Extension Of Standard Model Research Articles

Constraining GUP models using limits on SME coefficients

Generalized uncertainty principles (GUP) and, independently, Lorentz symmetry violations are two common features in many candidate theories of quantum gravity. Despite that, the overlap between both has received limited attention so far. In this brief paper, we carry out further investigations on this topic. At the nonrelativistic level and in the realm of commutative spacetime coordinates, a large class of both isotropic and anisotropic GUP models is shown to produce signals experimentally indistinguishable from those predicted by the standard model extension (SME), the common framework for studying Lorentz-violating phenomena beyond the standard model. This identification is used to constrain GUP models using current limits on SME coefficients. In particular, bounds on isotropic GUP models are improved by a factor of 107 compared to current spectroscopic bounds and anisotropic models are constrained for the first time.

Testing the scalar sector of the standard-model extension with neutron gravity experiments

In the present study we analyse, within the scalar sector of the standard-model extension framework, the influence of a spontaneous Lorentz symmetry breaking on gravitational quantum states of ultracold neutrons. The model is framed according to the laboratory conditions of the recent high-sensitivity GRANIT and qBounce experiments. The high-precision data achieved in such experiments allow us to set bounds on the symmetry breaking parameters of the model. The effective Hamiltonian governing the neutron’s motion along the axis of free fall is derived explicitly. It describes a particle in a gravitational field with an effective gravitational constant controlled non-trivially by the Lorentz-violating parameters. In particular, using the exact wave functions and the energy spectrum, we evaluate both the heights associated with the quantum states and the transition frequencies between neighborhoring quantum states. By comparing our theoretical results with those reported in the GRANIT and the qBounce experiments, upper bounds on the Lorentz-violating parameters are determined. We also consider for the first time the gravity-induced interference pattern in a COW-type experiment to test Lorentz–invariance. In this case, an upper bound for the parameters is established as well.

A Study of the Higgs Mass with the Effective Potential and Higgs Decays in the U(1)XSSM

As the U(1) extension of the minimal supersymmetric standard model, the U(1)XSSM has new superfields, such as right-handed neutrinos, and three Higgs singlets. In the U(1)XSSM, the lightest CP-even Higgs mass mh0 is studied by using the Higgs effective potential with one-loop corrections. We also calculate the Higgs decays h0→γγ, h0→VV(V=W,Z), h0→ll¯Z, and h0→νν¯Z. The obtained results are reasonable, and they are in favor of the study of the Higgs characteristic and the phenomenology of the U(1)XSSM.

Z boson decays Z→li±lj∓ and Higgs boson decays h→li±lj∓ with lepton flavor violation in a U(1) extension of the MSSM

$U(1)_X$SSM is the extension of the minimal supersymmetric standard model (MSSM) and its local gauge group is $SU(3)_C\times SU(2)_L \times U(1)_Y \times U(1)_X$. We study lepton flavor violating (LFV) decays $Z\rightarrow{{l_i}^{\pm}{l_j}^{\mp}}$($Z\rightarrow e{\mu}$, $Z\rightarrow e{\tau}$, and $Z\rightarrow {\mu}{\tau}$) and $h\rightarrow{{l_i}^{\pm}{l_j}^{\mp}}$($h\rightarrow e{\mu}$, $h\rightarrow e{\tau}$, and $h\rightarrow {\mu}{\tau}$), in this model. In the numerical results, the branching ratios of $Z\rightarrow{{l_i}^{\pm}{l_j}^{\mp}}$ are from $10^{-9}$ to $10^{-13}$ and the branching ratios of $h\rightarrow{{l_i}^{\pm}{l_j}^{\mp}}$ are from $10^{-3}$ to $10^{-9}$, which can approach the present experimental upper bounds. Based on the latest experimental data, we analyze the influence of different sensitive parameters on the branching ratio, and make reasonable predictions for future experiments. The main sensitive parameters and LFV sources are the non-diagonal elements corresponding to the initial and final generations of leptons, which can be seen from the numerical analysis.

A bridge to new physics: proposing new — and reviving old — explanations of aμ

The 4.2 σ tension in the combined measurement of the anomalous magnetic moment of the muon, aμ, and the Standard Model prediction strongly suggests the existence of beyond the Standard Model physics. Following the Standard Model Effective Field Theory approach, we study a particular topology, the bridge diagram, which gives a chirally enhanced contribution to aμ. We classify all possible 2- and 3-field SM extensions that can generate this contribution and present the full aμ result for them. Within our approach, we find that several 2-field fermion-scalar extensions which had been previously discarded in the literature — when only the Yukawa-suppressed contribution was considered — can actually be viable models to explain the observed anomaly. Furthermore, the 3-field extensions which generate the bridge diagram represent a new class of models to account for aμ. We explore a particular 3-field extension which, beyond explaining aμ, can also account for the neutral B-meson anomalies and the Cabibbo angle anomaly. We present the full one-loop matching for this model and a one-loop phenomenological study.

Search for a light Z′ in the Lμ−Lτ scenario with the NA64- e experiment at CERN

The extension of Standard Model made by inclusion of additional $U(1)$ gauge $L_\mu-L_\tau$ symmetry can explain the difference between the measured and the predicted value of the muon magnetic moment and solve the tension in $B$ meson decays. This model predicts the existence of a new, light $Z^\prime$ vector boson, predominantly coupled to second and third generation leptons, whose interaction with electrons is due to a loop mechanism involving muons and taus. In this work, we present a rigorous evaluation of the upper limits in the $Z^\prime$ parameter space, obtained from the analysis of the data collected by the NA64-$e$ experiment at CERN SPS, that performed a search for light dark matter with $2.84\times10^{11}$ electrons impinging with 100 GeV on an active thick target. The resulting limits, despite being included in a region already investigated by neutrino experiments,touch the muon $g-2$ preferred band for values of the $Z^\prime$ mass of order of 1 MeV. The sensitivity projections for the future high-statistics NA64-$e$ runs demonstrate the power of the electrons/positron beam approach in this theoretical scenario.

Effects of lorentz violation in the higgs sector of the minimal standard model extension

A bound on the CPT-odd four-vector coefficient [Formula: see text] that appears in Higgs sector of the minimal Standard Model Extended (mSME) is presented. The analysis is based on the contributions arising from the sector in question to the anomalous magnetic dipole moment (AMDM) for leptons calculated at the one-loop level, for which an analytical expression is obtained. The largest contribution of this Lorentz violating coefficient is on the lightest lepton, which results as a consequence of a strong nondecoupling effect. By using the experimental uncertainty of the electron AMDM we predict that [Formula: see text].

Bounds on the absorptive parts of the chromomagnetic and chromoelectric dipole moments of the top quark from LHC data

Bounds on the absorptive (imaginary) parts of the top quark chromomagnetic \({\hat{\mu }}_t\) and chromoelectric \({\hat{d}}_t\) dipole moments are obtained by reinterpreting the most recent LHC data in top quark pair production. It is found that both limits are of the order of \(10^{-1}-10^{-2}\), which are consistent with the standard model prediction of \(\mathrm{Im}\big [{\hat{\mu }}_t\big ]\). The effects of the absorptive parts of the top quark dipole moments are also studied via some kinematic distributions of \({\overline{t}}t\) production, though no significant deviation from the standard model leading-order contribution is observed. Our bounds can be useful to constrain the parameter space of standard model extensions.

Renormalizable standard model extension with S4 symmetry for neutrino mass and mixing

We suggest a renormalizable standard model extension based on S4 symmetry that accommodates the recent observed neutrino oscillation pattern. Through the type-I seesaw mechanism, the smallness of the active neutrino mass and its hierarchy are produced. The model generates the updated data on neutrino parameters in which the reactor neutrino mixing angle θ13, the atmospheric neutrino mixing θ23, and the Dirac phase δ for both NH and IH belong to 1σ range, while the solar mixing angle θ12 = 35.70° belongs to 2σ range. The effective masses are found to be 〈 mee〉 = 5.74 meV for NH and 〈 mee〉 = 48.1 meV for IH within their allowed constraints.

Flavour and dark matter in a scoto/type-II seesaw model

The neutrino mass and dark matter (DM) problems are addressed in a Standard Model extension where the type-II seesaw and scotogenic mechanisms coexist. The model features a flavour \U0001d4b58 discrete symmetry which is broken down to a \U0001d4b52, stabilising the (scalar or fermion) DM particle. Spontaneous CP violation is implemented through the complex vacuum expectation value of a singlet scalar field, inducing observable CP-violating effects in the lepton sector. The structure of the effective neutrino mass matrix leads to constraints on the low-energy neutrino observables, namely the atmospheric neutrino mixing angle θ23, the Dirac CP-violating phase δ and the absolute neutrino mass scale mlightest. In particular, in most cases, the model selects one θ23 octant with δ ≃ 3π/2. Moreover, the obtained lower bounds on mlightest are typically in the range probed by cosmology. We also analyse the constraints imposed on the model by current experimental limits on charged lepton flavour violating (cLFV) processes, as well as future projected sensitivities. It is shown that the Higgs triplet and scotogenic contributions to cLFV never overlap and that the interplay among Yukawa couplings, dark charged scalar masses and mixing leads to a wide parameter-space region compatible with current experimental bounds. We investigate the scalar and fermion DM parameter space of our model by considering relic density, direct-detection (DD) and collider constraints. For scalar DM the mass interval 68 GeV ≲ mDM ≲ 90 GeV is viable and will be probed by future DD searches. In the fermion DM case, correct relic density is always obtained for mDM ≳ 45 GeV thanks to dark fermion-scalar coannihilation channels.

Hyperfine Spectroscopy of Antihydrogen, Hydrogen, and Deuterium

The prospects of tests of CPT symmetry using precision spectroscopy of antihydrogen are discussed with special emphasis on the ground-state hyperfine structure, a measurement of which is the aim of the ASACUSA collaboration at the AD/ELENA facility of CERN. Ongoing parallel experiments using hyperfine spectroscopy of hydrogen and deuterium aiming at studying Lorentz invariance by determining coefficients of the Standard Model Extension framework are described.

Topological chiral currents in the Gross-Neveu model extension

We unveil an interesting connection of Lorentz-violating quantum field theories, studied in the context of the standard model extension, and Hubbard-type models of topological crystalline phases. These models can be interpreted as a regularisation of the former and, as hereby discussed, explored with current quantum simulators based on ultra-cold atoms in optical Raman lattices. In particular, we present a complete analysis of the Creutz-Hubbard ladder under a generic magnetic flux, which regularises a Gross-Neveu model extension, and presents a characteristic circulating chiral current whose non-zero value arises from a specific violation of Lorentz invariance. We present a complete phase diagram with trivial insulators, ferromagnetic and anti-ferromagnetic phases, and current-carrying topological crystalline phases. These predictions are benchmarked using tools from condensed matter and quantum-information science, showing that self-consistent Hartree-Fock and strong-coupling Dzyaloshinskii-Moriya methods capture the essence of the phase diagram in different regimes, which is further explored using extensive numerical simulations based on matrix-product states.

Cosmology in the presence of diffeomorphism-violating, nondynamical background fields

We consider diffeomorphism violation, which is parametrized by nondynamical background fields of the gravitational Standard-Model Extension, and study its effects on the time evolution of the Universe. Our goal is to identify background field configurations that imply stages of accelerated expansion without exotic forms of matter and radiation present. Although our approach gives rise to a set of restrictive conditions, configurations are encountered that exhibit this property or show other interesting behaviors. The findings of our article, which is among the first to apply the Standard-Model Extension to a cosmological setting, provide an initial understanding of how to technically incorporate background fields into the cosmological evolution equations and what their phenomenological impact may be.

Exact modifications on a vacuum spacetime due to a gradient bumblebee field at its vacuum expectation value

This work belongs to the context of the standard-model extension, in which a Lorentz symmetry violation is induced by a bumblebee field as it acquires a nonzero vacuum expectation value. The mathematical formulation of a generic bumblebee model and its associated dynamical equations are presented. Then, these equations are considered for the vacuum and a substantial simplification is performed for the particular case of a gradient bumblebee field at its vacuum expectation value. After some further manipulation, a method to easily find solutions to the model is developed, in which the exact effect on the spacetime description due to the presence of this bumblebee field is explicitly provided. As some examples, the method is applied to determine the implications of the bumblebee field on the Schwarzschild spacetime and also on a rotating one. A previously published solution is recovered and some new ones are obtained. In the rotating situation, a simple solution is found which contains both the Kerr solution and the already published one as special cases. It is also shown its distinguished surfaces are still given by the same corresponding expressions for the Kerr solution. In conclusion, the mathematical improvement made is considered to be a significant contribution to the theory as a powerful tool to investigate its many aspects and consequences.

Pair production of charged IDM scalars at high energy CLIC

The Compact Linear Collider (CLIC) was proposed as the next energy-frontier infrastructure at CERN, to study e^++e^-− collisions at three centre-of-mass energy stages: 380,GeV, 1.5,TeV and 3,TeV. The main goal of its high-energy stages is to search for the new physics beyond the Standard Model (SM). The Inert Doublet Model (IDM) is one of the simplest SM extensions and introduces four new scalar particles: H^\pm±, A and H; the lightest, H, is stable and hence a natural dark matter (DM) candidate. A set of benchmark points is considered, which are consistent with current theoretical and experimental constraints and promise detectable signals at future colliders.Prospects for observing pair-production of the IDM scalars at CLIC were previously studied using signatures with two leptons in the final state. In the current study, discovery reach for the IDM charged scalar pair-production is considered for the semi-leptonic final state at the two high-energy CLIC stages. Full simulation analysis, based on the current CLIC detector model, is presented for five selected IDM scenarios. Results are then extended to the larger set of benchmarks using the Delphes fast simulation framework. The CLIC detector model for Delphes has been modified to take pile-up contribution from the beam-induced \gamma\gammaγγ interactions into account, which is crucial for the presented analysis. Results of the study indicate that heavy, charged IDM scalars can be discovered at CLIC for most of the proposed benchmark scenarios, with very high statistical significance.

CP-violating axion interactions in effective field theory

Axions are introduced to explain the observed smallness of the overline{theta} term of QCD. Standard Model extensions typically contain new sources of CP violation, for instance to account for the baryon asymmetry of the universe. In the presence of additional CP-violating sources a Peccei-Quinn mechanism does not remove all CP violation, leading to CP-odd interactions among axions and Standard Model fields. In this work, we use effective field theory to parametrize generic sources of beyond-the-Standard-Model CP violation. We systematically compute the resulting CP-odd couplings of axions to leptons and hadrons by using chiral perturbation theory. We discuss in detail the phenomenology of the CP-odd axion couplings and compare limits from axion searches, such as fifth force and monopole-dipole searches and astrophysics, to direct limits on the CP-violating operators from electric dipole moment experiments. While limits from electric dipole moment searches are tight, the proposed ARIADNE experiment can potentially improve the existing constraints in a window of axion masses.

Purely radiative Higgs mass in scale invariant models

In this work, we investigate the possibility of having scale invariant (SI) standard model (SM) extensions, where the light CP-even scalar matches the SM-like Higgs instead of being a light dilaton. After deriving the required conditions for this scenario, we show that the radiative corrections that give rise to the Higgs mass can trigger the scalar mixing to the experimentally allowed values. In addition, we discuss the constraints on the parameters space that makes the CP-even scalars properties in a good agreement with all the recent ATLAS and CMS measurements. We illustrate this scenario by considering the SI-scotogenic model as an example, while imposing all the theoretical and experimental constraints. We show that the model is viable and leads to possible modifications of the di-Higgs signatures at current/future with respect to the SM.

Testing Lepton Flavor Universality with Pion, Kaon, Tau, and Beta Decays

We present an overview of searches for violation of lepton flavor universality with a focus on low energy precision probes using π, K, τ, and nuclear beta decays. We review the current experimental results, summarize the theoretical status within the context of the Standard Model, and discuss future prospects (both experimental and theoretical). We review the implications of these measurements for physics beyond the Standard Model by performing a global model-independent fit to modified W couplings to leptons and four-fermion operators. We also discuss new physics in the context of simplified models and review Standard Model extensions with a focus on those that can explain a possible deviation from unitarity of the Cabibbo–Kobayashi–Maskawa quark mixing matrix.

Influences of the Lorentz symmetry violation on the interaction of the relativistic spin-zero particle with the Cornell-type non-minimal coupling

Based on the Standard Model Extension, we study the influences of Lorentz symmetry breaking effects on the interaction of a neutral spin-zero Duffin–Kemmer–Petiau particle. This particle is non-minimal coupled to a Cornell-type potential, which represents a generalized relativistic quantum oscillator model. This system is considered in the background of the Lorentz symmetry breaking mechanics generated by an electric field and a fixed vector field, which in turn provides a type of magnetic dipole moment. The generalized Duffin–Kemmer–Petiau equation is constructed incorporating that non-minimal CPT-odd coupling. Exact analytical spectral properties are derived for two special configurations of the electric and fixed vector field, both exhibiting a cylindric symmetry.

Constraining the cosmic strings gravitational wave spectra in no-scale inflation with viable gravitino dark matter and nonthermal leptogenesis

We revisit the hybrid inflation model gauged by $U(1)_{B-L}$ extension of the Minimal Supersymmetric Standard Model (MSSM) in a no-scale background. Considering a single predictive framework, we study inflation, leptogenesis, gavitino cosmology, and the stochastic background of gravitational waves produced by metastable cosmic strings. The spontaneous breaking of $U(1)_{B-L}$ at the end of inflation produces a network of metastable cosmic strings while, the interaction between $U(1)_{B-L}$ Higgs field and the neutrinos generate heavy Majorana masses for the right-handed neutrinos. The heavy Majorana masses explain the tiny neutrino masses via the seesaw mechanism, a realistic scenario for reheating and non-thermal leptogenesis. We show that a successful non-thermal leptogenesis and a stable gravitino as a dark matter candidate can be achieved for a wide range of reheating temperatures and $U(1)_{B-L}$ symmetry breaking scales. The possibility of realizing metastable cosmic strings in a grand unified theory (GUT) setup is briefly discussed. We find that a successful reheating with non-thermal leptogenesis and gravitino dark matter restrict the allowed values of string tension to a narrow range $10^{-9} \lesssim G\mu_{CS} \lesssim 8 \times 10^{-6}$, predicting a stochastic gravitational-wave background that lies within the 1-$\sigma$ bounds of the recent NANOGrav 12.5-yr data, as well as within the sensitivity bounds of future GW experiments.