Standard Model Gauge Symmetry Research Articles

Electrobaryonic axion: hair of neutron stars

Axion-like particles are predicted in many physics scenarios beyond the Standard Model (SM). Their interactions with SM particles may arise from the triangle anomaly of the associated global symmetry, along with other SM global and gauge symmetries, including anomalies with the global baryon number and electromagnetic gauge symmetries. We initiate the phenomenological study of the corresponding “electrobaryonic axion”—a particle that couples with both the baryon chemical potential and the electromagnetic field. Neutron stars, particularly magnetars, possessing high baryon density and strong magnetic fields, can naturally develop a thin axion hair around their surface. In this study, we calculate this phenomenon, considering the effects of neutron star rotation and general relativity. For axion particles lighter than the neutron star rotation frequency, the anomalous interaction can also induce the emission of axion particles from the neutron star. In the light axion regime, this emission can significantly contribute to the neutron star cooling rate.

The QCD axion sum rule

We demonstrate that the true QCD axion that solves the strong CP problem can be found in all generality outside the customary standard QCD band, with QCD being the sole source of Peccei-Quinn breaking. The essential reason is that the basis of axion-gluon interactions does not need to coincide with the mass basis. Specifically, we consider the case in which the QCD axion field is not the only singlet scalar in Nature but it mixes with other singlet scalars (besides the η′). We determine the exact mathematical condition for an arbitrary N-scalar potential to be Peccei-Quinn invariant. Such potentials provide extra sources of mass for the customary axion without enlarging the Standard Model gauge symmetry. The contribution to the axion mass stemming from the QCD topological susceptibility is shown to be shared then among the N axion eigenstates through a precise sum rule. Their location can only be displaced to the right of the standard QCD band. We demonstrate that the axion closest to this band can be displaced from it by a factor of N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{N} $$\\end{document} at most, and this corresponds to the case in which all axion signals are maximally deviated. Conversely, if one axion is found on the standard QCD band, the other eigenstates will be out of experimental reach. Our results imply that any ALP experiment which finds a signal to the right of the standard QCD axion band can be solving the strong CP problem within QCD, with the associated N − 1 excitations to be found in an area of parameter space that we determine. We illustrate the results and phenomenology in some particular cases.

Three generations of colored fermions with S_3 family symmetry from Cayley–Dickson sedenions

An algebraic representation of three generations of fermions with SU(3)_C color symmetry based on the Cayley–Dickson algebra of sedenions {mathbb {S}} is constructed. Recent constructions based on division algebras convincingly describe a single generation of leptons and quarks with Standard Model gauge symmetries. Nonetheless, an algebraic origin for the existence of exactly three generations has proven difficult to substantiate. We motivate mathbb {S} as a natural algebraic candidate to describe three generations with SU(3)_C gauge symmetry. We initially represent one generation of leptons and quarks in terms of two minimal left ideals of mathbb {C}ell (6), generated from a subset of all left actions of the complex sedenions on themselves. Subsequently we employ the S_3 automorphism of order three, which is an automorphism of mathbb {S} but not of mathbb {O}, to generate two additional generations. Given the relative obscurity of sedenions, efforts have been made to present the material in a self-contained manner.

Trinification from E6 symmetry breaking

In the context of E6 Grand Unified Theories (GUTs), an intriguing possibility for symmetry breaking to the Standard Model (SM) group involves an intermediate stage characterized by either SU(3) × SU(3) × SU(3) (trinification) or SU(6) × SU(2). The more common choices of SU(5) and SO(10) GUT symmetry groups do not offer such breaking chains. We argue that the presence of a real (rank 2 tensor) representation 650 of E6 in the scalar sector is the minimal and likely only reasonable possibility to obtain one of the novel intermediate stages. We analyze the renormalizable scalar potential of a single copy of the 650 and find vacuum solutions that support regularly embedded subgroups SU(3) × SU(3) × SU(3), SU(6) × SU(2), and SO(10) × U(1), as well as specially embedded subgroups F4 and SU(3) × G2 that do not contain the SM gauge symmetry. We show that for a suitable choice of parameters, each of the regular cases can be obtained as the lowest among the analyzed minima in the potential.

Unitarity bounds on extensions of Higgs sector

It is widely believed that extensions of the minimal Higgs sector is one of the promising directions for resolving many puzzles beyond the Standard Model (SM). In this work, we study the unitarity bounds on the models by extending the two-Higgs-doublet model with an additional real or complex Higgs triplet scalar. By noting that the SM gauge symmetries SU(2)L × U(1)Y are recovered at high energies, we can classify the two-body scattering states by decomposing the direct product of two scalar multiplets into their direct sum of irreducible representations of electroweak gauge groups. In such state bases, the s-wave amplitudes of two-body scalar scatterings can be written in the form of block-diagonalized scattering matrices. Then the application of the perturbative unitarity conditions on the eigenvalues of scattering matrices leads to the analytic constraints on the model parameters. Finally, we numerically investigate the complex triplet scalar extension of the two-Higgs-doublet model, finding that the perturbative unitarity places useful stringent bounds on the model parameter space.

Asymmetric dark matter from gravitational waves

We investigate the prospects for probing asymmetric dark matter models through their gravitational wave signatures. We concentrate on a theory extending the Standard Model gauge symmetry by a non-Abelian group, under which leptons form doublets with new fermionic partners, one of them being a dark matter candidate. The breaking of this new symmetry occurs at a high scale and results in a strong first order phase transition in the early universe. The model accommodates baryogenesis in an asymmetric dark matter setting and predicts a gravitational wave signal within the reach of near-future experiments.

The complete search for the supersymmetric Pati-Salam models from intersecting D6-branes

We construct a systematic method to build all the possible three-family mathcal{N} = 1 supersymmetric Pati-Salam models from Type IIA orientifolds on \U0001d54b6/(ℤ2× ℤ2) with intersecting D6-branes, in which the SU(4)C× SU(2)L× SU(2)R gauge symmetry can be broken down to the SU(3)C× SU(2)L× U(1)Y Standard Model gauge symmetry by the D-brane splitting and supersymmetry preserving Higgs mechanism. This is essentially achieved by solving all the common solutions for three generation conditions, RR tadpole cancellation conditions, and mathcal{N} = 1 supersymmetry conditions with deterministic algorithm. We find that there are 202752 possible supersymmetric Pati-Salam models in total, and show that there are only 33 independent models with different gauge coupling relations at GUTs scale after modding out equivalent relations, such as T-dualities, etc. In particular, there is one and only one independent model which has gauge coupling unification. Furthermore, one can construct other types of intersecting D-brane models utilizing such deterministic algorithm, and therefore we suggest a brand new method for D-brane model building.

Aiming for unification of Lμ− Lτ and the standard model gauge group

In this letter we show a kind of Lμ− Lτ gauge symmetry can be unified into a simple group E7 with the standard model gauge symmetry in the context of coset space unification. We also discuss some implication from one of this kind of unification.

Implications of time-dependent inflaton decay on reheating and dark matter production

We discuss the production of radiation and dark matter assuming a time-dependent inflaton decay rate during the reheating period. It is shown that the time dependence of the inflaton decay rate can substantially modify the reheating dynamics. As an illustration, a leading interaction between the inflaton ϕ and the Higgs doublet h of the form ϕ|h|2 was adopted. In the presence of such interaction, the Higgs doublet acquires a ϕ-dependent mass which generates vacuum-expectation-value due to inflaton oscillations and breaks the Standard Model gauge symmetry. This leads to a time-dependent inflaton decay rate during the reheating period, and consequently, the production of radiation and dark matter during this period is modified. Regions of the parameter space that describe the observed value of the dark matter abundance were found and compared with the standard case when inflaton the decay rate is constant.

Higgs Boson-Induced Reheating and Dark Matter Production

We discuss a perturbative and non-instantaneous reheating model, adopting a generic post-inflationary scenario with an equation of state w. In particular, we explore the Higgs boson-induced reheating, assuming that it is achieved through a cubic inflaton-Higgs coupling ϕ|H|2. In the presence of such coupling, the Higgs doublet acquires a ϕ-dependent mass and a non-trivial vacuum–expectation–value that oscillates in time and breaks the Standard Model gauge symmetry. Furthermore, we demonstrate that the non-standard cosmologies and the inflaton-induced mass of the Higgs field modify the radiation production during the reheating period.This, in turn, affects the evolution of a thermal bath temperature, which has remarkable consequences for the ultraviolet freeze-in dark matter production.

Renormalizable models of flavor-specific scalars

New light singlet scalars with flavor-specific couplings represent a phenomenologically distinctive and flavor-safe alternative to the well-studied possibility of Higgs-portal scalars. However, in contrast to the Higgs portal, flavor-specific couplings require an ultraviolet completion involving new heavy states charged under the Standard Model gauge symmetries, leading to a host of additional novel phenomena. Focusing for concreteness on a scenario with up quark-specific couplings, we investigate two simple renormalizable completions, one with an additional vector-like quark and another featuring an extra scalar doublet. We consider the implications of naturalness, flavor- and CP-violation, electroweak precision observables, and direct searches for the new states at the LHC. These bounds, while being model-dependent, are shown to probe interesting regions in the parameter space of the scalar mass and its low-energy effective coupling, complementing the essential phenomenology of the low-energy effective theory at a variety of low and medium energy experiments.

Gravitino dark matter, nonthermal leptogenesis, and low reheating temperature in no-scale Higgs inflation

We revisit Higgs inflation in the framework of a minimal extension of the Standard Model gauge symmetry by a $U(1)_{B-L}$ factor. Various aspects are taken into account with particular focus on the role of the supersymmetry breaking (SUSY) scale and the cosmological constraints associated with the gravitino. The scalar potential of the model is considered in the context of no-scale supergravity consisting of the F-part constructed from the K\"ahler function, the D-terms and soft SUSY contributions. We investigate several limiting cases and by varying the SUSY scale from a few TeV up to intermediate energies, for a spectral index around $n_s\sim 0.9655$ and reheating temperature $T_r\le 10^{9}$ GeV we find that the value of the tensor-to-scalar ratio ranges from $r\approx 10^{-3}$ to $10^{-2}$. Furthermore, it is shown that for certain regions of the parameter space the gravitino can live sufficiently long and as such is a potential candidate for a dark matter component. In general, the inflationary scenario is naturally implemented and it is consistent with non-thermal leptogenesis whereas the dominant decay channel of the inflaton yields right-handed neutrinos. Other aspects of cosmology and particle physics phenomenology are briefly discussed. Finally, we investigate the case where the inflaton is initially relaxed in a false minimum and estimate its probability to decay to the true vacuum.

A Family-nonuniversal [formula omitted] Model for Excited Beryllium Decays

Excited beryllium has been observed to decay into electron-positron pairs with a 6.8σ anomaly. The process is properly explained by a 17 MeV proto-phobic vector boson. In present work, we consider a family-nonuniversal U(1)′ that is populated by a U(1)′ gauge boson Z′ and a scalar field S, charged under U(1)′ and singlet under the Standard Model (SM) gauge symmetry. The SM chiral fermion and scalar fields are charged under U(1)′ and we provide them to satisfy the anomaly-free conditions. The Cabibbo-Kobayashi-Maskawa (CKM) matrix is reproduced correctly by higher-dimension Yukawa interactions facilitated by S. The vector and axial-vector current couplings of the Z′ boson to the first generation of fermions do satisfy all the bounds from the various experimental data. The Z′ boson can have kinetic mixing with the hypercharge gauge boson and S can directly couple to the SM-like Higgs field. The kinetic mixing of Z′ with the hypercharge gauge boson, as we show by a detailed analysis, generates the observed beryllium anomaly. We find that beryllium anomaly can be properly explained by a MeV-scale sector with a minimal new field content. The minimal model we construct forms a framework in which various anomalous SM decays can be discussed.

A note on Jordan algebras, three generations and exceptional periodicity

It is shown that the algebra [Formula: see text] based on the complexified Exceptional Jordan, and the complex Clifford algebra in 4D, is rich enough to describe all the spinorial degrees of freedom of three generations of fermions in 4D, and include additional fermionic dark matter candidates. Furthermore, the model described in this paper can account also for the Standard Model gauge symmetries. We extend these results to the Magic Star algebras of Exceptional Periodicity developed by Marrani–Rios–Truini and based on the Vinberg cubic [Formula: see text] algebras which are generalizations of exceptional Jordan algebras. It is found that there is a one-to-one correspondence among the real spinorial degrees of freedom of four generations of fermions in 4D with the off-diagonal entries of the spinorial elements of the [Formula: see text] [Formula: see text] of Vinberg matrices at level [Formula: see text]. These results can be generalized to higher levels [Formula: see text] leading to a higher number of generations beyond 4. Three [Formula: see text] of [Formula: see text] algebras and their conjugates [Formula: see text] were essential in the Magic Star construction of Exceptional Periodicity that extends the [Formula: see text] algebra to [Formula: see text] with [Formula: see text] integer.

Sterile Higgs Boson

To address the “little hierarchy problem,” we introduce two extra scalar fields neutral under the standard model gauge symmetry on top of the standard model. One linear combination of them has an almost flat potential, and so it can dynamically compensate the large Higgs mass parameter, while its small negative mass parameter can play the role of the electroweak symmetry breaking source. Thus the smallness of its mass parameter is responsible for the relatively small Higgs vacuum expectation value compared to a cut-off energy scale of the standard model. This scenario should eventually be embedded e.g. in a supersymmetric model, where the small mass parameters of the neutral singlets can be explained by employing both the gravity- and gauge-mediated supersymmetry breaking mechanisms. Their mixing angles with the Higgs boson can be suppressed enough (∼ 10−2), avoiding the phenomenological constraints. The mass of the lighter scalar field is of order sub-electroweak scale (∼ 10 GeV), when the heavier one is above TeV scale (∼ 5 TeV).

Gravitational waves as a probe of left-right symmetry breaking

Left-right symmetry at high energy scales is a well-motivated extension of the Standard Model. In this paper we consider a typical minimal scenario in which it gets spontaneously broken by scalar triplets. Such a realization has been scrutinized over the past few decades chiefly in the context of collider studies. In this work we take a complementary approach and investigate whether the model can be probed via the search for a stochastic gravitational wave background induced by the phase transition in which SU(3)C × SU(2)L × SU(2)R × U(1)B−L is broken down to the Standard Model gauge symmetry group. A prerequisite for gravitational wave production in this context is a first-order phase transition, the occurrence of which we find in a significant portion of the parameter space. Although the produced gravitational waves are typically too weak for a discovery at any current or future detector, upon investigating correlations between all relevant terms in the scalar potential, we have identified values of parameters leading to observable signals. This indicates that, given a certain moderate fine-tuning, the minimal left-right symmetric model with scalar triplets features another powerful probe which can lead to either novel constraints or remarkable discoveries in the near future. Let us note that some of our results, such as the full set of thermal masses, have to the best of our knowledge not been presented before and might be useful for future studies, in particular in the context of electroweak baryogenesis.

Radiative Dirac neutrino mass, neutrinoless quadruple beta decay, and dark matter in B−L extension of the standard model

The Standard Model gauge symmetry is extended by $U(1)_{B-L}$ which when spontaneously broken leads to residual $\mathbb{Z}_4$ symmetry. $U(1)_{B-L}$ gauge symmetry made anomaly free by introducing exotic SM singlets with corresponding $U(1)_{B-L}$ charges of $13$, $-14$, and $15$. $\mathbb{Z}_4$ symmetry ensures the Dirac nature of neutrinos, simultaneously stabilizing dark matter. Dirac neutrino mass is generated through scotogenic scenario. Dark matter, direct detection, cosmological constraints, and collider constraints analysis is performed. $\mathbb{Z}_4$ symmetry predicts the exact absence of neutrinoless double beta decay ($0\nu 2\beta$) and gives a prediction for an enhanced neutrinoless quadruple beta decay ($0\nu 4\beta$) via which this model can be tested. Model allows for Majorana dark matter as well as for long-lived dark matter candidates.

Sub-GeV dark matter model

We propose an extension of the Standard Model gauge symmetry by the gauge group $U(1)_{T3R}$ in order to address the Yukawa coupling hierarchy between the third generation fermions and the first two generation fermions of the SM. We assume that only the right-handed fermions of the first two generations are charged under the $U(1)_{T3R}$. In addition to the new dark gauge boson, we have a dark scalar particle whose vacuum expectation value (vev) breaks the $U(1)_{T3R}$ symmetry down to $Z_2$ symmetry and also explains the hierarchy problem. A vev of $\cal O$(GeV) is required to explain the mass parameters of the light flavor sector naturally. The dark matter (DM) particle arising from the model naturally has mass in the $\mathcal {O}$(1-100) MeV range. The model satisfies all the current constraints. We discuss the various prospects of the direct detection of the dark matter. We get both elastic and inelastic spin independent DM-nucleon scattering. The dark matter obtains the correct thermal relic density by annihilation.

General neutrino interactions from an effective field theory perspective

General Neutrino Interactions (GNI) are scalar, pseudoscalar, vector, axial vector or tensor interactions of neutrinos with fermions, and generalise the often studied neutrino Non-Standard Interactions (NSI). If GNI arise from heavy new physics, they should be embeddable into effective field theory operators that respect the Standard Model (SM) gauge symmetry. Therefore we consider a full basis of gauge-invariant dimension-six operators involving SM fermions and right-handed singlet neutrinos and map their Wilson coefficients onto GNI parameters. In this embedding we discuss correlations of and bounds on different GNI in the context of charged lepton flavour violation processes and neutrino-fermion scattering, as well as beta decay and coherent neutrino-nucleus scattering. We also study possible UV completions of the relevant dimension-six operators for GNI via leptoquarks that can be related to radiative neutrino masses and B physics anomalies. Details on the numbers of free GNI parameters for Dirac or Majorana neutrinos and for CP violation or conservation are also provided.

Cosmological constraints on light flavons

The Froggatt-Nielsen mechanism is a well-motivated framework for generating the fermion mass hierarchy. This mechanism introduces flavons, complex scalars which are singlet under the Standard Model gauge symmetry and charged under a new global family symmetry. We make use of a leptophilic flavon to produce the charged lepton Yukawa matrix. The real part of the flavon mixes with the Higgs boson and introduces lepton flavour violating interactions which are bounded by experiment. The imaginary part of the flavon, η, is a long-lived light particle, whose abundance is restricted by cosmological observations. For mη< 2me where the decay of η to charged leptons is kinematically forbidden, we identify allowed regions of mη with respect to the vacuum expectation value of the flavon field where all experimental and cosmological constraints are satisfied.