arXiv subjects

Leon M. G. de la Vega

Publications and source records attributed to Leon M. G. de la Vega.

13 recordsLinked to original sources

arXiv2026

Dark Matter in the General 2HDM with Extra Top Yukawa Couplings

We extend the general two Higgs doublet model (G2HDM), which introduces extra Yukawa couplings, by an additional real scalar singlet (G2HDM+S), providing a viable scalar dark matter (DM) candidate. This setup provide a viable UV completion of top-window dark matter scenarios, in which DM communicates with the standard model predominantly through the top quark. We analyze the constraints on the visible scalar sector from Higgs signal strength measurements and direct searches for additional Higgs bosons at the LHC, and those on the dark sector from cosmological observables, including the observed DM relic density and spin-independent direct-detection as well as indirect detection. Within the surviving parameter space, we identify a rich and diverse LHC phenomenology governed by the interplay between the singlet portal, the extended Yukawa sector, and the heavy scalar mass hierarchy. To facilitate experimental investigation, we propose six benchmark scenarios spanning the singlet-portal, bosonic-cascade, fermiophilic, and flavor-violating regimes. In the latter, the nondiagonal top-charm coupling $ρ_{tc}$ induces the production channel $cg \to tH$, allowing the top quark to serve as a trigger for an otherwise invisible $H\to SS$ signal. This flavor-violating DM production is a distinct feature of the G2HDM+S.

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arXiv2025

Dark Z-mediated dark matter with verifiable exotic scalars

In this work, we study a dark matter scenario where a dark Z boson possessing mass mixing with the SM Z boson couples to the DM candidate and serves as the portal to the SM. The UV origin of the mass mixing in the form of an extra dark Higgs doublet and a scalar dark singlet provides new exotic scalars which can constitute the final state of DM annihilation during freeze-out. We find that existing constraints on the observed Higgs coupling strength, exotic Higgs searches and dark matter observables complement each other, while future searches for exotic Higgs decays and resonant heavy scalars at HL-LHC will be sensitive to part of the allowed parameter space.

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arXiv2025

Leptoquark-mediated Dirac neutrino mass and its impact on $B \to K ν\barν$ and $K \to πν\barν$ decays

Right-handed neutrinos $ν_R$ play a crucial role in flavor-changing neutral-current processes with missing energy, such as $b\to s + \slashed{E} $ and $d\to s + \slashed{E} $, where Belle-II reports unexpectedly large branching fraction in $B\to K ν\barν$ decays. Assuming $ν_R$ is the partner of the active neutrino $ν_L$ in the standard model, a Dirac-type neutrino framework emerges. We investigate a scenario of radiative Dirac neutrino mass generation in a scalar leptoquark (LQ) model with a global $U(1)_X$ symmetry to suppress Majorana mass, tree-level Dirac mass, and diquark couplings. The simplest LQ realization consists of two $S_1 = (3,1,-1/3)$ LQs with distinct $U(1)_X$ charges. A non-Casas-Ibarra parametrization is proposed to match neutrino data with fewer model parameters. Imposing current experimental constraints from meson mixing and lepton flavor-violating processes, we find that right-handed neutrino effects can significantly enhance $B\to K^{(*)} ν\barν$ and $K^+\to π^+ ν\barν$. Additionally, the model predicts excesses in $R_D$ from $B\to Dτ\barν$ that remain within $1σ$ of current experimental data.

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arXiv2024

Dark matter for Majorana neutrinos in a $\mathbb{Z}_4$ symmetry

In the minimal Scotogenic model with fermionic dark matter, the neutrino Yukawa matrix is fine-tuned to satisfy current bounds on $μ\rightarrow e γ$ while producing dark matter through thermal freeze-out. One way to avoid this bound is to open a new annihilation channel for dark matter (DM) with a scalar field that breaks the lepton number spontaneously. This introduces a physical Goldstone boson $a$, which can constitute a light relic and opens up the lepton flavor violating channel $μ\rightarrow e a$. In this work, we introduce a model that contains the new annihilation channel for fermionic dark matter but avoids the introduction of the Goldstone boson by using a discrete $\mathbb{Z}_4$ instead of a continuous symmetry. In this way, cosmological constraints on the light relic and experimental limits on lepton flavor violating decays to the Goldstone boson are avoided. We analyze the experimental viability of the model, identifying the region of parameter space where lepton flavor violating constraints are not saturated, DM has the correct relic density, and DM direct detection experiments are sensitive to the DM candidate.

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arXiv2024

The $L_μ-L_τ$ solution to the IceCube Ultra High Energy neutrino deficit in light of NA64

In this work we analyze the scenario where a MeV scale $L_μ- L_τ$ gauge boson can explain the deficit in the diffuse ultra high energy (UHE) astrophysical neutrino spectrum observed in IceCube, as well as the discrepancy between experimental and $e^+e^-$ dispersion data driven SM calculations of the muon anomalous magnetic moment. We map the parameter space of the model where the elastic resonant s-channel scattering of UHE neutrinos with the cosmic neutrino background, mediated by the new Z', can improve the description of the observed cascade and track spectra over the no-scattering hypothesis. Comparing to recent NA64$μ$ results, we find that some part of the parameter space remains unexplored, but at a data volume of $10^{11}$ muons on target NA64$μ$ will completely probe this region.

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arXiv2023

Closing the dark photon window to thermal dark matter

The nature of dark matter remains a central question in particle physics, cosmology, and astrophysics. The prevailing hypothesis postulates that dark matter consists of particles that interact only weakly with Standard Model particles. However, the knowledge of dark matter properties beyond these interactions is limited. This study explores a scenario involving a dark photon as a mediator between dark matter and the Standard Model, akin to the photon's role in electromagnetism. Recent cosmological and experimental evidence impose constraints on this scenario, focusing on results from direct detection experiments such as PICO-60, XENON-1T, and PANDAX-4T. The results reveal severe constraints, effectively closing the window for laboratory searches for dark photons as mediators between the Standard Model and the dark sector (dark electrons) in the secluded dark matter scenario. The findings underscore the need for alternative explanations and offer fresh perspectives on the ongoing quest to understand dark matter and its interactions since they are nearly independent of the dark electron fraction content for the total dark matter. This analysis significantly narrows down the parameter space for thermal dark matter scenarios involving a dark photon portal, reinforcing the urgency of exploring alternative models and designing new experiments to unravel the mysteries surrounding the nature of dark matter.

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arXiv2022

Neutrino masses and self-interacting dark matter with mass mixing $Z-Z^\prime$ gauge portal

New light gauge bosons can affect several low-energy experiments, such as atomic parity violation or colliders. Here, we explore the possibility that a dark sector is charged under a new $U(1)$ gauge symmetry, and the portal to the Standard Model is through a $Z-Z'$ mass mixing. In our approach, breaking the new gauge symmetry is crucial to generate neutrino masses. We investigate the parameter space to reproduce neutrino masses, the correct dark matter relic abundance, and to produce the observed core-like DM distribution in galactic centers.

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arXiv2021

Complementarity between dark matter direct searches and CE$ν$NS experiments in $U(1)'$ models

We explore the possibility of having a fermionic dark matter candidate within $U(1)'$ models for CE$ν$NS experiments in light of the latest COHERENT data and the current and future dark matter direct detection experiments. A vector-like fermionic dark matter has been introduced which is charged under $U(1)'$ symmetry, naturally stable after spontaneous symmetry breaking. We perform a complementary investigation using CE$ν$NS experiments and dark matter direct detection searches to explore dark matter as well as $Z^{\prime}$ boson parameter space. Depending on numerous other constraints arising from the beam dump, LHCb, BABAR, and the forthcoming reactor experiment proposed by the SBC collaboration, we explore the allowed region of $Z^{\prime}$ portal dark matter.

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arXiv2021

Flavored axion in the UV-complete Froggatt-Nielsen models

We propose UV-completions of Froggatt-Nielsen-Peccei-Quinn models of fermion masses and mixings with flavored axions, by incorporating heavy fields. Here, the $U(1)$ Froggatt-Nielsen symmetry is identified with the Peccei-Quinn symmetry to solve the strong CP problem along with the mass hierarchies of the Standard Model fermions. We take into account leading order contributions to the fermion mass matrices giving rise to Nearest-Neighbour-Interaction structure in the quark sector and $A_2$ texture in the neutrino sector. A comprehensive numerical analysis has been performed for the fermion mass matrices. Subsequently, we investigate the resulting axion flavor violating couplings and the axion-photon coupling arising from the model.

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arXiv2020

Neutrino phenomenology in a left-right $D_4$ symmetric model

We present a minimal left-right symmetric flavor model and analyze the predictions for the neutrino sector. In this scenario, the Yukawa sector is shaped by the dihedral $D_4$ symmetry which leads to correlations for the neutrino mixing parameters. We end up with four possible solutions within this model. We further analyzed the impact of the upcoming long-baseline neutrino oscillation experiment DUNE. Due to its high sensitivity, DUNE will be able to rule out two of the solutions. Finally, the prediction for the neutrinoless double beta decay for the model has also been examined.

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arXiv2020

Fermion Dark Matter and Radiative Neutrino Masses from Spontaneous Lepton Number Breaking

In this paper, we study the viability of having a fermion Dark Matter particle below the TeV mass scale in connection to the neutrino mass generation mechanism. The simplest realization is achieved within the scotogenic model where neutrino masses are generated at the 1-loop level. Hence, we consider the case where the dark matter particle is the lightest $\mathbb{Z}_2$-odd Majorana fermion running in the neutrino mass loop. We assume that lepton number is broken dynamically due to a lepton number carrier scalar singlet which acquires a non-zero vacuum expectation value. In the present scenario the Dark Matter particles can annihilate via $t$- and $s$-channels. The latter arises from the mixing between the new scalar singlet and the Higgs doublet. We identify three different Dark Matter mass regions below 1 TeV that can account for the right amount of dark matter abundance in agreement with current experimental constraints. We compute the Dark Matter-nucleon spin-independent scattering cross-section and find that the model predicts spin-independent cross-sections ``naturally'' dwelling below the current limit on direct detection searches of Dark Matter particles reported by XENON1T.

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arXiv2020

Dirac neutrinos from Peccei-Quinn symmetry: two examples

We aim to explain the nature of neutrinos using Peccei-Quinn symmetry. We discuss two simple scenarios, one based on a type-II Dirac seesaw and the other in a one-loop neutrino mass generation, which solve the strong CP problem and naturally lead to Dirac neutrinos. In the first setup latest neutrino mass limit gives rise to axion which is in the reach of conventional searches. Moreover, we have both axion as well as WIMP dark mater for our second set up.

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arXiv2019

Simple A4 models for dark matter stability with texture zeros

In a simple framework which naturally incorporates dark matter stability and neutrino phenomenology, we compute all the possible texture zeros which arise when the non-abelian flavor symmetry A4 is spontaneously broken to Z2. As a result, we obtain four textures with two vanishing matrix elements. Two of such textures predict a zero contribution to the neutrinoless double beta decay effective mass parameter at tree level, and as a one loop bound we get $m_{ee}<8\times 10^{-2}$ meV. These are compatible with the normal ordering for the neutrino masses and the allowed range for the lightest neutrino mass is between $m_{ν_{min}}\sim3$ meV and $m_{ν_{max}}\sim8$ meV. Additionally we obtain dark matter stability linked to the way the flavor symmetry is broken, leaving a residual Z2 symmetry

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