<p>We study and classify <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>S</mi><mi>U</mi><mo stretchy="false">(</mo><mn>5</mn><mo stretchy="false">)</mo></mrow></math>-grand unified theory (GUT) completions of accidental composite dark matter models. These theories postulate new vectorlike confining dark color dynamics and give an accidentally stable baryonic dark matter candidate. In realistic theories, dark fermion <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>U</mi><mo stretchy="false">(</mo><mn>5</mn><mo stretchy="false">)</mo></math> irreps split into light dark quarks, whose bound states include the dark matter, and their much heavier GUT partners. A simple analysis shows that such a mass hierarchy requires a fine-tuning of parameters and thus implies a naturalness problem. We select theories requiring that all dangerous metastable states decay before the onset of nucleosynthesis through higher-dimensional operators generated at the GUT scale or at the mass scale of dark quark GUT partners. Demanding Standard Model gauge coupling unification puts severe constraints on the landscape of viable theories. Under the assumption of an approximately degenerate spectrum of dark quark GUT partners, we find that only one model gives precision unification.</p>

Israel

Salvatore Bottaro

Italy

Roberto Contino

Belgium

Sonali Verma

Grand unified theory framework for accidental composite dark matter

Our recent works <cross-refs refid='br0010 br0020' id='crs0020'>[1,2]</cross-refs> revisit the proof of chiral symmetry breaking in the confining regime of four-dimensional QCD-like theories, i.e. <math altimg='si1.svg'><mi>S</mi><mi>U</mi><mo stretchy='false'>(</mo><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub><mo stretchy='false'>)</mo></math> gauge theories with <math altimg='si2.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>f</mi></mrow></msub></math> flavors of vectorlike quarks in the fundamental representation. The analysis relies on the structure of &#8216;t Hooft anomaly matching and persistent mass conditions for theories with same <math altimg='si3.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub></math> and different <math altimg='si2.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>f</mi></mrow></msub></math>. In this paper, we work out concrete examples with <math altimg='si4.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>3</mn></math> and <math altimg='si5.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>5</mn></math> to support and elucidate the results of <cross-refs refid='br0010 br0020' id='crs0030'>[1,2]</cross-refs>. Within the same examples, we also test some claims made in earlier works.

Luca Ciambriello

Ling-Xiao Xu

On the proof of chiral symmetry breaking through anomaly matching in QCD-like theories: An exemplification

We demonstrate that chiral symmetry breaking occurs in the confining regime of QCD-like theories with <math altimg='si1.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub></math> colors and <math altimg='si2.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>f</mi></mrow></msub></math> flavors. Our proof is based on a novel strategy, called &#8216;downlifting&#8217;, by which solutions of the 't Hooft anomaly matching and persistent mass conditions for a theory with <math altimg='si3.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>f</mi></mrow></msub><mo linebreak='goodbreak' linebreakstyle='after'>&#8722;</mo><mn>1</mn></math> flavors are constructed from those of a theory with <math altimg='si2.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>f</mi></mrow></msub></math> flavors, while <math altimg='si1.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub></math> is fixed. By induction, chiral symmetry breaking is proven for any <math altimg='si22.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>f</mi></mrow></msub><mo>&#8805;</mo><msub><mrow><mi>p</mi></mrow><mrow><mi>m</mi><mi>i</mi><mi>n</mi></mrow></msub></math> in the confining regime, where <math altimg='si5.svg'><msub><mrow><mi>p</mi></mrow><mrow><mi>m</mi><mi>i</mi><mi>n</mi></mrow></msub></math> is the smallest prime factor of <math altimg='si1.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub></math>. The proof can be extended to <math altimg='si6.svg'><msub><mrow><mi>N</mi></mrow><mrow><mi>f</mi></mrow></msub><mo linebreak='goodbreak' linebreakstyle='after'>&lt;</mo><msub><mrow><mi>p</mi></mrow><mrow><mi>m</mi><mi>i</mi><mi>n</mi></mrow></msub></math> under the additional assumption on the absence of phase transitions when quark masses are sent to infinity. Our results do not rely on assumptions on the spectrum of massless bound states other than the fact that they are color-singlet hadrons.

Andrea Luzio

France

Marcello Romano

A novel strategy to prove chiral symmetry breaking in QCD-like theories

We critically reconsider the argument based on ’t Hooft anomaly matching that aims at proving chiral symmetry breaking in confining four-dimensional quantum chromodynamics-like theories with <math><msub><mi>N</mi><mi>c</mi></msub><mo>&gt;</mo><mn>2</mn></math> colors and <math><msub><mi>N</mi><mi>f</mi></msub></math> flavors. The main line of reasoning relies on a property of the solutions of the anomaly matching and persistent mass equations called <math><msub><mi>N</mi><mi>f</mi></msub></math>-independence. In previous works, the validity of <math><msub><mi>N</mi><mi>f</mi></msub></math>-independence was assumed based on qualitative arguments, but it was never proven rigorously. We provide a detailed proof and clarify under which (dynamical) conditions it holds. Our results are valid for a generic spectrum of massless composite fermions including baryons and exotics.

Proof of chiral symmetry breaking from anomaly matching in QCD-like theories

We introduce a class of composite axion models that provide a natural solution to the strong CP problem, and possibly account for the observed dark matter abundance. The QCD axion arises as a composite Nambu-Goldstone boson (NGB) from the dynamics of a chiral gauge theory with a strongly-interacting and confining SU(N) factor and a weakly-interacting U(1), with no fundamental scalar fields. The Peccei-Quinn (PQ) symmetry is accidental and all the mass scales are generated dynamically. We analyze specific models where the PQ symmetry is broken only by operators of dimension 12 or higher. We also classify several other models where the PQ symmetry can be potentially protected up to the dimension 15 or 18 level. Our framework can be easily extended to a scenario where the Standard Model (SM) is unified into a simple gauge group, and we discuss the case of non-supersymmetric SU(5) unification. The GUT models predict the existence of additional pseudo NGBs, parametrically lighter than the GUT and PQ scales, which could have an impact on the cosmological evolution and leave observable signatures. We also clarify the selection rules under which higher-dimensional PQ-violating operators can generate a potential for the axion in the IR, and provide a discussion of the discrete symmetries in composite axion models associated to the number of domain walls. These results can be of general interest for composite axion models based on a QCD-like confining gauge group.

United States

Alessandro Podo

United Kingdom

Filippo Revello

Chiral models of composite axions and accidental Peccei-Quinn symmetry

We consider the possible existence of a SM-neutral and light dark sector coupled to the visible sector through irrelevant portal interactions. Scenarios of this kind are motivated by dark matter and arise in various extensions of the Standard Model. We characterize the dark dynamics in terms of one ultraviolet scale Λuv, at which the exchange of heavy mediator fields generates the portal operators, and by one infrared scale ΛIR, setting the mass gap. At energies ΛIR « E « Λuv the dark sector behaves like a conformal field theory and its phenomenology can be studied model independently. We derive the constraints set on this scenario by high- and low-energy laboratory experiments and by astrophysical observations. Our results are conservative and serve as a minimum requirement that must be fulfilled by the broad class of models satisfying our assumptions, of which we give several examples. The experimental constraints are derived in a manner consistent with the validity of the effective field theory used to define the portal interactions. We find that high-energy colliders give the strongest bounds and exclude UV scales up to a few TeV, but only in specific ranges of the IR scale. The picture emerging from current searches can be taken as a starting point to design a future experimental strategy with broader sensitivity.

Kevin Max

Rashmish Mishra

Searching for elusive dark sectors with terrestrial and celestial observations

A class of chiral gauge theories is studied with accidentally-stable pseudo Nambu-Goldstone bosons playing the role of dark matter (DM). The gauge group contains a vector-like dark color factor that confines at energies larger than the electroweak scale, and a U(1) D  factor that remains weakly coupled and is spontaneously broken. All new scales are generated dynamically, including the DM mass, and the IR dynamics is fully calculable. We analyze minimal models of this kind with dark fermions transforming as non-trivial vector-like representations of the Standard Model (SM) gauge group. In realistic models, the DM candidate is a SM singlet and comes along with charged partners that can be discovered at high-energy colliders. The phenomenology of the lowest-lying new states is thus characterized by correlated predictions for astrophysical observations and laboratory experiments.

Composite dark matter from strongly-interacting chiral dynamics

We introduce the gluequark Dark Matter candidate, an accidentally stable bound state made of adjoint fermions and gluons from a new confining gauge force. Such scenario displays an unusual cosmological history where perturbative freeze-out is followed by a non-perturbative re-annihilation period with possible entropy injection. When the gluequark has electroweak quantum numbers, the critical density is obtained for masses as large as PeV. Independently of its mass, the size of the gluequark is determined by the confinement scale of the theory, leading at low energies to annihilation rates and elastic cross sections which are large for particle physics standards and potentially observable in indirect detection experiments.

Andrea Mitridate

Michele Redi

Gluequark dark matter

The production of pairs of Higgs bosons at hadron colliders provides unique information on the Higgs sector and on the mechanism underlying electroweak symmetry breaking (EWSB). Most studies have concentrated on the gluon-fusion production mode which has the largest cross section. However, despite its small production rate, the vector-boson fusion channel can also be relevant since even small modifications of the Higgs couplings to vector bosons induce a striking increase of the cross section as a function of the invariant mass of the Higgs boson pair. In this work we exploit this unique signature to propose a strategy to extract the hhVV quartic coupling and provide model-independent constraints on theories where EWSB is driven by new strong interactions. We take advantage of the higher signal yield of the bb¯bb¯ final state and make extensive use of jet-substructure techniques to reconstruct signal events with a boosted topology, characteristic of large partonic energies, where each Higgs boson decays to a single collimated jet. Our results demonstrate that the hhVV coupling can be measured with 45% (20%) precision at the LHC for L=300 (3000) fb -1 , while a 1% precision can be achieved at a 100 TeV collider.

Fady Bishara

CERN

Switzerland

Netherlands

Juan Rojo

Higgs pair production in vector-boson fusion at the LHC and beyond

We discuss the conditions for an effective field theory (EFT) to give an adequate low-energy description of an underlying physics beyond the Standard Model (SM). Starting from the EFT where the SM is extended by dimension-6 operators, experimental data can be used without further assumptions to measure (or set limits on) the EFT parameters. The interpretation of these results requires instead a set of broad assumptions (e.g. power counting rules) on the UV dynamics. This allows one to establish, in a bottom-up approach, the validity range of the EFT description, and to assess the error associated with the truncation of the EFT series. We give a practical prescription on how experimental results could be reported, so that they admit a maximally broad range of theoretical interpretations. Namely, the experimental constraints on dimension-6 operators should be reported as functions of the kinematic variables that set the relevant energy scale of the studied process. This is especially important for hadron collider experiments where collisions probe a wide range of energy scales.