arXiv subjects

Maura E. Ramirez-Quezada

Publications and source records attributed to Maura E. Ramirez-Quezada.

14 recordsLinked to original sources

arXiv2026

Beyond the Daisy Chain: Running and the 3D EFT View of Supercooled Phase Transitions

Pulsar timing arrays have recently observed a stochastic gravitational wave background at nano-Hertz frequencies. This raises the question whether the signal can be of primordial origin. Supercooled first-order phase transitions are among the few early Universe scenarios that can successfully explain it. To further scrutinise this possibility, a precise theoretical understanding of the dynamics of the phase transition is required. Here we perform such an analysis for a dark sector with an Abelian Higgs model in the conformal limit, which is known to admit large supercooling. We compare simple analytic parametrisations of the bounce action, one-loop finite temperature calculations including Daisy resummation, and results of a dimensionally reduced (3D) effective theory including up to two-loop corrections using the DRalgo framework. Consistent renormalisation group evolution (RGE) of the couplings is essential for a meaningful interpretation of the results. We find that the 3D EFT with consistent expansion in the 4D parameters gives a significantly reduced scale dependence of the phase transition parameters. With a suitable choice of RGE scale, the 4D high temperature expanded effective potential yields results consistent with the 3D calculations, while the analytic parametrisation deviates significantly in the limit of large supercooling.

hep-ph↗

arXiv2026

Dark Matter Heating of Compact Stars Beyond Capture: A Relativistic Framework for Energy Deposition by Particle Beams

Compact astrophysical objects, such as neutron stars and white dwarfs, can act as detectors of energetic particle fluxes originating from astrophysical accelerators. While most existing capture and heating calculations assume isotropic very low energetic incident fluxes from the halo dark matter, many realistic sources produce highly directional beams or jets, for which gravitational focusing, trajectory multiplicity, and local energy deposition must be treated consistently. In this work, we develop a general relativistic formalism to compute the local density, capture probability, and energy deposition of particles arriving as directed beams onto compact objects. The framework is based on the mapping of an asymptotic particle flux to local densities through geodesic congruences, allowing for gravitational focusing, multi-stream regions, and optical depth effects to be incorporated in a unified way. The formalism applies to arbitrary particle species and interaction models, and separates capture from through-going energy deposition in a frame-consistent manner. As an explicit application, we consider relativistic particle beams generated in astrophysical jets and evaluate their interaction with two compact objects samples: a white dwarf and a neutron star. In particular, we illustrate the framework using boosted dark matter produced in a list of 324 blazars as a representative case study, computing the resulting fluxes and the associated heating in the selected stars. Additional regimes such as the interaction roof and geometric limit are discussed, highlighting the conditions under which compact objects can efficiently convert incident beam energy into observable heating.

hep-ph↗

arXiv2025

Insights on the Scale of Leptogenesis from Neutrino Masses and Neutrinoless Double-Beta Decay

We revisit the thermal leptogenesis scenario in the type-I seesaw framework featuring three heavy Majorana neutrinos with a hierarchical mass spectrum. We focus on low energy observables, specifically the lightest neutrino mass $m_ν^{\rm lightest}$ and the neutrinoless double-beta decay effective mass parameter $m^{\rm eff}_{ββ}$. In particular, we numerically calculate the minimum mass of the lightest heavy Majorana neutrino, $M_1^{\rm min}$, required for successful leptogenesis as a function of $m_ν^{\rm lightest}$ and $m_{ββ}^{\rm eff}$, considering both normal and inverted light neutrino mass orderings. Flavour effects are taken into account within the flavoured density matrix formalism. We also examine the interplay between fine-tuned cancellations in the seesaw relation and $M_1^{\rm min}$. Recent and forthcoming searches for neutrinoless double-beta decay, along with cosmological probes of the sum of neutrino masses, motivate this analysis, as they can provide key insights into the minimal scale of thermal leptogenesis and its broader implications.

hep-ph↗

arXiv2025

Dark Matter Interactions in White Dwarfs: A Multi-Energy Approach to Capture Mechanisms

White dwarfs offer a compelling avenue for probing interactions of dark matter particles, particularly in the challenging sub-GeV mass regime. The constraints derived from these celestial objects strongly depend on the existence of high dark matter densities in the corresponding regions of the Universe, where white dwarfs are observed. This implies that excluding the parameter space using local white dwarfs would present a significant challenge, primarily due to the low dark matter density in the solar neighbourhood. This limitation prompts the exploration of alternative scenarios involving dark matter particles with a diverse spectrum of kinetic energies. In this work, we investigate how these dark matter particles traverse the star, interact with stellar matter, and ultimately get captured. To accomplish this, we approximate the dark matter flux as a delta function and inspired on the Three Portal Model, we assume that fermionic dark matter interacts with stellar matter either through a broken $U(1)$ gauge vector mediator or a scalar. In our computations, we consider how interactions might vary across different energy regimes, from high-energy deep inelastic scattering and inelastic scatterings via the production of $N-$ and $Δ-$ resonances to lower-energy elastic interactions with nucleons and nuclei. Our study models these inelastic resonant interactions with dark matter and vector or scalar mediators for the very first time. We provide insights into the specific conditions required for successfully boosted dark matter capture in white dwarfs. We found that, in general, dark matter capture is most likely to occur at low energies, as expected. However, in the high-energy regime, there remains a small window for capture through resonant and deep inelastic scattering processes.

hep-ph↗

arXiv2025

Single pion resonant production in BSM scenarios: cross sections and amplitudes

We present a comprehensive theoretical framework describing single pion resonant production through inelastic dark fermion-nucleon interactions mediated by resonances in the GeV-scale regime. Building upon the Rein-Sehgal approach, we derive differential cross sections for processes in which an incoming dark fermion scatters off a nucleon, exciting a resonance that subsequently decays into a nucleon and a pion. Our formulation accommodates various mediator types-namely, dark photons with vector and axial couplings, as well as scalar and pseudoscalar mediators-thereby extending the conventional approach that Rein, Sehgal and Berger performed for neutrino interactions. Transition amplitudes for the nucleon-to-resonance conversion are computed using the relativistic harmonic-oscillator quark model from Feynman, Kislinger and Ravndal, while a Breit-Wigner prescription is employed to incorporate finite resonance widths. This framework offers a robust tool for interpreting experimental data in dark sector and matter searches and represents a contribution to elucidate the role of resonances in GeV-scale phenomenology.

hep-ph↗

arXiv2023

Thermal Leptogenesis in the Minimal Gauged $U(1)_{L_μ-L_τ}$ Model

We discuss the thermal leptogenesis mechanism within the minimal gauged U(1)$_{L_μ-L_τ}$ model to explain the observed baryon asymmetry of the Universe (BAU). In such framework, the phases of the Pontecorvo-Maki-Nakagawa-Sakata neutrino mixing matrix and the sum of the Standard Model neutrino masses are predictable because of a restricted neutrino mass matrix structure. Additionally, in the context of thermal leptogenesis, the BAU can be computed in terms of the three remaining free variables that parameterise the right-handed neutrino masses and their Yukawa couplings to the Higgs and lepton doublets. We identify the ranges of such parameters for which the correct BAU can be reproduced. We adopt the formalism of the density matrix equations to fully account for flavour effects and consider the decays of all the three right-handed neutrinos. Our analysis reveals that thermal leptogenesis is feasible within a wide parameter space, specifically for Yukawa couplings ranging from approximate unity to $\mathcal{O}(0.03-0.05)$ and mass of the lightest right-handed neutrino $M_1\gtrsim 10^{11-12}\,\text{GeV}$, setting a leptogenesis scale in the considered model which is higher than that of the non-thermal scenario.

hep-ph↗

arXiv2023

Vortex Creep Heating vs. Dark Matter Heating in Neutron Stars

Dark matter particles captured in neutron stars deposit their energy as heat. This DM heating effect can be observed only if it dominates over other internal heating effects in NSs. In this work, as an example of such an internal heating source, we consider the frictional heating caused by the creep motion of neutron superfluid vortex lines in the NS crust. The luminosity of this heating effect is controlled by the strength of the interaction between the vortex lines and nuclei in the crust, which can be estimated from the many-body calculation of a high-density nuclear system as well as through the temperature observation of old NSs. We show that both the temperature observation and theoretical calculation suggest that the vortex creep heating dominates over the DM heating. The vortex-nuclei interaction must be smaller than the estimated values by several orders of magnitude to overturn this.

hep-ph↗

arXiv2023

Exploring the dark sectors via the cooling of white dwarfs

As dense and hot bodies with a well-understood equation of state, white dwarfs offer a unique opportunity to investigate new physics. In this paper, we examine the role of dark sectors, which are extensions of the Standard Model of particle physics that are not directly observable, in the cooling process of white dwarfs. Specifically, we examine the role of a dark photon, within the framework of a three-portal Model, in enhancing the neutrino emission during the cooling process of white dwarfs. We compare this scenario to the energy release predicted by the Standard Model. By analyzing the parameter space of dark sectors, our study aims to identify regions that could lead to significant deviations from the expected energy release of white dwarfs.

hep-ph↗

arXiv2023

Vortex Creep Heating in Neutron Stars

Recent observations of old warm neutron stars suggest the presence of a heating source in these stars, requiring a paradigm beyond the standard neutron-star cooling theory. In this work, we study the scenario where this heating is caused by the friction associated with the creep motion of neutron superfluid vortex lines in the crust. As it turns out, the heating luminosity in this scenario is proportional to the time derivative of the angular velocity of the pulsar rotation, and the proportional constant $J$ has an approximately universal value for all neutron stars. This $J$ parameter can be determined from the temperature observation of old neutron stars because the heating luminosity is balanced with the photon emission at late times. We study the latest data of neutron star temperature observation and find that these data indeed give similar values of $J$, in favor of the assumption that the frictional motion of vortex lines heats these neutron stars. These values turn out to be consistent with the theoretical calculations of the vortex-nuclear interaction.

astro-ph.HE↗

arXiv2023

Light scalar explanation for 18 TeV GRB 221009A

Recent astrophysical transient Swift J1913.1+1946 may be associated with the $γ$-ray burst GRB 221009A. The redshift of this event is $z\simeq 0.151$. Very high-energy $γ$-rays (up to 18 TeV) followed the transient and were observed by LHAASO, additionally Carpet-2 detected a photon-like air shower of 251 TeV. Photons of such high energy are expected to readily annihilate with the diffuse extragalactic background light (EBL) before reaching Earth. If the $γ$-ray identification and redshift measurements are correct, new physics could be necessary to explain these measurements. This letter provides the first CP-even scalar explanation of the most energetic 18 TeV event reported by LHAASO. In this minimal scenario, the light scalar singlet $S$ mixes with the Standard Model (SM) Higgs boson $h$. The highly boosted $S$ particles are produced in the GRB and then undergo the radiative decay di-photon $S\rightarrow γγ$ while propagating to Earth. The resulting photons may thus be produced at a remote region without being nullified by the EBL. Hence, the usual exponential reduction of $γ$-rays is lifted due to an attenuation that is inverse in the optical depth, which becomes much larger due to the scalar carriers.

hep-ph↗

arXiv2023

Constraining dark matter interactions mediated by a light scalar with white dwarfs

Observations of white dwarfs in dark matter-rich environments can provide strong limits on the strength of dark matter interactions. Here we apply the recently improved formalism of the dark matter capture rate in white dwarfs to a general model in which dark matter interacts with the white dwarf ion components via a light scalar mediator. We compute the dark matter capture rate in the optically thin limit in a cold white dwarf from the globular cluster Messier. We then estimate the threshold cross-section, which significantly varies as a function of the light scalar mediator mass $m_ϕ$ in the range of $0.05\, m_χ m_χ$. We also show that the bounds obtained from the dark matter capture in a white dwarf from the globular cluster Messier 4 are complementary to direct detection experiments and particularly strong in the sub-GeV regime.

hep-ph↗

arXiv2022

Radio sky reveals primordial electron-proton interactions

For several decades, astronomers have measured the electromagnetic emission in the universe from the lowest to the highest energies with incredible precision. The lowest end of the spectrum, corresponding to radio waves, is fairly well studied and understood. Yet there is a long standing discrepancy between measurements and predictions, which has prompted the construction of many new models of radio emitters. Here we show that remnant electron-proton interactions, leading to photon production in the early universe, also referred to as cosmic free-free emission, solves the discrepancy between theory and observations. While the possibility of cosmic free-free emission has been postulated for several decades, this is the first time that the amplitude and shape of the signal has been computed and its existence demonstrated. Using current measurements we estimate this emission to become important from around a redshift of $z \simeq 2150$. This contribution from fundamental particles and interactions represents the lowest energy test from the early universe of one of the pillars of modern physics, Quantum Electrodynamics. The next generation of deep radio surveys will be able to measure primordial signals from this cosmic era with greater precision and further solidify our understanding of the radio sky.

astro-ph.CO↗

arXiv2022

Neutron Star Heating in Dark Matter Models for the Muon $g-2$ Discrepancy

The observed value of the muon magnetic dipole moment, which deviates from the Standard Model prediction by $4.2σ$, can be explained in models with weakly-interacting massive particles (WIMPs) coupled to muons. However, a considerable range of parameter space of such models will remain unexplored in the future LHC experiments and dark matter (DM) direct searches. In this work we discuss the temperature observation of neutron stars (NSs) as a promising way to probe such models given that WIMPs are efficiently captured by NSs through DM-muon or spin-dependent DM-nucleon scattering. The captured WIMPs eventually annihilate in the star core and heat the NS. This effect can be observed in old NSs as it keeps the NS surface temperature at a few thousand K at most, which is much higher than the predicted values of the standard NS cooling theory for NSs older than $\sim 10^7$ years. We consider two classes of representative models, where the DM couples or does not couple to the Higgs field at tree level, and show that the maximal DM heating is realized in both scenarios.

hep-ph↗

arXiv2021

Improved Treatment of Dark Matter Capture in White Dwarfs

White dwarfs, the most abundant stellar remnants, provide a promising means of probing dark matter (DM) interactions, complimentary to terrestrial searches. The scattering of dark matter from stellar constituents leads to gravitational capture, with important observational consequences. In particular, white dwarf heating occurs due to the energy transfer in the dark matter capture and thermalisation processes, and the subsequent annihilation of captured dark matter. We consider the capture of dark matter by scattering on either the ion or the degenerate electron component of white dwarfs. For ions, we account for the stellar structure, the star opacity, realistic nuclear form factors that go beyond the simple Helm approach, and finite temperature effects pertinent to sub-GeV dark matter. Electrons are treated as relativistic, degenerate targets, with Pauli blocking, finite temperature and multiple scattering effects all taken into account. We also estimate the dark matter evaporation rate. The DM-nucleon/electron scattering cross sections can be constrained by comparing the heating rate due to dark matter capture with observations of cold white dwarfs in dark matter-rich environments. We apply this technique to observations of old white dwarfs in the globular cluster Messier 4, which we assume to be located in a DM subhalo. For DM-nucleon scattering, we find that white dwarfs can probe the sub-GeV mass range inaccessible to direct detection searches, with the low mass reach limited only by either evaporation or dominant DM annihilation to neutrinos, and can be competitive with direct detection in the $1-10^4$ GeV range. White dwarf limits on dark matter-electron scattering are found to outperform current electron recoil experiments over the full mass range considered, and extend well beyond the $\sim 10$ GeV mass regime where the sensitivity of electron recoil experiments is reduced.

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