenon in quantum cosmology: self-organised localisation. When the fundamental parameters of a theory are functions of a scalar field subject to large fluctuations during inflation, quantum phase transitions can act as dynamical attractors. As a result, the theory parameters are probabilistically localised around the critical value and the Universe finds itself at the edge of a phase transition. We illustrate how self-organised localisation could account for the observed near-criticality of the Higgs self-coupling, the naturalness of the Higgs mass, or the smallness of the cosmological constant.
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Submitted 19 September, 2021; v1 submitted 18 May, 2021;
originally announced May 2021.
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Charting the Fifth Force Landscape
Authors:
Hannah Banks,
Matthew McCullough
Abstract:
Fifth forces arising from hidden sector scalar operator exchange, as probed in a variety of present and planned experiments, can be captured by a general dispersion relation involving one real, positive, spectral density function. Previously considered scalar fifth forces, from tree-level to more exotic loop-level possibilities, are derived in this formalism, without explicitly performing conventi…
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Fifth forces arising from hidden sector scalar operator exchange, as probed in a variety of present and planned experiments, can be captured by a general dispersion relation involving one real, positive, spectral density function. Previously considered scalar fifth forces, from tree-level to more exotic loop-level possibilities, are derived in this formalism, without explicitly performing conventional loop calculations. A variety of experimental observables commonly used in fifth force searches are also presented in the same formalism, allowing the straightforward extraction of limits on any specific model. The speculative possibility of probing hidden sector violations of unitarity, causality, or locality, manifested as a breakdown of the positivity of the spectral density, is also discussed.
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Submitted 25 September, 2020;
originally announced September 2020.
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An Update to the Letter of Intent for MATHUSLA: Search for Long-Lived Particles at the HL-LHC
Authors:
Cristiano Alpigiani,
Juan Carlos Arteaga-Velázquez,
Austin Ball,
Liron Barak,
Jared Barron,
Brian Batell,
James Beacham,
Yan Benhammo,
Karen Salomé Caballero-Mora,
Paolo Camarri,
Roberto Cardarelli,
John Paul Chou,
Wentao Cui,
David Curtin,
Miriam Diamond,
Keith R. Dienes,
Liam Andrew Dougherty,
Giuseppe Di Sciascio,
Marco Drewes,
Erez Etzion,
Rouven Essig,
Jared Evans,
Arturo Fernández Téllez,
Oliver Fischer,
Jim Freeman
, et al. (58 additional authors not shown)
Abstract:
We report on recent progress in the design of the proposed MATHUSLA Long Lived Particle (LLP) detector for the HL-LHC, updating the information in the original Letter of Intent (LoI), see CDS:LHCC-I-031, arXiv:1811.00927. A suitable site has been identified at LHC Point 5 that is closer to the CMS Interaction Point (IP) than assumed in the LoI. The decay volume has been increased from 20 m to 25 m…
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We report on recent progress in the design of the proposed MATHUSLA Long Lived Particle (LLP) detector for the HL-LHC, updating the information in the original Letter of Intent (LoI), see CDS:LHCC-I-031, arXiv:1811.00927. A suitable site has been identified at LHC Point 5 that is closer to the CMS Interaction Point (IP) than assumed in the LoI. The decay volume has been increased from 20 m to 25 m in height. Engineering studies have been made in order to locate much of the decay volume below ground, bringing the detector even closer to the IP. With these changes, a 100 m x 100 m detector has the same physics reach for large c$τ$ as the 200 m x 200 m detector described in the LoI and other studies. The performance for small c$τ$ is improved because of the proximity to the IP. Detector technology has also evolved while retaining the strip-like sensor geometry in Resistive Plate Chambers (RPC) described in the LoI. The present design uses extruded scintillator bars read out using wavelength shifting fibers and silicon photomultipliers (SiPM). Operations will be simpler and more robust with much lower operating voltages and without the use of greenhouse gases. Manufacturing is straightforward and should result in cost savings. Understanding of backgrounds has also significantly advanced, thanks to new simulation studies and measurements taken at the MATHUSLA test stand operating above ATLAS in 2018. We discuss next steps for the MATHUSLA collaboration, and identify areas where new members can make particularly important contributions.
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Submitted 3 September, 2020;
originally announced September 2020.
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Undulating Dark Matter
Authors:
Joe Davighi,
Matthew McCullough,
Joseph Tooby-Smith
Abstract:
We suggest that an interplay between microscopic and macroscopic physics can give rise to dark matter (DM) whose interactions with the visible sector fundamentally undulate in time, independent of celestial dynamics. A concrete example is provided by fermionic DM with an electric dipole moment (EDM) sourced by an oscillating axion-like field, resulting in undulations in the scattering rate. The di…
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We suggest that an interplay between microscopic and macroscopic physics can give rise to dark matter (DM) whose interactions with the visible sector fundamentally undulate in time, independent of celestial dynamics. A concrete example is provided by fermionic DM with an electric dipole moment (EDM) sourced by an oscillating axion-like field, resulting in undulations in the scattering rate. The discovery potential of light DM searches can be enhanced by additionally searching for undulating scattering rates, especially in detection regions where background rates are large and difficult to estimate, such as for DM masses in the vicinity of 1 MeV where DM-electron scattering dominantly populates the single electron bin. An undulating signal could also reveal precious dark sector information after discovery. In this regard we emphasise that, if the recent XENON1T excess of events is due to light DM scattering exothermically off electrons, future analyses of the time-dependence of events could offer clues as to the microscopic origins of the putative signal.
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Submitted 7 July, 2020;
originally announced July 2020.
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Supersoft Stops
Authors:
Timothy Cohen,
Nathaniel Craig,
Seth Koren,
Matthew McCullough,
Joseph Tooby-Smith
Abstract:
In a supersymmetric (SUSY) theory, the IR-contributions to the Higgs mass are calculable below the mediation scale $Λ_{\text{UV}}$ in terms of the IR field content and parameters. However, logarithmic sensitivity to physics at $Λ_{\text{UV}}$ remains. In this work we present a first example of a framework, dictated by symmetries, to supersoften these logarithms from the matter sector. The result i…
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In a supersymmetric (SUSY) theory, the IR-contributions to the Higgs mass are calculable below the mediation scale $Λ_{\text{UV}}$ in terms of the IR field content and parameters. However, logarithmic sensitivity to physics at $Λ_{\text{UV}}$ remains. In this work we present a first example of a framework, dictated by symmetries, to supersoften these logarithms from the matter sector. The result is a model with finite, IR-calculable corrections to the Higgs mass. This requires the introduction of new fields -- the `lumberjacks' -- whose role is to screen the UV-sensitive logs. These models have considerably reduced fine-tuning, by more than an order of magnitude for high scale supersymmetry. This impacts interpretations of the natural parameter space, suggesting it may be premature to declare a naturalness crisis for high-scale SUSY.
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Submitted 28 February, 2020;
originally announced February 2020.
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Interaction of SN~Ib 2004dk with a Previously-Expelled Envelope
Authors:
David Pooley,
J. Craig Wheeler,
Jozsef Vinkó,
Vikram V. Dwarkadas,
Tamas Szalai,
Jeffrey M. Silverman,
Madelaine Griesel,
Molly McCullough,
G. H. Marion,
Phillip MacQueen
Abstract:
The interaction between the expanding supernova (SN) ejecta with the circumstellar material (CSM) that was expelled from the progenitor prior to explosion is a long-sought phenomenon, yet observational evidence is scarce. Here we confirm a new example: SN 2004dk, originally a hydrogen-poor, helium-rich Type Ib SN that reappeared as a strong H$α$-emitting point-source on narrowband H$α$ images. We…
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The interaction between the expanding supernova (SN) ejecta with the circumstellar material (CSM) that was expelled from the progenitor prior to explosion is a long-sought phenomenon, yet observational evidence is scarce. Here we confirm a new example: SN 2004dk, originally a hydrogen-poor, helium-rich Type Ib SN that reappeared as a strong H$α$-emitting point-source on narrowband H$α$ images. We present follow-up optical spectroscopy that reveals the presence of a broad H$α$ component with full width at half maximum of ~290 km/s in addition to the narrow H$α$ +[NII] emission features from the host galaxy. Such a broad component is a clear sign of an ejecta-CSM interaction. We also present observations with the XMM-Newton Observatory, the Swift satellite, and the Chandra X-ray Observatory that span 10 days to 15 years after discovery. The detection of strong radio, X-ray, and H$α$ emission years after explosion allows various constraints to be put on pre-SN mass-loss processes. We present a wind-bubble model in which the CSM is "pre-prepared" by a fast wind interacting with a slow wind. Much of the outer density profile into which the SN explodes corresponds to no steady-state mass-loss process. We estimate that the shell of compressed slow wind material was ejected ~1400 yr prior to explosion, perhaps during carbon burning, and that the SN shock had swept up about 0.04 M_sun of material. The region emitting the H$α$ has a density of order $10^{-20}$ g/cc.
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Submitted 14 October, 2019;
originally announced October 2019.
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The $\hat{H}$-Parameter: An Oblique Higgs View
Authors:
Christoph Englert,
Gian F. Giudice,
Admir Greljo,
Matthew McCullough
Abstract:
We study, from theoretical and phenomenological angles, the Higgs boson oblique parameter $\hat{H}$, as the hallmark of off-shell Higgs physics. $\hat{H}$ is defined as the Wilson coefficient of the sole dimension-6 operator that modifies the Higgs boson propagator, within a Universal EFT. Theoretically, we describe self-consistency conditions on Wilson coefficients, derived from the Källén-Lehman…
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We study, from theoretical and phenomenological angles, the Higgs boson oblique parameter $\hat{H}$, as the hallmark of off-shell Higgs physics. $\hat{H}$ is defined as the Wilson coefficient of the sole dimension-6 operator that modifies the Higgs boson propagator, within a Universal EFT. Theoretically, we describe self-consistency conditions on Wilson coefficients, derived from the Källén-Lehmann representation. Phenomenologically, we demonstrate that the process $gg\to h^\ast \to VV$ is insensitive to propagator corrections from $\hat{H}$, and instead advertise four-top production as an effective high-energy probe of off-shell Higgs behaviour, crucial to break flat directions in the EFT.
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Submitted 10 May, 2019; v1 submitted 18 March, 2019;
originally announced March 2019.
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Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider
Authors:
Juliette Alimena,
James Beacham,
Martino Borsato,
Yangyang Cheng,
Xabier Cid Vidal,
Giovanna Cottin,
Albert De Roeck,
Nishita Desai,
David Curtin,
Jared A. Evans,
Simon Knapen,
Sabine Kraml,
Andre Lessa,
Zhen Liu,
Sascha Mehlhase,
Michael J. Ramsey-Musolf,
Heather Russell,
Jessie Shelton,
Brian Shuve,
Monica Verducci,
Jose Zurita,
Todd Adams,
Michael Adersberger,
Cristiano Alpigiani,
Artur Apresyan
, et al. (176 additional authors not shown)
Abstract:
Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton-proton collision. Such LLP signatures are distinct from those of promptly decaying particles t…
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Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton-proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments --- as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER --- to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the High-Luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity "dark showers", highlighting opportunities for expanding the LHC reach for these signals.
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Submitted 11 March, 2019;
originally announced March 2019.
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MATHUSLA: A Detector Proposal to Explore the Lifetime Frontier at the HL-LHC
Authors:
Henry Lubatti,
Cristiano Alpigiani,
Juan Carlos Arteaga-Velázquez,
Austin Ball,
Liron Barak James Beacham,
Yan Benhammo,
Karen Salomé Caballero-Mora,
Paolo Camarri,
Tingting Cao,
Roberto Cardarelli,
John Paul Chou,
David Curtin,
Albert de Roeck,
Giuseppe Di Sciascio,
Miriam Diamond,
Marco Drewes,
Sarah C. Eno,
Rouven Essig,
Jared Evans,
Erez Etzion,
Arturo Fernández Téllez,
Oliver Fischer,
Jim Freeman,
Stefano Giagu,
Brandon Gomes
, et al. (38 additional authors not shown)
Abstract:
The observation of long-lived particles at the LHC would reveal physics beyond the Standard Model, could account for the many open issues in our understanding of our universe, and conceivably point to a more complete theory of the fundamental interactions. Such long-lived particle signatures are fundamentally motivated and can appear in virtually every theoretical construct that address the Hierar…
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The observation of long-lived particles at the LHC would reveal physics beyond the Standard Model, could account for the many open issues in our understanding of our universe, and conceivably point to a more complete theory of the fundamental interactions. Such long-lived particle signatures are fundamentally motivated and can appear in virtually every theoretical construct that address the Hierarchy Problem, Dark Matter, Neutrino Masses and the Baryon Asymmetry of the Universe. We describe in this document a large detector, MATHUSLA, located on the surface above an HL-LHC $pp$ interaction point, that could observe long-lived particles with lifetimes up to the Big Bang Nucleosynthesis limit of 0.1 s. We also note that its large detector area allows MATHUSLA to make important contributions to cosmic ray physics. Because of the potential for making a major breakthrough in our conceptual understanding of the universe, long-lived particle searches should have the highest level of priority.
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Submitted 13 January, 2019;
originally announced January 2019.
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Beyond the Standard Model Physics at the HL-LHC and HE-LHC
Authors:
X. Cid Vidal,
M. D'Onofrio,
P. J. Fox,
R. Torre,
K. A. Ulmer,
A. Aboubrahim,
A. Albert,
J. Alimena,
B. C. Allanach,
C. Alpigiani,
M. Altakach,
S. Amoroso,
J. K. Anders,
J. Y. Araz,
A. Arbey,
P. Azzi,
I. Babounikau,
H. Baer,
M. J. Baker,
D. Barducci,
V. Barger,
O. Baron,
L. Barranco Navarro,
M. Battaglia,
A. Bay
, et al. (272 additional authors not shown)
Abstract:
This is the third out of five chapters of the final report [1] of the Workshop on Physics at HL-LHC, and perspectives on HE-LHC [2]. It is devoted to the study of the potential, in the search for Beyond the Standard Model (BSM) physics, of the High Luminosity (HL) phase of the LHC, defined as $3~\mathrm{ab}^{-1}$ of data taken at a centre-of-mass energy of $14~\mathrm{TeV}$, and of a possible futu…
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This is the third out of five chapters of the final report [1] of the Workshop on Physics at HL-LHC, and perspectives on HE-LHC [2]. It is devoted to the study of the potential, in the search for Beyond the Standard Model (BSM) physics, of the High Luminosity (HL) phase of the LHC, defined as $3~\mathrm{ab}^{-1}$ of data taken at a centre-of-mass energy of $14~\mathrm{TeV}$, and of a possible future upgrade, the High Energy (HE) LHC, defined as $15~\mathrm{ab}^{-1}$ of data at a centre-of-mass energy of $27~\mathrm{TeV}$. We consider a large variety of new physics models, both in a simplified model fashion and in a more model-dependent one. A long list of contributions from the theory and experimental (ATLAS, CMS, LHCb) communities have been collected and merged together to give a complete, wide, and consistent view of future prospects for BSM physics at the considered colliders. On top of the usual standard candles, such as supersymmetric simplified models and resonances, considered for the evaluation of future collider potentials, this report contains results on dark matter and dark sectors, long lived particles, leptoquarks, sterile neutrinos, axion-like particles, heavy scalars, vector-like quarks, and more. Particular attention is placed, especially in the study of the HL-LHC prospects, to the detector upgrades, the assessment of the future systematic uncertainties, and new experimental techniques. The general conclusion is that the HL-LHC, on top of allowing to extend the present LHC mass and coupling reach by $20-50\%$ on most new physics scenarios, will also be able to constrain, and potentially discover, new physics that is presently unconstrained. Moreover, compared to the HL-LHC, the reach in most observables will generally more than double at the HE-LHC, which may represent a good candidate future facility for a final test of TeV-scale new physics.
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Submitted 13 August, 2019; v1 submitted 19 December, 2018;
originally announced December 2018.
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A Letter of Intent for MATHUSLA: a dedicated displaced vertex detector above ATLAS or CMS
Authors:
Cristiano Alpigiani,
Austin Ball,
Liron Barak,
James Beacham,
Yan Benhammo,
Tingting Cao,
Paolo Camarri,
Roberto Cardarelli,
Mario Rodriguez-Cahuantzi,
John Paul Chou,
David Curtin,
Miriam Diamond,
Giuseppe Di Sciascio,
Marco Drewes,
Sarah C. Eno,
Erez Etzion,
Rouven Essig,
Jared Evans,
Oliver Fischer,
Stefano Giagu,
Brandon Gomes,
Andy Haas,
Yuekun Heng,
Giuseppe Iaselli,
Ken Johns
, et al. (39 additional authors not shown)
Abstract:
In this Letter of Intent (LOI) we propose the construction of MATHUSLA (MAssive Timing Hodoscope for Ultra-Stable neutraL pArticles), a dedicated large-volume displaced vertex detector for the HL-LHC on the surface above ATLAS or CMS. Such a detector, which can be built using existing technologies with a reasonable budget in time for the HL-LHC upgrade, could search for neutral long-lived particle…
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In this Letter of Intent (LOI) we propose the construction of MATHUSLA (MAssive Timing Hodoscope for Ultra-Stable neutraL pArticles), a dedicated large-volume displaced vertex detector for the HL-LHC on the surface above ATLAS or CMS. Such a detector, which can be built using existing technologies with a reasonable budget in time for the HL-LHC upgrade, could search for neutral long-lived particles (LLPs) with up to several orders of magnitude better sensitivity than ATLAS or CMS, while also acting as a cutting-edge cosmic ray telescope at CERN to explore many open questions in cosmic ray and astro-particle physics. We review the physics motivations for MATHUSLA and summarize its LLP reach for several different possible detector geometries, as well as outline the cosmic ray physics program. We present several updated background studies for MATHUSLA, which help inform a first detector-design concept utilizing modular construction with Resistive Plate Chambers (RPCs) as the primary tracking technology. We present first efficiency and reconstruction studies to verify the viability of this design concept, and we explore some aspects of its total cost. We end with a summary of recent progress made on the MATHUSLA test stand, a small-scale demonstrator experiment currently taking data at CERN Point 1, and finish with a short comment on future work.
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Submitted 2 November, 2018;
originally announced November 2018.
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Long-Lived Particles at the Energy Frontier: The MATHUSLA Physics Case
Authors:
David Curtin,
Marco Drewes,
Matthew McCullough,
Patrick Meade,
Rabindra N. Mohapatra,
Jessie Shelton,
Brian Shuve,
Elena Accomando,
Cristiano Alpigiani,
Stefan Antusch,
Juan Carlos Arteaga-Velázquez,
Brian Batell,
Martin Bauer,
Nikita Blinov,
Karen Salomé Caballero-Mora,
Jae Hyeok Chang,
Eung Jin Chun,
Raymond T. Co,
Timothy Cohen,
Peter Cox,
Nathaniel Craig,
Csaba Csáki,
Yanou Cui,
Francesco D'Eramo,
Luigi Delle Rose
, et al. (63 additional authors not shown)
Abstract:
We examine the theoretical motivations for long-lived particle (LLP) signals at the LHC in a comprehensive survey of Standard Model (SM) extensions. LLPs are a common prediction of a wide range of theories that address unsolved fundamental mysteries such as naturalness, dark matter, baryogenesis and neutrino masses, and represent a natural and generic possibility for physics beyond the SM (BSM). I…
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We examine the theoretical motivations for long-lived particle (LLP) signals at the LHC in a comprehensive survey of Standard Model (SM) extensions. LLPs are a common prediction of a wide range of theories that address unsolved fundamental mysteries such as naturalness, dark matter, baryogenesis and neutrino masses, and represent a natural and generic possibility for physics beyond the SM (BSM). In most cases the LLP lifetime can be treated as a free parameter from the $μ$m scale up to the Big Bang Nucleosynthesis limit of $\sim 10^7$m. Neutral LLPs with lifetimes above $\sim$ 100m are particularly difficult to probe, as the sensitivity of the LHC main detectors is limited by challenging backgrounds, triggers, and small acceptances. MATHUSLA is a proposal for a minimally instrumented, large-volume surface detector near ATLAS or CMS. It would search for neutral LLPs produced in HL-LHC collisions by reconstructing displaced vertices (DVs) in a low-background environment, extending the sensitivity of the main detectors by orders of magnitude in the long-lifetime regime. In this white paper we study the LLP physics opportunities afforded by a MATHUSLA-like detector at the HL-LHC. We develop a model-independent approach to describe the sensitivity of MATHUSLA to BSM LLP signals, and compare it to DV and missing energy searches at ATLAS or CMS. We then explore the BSM motivations for LLPs in considerable detail, presenting a large number of new sensitivity studies. While our discussion is especially oriented towards the long-lifetime regime at MATHUSLA, this survey underlines the importance of a varied LLP search program at the LHC in general. By synthesizing these results into a general discussion of the top-down and bottom-up motivations for LLP searches, it is our aim to demonstrate the exceptional strength and breadth of the physics case for the construction of the MATHUSLA detector.
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Submitted 5 March, 2019; v1 submitted 19 June, 2018;
originally announced June 2018.
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Les Houches 2017: Physics at TeV Colliders New Physics Working Group Report
Authors:
G. Brooijmans,
M. Dolan,
S. Gori,
F. Maltoni,
M. McCullough,
P. Musella,
L. Perrozzi,
P. Richardson,
F. Riva,
A. Angelescu,
S. Banerjee,
D. Barducci,
G. Bélanger,
B. Bhattacherjee,
M. Borsato,
A. Buckley,
J. M. Butterworth,
G. Cacciapaglia,
H. Cai,
A. Carvalho,
A. Chakraborty,
G. Cottin,
A. Deandrea,
J. de Blas,
N. Desai
, et al. (58 additional authors not shown)
Abstract:
We present the activities of the `New Physics' working group for the `Physics at TeV Colliders' workshop (Les Houches, France, 5--23 June, 2017). Our report includes new physics studies connected with the Higgs boson and its properties, direct search strategies, reinterpretation of the LHC results in the building of viable models and new computational tool developments.
We present the activities of the `New Physics' working group for the `Physics at TeV Colliders' workshop (Les Houches, France, 5--23 June, 2017). Our report includes new physics studies connected with the Higgs boson and its properties, direct search strategies, reinterpretation of the LHC results in the building of viable models and new computational tool developments.
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Submitted 27 March, 2018;
originally announced March 2018.
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The Hyperbolic Higgs
Authors:
Timothy Cohen,
Nathaniel Craig,
Gian F. Giudice,
Matthew McCullough
Abstract:
We introduce the Hyperbolic Higgs, a novel solution to the little hierarchy problem that features Standard Model neutral scalar top partners. At one-loop order, the protection from ultraviolet sensitivity is due to an accidental non-compact symmetry of the Higgs potential that emerges in the infrared. Once the general features of the effective description are detailed, a completion that relies on…
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We introduce the Hyperbolic Higgs, a novel solution to the little hierarchy problem that features Standard Model neutral scalar top partners. At one-loop order, the protection from ultraviolet sensitivity is due to an accidental non-compact symmetry of the Higgs potential that emerges in the infrared. Once the general features of the effective description are detailed, a completion that relies on a five dimensional supersymmetric framework is provided. Novel phenomenology is compared and contrasted with the Twin Higgs scenario.
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Submitted 11 September, 2019; v1 submitted 9 March, 2018;
originally announced March 2018.
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Clockwork / Linear Dilaton: Structure and Phenomenology
Authors:
Gian F. Giudice,
Yevgeny Kats,
Matthew McCullough,
Riccardo Torre,
Alfredo Urbano
Abstract:
The linear dilaton geometry in five dimensions, rediscovered recently in the continuum limit of the clockwork model, may offer a solution to the hierarchy problem which is qualitatively different from other extra-dimensional scenarios and leads to distinctive signatures at the LHC. We discuss the structure of the theory, in particular aspects of naturalness and UV completion, and then explore its…
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The linear dilaton geometry in five dimensions, rediscovered recently in the continuum limit of the clockwork model, may offer a solution to the hierarchy problem which is qualitatively different from other extra-dimensional scenarios and leads to distinctive signatures at the LHC. We discuss the structure of the theory, in particular aspects of naturalness and UV completion, and then explore its phenomenology, suggesting novel strategies for experimental searches. In particular, we propose to analyze the diphoton and dilepton invariant mass spectra in Fourier space in order to identify an approximately periodic structure of resonant peaks. Among other signals, we highlight displaced decays from resonantly-produced long-lived states and high-multiplicity final states from cascade decays of excited gravitons.
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Submitted 14 June, 2018; v1 submitted 22 November, 2017;
originally announced November 2017.
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Comment on "Disassembling the Clockwork Mechanism"
Authors:
Gian F. Giudice,
Matthew McCullough
Abstract:
We respond to the criticism raised in the paper arXiv:1704.07831.
We respond to the criticism raised in the paper arXiv:1704.07831.
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Submitted 29 May, 2017;
originally announced May 2017.
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Simplified Models for Displaced Dark Matter Signatures
Authors:
Oliver Buchmueller,
Albert De Roeck,
Matthew McCullough,
Kristian Hahn,
Kevin Sung,
Pedro Schwaller,
Tien-Tien Yu
Abstract:
We propose a systematic programme to search for long-lived neutral particle signatures through a minimal set of displaced searches requiring significant missing transverse energy (dMETs).
Our approach is to extend the well-established dark matter simplified models to include displaced vertices. The dark matter simplified models are used to describe the primary production vertex. A displaced seco…
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We propose a systematic programme to search for long-lived neutral particle signatures through a minimal set of displaced searches requiring significant missing transverse energy (dMETs).
Our approach is to extend the well-established dark matter simplified models to include displaced vertices. The dark matter simplified models are used to describe the primary production vertex. A displaced secondary vertex, characterised by the mass of the long-lived particle and its lifetime, is added for the displaced signature. We show how these models can be motivated by, and mapped onto, complete models such as gauge-mediated SUSY breaking and models of neutral naturalness. We also outline how this approach may be used to extend other simplified models to incorporate displaced signatures and to characterise searches for long-lived charged particles. Displaced vertices are a striking signature with virtually no backgrounds from SM processes, and thus provide an excellent target for the high-luminosity run of the Large Hadron Collider. The proposed models and searches provide a first step towards a systematic broadening of the displaced dark matter search programme.
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Submitted 21 April, 2017;
originally announced April 2017.
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Colorful Twisted Top Partners and Partnerium at the LHC
Authors:
Yevgeny Kats,
Matthew McCullough,
Gilad Perez,
Yotam Soreq,
Jesse Thaler
Abstract:
In scenarios that stabilize the electroweak scale, the top quark is typically accompanied by partner particles. In this work, we demonstrate how extended stabilizing symmetries can yield scalar or fermionic top partners that transform as ordinary color triplets but carry exotic electric charges. We refer to these scenarios as "hypertwisted" since they involve modifications to hypercharge in the to…
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In scenarios that stabilize the electroweak scale, the top quark is typically accompanied by partner particles. In this work, we demonstrate how extended stabilizing symmetries can yield scalar or fermionic top partners that transform as ordinary color triplets but carry exotic electric charges. We refer to these scenarios as "hypertwisted" since they involve modifications to hypercharge in the top sector. As proofs of principle, we construct two hypertwisted scenarios: a supersymmetric construction with spin-0 top partners, and a composite Higgs construction with spin-1/2 top partners. In both cases, the top partners are still phenomenologically compatible with the mass range motivated by weak-scale naturalness. The phenomenology of hypertwisted scenarios is diverse, since the lifetimes and decay modes of the top partners are model dependent. The novel coupling structure opens up search channels that do not typically arise in top-partner scenarios, such as pair production of top-plus-jet resonances. Furthermore, hypertwisted top partners are typically sufficiently long lived to form "top-partnerium" bound states that decay predominantly via annihilation, motivating searches for rare narrow resonances with diboson decay modes.
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Submitted 28 June, 2017; v1 submitted 11 April, 2017;
originally announced April 2017.
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A Clockwork Theory
Authors:
Gian F. Giudice,
Matthew McCullough
Abstract:
The clockwork is a mechanism for generating light particles with exponentially suppressed interactions in theories which contain no small parameters at the fundamental level. We develop a general description of the clockwork mechanism valid for scalars, fermions, gauge bosons, and gravitons. This mechanism can be implemented with a discrete set of new fields or, in its continuum version, through a…
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The clockwork is a mechanism for generating light particles with exponentially suppressed interactions in theories which contain no small parameters at the fundamental level. We develop a general description of the clockwork mechanism valid for scalars, fermions, gauge bosons, and gravitons. This mechanism can be implemented with a discrete set of new fields or, in its continuum version, through an extra spatial dimension. In both cases the clockwork emerges as a useful tool for model-building applications. Notably, the continuum clockwork offers a solution to the Higgs naturalness problem, which turns out to be the same as in linear dilaton duals of Little String Theory. We also elucidate the similarities and differences of the continuum clockwork with large extra dimensions and warped spaces. All clockwork models, in the discrete and continuum, exhibit novel phenomenology with a distinctive spectrum of closely spaced resonances.
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Submitted 20 October, 2016;
originally announced October 2016.
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Physics at a 100 TeV pp collider: beyond the Standard Model phenomena
Authors:
T. Golling,
M. Hance,
P. Harris,
M. L. Mangano,
M. McCullough,
F. Moortgat,
P. Schwaller,
R. Torre,
P. Agrawal,
D. S. M. Alves,
S. Antusch,
A. Arbey,
B. Auerbach,
G. Bambhaniya,
M. Battaglia,
M. Bauer,
P. S. Bhupal Dev,
A. Boveia,
J. Bramante,
O. Buchmueller,
M. Buschmann,
J. Chakrabortty,
M. Chala,
S. Chekanov,
C. -Y. Chen
, et al. (89 additional authors not shown)
Abstract:
This report summarises the physics opportunities in the search and study of physics beyond the Standard Model at a 100 TeV pp collider.
This report summarises the physics opportunities in the search and study of physics beyond the Standard Model at a 100 TeV pp collider.
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Submitted 2 June, 2016;
originally announced June 2016.
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Hunting for Dark Particles with Gravitational Waves
Authors:
Gian F. Giudice,
Matthew McCullough,
Alfredo Urbano
Abstract:
The LIGO observation of gravitational waves from a binary black hole merger has begun a new era in fundamental physics. If new dark sector particles, be they bosons or fermions, can coalesce into exotic compact objects (ECOs) of astronomical size, then the first evidence for such objects, and their underlying microphysical description, may arise in gravitational wave observations. In this work we…
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The LIGO observation of gravitational waves from a binary black hole merger has begun a new era in fundamental physics. If new dark sector particles, be they bosons or fermions, can coalesce into exotic compact objects (ECOs) of astronomical size, then the first evidence for such objects, and their underlying microphysical description, may arise in gravitational wave observations. In this work we study how the macroscopic properties of ECOs are related to their microscopic properties, such as dark particle mass and couplings. We then demonstrate the smoking gun exotic signatures that would provide observational evidence for ECOs, and hence new particles, in terrestrial gravitational wave observatories. Finally, we discuss how gravitational waves can test a core concept in general relativity: Hawking's area theorem.
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Submitted 3 October, 2016; v1 submitted 4 May, 2016;
originally announced May 2016.
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S-Channel Dark Matter Simplified Models and Unitarity
Authors:
Christoph Englert,
Matthew McCullough,
Michael Spannowsky
Abstract:
The ultraviolet structure of $s$-channel mediator dark matter simplified models at hadron colliders is considered. In terms of commonly studied $s$-channel mediator simplified models it is argued that at arbitrarily high energies the perturbative description of dark matter production in high energy scattering at hadron colliders will break down in a number of cases. This is analogous to the well d…
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The ultraviolet structure of $s$-channel mediator dark matter simplified models at hadron colliders is considered. In terms of commonly studied $s$-channel mediator simplified models it is argued that at arbitrarily high energies the perturbative description of dark matter production in high energy scattering at hadron colliders will break down in a number of cases. This is analogous to the well documented breakdown of an EFT description of dark matter collider production. With this in mind, to diagnose whether or not the use of simplified models at the LHC is valid, perturbative unitarity of the scattering amplitude in the processes relevant to LHC dark matter searches is studied. The results are as one would expect: at the LHC and future proton colliders the simplified model descriptions of dark matter production are in general valid. As a result of the general discussion, a simple new class of previously unconsidered `Fermiophobic Scalar' simplified models is proposed, in which a scalar mediator couples to electroweak vector bosons. The Fermiophobic simplified model is well motivated and exhibits interesting collider and direct detection phenomenology.
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Submitted 27 April, 2016;
originally announced April 2016.
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Theory Advances in BSM Physics
Authors:
Matthew McCullough
Abstract:
Rather than attempting to summarise the full spectrum of recent advances in Beyond the Standard Model (BSM) theory, which are many, in this talk I will instead take the opportunity to focus on two frameworks related to the hierarchy problem currently receiving significant attention. They are the `Twin Higgs' and the `Relaxion'. I will summarise the basic underlying structure of these theories at a…
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Rather than attempting to summarise the full spectrum of recent advances in Beyond the Standard Model (BSM) theory, which are many, in this talk I will instead take the opportunity to focus on two frameworks related to the hierarchy problem currently receiving significant attention. They are the `Twin Higgs' and the `Relaxion'. I will summarise the basic underlying structure of these theories at a non-expert level and highlight some interesting phenomenological signatures or outstanding problems.
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Submitted 25 April, 2016;
originally announced April 2016.
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Digamma, what next?
Authors:
Roberto Franceschini,
Gian F. Giudice,
Jernej F. Kamenik,
Matthew McCullough,
Francesco Riva,
Alessandro Strumia,
Riccardo Torre
Abstract:
If the 750 GeV resonance in the diphoton channel is confirmed, what are the measurements necessary to infer the properties of the new particle and understand its nature? We address this question in the framework of a single new scalar particle, called digamma ($\digamma$). We describe it by an effective field theory, which allows us to obtain general and model-independent results, and to identify…
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If the 750 GeV resonance in the diphoton channel is confirmed, what are the measurements necessary to infer the properties of the new particle and understand its nature? We address this question in the framework of a single new scalar particle, called digamma ($\digamma$). We describe it by an effective field theory, which allows us to obtain general and model-independent results, and to identify the most useful observables, whose relevance will remain also in model-by-model analyses. We derive full expressions for the leading-order processes and compute rates for higher-order decays, digamma production in association with jets, gauge or Higgs bosons, and digamma pair production. We illustrate how measurements of these higher-order processes can be used to extract couplings, quantum numbers, and properties of the new particle.
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Submitted 11 May, 2016; v1 submitted 21 April, 2016;
originally announced April 2016.
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What is the gamma gamma resonance at 750 GeV?
Authors:
Roberto Franceschini,
Gian F. Giudice,
Jernej F. Kamenik,
Matthew McCullough,
Alex Pomarol,
Riccardo Rattazzi,
Michele Redi,
Francesco Riva,
Alessandro Strumia,
Riccardo Torre
Abstract:
Run 2 LHC data show hints of a new resonance in the diphoton distribution at an invariant mass of 750 GeV. We analyse the data in terms of a new boson, extracting information on its properties and exploring theoretical interpretations. Scenarios covered include a narrow resonance and, as preliminary indications suggest, a wider resonance. If the width indications persist, the new particle is likel…
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Run 2 LHC data show hints of a new resonance in the diphoton distribution at an invariant mass of 750 GeV. We analyse the data in terms of a new boson, extracting information on its properties and exploring theoretical interpretations. Scenarios covered include a narrow resonance and, as preliminary indications suggest, a wider resonance. If the width indications persist, the new particle is likely to belong to a strongly-interacting sector. We also show how compatibility between Run 1 and Run 2 data is improved by postulating the existence of an additional heavy particle, whose decays are possibly related to dark matter.
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Submitted 19 February, 2016; v1 submitted 15 December, 2015;
originally announced December 2015.
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Natural Heavy Supersymmetry
Authors:
Brian Batell,
Gian F. Giudice,
Matthew McCullough
Abstract:
We study how, as a result of the scanning of supersymmetry breaking during the cosmological evolution, a relaxation mechanism can naturally determine a hierarchy between the weak scale and the masses of supersymmetric particles. Supersymmetry breaking is determined by QCD instanton effects, in an extremely minimal setup in which a single field drives the relaxation and breaks supersymmetry. Since…
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We study how, as a result of the scanning of supersymmetry breaking during the cosmological evolution, a relaxation mechanism can naturally determine a hierarchy between the weak scale and the masses of supersymmetric particles. Supersymmetry breaking is determined by QCD instanton effects, in an extremely minimal setup in which a single field drives the relaxation and breaks supersymmetry. Since gauginos are lighter than the other supersymmetric particles by a one-loop factor, the theory is a realisation of Split Supersymmetry free from the naturalness problem.
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Submitted 24 November, 2015; v1 submitted 2 September, 2015;
originally announced September 2015.