arXiv subjects

C. Albertus

Publications and source records attributed to C. Albertus.

At least 19 recordsLinked to original sources

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 $m_a \in [50,170] \,\rm \mu eV$ and set $g_{a \gamma} \lesssim 10^{-11}\rm \,GeV^{-1}$ 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 ${\bf B}(r,\theta)$ 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, $a(r,\theta)$, 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↗

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↗

arXiv2023

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

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, $\Gamma_C$, along with the usual screening parameter, $\kappa$, due to charge neutralizing electron polarizable background, must be complemented with an additional parameter, $\eta$, 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

Hubble constant and nuclear equation of state from kilonova spectro-photometric light curves

The merger of two compact objects of which at least one is a neutron star is signalled by transient electromagnetic emission in a kilonova (KN). This event is accompanied by gravitational waves and possibly other radiation messengers such as neutrinos or cosmic rays. The electromagnetic emission arises from the radioactive decay of heavy $r-$process elements synthesized in the material ejected during and after the merger. In this paper we show that the analysis of KNe light curves can provide cosmological distance measurements and constrain the properties of the ejecta. In this respect, MAAT, the new Integral Field Unit in the OSIRIS spectrograph on the $10.4$ m Gran Telescopio CANARIAS (GTC), is well suited for the study of KNe by performing absolute spectro-photometry over the entire 3600-10000 Angstron spectral range. Here, we study the most representative cases regarding the scientific interest of KNe from binary neutron stars, and we evaluate the observational prospects and performance of MAAT on the GTC to do the following: a) study the impact of the equation of state on the KN light curve, and determine to what extent bounds on neutron star (NS) radii or compactness deriving from KN peak magnitudes can be identified and b) measure the Hubble constant, $H_0$, with precision improved by up to 40$\%$, when both gravitational wave data and photometric-light curves are used. In this context we discuss how the equation of state, the viewing angle, and the distance affect the precision and estimated value of $H_0$.

astro-ph.CO↗

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), $\chi$. We focus on a particular case study assuming a generic light candidate with mass $m_\chi=0.1$ $\rm GeV/c^2$ 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↗

arXiv2020

Weak B Decays into Orbitally Excited Charmed Mesons

The BaBar Collaboration has recently reported branching fractions for semileptonic decays of the $B$ meson into final states with charged and neutral $D_{1}(2420)$ and $D_{2}^{\ast}(2460)$, two narrow orbitally excited charmed mesons. We evaluate these branching fractions within the framework of a constituent quark model in two steps, one which involves a semileptonic decay and the other one mediated by a strong process. Our results are in agreement with the experimental data.

hep-ph↗

arXiv2019

Second look to the Polyakov Loop Nambu-Jona-Lasinio model at finite baryonic density

We revisit the Polyakov Loop coupled Nambu-Jona-Lasinio model that maintains the Polyakov loop dynamics in the limit of zero temperature. This is of interest for astrophysical applications in the interior of neutron stars. For this purpose we re-examine the form of the potential for the deconfinement order parameter at finite baryonic densities. Since the modification of this potential at any temperature is formally equivalent to assigning a baryonic charge to gluons, we develop a more general formulation of the present model that cures this spurious effect and is normalized to match the asymptotic behaviour of the QCD equation of state given by $\mathcal{O}(\alpha_s^2)$ and partial $\mathcal{O}(\alpha_s^3\ln^2\alpha_s)$ perturbative results.

hep-ph↗

arXiv2019

Dark matter and bubble nucleation in old neutron stars

We study the probability for nucleation of quark matter droplets in the dense cold cores of old neutron stars induced by the presence of a self-annihilating dark matter component, $\chi$. Using a parameterized form of the equation of state for hadronic and quark phases of ordinary matter, we explore the thermodynamic conditions under which droplet formation is facilitated by the energy injection from $\chi$ self-annihilations. We obtain the droplet nucleation time as a function of the dark matter candidate mass, $m_\chi$. We discuss further observational consequences.

hep-ph↗

arXiv2019

Tetraneutron condensation in neutron rich matter

In this work we investigate the possible condensation of tetraneutron resonant states in the lower density neutron rich gas regions inside Neutron Stars (NSs). Using a relativistic density functional approach we characterize the system containing different hadronic species including, besides tetraneutrons, nucleons and a set of light clusters ($^3$He, $\alpha$ particles, deuterium and tritium). $\sigma,\omega$ and $\rho$ mesonic fields provide the interaction in the nuclear system. We study how the tetraneutron presence could significantly impact the nucleon pairing fractions and the distribution of baryonic charge among species. For this we assume that they can be thermodynamically produced in an equilibrated medium and scan a range of coupling strengths to the mesonic fields from prescriptions based on isospin symmetry arguments. We find that tetraneutrons may appear over a range of densities belonging to the outer NS crust carrying a sizable amount of baryonic charge thus depleting the nucleon pairing fractions.

nucl-th↗

arXiv2017

Science with e-ASTROGAM (A space mission for MeV-GeV gamma-ray astrophysics)

e-ASTROGAM (enhanced ASTROGAM) is a breakthrough Observatory space mission, with a detector composed by a Silicon tracker, a calorimeter, and an anticoincidence system, dedicated to the study of the non-thermal Universe in the photon energy range from 0.3 MeV to 3 GeV - the lower energy limit can be pushed to energies as low as 150 keV for the tracker, and to 30 keV for calorimetric detection. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. Thanks to its performance in the MeV-GeV domain, substantially improving its predecessors, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on the surroundings. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous generation instruments, e-ASTROGAM will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LIGO-Virgo-GEO600-KAGRA, SKA, ALMA, E-ELT, TMT, LSST, JWST, Athena, CTA, IceCube, KM3NeT, and LISA.

astro-ph.HE↗

arXiv2015

Production of unstable heavy neutrinos in proto-neutron stars

We discuss the production of a class of heavy sterile neutrinos $ν_h$ in proto-neutron stars. The neutrinos, of mass around $50$ MeV, have a negligible mixing with the active species but relatively large dimension-5 electromagnetic couplings. In particular, a magnetic dipole moment $μ\approx 10^{-6}$ GeV$^{-1}$ implies that they are thermally produced through $e^+ e^-\to \bar ν_h ν_h$ in the early phase of the core collapse, whereas a heavy--light transition moment $μ_{\rm tr}\approx 10^{-8}$ GeV$^{-1}$ allows their decay $ν_h\to ν_i γ$ with a lifetime around $10^{-3}$ s. This type of electromagnetic couplings has been recently proposed to explain the excess of electron-like events in baseline experiments. We show that the production and decay of these heavy neutrinos would transport energy from the central regions of the star to distances $d\approx 400$ km, providing a very efficient mechanism to enhance the supernova shock front and heat the material behind it.

astro-ph.HE↗

arXiv2015

Heavy baryons in the large Nc limit

It is shown that in the large Nc limit heavy baryon masses can be estimated quantitatively in a 1/Nc expansion using the Hartree approximation. The results are compared with available lattice calculations for different values of the ratio between the square root of the string tension and the heavy quark mass tension independent of Nc. Using a potential adjusted to agree with the one obtained in lattice QCD, a variational analysis of the ground state spin averaged baryon mass is performed using Gaussian Hartree wave functions. Relativistic corrections through the quark kinetic energy are included. The results provide good estimates for the first sub-leading in 1/Nc corrections.

hep-ph↗

arXiv2015

2p-2h excitations in neutrino scattering: angular distribution and frozen approximation

We study the phase-space dependence of 2p-2h excitations in neutrino scattering using the relativistic Fermi gas model. We follow a similar approach to other authors, but focusing in the phase-space properties, comparing with the non-relativistic model. A careful mathematical analysis of the angular distribution function for the outgoing nucleons is performed. Our goals are to optimize the CPU time of the 7D integral to compute the hadron tensor in neutrino scattering, and to conciliate the different relativistic and non relativistic models by describing general properties independently of the two-body current. For some emission angles the angular distribution becomes infinite in the Lab system, and we derive a method to integrate analytically around the divergence. Our results show that the frozen approximation, obtained by neglecting the momenta of the two initial nucleons inside the integral of the hadron tensor, reproduces fairly the exact response functions for constant current matrix elements.

nucl-th↗

arXiv2014

Testing nuclear models via neutrino scattering

Recent progresses on the relativistic modeling of neutrino-nucleus reactions are presented and the results are compared with high precision experimental data in a wide energy range.

nucl-th↗

arXiv2014

$B\to ρ$ semileptonic decays and $|V_{ub}|$

We reevaluate the $B\toρ\,l^+ν_l$ decay width as a full $B\toππ\,l^+ν_l$ four-particle decay, in which the two final pions are produced via an intermediate $ρ$ meson. The decay width can be written as a convolution of the $B\toρ\,l^+ν_l$ decay width, for an off-shell $ρ$, with the $ρ\toππ$ line shape. This allows to fully incorporate the effects of the finite $ρ$ meson width. As shown, consideration of the $ρ$ meson width effects increase the $|V_{ub}|$ value by some 8%, rendering it in better agreement with the determination based in the $B\toπ$ decay. We take the $q^2$ dependence of the $B\to ρ$ semileptonic form factors from a dispersive Omnès representation. The Omnès subtraction constants and the overall normalization parameter $|V_{ub}|$ are fitted to light cone sum rules and lattice QCD theoretical form-factor calculations, in the low and high $q^2$ regions respectively, together to the CLEO, BaBar and Belle experimental partial branching fraction distributions. The extracted value from this global fit is $|V_{ub}|=(3.12\pm 0.13)\times 10^{-3}$, in agreement with the average $B\to π$ exclusive value $|V_{ub}|=(3.23\pm 0.31)\times 10^{-3}$ quoted by the Particle Data Group. The extracted value increases to $|V_{ub}|=(3.51\pm 0.16)\times 10^{-3}$ if only the most recent Belle Collaboration data is used. This latter value is in agreement with different theoretical determinations based in the $B\toπ$ semileptonic decay and the values obtained by the CKMfitter and UTfit groups. In any case a clear tension with the $|V_{ub}|$ value extracted from inclusive semileptonic $b\to u$ decays still persists.

hep-ph↗