arXiv subjects

B. L. Sánchez-Vega

Publications and source records attributed to B. L. Sánchez-Vega.

At least 19 recordsLinked to original sources

arXiv2026

Strong First-Order Electroweak Phase Transition and Gravitational Waves in a $\mathbb{Z}_4$ Fermion-Scalar Dark Matter Model

We investigate whether a minimal $\mathbb{Z}_4$-symmetric fermion-scalar extension of the Standard Model can simultaneously realise viable dark matter, a strong electroweak phase transition, and a stochastic gravitational-wave signal. The model contains a real scalar singlet and a Dirac fermion, allowing thermal two-component dark matter, mixed WIMP-FIMP histories, and an effectively fermionic relic abundance generated by scalar decays. We impose theoretical consistency, the correct electroweak vacuum, and dark-matter constraints from relic density, direct detection, and invisible Higgs decays before using the surviving points as input for the finite-temperature analysis. This reveals that the compatibility between dark matter and a strong first-order electroweak phase transition is highly selective. After current dark-matter constraints are imposed, the strong-transition criterion along the Higgs direction is satisfied only in two viable regimes: the thermal two-component case with $M_ψ 2M_ψ$. By contrast, the thermal regime with $M_S<M_ψ$ and the stable mixed WIMP-FIMP scenario with $M_S<2M_ψ$ are largely concentrated at small portal couplings or near the Higgs-resonance region, and do not yield a strong transition in the parameter space considered. The successful transitions typically proceed through an intermediate singlet-like phase. For representative nucleating benchmark points in the viable strong-transition regions, we compute the gravitational-wave spectra from sound waves and turbulence. Some spectra overlap the projected sensitivity curves of future space-based interferometers, indicating potentially observable signals in selected dark-matter-compatible regions where a sufficiently active Higgs portal appears in correlated combination with the scalar mass and the remaining dark sector parameters.

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arXiv2026

Dark matter in the scale-invariant 3-3-1-1 model

We propose a novel scale-invariant model with the 3-3-1-1 gauge symmetry featuring a universal see-saw mechanism for all fermion masses, which, through the inclusion of additional vector-like quarks, provides a partial explanation for the observed fermion mass hierarchies. A discrete remnant of the gauge group, the matter parity ($P_M$), stabilises a fermionic dark matter candidate, and the scalar sector includes two triplets (minimal for 3-3-1 breaking) and two scalar singlets. We identify the lightest $ P_M $-odd fermion, $f_d$, as a viable dark matter candidate. Our analysis shows that $f_d$ satisfies the observed relic density constraint within the mass range 220 GeV $< m_{f_d}$ 555 GeV , primarily due to resonant annihilation via the new scalar $H_2$. While this mass range depends on the symmetry-breaking scale $v_χ$, which has a lower bound of $ v_χ\gtrsim 3.6$ TeV from LEP constraints on the $ρ_0$ parameter, we adopt a more conservative lower bound of $v_χ> 10$ TeV. This choice is made to ensure that the $Z'$ boson mass remains above approximately $ 4$ TeV, and is motivated by recent LHC results and future projections for Z' boson searches, which provide more stringent constraints than previous bounds or those from the $ρ_0$ parameter. Spin-independent (SI) interactions dominate the direct detection phenomenology of $f_d$. We calculate the SI elastic scattering cross-section and find that parameter points satisfying the relic density constraint are consistent with current experimental limits from LZ and PandaX-4T for certain parameter choices, particularly depending on the $α_{12}$ angle. Some regions of the viable parameter space lie below the neutrino floor. Prospects for detection by future experiments like XLZD and PandaX-xT are also presented and discussed.

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arXiv2026

Energy-independent neutrino dephasing from an ultralight axion-like background

We study neutrino oscillations in an ultralight axion-like particle (ALP) dark-matter background using a bottom-up derivative interaction for active neutrinos. For couplings diagonal in the neutrino mass basis, the leading relative phase is fixed by the difference of the ALP field between production and detection. More generally, an unresolved background multiplies each interference term by the characteristic function of this endpoint field difference. For a single fixed-amplitude coherent mode with uniformly sampled phase, the factor is $J_0(A_{ij})$. In the slow-flight and small-dephasing regimes, this result and a Gaussian virialized-halo treatment agree at quadratic order and produce a leading $L^2E^0$ suppression. We identify the finite-exposure and coherence conditions under which the two statistical descriptions apply. As an application, we analytically map the energy-independent damping constraint derived from the first JUNO data onto the flavor benchmark $g_2=g_3$. For a local ALP density of $0.4\mathrm{GeV}/\mathrm{cm}^3$, the low-mass plateau gives $|Δg_{21}|=|Δg_{31}|\lesssim0.90\mathrm{GeV}^{-1}$. This number is a baseline-matched EFT recast of the reference damping analysis. No specific ultraviolet completion is assumed.

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arXiv2026

Mixed Freeze-In and Freeze-Out Histories and Dark-Sector Decays in a $\mathbb{Z}_4$ Two-Scalar Model

We present a systematic non-equilibrium analysis of a renormalisable $\mathbb{Z}_4$ Higgs-portal dark sector with a complex scalar $S_A$ and a real scalar $S_B$, including conversion, semi-annihilation, and, when kinematically allowed, the dark-sector decay $S_B\to S_A S_A$. We impose theoretical consistency, Higgs invisible-decay limits, relic-fraction-rescaled LZ bounds, and an a posteriori thermalisation check of the WIMP/FIMP assignments. Allowing one or both dark states to remain out of equilibrium qualitatively enlarges the set of viable cosmological histories. In the stable regime, FIMP--FIMP and mixed WIMP--FIMP configurations can share the observed relic density between the two components, while the WIMP-like state remains subject to the usual Higgs-portal correlation between freeze-out and spin-independent scattering and the FIMP-like state can provide a substantial abundance with a negligible direct-detection rate. For $M_{S_B}>2M_{S_A}$, the decay of the unstable $S_B$ opens three distinct abundance-transfer mechanisms: SuperWIMP production, injection-assisted freeze-out, and sequential freeze-in. Because the decay proceeds entirely within the dark sector, the usual electromagnetic and hadronic BBN energy-injection bounds do not apply; we instead track the parent energy fraction and use an equivalent thermal-WDM mass to diagnose the warmness of the decay-produced daughter population. The minimal $\mathbb{Z}_4$ Higgs portal thus supports thermal, mixed, and fully non-thermal relic histories within the same renormalisable framework, with dark-sector decay linking relic-density production to small-scale structure.

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arXiv2026

Photon Propagation through Axion Clouds around Magnetized Compact Objects: Time Delays and Polarimetric Signatures

Temporal offsets between Gamma-Ray Bursts (GRBs) and high-energy neutrinos probe propagation effects in extreme astrophysical environments. We investigate whether such offsets can be generated by photon propagation through dense axion clouds gravitationally bound to strongly magnetized compact objects, such as canonical pulsars. Working within the Euler--Heisenberg effective theory extended by the axion sector, we derive the photon dispersion relations in a strong magnetic background permeated by an oscillating axion field. The magnetized vacuum is birefringent already at the Euler--Heisenberg level and the axion cloud superimposes density-dependent, time-dependent, and parity-odd structure on this baseline. The resulting geometry-dependent deviations from luminal propagation yield kinematic time delays reaching $Δt_{\perp} \simeq 9.3 \times 10^{-12}$ s for $\mathbf{k} \perp \mathbf{B}$, far too small to account for macroscopic multimessenger offsets, so that propagation through such environments cannot, by itself, rule out Lorentz-invariance violation as an explanation for GRB offsets. In the polarization sector, we show that the axion-induced circular birefringence is an endpoint effect and therefore does not produce a leading net rotation for a complete vacuum-to-vacuum transit through a localized cloud. For configurations with a nonzero axion-field endpoint contrast, the same parity-odd phase defines a conditional environmental sensitivity benchmark. We find that this mechanism is optimally sensitive in the ultralight regime, yielding a benchmark reach of $g_{aγγ} \lesssim 2.5 \times 10^{-10}\,\mathrm{GeV}^{-1}$ for canonical pulsar fields and axion masses near $m_a \sim 10^{-9}$ eV, and we identify the parity-odd (chiral) birefringence induced by the oscillating cloud as the signature that distinguishes the axion contribution from the calculable QED baseline.

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arXiv2025

Theoretical and Experimental Constraints on $\mathbb{Z}_{2n}$ Multi-Component Dark Matter Models

A complete assessment of any dark matter model requires confronting its low-energy phenomenology with its high-scale theoretical viability. We undertake such a dual analysis for a class of two-component scalar dark matter models stabilized by $\mathbb{Z}_{2n}$ symmetries, specifically the $\mathbb{Z}_4$, $\mathbb{Z}_6(23)$, and $\mathbb{Z}_6(13)$ frameworks. Each model is tested against the latest observational data, including the Planck relic abundance and stringent direct detection limits from the LUX-ZEPLIN (LZ) experiment. Simultaneously, we evaluate their theoretical integrity up to the GUT and Planck scales by enforcing vacuum stability and perturbative unitarity with one-loop Renormalization Group Equations. This combined approach reveals a rich and varied landscape of possibilities. We demonstrate that the $\mathbb{Z}_4$ model offers a broadly viable parameter space sustained by efficient semi-annihilation. In stark contrast, the $\mathbb{Z}_6(13)$ scenario is shown to be highly fine-tuned, with solutions confined to the Higgs resonance. Our most significant finding concerns the $\mathbb{Z}_6(23)$ model: we show that an apparent conflict between experimental data and high-scale consistency is resolved when the model is viewed as an effective field theory, yielding a concrete prediction for new physics at or below the $10^6$ GeV scale. This work provides a definitive guide to the viability of these $\mathbb{Z}_{2n}$ scenarios and serves as a compelling demonstration of how high-energy consistency checks can yield crucial insights into the nature of dark matter.

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arXiv2025

Very Special Relativity: Cherenkov Effect and an Analogy with Minkowski's Electrodynamics of Continuous Media

In this work, we explore the implications of the Cohen and Glashow Very Special Relativity (VSR) theory, a framework that introduces Lorentz invariance violation through the presence of a preferred direction. Our analysis focuses on the impact of VSR on the Cherenkov angle, revealing modifications to the dispersion relation of particles, particularly the photon and the electron, which acquire an effective inertial mass. This modification also implies a deviation in the speed of light, which can be constrained through precise experimental measurements. Using data from the RICH system of the LHCb experiment, we take advantage of its capability to reconstruct Cherenkov angles within the momentum range of the particles of 2.6-100 GeV/c. These measurements, combined with the most stringent laboratory tests of the isotropy of the speed of light ($Δc / c \sim 10^{-17}$), allow us to impose new upper bounds on the parameter $Ω$, which quantifies a deviation from the standard Special Relativity. Furthermore, we establish an analogy between VSR and Minkowski's electrodynamics in a dielectric medium for particles with very high velocity, offering a physically intuitive interpretation of the parameter $Ω$.

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arXiv2024

Vacuum Stability in the one-loop approximation of a 331 Model

In this study, we analyze the vacuum stability of the economical 331 model at the one-loop level using the renormalization group equations and a single-scale renormalization method. By integrating these equations, we determine stability conditions up to the Planck scale, incorporating constraints from recent experimental data on new Higgs-like bosons, charged scalars, and charged and neutral gauge bosons. Our analysis uncovers intriguing relations between the mass of the heaviest scalar and the masses of exotic quarks, in order to ensure stability of the model up to the Planck scale. For the 331 energy scale used in this work, $18$ TeV, we find an upper bound on the heaviest quark mass of the model, which is not so distant from future LHC runs, serving as bounds to be searched. Additionally, we explore relations between the scalar couplings coming stability and perturbativity conditions. These impose unprecedented constraints on the economical 331 model.

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arXiv2022

Scale-invariant 3-3-1-1 model with $B-L$ symmetry

Motivated by a possible interplay between the mechanism of dynamical symmetry breaking and the seesaw mechanism for generating fermion masses, we present a scale-invariant model that extends the gauge symmetry of the Standard Model electroweak sector to SU(3)$_L\otimes$U(1)$_X\otimes$U(1)$_N$, with a built-in $B-L$ symmetry. The model is based on the symmetry structure of the known 3-3-1 models and, thus, it relates the number of the three observed fermion generations with the cancellation of gauge anomalies. Symmetry breaking is triggered via the Coleman-Weinberg mechanism taking into account a minimal set of scalar field multiplets. We establish the stability conditions for the tree-level scalar potential imposing the copositivity criteria and use the method of Gildener-Weinberg for computing the one-loop effective potential when one has multiple scalar fields. With the addition of vectorial fermions, getting their mass mainly through the vacuum expectation value of scalar singlets at $10^3$ TeV, the $B-L$ symmetry leads to textures for the fermion mass matrices, allowing seesaw mechanisms for neutrinos and quarks to take place. In particular, these mechanisms could partly explain the mass hierarchies of the quarks. Once the breakdown of the SU(3)$_L$ symmetry is supposed to occur around 10 TeV, the model also predicts new particles with TeV-scale masses, such as a neutral scalar, $H_{1}$, a charged scalar, $H^\pm$, and the gauge bosons $Z^{\prime}$, $W^{\prime\pm}$ and $Y^0$, that could be searched with the high-luminosity LHC.

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arXiv2022

Spin-1/2 "bosons'' with mass dimension 3/2 and fermions with mass dimension 1 cannot represent physical particle states

We delve into the first principles of quantum field theory to prove that the so-called spin-1/2 ''bosons'' and the fermions with mass dimension 1, including ELKO, cannot represent physical particle states with spin $1/2$. Specifically, we first demonstrate that both aforementioned fields are not invariant under rotational symmetry, which implies that the particles created for these fields are not eigenstates of the spin operator in the $(\frac{1}{2},0)\oplus(0,\frac{1}{2})$ representation of the Lorentz group, nor is it possible to construct a Hamiltonian density scalar under the rotational group from them. Furthermore, following Weinberg's approach to local causal fields, we prove that regardless of any discrete symmetry or adjoint structure, the relativistic fields in the $(\frac{1}{2}, 0) \oplus (0,\frac{1}{2})$ representation satisfy the Fermi-Dirac statistics in complete agreement with the well-established spin-statistics theorem and experimental results.

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arXiv2020

Dynamical Symmetry Breaking and Fermion Mass Hierarchy in the Scale-Invariant 3-3-1 Model

We propose an extension of the Standard Model (SM) based on the $SU(3)_C\otimes SU(3)_L\otimes U(1)_X$ (3-3-1) gauge symmetry and scale invariance. Maintaining the main features of the so-called 3-3-1 models, such as the cancellation of gauge anomalies related to the number of chiral fermion generations, this model exhibits a very compact scalar sector. Only two scalar triplets and one singlet are necessary and sufficient to break the symmetries dynamically via the Coleman-Weinberg mechanism. With the introduction of an Abelian discrete symmetry and assuming a natural hierarchy among the vacuum expectation values of the neutral scalar fields, we show that all particles in the model can get phenomenologically consistent masses. In particular, most of the standard fermion masses are generated via a seesaw mechanism involving some extra heavy fermions introduced for consistency. This mechanism provides a partial solution for the fermion mass hierarchy problem in the SM. Furthermore, the simplicity of the scalar sector allows us to analytically find the conditions for the potential stability up to one-loop level and show how they can be easily satisfied. Some of the new particles, such as the scalars $H$, $H^\pm$ and all the non-SM vector bosons, are predicted to get masses around the TeV scale and, therefore, could be produced at the high-luminosity LHC. Finally, we show that the model features a residual symmetry which leads to the stability of a heavy neutral particle; the latter is expected to show up in experiments as missing energy.

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arXiv2019

Vacuum stability conditions of the economical 3-3-1 model from copositivity

By applying copositivity criterion to the scalar potential of the economical $3-3-1$ model, we derive necessary and sufficient bounded-from-below conditions at tree level. Although these are a large number of intricate inequalities for the dimensionless parameters of the scalar potential, we present general enlightening relations in this work. Additionally, we use constraints coming from the minimization of the scalar potential by means of the orbit space method, the positivity of the squared masses of the extra scalars, the Higgs boson mass, the $Z'$ gauge boson mass and its mixing angle with the SM $Z$ boson in order to further restrict the parameter space of this model.

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arXiv2018

Mu-tau reflection symmetry with a high scale texture-zero

The $μτ$-reflection symmetric neutrino mass matrix can accommodate all known neutrino mixing angles, with maximal atmospheric angle fixed, and predicts all the unknown CP phases of the lepton sector but is unable to predict the absolute neutrino mass scale. Here we present a highly predictive scenario where $μτ$-reflection is combined with a discrete abelian symmetry to enforce a texture-zero in the mass matrix of the heavy right-handed neutrinos that generate the light neutrino masses. Such a restriction reduces the free parameters of the low energy theory to zero and the absolute neutrino mass scale is restricted to few discrete regions, three in the few meV range and one extending up to around 30 meV. The heavy neutrino sector is dependent only on two free parameters which are further restricted to small regions from the requirement of successful leptogenesis. Mass degenerate heavy neutrinos are possible in one case but there is no resonant enhancement of the CP asymmetry.

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arXiv2018

Axion dark matter in a $3-3-1$ model

Slightly extending a right-handed neutrino version of the $3-3-1$ model, we show that it is not only possible to solve the strong CP problem but also to give the total dark matter abundance reported by the Planck collaboration. Specifically, we consider the possibility of introducing a $3-3-1$ scalar singlet to implement a gravity stable Peccei-Quinn mechanism in this model. Remarkably, for allowed regions of the parameter space, the arising axions with masses $m_a\approx$ meV can both make up the total dark matter relic density through non-thermal production mechanisms and be very close to the region to be explored by the IAXO helioscope.

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arXiv2017

Linking axionlike dark matter to neutrino masses

We present a framework linking axionlike particles (ALPs) to neutrino masses through the minimal inverse seesaw (ISS) mechanism in order to explain the dark matter (DM) puzzle. Specifically, we explore three minimal ISS cases where mass scales are generated through gravity-induced operators involving a scalar field hosting ALPs. In all of these cases, we find gravity-stable models providing the observed DM relic density and, simultaneously, consistent with the phenomenology of neutrinos and ALPs. Remarkably, in one of the ISS cases, the DM can be made of ALPs and sterile neutrinos. Furthermore, other considered ISS cases have ALPs with parameters inside regions to be explored by proposed ALPs experiments.

hep-ph↗

arXiv2017

Mu-tau reflection symmetry with a texture-zero

The $μτ$-reflection symmetry is a simple symmetry capable of predicting all the unknown CP phases of the lepton sector and the atmospheric angle but too simple to predict the absolute neutrino mass scale or the mass ordering. We show that by combining it with a discrete abelian symmetry in a nontrivial way we can additionally enforce a texture-zero and obtain a highly predictive scenario where the lightest neutrino mass is fixed to be in the few meV range for two normal ordering (NO) solutions or in the tens of meV in one inverted ordering (IO) solution. The rate for neutrinoless double beta decay is predicted to be negligible for NO or have effective mass $m_{ββ}\approx 14\text{ -- }29\,{\rm meV}$ for IO, right in the region to be probed in future experiments.

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arXiv2016

New constraints on the 3-3-1 model with right-handed neutrinos

In the framework of a 3-3-1 model with right-handed neutrinos and three scalar triplets we consider different spontaneous symmetry breaking patterns seeking for a non-linear realization of accidental symmetries of the model, which will produce physical Nambu-Goldstone (NG) bosons in the neutral scalar spectrum. We make a detailed study of the safety of the model concerning the NG boson emission in energy loss processes which could affect the standard evolution of astrophysical objects. We consider the model with a $\mathbb{Z}_2$ symmetry, conventionally used in the literature, finding that in all of the symmetry breaking patterns the model is excluded. Additionally, looking for solutions for that problem, we introduce soft $\mathbb{Z}_2$-breaking terms in the scalar potential in order to remove the extra accidental symmetries and at the same time maintain the model as simple as possible. We find that there is only one soft $\mathbb{Z}_2$-violating term that can get rid of the problematic NG bosons.

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arXiv2016

Supersymmetric $U(1)_{Y^{\prime}}\otimes U(1)_{B-L}$ extension of the standard model

We build a supersymmetric version with $SU(3)_C\otimes SU(2)_L\otimes U(1)_{Y^\prime}\otimes U(1)_{B-L}$ gauge symmetry, where $Y^\prime$ is a new charge and $B$ and $L$ are the usual baryonic and leptonic numbers. The model has three right-handed neutrinos with identical $B-L$ charges, and can accommodate all fermion masses at the tree level. In particular, the type-I seesaw mechanism is implemented for the generation of the active neutrino masses. We obtain the mass spectra of all sectors and for the scalar one we also give the flat directions allowed by the model.

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