Standard Model Fields Research Articles

Theoretical constraints on models with vectorlike fermions

We provide a set of theoretical constraints on models in which the Standard Model field content is extended by vectorlike fermions and in some cases also by a real scalar singlet. Our approach is based on the study of electroweak vacuum stability, perturbativity of model couplings, and gauge couplings unification with the use of renormalization group equations. We show that careful analysis of these issues leads to strong constraints on the parameter space of the considered models. This, in turn, has important implications for phenomenology, as we show using examples of the double Higgs boson production, electroweak precision observables, and the electroweak phase transition. Published by the American Physical Society 2024

Complex dark photon dark matter EFT

We construct an effective field theory for complex Stueckelberg dark photon dark matter. Such an effective construction can be realized by writing down a complete set of operators up to dimension six built with the complex dark photon and Standard Model fields. Classifying the effective operators, we find that in order to properly take into account the non-renormalizable nature of an interacting massive vector, the size of the Wilson coefficients should be naturally smaller than naively expected. This can be consistently taken into account by a proper power counting, that we suggest. First we apply this to collider bounds on light dark matter, then to direct detection searches by extending the list of non-relativistic operators to include the case of complex vectors. In the former we correctly find scaling limits for small masses, while in the latter we mostly focus on electric dipole interactions, that are the signatures of this type of dark matter. Simple UV completions that effectively realize the above scenarios are also outlined.

Lorentz violating backgrounds from quadratic, shift-symmetric, ultralight dark matter

We consider an effective theory for a shift-symmetric, quadratically-coupled, ultralight spin-0 field. The leading CP conserving interactions with Standard Model fields in the effective theory arise at dimension 8. We discuss the renormalization group evolution and positivity bounds on these operators, as well as their possible UV origins. Assuming that the spin-0 field is associated with an ultralight dark matter candidate, we discuss the effects of the dimension-8 operators on experiments searching for the oscillation of fundamental constants and Lorentz violation. We find that the direct bounds on these two effects are of similar strength but rather weak, corresponding to a UV cutoff scale of keV order, as they are mediated by dimension-8 operators.

Astrophysical constraints from synchrotron emission on very massive decaying dark matter

If the cosmological dark matter (DM) couples to Standard Model (SM) fields, it can decay promptly to SM states in a highly energetic hard process, which subsequently showers and hadronizes to give stable particles including e±, γ, p±, and νν¯ at lower energy. If the DM particle is very heavy, the high-energy e±, due to the Klein-Nishina cross section suppression, preferentially lose energy via synchrotron emission which, in turn, can be of unusually high energies. Here, we present previously unexplored bounds on heavy decaying DM up to the Planck scale, by studying the synchrotron emission from the e± produced in the ambient Galactic magnetic field. In particular, we explore the sensitivity of the resulting constraints on the DM decay width to (i) different SM decay channels, to (ii) the Galactic magnetic field configurations, and to (iii) various different DM density profiles proposed in the literature. We find that constraints from the synchrotron component complement and improve on constraints from very high-energy cosmic-ray and gamma-ray observatories targeting the prompt emission when the DM is sufficiently massive, most significantly for masses in excess of 1012 GeV. Published by the American Physical Society 2024

Supermassive gauginos in supergravity inflation with high-scale SUSY breaking

A model of supergravity inflation we recently proposed can produce slow roll inflation and a realistic spectrum of particles even without F-term supersymmetry breaking. Supersymmetry is broken only by a D-term induced by a recently discovered new type of Fayet-Iliopoulos (FI) term. Almost all supersymmetric partners of the standard model fields can get masses as high as the inflationary Hubble scale. The exception is gauginos, for which the vanishing of F-terms implies an exact cancellation that keeps their masses exactly zero. To cure this problem without spoiling the simplicity of our model we introduce a new term that further enlarges the space of supergravity effective actions. It is an F-term that, similarly to the new FI term, becomes singular in the supersymmetric limit. We show that this term can produce large gaugino masses without altering the spectrum of other states and without lowering the cutoff of the effecive theory.

Exotic compact objects and light bosonic fields

In this article, we discuss the effect of light, nongauge, bosonic degrees of freedom on the exterior spacetime of an exotic compact object. We show that such fields generically introduce large deviations from black hole spacetimes of general relativity near and outside the surfaces of ultracompact exotic objects unless one assumes they totally decouple from the standard model or new heavy fields. Hence, using black hole spacetimes of general relativity to model ultracompact exotic objects and their perturbations relies implicitly on this assumption or on the absence of such fields. Published by the American Physical Society 2024

Axion-like particles in radiative quarkonia decays

Radiative quarkonia decays offer an ideal setting for probing Axion-Like Particle (ALP) interactions. This paper provides a comprehensive review of ALP production mechanisms through the e+e− → γa process at B- and Charm-factories, alongside an analysis of potential ALP decay channels. We derive constraints on ALP couplings to Standard Model (SM) fields, based on recent experimental results on quarkonia decays by the Belle II and BESIII collaborations. The analysis distinguishes between “invisible” and “visible” ALP decay scenarios. The “invisible” scenario, characterised by a mono-γ plus missing-energy signature, enables stringent limits on ALP-photon and ALP-quark (b or c) couplings. Moreover, extensive research at flavour factories has explored various “visible” ALP decays into SM final states, which depend on a larger set of ALP-SM couplings. To streamline the “visible” ALP scenario, we introduce additional theoretical assumptions, such as universal ALP-fermion couplings, or we adopt specific benchmark ALP models, aiming to minimise the number of independent variables in our analysis.

Model-independent estimates for loop-induced baryon-number-violating nucleon decays

Baryon number is an accidental symmetry of the Standard Model (SM) Lagrangian that so far has been measured to be exactly preserved, although it is expected to be violated at higher energies. In this work we compute order-of-magnitude estimates for the matching contributions of generic ultraviolet models to effective operators that generate nucleon decay processes. This is done in a systematic and automated way using operators constructed from SM fields up to dimension nine and working in a framework that has proved useful in the study of lepton-number violation. For each of the operators we derive estimates for the rates of different nucleon-decay channels. These allow us to establish model-independent lower bounds on the underlying new-physics scale and identify potential correlations between the various decay modes. The results are most relevant for families of models that generate the considered operator. This analysis is especially timely given the expected future sensitivities in numerous experiments such as Hyper-K, DUNE, JUNO and THEIA.

Heavy neutral leptons from kaons in effective field theory

In the framework of the low-energy effective theory containing, in addition to the Standard-Model fields, heavy neutral leptons (HNLs), we compute the decay rates of neutral and charged kaons into HNLs. We consider both lepton-number-conserving and lepton-number-violating four-fermion operators, taking into account also the contribution of active-heavy neutrino mixing. Assuming that the produced HNLs are long-lived, we perform simulations and calculate the sensitivities of future long-lived-particle (LLP) detectors at the high-luminosity LHC as well as the near detector of the Deep Underground Neutrino Experiment (DUNE-ND) to the considered scenario. When applicable, we also recast the existing bounds on the minimal mixing case obtained by NA62, T2K, and PS191. Our findings show that, while the future LHC LLP detectors can probe currently allowed parameter space only in certain benchmark scenarios, DUNE-ND should be sensitive to parameter space beyond the current bounds in almost all the benchmark scenarios, and, for some of the effective operators considered, it can even probe new-physics scales in excess of 3000 TeV. Published by the American Physical Society 2024

Leptoquark-induced CLFV decays with a light SM-singlet scalar

The Standard Model (SM), if augmented with a light SM-singlet scalar ϕ and a TeV-scale scalar leptoquark (LQ) S1, 2-body charged lepton flavor violating (CLFV) decay channels can be accessed with ϕ as one of the final states, where the leading order effective interactions between ϕ and the SM fields arise at one-loop level. Further, in the presence of S1, ϕ can mediate 3-body CLFV processes with either two photons or two gluons in the final states. Thus, the model predicts an exotic 3-body CLFV channel: ℓA→ℓBgg, which can be tested/constrained only through some future high-energy experiments looking for di-gluon signals from a leptonic decay.

Collider imprints of a right handed neutrino magnetic moment operator

We consider the most general effective Lagrangian up to dimension five, built with Standard Model fields and right-handed neutrinos (RHNs) Ni. Assuming that the RHNs are present near the electroweak scale, we study the phenomenology of the RHNs and highlight the differences that arise due to the inclusion of dimension five operators. We specifically focus on the production process e+e−/pp→NiNj, which comes from the dimension five magnetic moment operator. We find that this production process followed by the decay chains such as Ni→Njγ, Ni→νjγ, and Ni→ℓ±jj leads to striking collider signatures, which might help to probe the Majorana nature of neutrinos. We discuss the current collider constraints on this operator, as well as projected limit at future colliders. In addition, we discuss the stellar-cooling bounds applicable to the RHN mass below 0.1 GeV. Published by the American Physical Society 2024

Direct production of SM-singlet scalars at the muon collider

The present work proposes a minimal extension of the Standard Model (SM) where a gauge-singlet scalar (ϕ) can be directly produced at the muon colliders without relying on its mixing with any other doublet state present in the theory. The New Physics (NP) interactions include a TeV-scale scalar leptoquark of electromagnetic charge 1/3 arising naturally in a grand unifying gauge formulation. Within the proposed framework, the SM-singlet scalar can effectively couple to various SM fields at the one-loop level, out of which the μ¯μϕ and γγϕ couplings are crucial to produce it at the future muon colliders. Assuming O(1) NP couplings, the decay widths and production cross-section of the singlet scalar have been discussed in detail over the considered parameter space. Depending on the resonance scale, di-lepton and/or di-gluon channels can be significant to test/falsify the model.

A closer look at the U(1)B−L explanation of the ATOMKI nuclear anomalies

We revisit the gauged U(1)B−L explanation of the ATOMKI nuclear anomalies, in which the new gauge boson is the hypothetical X(17) particle. It is known that the vanilla B − L scenario is unable to account for appropriate couplings, namely the suppression of the couplings of X(17) to neutrinos, which motivates adding vector-like leptons. The simplest case, in which the new fields have B − L charges equal to 1, is highly disfavoured since it requires large mixing with the Standard Model fields. One solution recently put forward is to consider large B − L charges to counterbalance small mixing. We show that, in this scenario, and after taking into account several phenomenological constraints, the dominant contribution to the muon anomalous magnetic moment (g − 2)μ is expected to be extremely large and with a negative sign, being thus excluded by experiment.

Nonabelian kinetic mixing in a confining phase: a framework for composite dark photons

Dark matter from a hidden sector with SU(N) gauge symmetry can have a nonabelian kinetic mixing portal with the standard model. The dark photon becomes massive in the confining phase without the need for spontaneous symmetry breaking. Depending on the particle content of the dark sector, there can be two or more composite vectors that get kinetic mixing through a heavy mediator particle X. This provides a model of composite dark photons giving a portal for direct detection of dark baryons. Avoiding exotic charged relics requires additional couplings allowing X to decay to dark quarks and standard model fields, leading to further portals between the dark matter and the standard model. We comprehensively study the constraints on such models from colliders, rare decays, direct detection, and big bang nucleosynthesis.

Foundations of time-symmetric physics. 2. Quantum field theory

Time symmetric theory (TST), described in the first article and based on the equivalence principle of particle physics, is applied to quantum fields and time-symmetric quantum field theory is formulated. This principle is based on the Zisman-Stückelberg-Feynman interpretation, where antiparticles are described as negative energy particles moving backward in time, and generalizes it to the rest frames of such particles also moving backward in time. In TST, relativistic fields are described by complex field operators, and observables are automatically normally ordered. For this reason, at time-symmetric quantization (TSQ) of fields, the vacuum energy and charge disappear and there is no cosmological constant problem. In TST, the probabilities of states are positive, and the probability currents can have two signs depending on the direction of evolution along the time axis. The operator of interaction current is defined as the product of the probability current and the matrix of interaction constants. Applications of TST to the Standard Model fields and graviton field are considered. In TSQ correctly describes the observable effects, since in terms of ordinary time it leads to a standard diagram technique, transforming mathematical recipes of the latter into logical consequences of physical principles.

Aspects of the Domain-Wall Standard Model

Abstract In the “Domain-Wall Standard Model,” all the Standard Model (SM) fields are localized in certain domains in a non-compact 5D space-time. While the SM is realized as a 4D effective theory at low energies, the model involves Kaluza–Klein (KK) modes of the SM particles. In this paper we introduce two simple solvable examples which lead to domain-wall configurations for the SM particles and their KK-modes. Based on the examples, we address a variety of phenomenologies of the Domain-Wall SM, such as the KK-mode gauge boson phenomenology at the Large Hadron Collider (LHC), the effect of the KK-mode SM fermions on Higgs boson phenomenology, and the KK-mode fermion search at the LHC with its decay into a corresponding SM fermion and a Nambu–Goldstone boson associated with a spontaneous breaking of the translational invariance in the 5th dimension. We also propose a simple unified picture of localizing all the SM fields.

Exploring mixed lepton-quark interactions in non-resonant leptoquark production at the LHC

Searches for new physics (NP) at particle colliders typically involve multivariate analysis of kinematic distributions of final state particles produced in a decay of a hypothetical NP resonance. Since the pair-production cross-sections mediated by such resonances are strongly suppressed by the NP scale, this analysis becomes less relevant for NP searches for masses of the BSM resonance above 1 TeV. On the other hand, t-channel processes are less sensitive to the mass of the virtual mediator and therefore larger phase-space can be potentially probed as well as the couplings between the NP particles and the Standard Model fields. The fact that transitions between different generations of quarks and leptons may exist, the potential of the search presented in this article can be used, as a reference guide, to enlarge significantly the scope of searches performed at the LHC to flavour off-diagonal channels, in a theoretically consistent approach. In this work, we study non-resonant production of scalar leptoquarks which have been proposed in the literature to provide a potential avenue for radiative generation of neutrino masses, accommodating as well the existing flavour physics data. Final states involving just two muons at the LHC (μ+μ−), are used as a well-motivated case study.

Heavy resonances and the oblique parameters S and T

It has been confirmed experimentally the existence of a mass gap between Standard Model (SM) and eventual Beyond Standard Model (BSM) fields. Therefore, the use of effective approaches to search for fingerprints of New Physics is very appealing. A non-linear realizations of the Electroweak Symmetry Breaking is considered here, where the Higgs is a singlet with free couplings and the SM fields are also coupled to bosonic heavy resonances. A one-loop-level calculation of the oblique S and T parameters is presented here. This analysis allows us to constrain resonance masses to be above the TeV scale, ▪TeV, in good agreement with our previous determinations, where these observables were computed with a more simplified Lagrangian.

CP-violating axion interactions II: axions as dark matter

Axions provide a solution to the strong CP problem and are excellent dark matter candidates. The presence of additional sources of CP violation, for example to account for the matter/antimatter asymmetry of the universe, can lead to CP-violating interactions between axions and Standard Model fields. In case axions form a coherent dark matter background, this leads to time-oscillating fundamental constants such as the fine-structure constant and particle masses. In this work we compare the sensitivity of various searches for CP-odd axion interactions. These include fifth-force experiments, searches for time-oscillating constants induced by axion dark matter, and direct limits from electric dipole moment experiments. We show that searches for oscillating constants can outperform fifth-force experiments in the regime of small axion masses, but, in general, do not reach the sensitivity of electric dipole moment experiments.

Contributions of inert electroweak multiplets to Higgs properties

New physics could manifest itself in the form of electroweak multiplets that interact at tree level with the Higgs boson but do not mix with Standard Model fields or acquire expectation values. In this paper, we study the potential contributions of such inert multiplets to several crucial Higgs properties, namely, the branching ratio of the Higgs to a Z boson and a photon (or massless dark photon) and the triple Higgs coupling. Constraints from the Higgs signal strengths, oblique parameters and unitarity are taken into account.