arXiv subjects

M. Ángeles Pérez-García

Publications and source records attributed to M. Ángeles Pérez-García.

At least 19 recordsLinked to original sources

arXiv2026

Neutrino diagnostics of hadron-quark phase transition in Neutron Stars

We investigate neutrino signatures of a hadron-quark phase transition (HQPT) in neutron stars (NS) leading to quark star (QS) formation. We use representative hadronic and quark equations of state i.e. DD2 and MIT bag model along with a phenomenological neutrino emission model including the dominant leptonic and hadronic processes. Rather than aiming at a fully consistent hydrodynamical simulation, our goal is to identify generic temporal diagnostics that may arise when deconfinement occurs during the evolution of a compact star. We identify characteristic diagnostic features that may emerge in the neutrino light curve on $\simeq 10-50$ ms timescales. These include an enhanced peak-to-plateau ratio, a delay tracing the central density evolution, and a transient spectral hardening. After standard MSW flavor conversion, these temporal and spectral signatures remain potentially detectable for Galactic events under optimistic assumptions with detectors such as IceCube and Hyper-Kamiokande. Our results suggest possible temporal and spectral diagnostics of quark deconfinement in future Galactic neutrino bursts.

astro-ph.HE↗

arXiv2026

Equation of State for warm Neutron Star outer crusts

We describe the equation of state (EoS) of a warm ion plasma as obtained by performing microscopic many-body simulations using Molecular Dynamics computational techniques. Using the cold one-component plasma (OCP) composition in the Neutron Star (NS) outer crust assumed in Murarka et al. (2022) with a representative heavy nucleus for each density, we refine previous calculations. We include electron screening and modeling of ions as finite-size Gaussian distributions in the interaction potential, together with an efficient Ewald energy summation procedure. From this, the EoS relation $P(n_B,T)$ is obtained as a function of baryonic density and temperature in the NS outer crust under conditions $n_B\in[7.48\times 10^{-10},2.09\times10^{-4}]$ $ \rm fm^{-3}$ , $k_{B}T\in[1,5]$ MeV. In order to improve the usability of our results we provide tabulated data values along with a neural network parametrization available in the Zenodo repository, see https://zenodo.org/records/15348712. We find that even at moderate temperatures, thermal effects of ions are key in the higher density region closer to the inner crust, when described using a thermal effective parametrization based on the thermal adiabatic index $Γ_{th}$. We compare our results with other EoS in the literature performing a critical discussion.

astro-ph.HE↗

arXiv2026

Deeper analysis of Fermi-LAT unassociated 4FGL J2112.5-3043 for possible identification

In the 4FGL-DR4 point-source catalog of the Large Area Telescope (LAT) onboard NASA's Fermi Gamma-ray Observatory (Fermi-LAT), around a third of the sources are still unidentified (unIDs). In this work, we perform a detailed study of one of them, namely 4FGL J2112.5-3043. Only gamma-ray emission has been detected from this unidentified source, with no counterpart observed at any other wavelength as of today. Together with its high detection significance, this makes 4FGL J2112.5-3043 a particularly compelling target for further investigation. The results of our spectral and spatial analyses show that the source photon spectrum is better described with a subexponential cutoff power-law spectral model, with no significant flux variability over time, and a morphology consistent with being a point-like source. We investigate and discuss the characterized emission within the context of both conventional and exotic astrophysics, namely a pulsar origin or potential dark matter (DM) annihilations in a nearby Galactic subhalo. Although our results are inconclusive and neither confirm a DM origin nor firmly establish an astrophysical nature, we find a spectral preference for the $b\bar{b}$ and $c\bar{c}$ DM annihilation channels over a pulsar origin, thus making this unID a particularly intriguing candidate for next multiwavelength observations.

astro-ph.HE↗

arXiv2026

Resonant Axion-Photon Conversion in the Early Inspiral of Neutron Star Binaries

We consider the early binary neutron star inspiral phase as a scenario to probe environmental axion--photon resonant conversion. For this we approximately model the merger site electromagnetic fields as the superposition of two rotating dipolar stellar magnetic fields at the thousand--km scale when both magnetospheres are not largely distorted. We capture the time-sliced near-zone magnetospheric geometry relevant for axion--photon mixing. Plasma effects are incorporated through an effective Goldreich--Julian charge density, used to determine the effective plasma frequency and the location of resonant conversion surfaces. Our results show that axion--photon resonant conversion in binary magnetospheres mostly occurs on extended peanut-shaped surfaces whose global geometry evolves as the binary inspiral evolves. As a consequence, the total electromagnetic power emitted through axion--photon conversion exhibits a characteristic dependence on axion mass and a slow temporal modulation correlated with the gravitational wave frequency emission. This feature is potentially detectable for $m_a \in [50,170] \,\rm μeV$ and set $g_{a γ} \lesssim 10^{-11}\rm \,GeV^{-1}$ as it lies within the sensitivity limits of current or planned radio observation missions. In light of our results we discuss the opportunity of binary neutron star inspirals as time-dependent, multimessenger probes of axion physics, and motivate coordinated searches combining gravitational wave observations with radio and millimeter wavelength electromagnetic measurements.

astro-ph.HE↗

arXiv2025

Probing ALP-photon couplings in Neutron Stars: Scalar versus pseudoscalar cases

We investigate the distribution of an interacting axion-like massive field within a magnetized Neutron Star. For this we consider the effect of an intense density-dependent axially symmetric stellar magnetic field ${\bf B}(r,θ)$ adding another much weaker, but non-vanishing, electric field. We particularize the latter for the case when a finite chiral charge density is present. The axion field is thus coupled to a generic function $Q(F_0,G_0)$ depending on Lorentz invariants $F_0, G_0$ which can be constructed from these electromagnetic fields. From this, the static axion field equations are solved as function of stellar radial coordinate and angular direction, $a(r,θ)$, using a prescribed linear form for $Q$. In addition, we use a semi-analytical approach to calculate the stellar structure in this hybrid system where pressure components are treated under a perturbative scheme, provided induced deformations with respect to spherical symmetry are tiny. Our results show that the axion couplings to magnetic and electric fields along with its mass, critically determine the axion spatial distribution. Furthermore, we focus on the possibility that the axion field might accumulate in specific outer regions of the star, particularly within the crust, where it could form a condensate. We explore the possible presence of magnetic flux tubes from superconductor phases in this outer layers and qualitatively show they may enhance local conversion into photons. We explore prospects of detectability through indirect methods.

astro-ph.HE↗

arXiv2025

Anomalous thermal relaxation in warm ion plasmas

We perform microscopic simulations of the thermal relaxation of warm neutral plasmas of astrophysical importance. Using Molecular Dynamics we study the thermal relaxation of a hot neutral fluid of finite-size neutron-rich ions kept in a fixed-wall cool box. We show how the interplay among particle size, Yukawa interaction range and density are key to understand the features of the time-dependent thermal relaxation curve $T(t)$. We show that, under certain conditions, these systems exhibit faster cooling from increasingly larger initial temperature values. They also display non-Newtonian thermal behavior, including oscillations, that can be {\it effectively} interpreted as the consequence of the existence of a non-trivial system memory function. Finally, we consider the impact of multicomponent admixtures in the simulated system. We discuss these results and their possible extensions to astrophysical scenarios, where screened plasmas with Yukawa-like electrostatic potentials are usually involved.

physics.plasm-ph↗

arXiv2024

Gravitational Wave emission in Binary Neutron Star early post-merger within a dark environment

Using an effective Lagrangian model inspired by Takami et al. 2015 we qualitatively study the early post-merger of a nearly symmetric binary Neutron Star (BNS) merger event with a non-vanishing ambient fraction of dark matter. For this we first mimic the dynamics of two oscillating Neutron Star (NS) masses in the gravitational potential well as they merge. We parametrize the dynamics and ejecta properties in the coalescence event allowing the formation of a surrounding debris disk that may be containing a non-vanishing dark matter fraction. In order to analyze the possible novel dark contribution, we start from a dark-matter free modellization as a benchmark. Using Monte Carlo Markov Chain (MCMC) techniques we approximately recover the gravitational waveforms, restricted to early post-merger time interval from existing simulations in the CoRe database. Later, we explore the impact of an additional dark viscous fluid under a prescribed velocity dependent force in the Lagrangian and obtain the resulting waveforms and some spectral features originating in the first few ms in the BNS post-merger. Finally we discuss our qualitative findings and its range of validity in light of the prospects of detectability in present or future experimental settings.

gr-qc↗

arXiv2024

Gauge-invariant perturbations of relativistic non-perfect fluids in spherical spacetime

Astrophysical compact objects are usually studied using a perfect fluid model. However, in astrophysical processes out-of-equilibrium, dissipative effects become important to describe the dynamics of the system. In this work, we obtain gauge-invariant non-spherical perturbations of a self-gravitating non-perfect fluid in spherical spacetime. We use the Gerlach-Sengupta formalism to work with gauge-invariant metric perturbations, and the Gundlach-Martín-García approach to transform the equations of tensor perturbations into scalar equations. We calculate the dynamics of the dissipative contributions, e.g., viscosity and heat flux, using the Müller-Israel-Stewart equations in the gauge-invariant formalism. We obtain a set of field equations for the evolution of matter and metric perturbations in the polar and axial sectors. Specifically, in the former we find two wave equations sourced by the anisotropic contributions, and the evolution of all matter perturbations for radiative modes ($l\geq 2$). In the axial sector, we find one wave equation coupled to the evolution of matter perturbations. Finally, we comment on the contribution of dissipative effects in the lower-order multipoles ($l=0,1$) for both sectors.

gr-qc↗

arXiv2024

Virialized equation of state for warm and dense stellar plasmas in proto-neutron stars and Supernova matter

We present microscopic Molecular Dynamics simulations including the efficient Ewald sum procedure to study warm and dense stellar plasmas consisting of finite-size ion charges immerse in a relativistic neutralizing electron gas. For densities typical of Supernova matter and crust in a proto-neutron star, we select a representative single ion composition and obtain the virialized equation of state (vEoS). We scrutinize the finite-size and screening corrections to the Coulomb potential appearing in the virial coefficients $B_2, B_3$ and $B_4$ as a function of temperature. In addition, we study the thermal heat capacity at constant volume, $C_V$, and the generalized Mayer's relation i.e. the difference $C_P-C_V$ with $C_P$ being the heat capacity at constant pressure, obtaining clear features signaling the onset of the liquid-gas phase transition. Our findings show that microscopic simulations reproduce the discontinuity in $C_V$, whose value lies between that of idealized gas and crystallized configurations. We study the pressure isotherms marking the boundary of the metastable region before the gaseous transition takes place. The resulting vEoS displays a behaviour where effective virial coefficients include extra density dependence showing a generalized density-temperature form. As an application we parametrize pressure as a function of density and temperature under the form of an artificial neural network showing the potential of machine learning for future regression analysis in more refined multicomponent approaches. This is of interest to size the importance of these corrections in the liquid-gas phase transition in warm and dense plasma phases contributing to the cooling behaviour of early Supernova phases and proto-neutron stars.

astro-ph.HE↗

arXiv2023

Constraining self-interacting fermionic dark matter in admixed neutron stars using multimessenger astronomy

We investigate the structure of admixed neutron stars with a regular hadronic component and a fraction of fermionic self-interacting dark matter. Using two limiting equations of state for the dense baryonic interior, constructed from piecewise generalised polytropes, and an asymmetric self-interacting fermionic dark component, we analyse different scenarios of admixed neutron stars depending on the mass of dark fermions $m_χ$, interaction mediators $m_ϕ$, and self-interacting strengths $g$. We find that the contribution of dark matter to the masses and radii of neutron stars leads to tension with mass estimates of the pulsar J0453+1559, the least massive neutron star, and with the constraints coming from the GW170817 event. We discuss the possibilities of constraining dark matter model parameters $g$ and $y \equiv m_χ/m_ϕ$, using current existing knowledge on neutron star estimations of mass, radius, and tidal deformability, along with the accepted cosmological dark matter freeze-out values and self-interaction cross-section to mass ratio, $σ_\mathrm{SI}/m_χ$, fitted to explain Bullet, Abell, and dwarf galaxy cluster dynamics. By assuming the most restrictive upper limit, $σ_\mathrm{SI}/m_χ< 0.1$ cm$^2$/g, along with dark matter freeze-out range values, the allowed $g$-$y$ region is $0.01 \lesssim g \lesssim 0.1$, with $0.5 \lesssim y \lesssim 200$. For the first time, the combination of updated complementary restrictions is used to set constraints on self-interacting dark matter.

astro-ph.HE↗

arXiv2023

Remarks on propagating waves in non-linear vacuum electrodynamics

Using the quadratic expansion in the photon fields of Euler-Heisenberg (EH) non-linear electrodynamics (NLED) Lagrangian model we study relevant vacuum properties in a scenario involving the propagation of a photon probe in the presence of a background constant and static magnetic field, ${\bf B_e}$. We compute the gauge invariant, symmetric and conserved energy-momentum tensor (EMT) and angular momentum tensor (AMT) for arbitrary magnetic field strength using the Hilbert method under the soft-photon approximation. We discuss how the presence of magneto-electric terms in the EH Lagrangian is a source of anisotropy, induce the non-zero trace in the EMT and leads to differences between EMT calculated by the Hilbert or Noether method. From the Hilbert EMT we analyze some quantities of interest such as the energy density, pressures, Poynting vector, and angular momentum vector, comparing and discussing the differences with respect to the improved Noether method. The magnetized vacuum properties are also studied showing that a photon effective magnetic moment can be defined for different polarization modes. The calculations are done in terms of derivatives of the two scalar invariants of electrodynamics, hence, extension to other NLED Lagrangian is straightforward. We discuss further physical implications and experimental strategies to test magnetization, photon pressure, and effective magnetic moment.

hep-ph↗

arXiv2023

Influence of the tetraneutron on the EoS under core-collapse supernovae and heavy-ion collisions conditions

Recently, a resonant state of four neutrons (tetraneutron) with an energy of $E_{4n}=2.37\pm 0.38 \rm{(stat)} \pm 0.44 \rm{(sys)}$ MeV and a width of $Γ=1.75\pm 0.22 \rm{(stat)} \pm 0.30 \rm{(sys)}$ MeV was reported. In this work, we analyse the effect of including such an exotic state on the yields of other light clusters, that not only form in astrophysical sites, such as core-collapse supernovae and neutron star mergers, but also in heavy-ion collisions. To this aim, we use a relativistic mean-field formalism, where we consider in-medium effects in a two-fold way, via the couplings of the clusters to the mesons, and via a binding energy shift, to compute the low-density equation of state for nuclear matter at finite temperature and fixed proton fraction. We consider five light clusters, deuterons, tritons, heliums, $α$-particles, and $^6$He, immersed in a gas of protons and neutrons, and we calculate their abundances and chemical equilibrium constants with and without the tetraneutron. We also analyse how the associated energy of the tetraneutron would influence such results. We find that the low-temperature, neutron-rich systems, are the ones most affected by the presence of the tetraneutron, making neutron stars excellent environments for their formation. Moreover, its presence in strongly asymmetric matter may increase considerably the proton and the $α$-particle fractions. This may have an influence on the dissolution of the accretion disk of the merger of two neutron stars.

nucl-th↗

arXiv2023

Neutrino signals from Neutron Star implosions to Black Holes

We calculate the neutrino luminosity in an astrophysical scenario where dark matter is captured by a neutron star which eventually implodes to form a low mass black hole. The Trojan horse scenario involves the collapse of a neutron star (NS) due to the accumulation of a critical amount of dark matter (DM) during its lifetime. As a result, a central disk forms out of the ejected material with a finite radial extension, density, temperature, and lepton fraction, producing fainter neutrino luminosities and colder associated spectra than found in a regular core-collapse supernova. The emitted gravitational wave (GW) signal from the imploding NS should be detectable at ultra-high $\gtrsim 0.1$ GHz frequencies.

astro-ph.CO↗

arXiv2022

Crystallization in single and multicomponent Neutron Star crusts

We use Molecular Dynamics simulations to study the formation and stability of single and multicomponent lattices in the outer crust of Neutron Stars. Including an improved treatment for Gaussian charge distributions of ions we obtain the expressions for the potential and forces arising from electron screened Coulomb interactions using the efficient Ewald sum procedure. %in the plasma. Our findings show that for baryon densities in the outer crust a point-like ion treatment can not fully describe the crystallization behaviour thus the Coulomb parameter, $Γ_C$, along with the usual screening parameter, $κ$, due to charge neutralizing electron polarizable background, must be complemented with an additional parameter, $η$, providing information on the finite size of ions. In our approach we find that including beyond point-like approaches in screened plasmas has a robust impact on calculated lattice energetic stability decreasing crystallization energies per baryon up to $\sim 40\%$ with respect to point-like interaction and, as a consequence, melting point resulting displaced to lower temperatures.

astro-ph.HE↗

arXiv2022

Cooling of Neutron Stars admixed with Light Dark Matter: a case study

Neutron Stars (NSs) are born as hot, lepton-rich objects that evolve according to the standard paradigm through subsequent stages where they radiate the excess of energy by emitting, first, neutrinos and, later on, photons. Current descriptions based on Standard Model calculations cannot fully explain all the existing cooling data series for the dozens of objects that have been reported. In this work, we consider the intriguing possibility that cooling NSs could be actually admixed with a fraction of light dark matter (LDM), $χ$. We focus on a particular case study assuming a generic light candidate with mass $m_χ=0.1$ $\rm GeV/c^2$ that undergoes self-annihilating reactions through pseudoscalar mediators producing neutrinos in the final state. We include one additional feature, allowing thermal conduction from LDM while inside the dark core. By performing simulations of the temperature evolution in the NS, we find that cooling patterns could be distorted by the presence of LDM and discuss these results in light of their observability.

hep-ph↗

arXiv2022

Non-linear interaction of laser light with vacuum: contributions to the energy density and pressure in presence of an intense magnetic field

Recent simulations show that very large electric and magnetic fields near the kilo Tesla strength will likely be generated by ultra-intense lasers at existing facilities over distances of hundreds of microns in underdense plasmas. Stronger ones are even expected in the future although some technical dificulties must be overcome. In addition, it has been shown that vacuum exhibits a peculiar non-linear behaviour in presence of high magnetic and electric field strengths. In this work we are interested in the analysis of thermodynamical contributions of vacuum to the energy density and pressure when radiation interacts with it in the presence of an external magnetic field. Using the Euler-Heisenberg formalism in the regime of weak fields i.e. smaller than critical Quantum Electrodynamics field strength values, we evaluate these magnitudes and analyze the highly anisotropic behaviour we find. Our work has implications for photon-photon scattering with lasers and astrophysically magnetized underdense systems far outside their surface where matter effects are increasingly negligible.

physics.plasm-ph↗

arXiv2021

Medium effects in supernovae constraints on light mediators

In this article, we reevaluate supernovae (SN) constraints on the diffusion time of neutrinos for a family of extensions of the Standard Model that incorporate new light scalar and vector mediators. We compute the neutrino mean free path, taking into account medium effects in the neutrino-nucleon scattering cross-section, and a radial dependence of the density, energy, and temperature inside the proto-neutron star to determine the coupling strengths compatible with SN1987A constraints on the time duration signal of diffusing neutrinos. We show that medium effects can induce an order of magnitude enhancement in the neutrino mean free path with respect to the vacuum calculation. The increase is more significant when new physics terms dominate over the Standard Model contribution (that is, for small mediator mass and large couplings). Finally, we interpret these results as bounds on the parameter space of a vector $U(1)_{B-L}$ model and scalar lepton number conserving and lepton number violating scenarios, improving on previous results in the literature where medium effects were ignored. We show that SN constraints on the neutrino diffusion time lie within regions of the parameter space that are already ruled out by other experimental constraints. We also comment on potential limits due to changes in the SN equation of state or right-handed neutrino free-streaming, but argue that detailed numerical simulations are needed to improve the reliability of these limits.

hep-ph↗

arXiv2021

Neutron Stars Mass-Radius relationship and Electromagnetic follow-up of Kilonovae

When two Neutron Stars collide a multi-band electromagnetic emission, known as Kilonova (KN), follows being powered by the radioactive decay of ejecta products. In this contribution we discuss how the equation of state of dense matter, impacts the mass and velocity in the KN ejecta and thus its light curve. Using this information encoded in the stellar mass-radius relationship, we ellaborate on how the future experimental observations in photon channels, in addition to complementary multimessenger probes, could provide a new and more detailed insight into the equation of state of nuclear matter.

astro-ph.HE↗