arXiv subjects

M. Veselsky

Publications and source records attributed to M. Veselsky.

At least 19 recordsLinked to original sources

arXiv2026

Impact of Kaon Condensation on the Thermal Evolution of the CCO in HESS J1731--347 Supernova Remnant

Recent analyses of the central compact object in the HESS J1731--347 supernova remnant suggest an unusual combination of a low mass and small radius, while its thermal emission indicates a relatively high surface temperature at its estimated age. Reconciling these structural and thermal properties within a unified theoretical framework may provide important constraints on the equation of state and composition of dense matter. In this work, we investigate the thermal consequences of negatively charged kaon condensation, an exotic phase that softens the equation of state and facilitate the reproduction of the inferred bulk properties of HESS J1731--347. We find that the onset of kaon condensation strongly accelerates the thermal evolution, leading to surface temperature substantially below the observationally inferred range. Within the adopted cooling framework, kaon condensation therefore cannot simultaneously account for the structural and thermal properties of HESS J1731--347.

astro-ph.HE↗

arXiv2026

Neutron Dark Decay and Exotic Compact Objects

Recent measurements of the compact star XTE J1814-338, with a mass of $M=1.2_{-0.05}^{+0.05}\ M_{\odot}$ and a radius of $R=7_{-0.4}^{+0.4} \ {\rm Km}$ alongside those of HESS J1731-347, which has a mass of $M=0.77_{-0.17}^{+0.20}\ M_{\odot}$ and a radius of $R=10.4_{-0.78}^{+0.86} \ {\rm Km}$, provide compelling evidence for the potential existence of exotic matter in neutron star cores. These observations offer important insights into the equation of state of dense nuclear matter. Recently, Fornal and Grinstein, in order to overcame the discrepancy between the neutron lifetime measured in beam and bottle experiments, proposed the existence of neutron dark decay. In the present work, an effort is made to connect the interpretation of the above exotic compact objects with the possible existence of dark particles, assumed to be products of neutron dark decay. Our hypothesis offers an advantage over comparable proposals, as the coexistence of dark matter and hadronic matter within neutron stars emerges from an intrinsic mechanism, thereby obviating the need to invoke external merger-related processes. It is still unclear to what extent the proposed dark decay of the neutron is affected by the extreme environment within neutron stars. Within this framework, we examined the case in which a mechanism suppressing the dark neutron decay becomes operative at densities few times above nuclear saturation density. We found that the proposed alternative explanation accommodates the simultaneous existence of neutron dark decay while consistently predicting both the two solar mass limit and the presence of compact objects with subsolar masses.

nucl-th↗

arXiv2025

Simultaneous explanation of XTE J1814-338 and HESS J1731-347 objects using ${K^{-}}$ and ${\bar{K}^{0}}$ condensates

The recent observation of the compact star XTE J1814-338 with a mass of $M=1.2^{+0.05}_{-0.05}~{\rm M_{\odot}}$ and a radius of $R=7^{+0.4}_{-0.4}$ km, together with the HESS J1731-347, which has a mass of $M=0.77^{+0.20}_{-0.17}~{\rm M_{\odot}}$ and a radius of $R=10.4^{+0.86}_{-0.78}$ km, shows they provide evidence for the possible presence of exotic matter in the core of neutron stars and significantly enhance our understanding of the equation of state for the dense nuclear matter. In the present study, we investigate the possible existence of negative charged kaons and neutral anti-kaons in neutron stars by employing the relativistic mean field model with first order kaonic (${K^{-}}$ and ${\bar{K}^{0}}$) condensates. To the best of our knowledge, this represents a first alternative attempt aimed to explain the bulk properties of the XTE J1814-338 object and at the same time the HESS J1731-347 object, using a mixture of kaons condensation in dense nuclear matter. In addition, we compare our analysis approach with the recent observation of PSR J0437-4715 and PSR J1231-1411 pulsars, proposing that to simultaneously explain the current variety of astrophysical objects, it is essential to resurrect a scenario of two distinct branches, each corresponding to a different composition of nuclear matter.

nucl-th↗

arXiv2025

Neutron Star with Dark Matter Admixture: A Candidate for Bridging the Mass Gap

Neutron stars, white dwarfs and black holes are the after death remnants of massive stars. However, according to the most recent observations, the neutron stars maximum mass is between $2.0-2.5 M_{\odot}$ while black holes of less than 5 $M_{\odot}$ has not yet been observed. The region between the most massive neutron star and the least massive black hole is called the mass-gap. If indeed its existence is confirmed by future observations, that indicates a gap in our understanding which seeks for explanation. In addition, the existence of compact objects within the mass-gap should also be supported with the help of possible new theoretical scenarios. In this study, we propose a possible explanation for the existence of compact objects within the mass-gap region. Specifically, we propose that the mass-gap region could be bridged by the existence of a hybrid compact object, composed of hadronic and self interacting and non-annihilating fermionic dark matter, considering that the interaction between these two fluids it is only gravitational. Fundamental questions about how these objects form and how they can be detected are also addressed.

astro-ph.HE↗

arXiv2024

How the HESS J1731-347 event could be explained using $\bf{K^{-}}$ condensation

The recent observation of a compact star with a mass of $M=0.77^{+0.20}_{-0.17}~{\rm M_{\odot}}$ and a radius of $R=10.4^{+0.86}_{-0.78}$ km, located within the supernova remnant HESS J1731-347, has substantially reinforced the evidence for the presence of exotic matter in neutron stars core. This finding has markedly enhanced our comprehension of the equation of state for dense nuclear matter. In the present work, we investigate the possible existence of a kaon condensation in hadronic neutron stars by employing and comparing two theoretical frameworks: the Relativistic Mean Field model with first order kaon condensate and the Momentum-Dependent Interaction model complemented by chiral effective theory. To the best of our knowledge, this represents a first alternative attempt aimed to explain the bulk properties of the specific object with the inclusion of a kaon condensation in dense nuclear matter. The application of two different models enriches the research, providing insights from the aspect of different theoretical frameworks that accurately predict the existence of HESS J1731-347. In both cases significant insights are extracted for the parameter space of models, emphasizing to those concerning the nucleon-kaon potential, the threshold density for the appearance of a kaon condensation, as well as the parameter $a_{3}m_{s}$ which is related to the strangeness content of the proton. Concluding, the present research indicates that a more systematic investigation of similar objects could offer valuable constraints on the properties of dense nuclear matter.

nucl-th↗

arXiv2024

Configurational entropy and stability conditions of fermion and boson stars

In a remarkable study by M. Gleiser and N. Jiang [Phys. Rev. D {\bf 92}, 044046, 2015], the authors demonstrated that the stability regions of neutron stars, within the framework of the simple Fermi gas model, and self-gravitating configurations of complex scalar field (boson stars) with various self couplings, obtained through traditional perturbation methods, correlate with critical points of the configurational entropy with an accuracy of a few percent. Recently, P. Koliogiannis \textit{et al.} [Phys. Rev. D {\bf 107}, 044069 2023] found that while the minimization of the configurational entropy generally anticipates qualitatively the stability point for neutron stars and quark stars, this approach lacks universal validity. In this work, we aim to further elucidate this issue by seeking to reconcile these seemingly contradictory findings. Specifically, we calculate the configurational entropy of bosonic and fermionic systems, described by interacting Fermi and boson gases, respectively, that form compact objects stabilized by gravity. We investigate whether the minimization of configurational entropy coincides with the stability point of the corresponding compact objects. Our results indicate a strong correlation between the stability points predicted by configurational entropy and those obtained through traditional methods, with the accuracy of this correlation showing a slight dependence on the interaction strength. Consequently, the stability of compact objects, composed of components obeying Fermi or boson statistics, can alternatively be assessed using the concept of configurational entropy.

gr-qc↗

arXiv2024

Supramassive dark objects with neutron star origin

Till today, the nature of Dark Matter (DM) remains elusive despite all our efforts. This missing matter of the universe has not been observed by the already operating DM direct-detection experiments, but we can infer its gravitational effects. Galaxies and clusters of galaxies are most likely to contain DM trapped to their gravitational field. This leads us to the natural assumption that compact objects might contain DM too. Among the compact objects exist in galaxies, neutron stars are considered as natural laboratories, where theories can be tested, and observational data can be received. Thus, many models of DM have proposed it's presence in those stars. In particular, in the present study we focus on two types of dark matter particles, namely fermions and bosons with a mass range of [0.01-1.5] GeV and self-interaction strength in the range [10$^{-4}$-10$^{-1}$] MeV$^{-1}$. By employing the two-fluid model, we discovered a stable area in the M-R diagram of a celestial formation consisting of neutron star matter and DM that is substantial in size. This formation spans hundreds of kilometers in diameter and possesses a mass equivalent to 100 or more times the Solar mass. To elucidate, this entity resembles an enormous celestial body of DM, with a neutron star at its core. This implies that a supramassive stellar compact entity can exist without encountering any issues of stability and without undergoing a collapse into a black hole. In any case, the present theoretical prediction can, if combined with corresponding observations, shed light on the existence of DM and even more on its basic properties.

astro-ph.HE↗

arXiv2023

Constraints for the X17 boson from compacts objects observations

We investigate the hypothetical X17 boson on neutron stars and Quark Stars (QSs) using various hadronic Equation of States (EoSs) with phenomenological or microscopic origin. Our aim is to set realistic constraints on its coupling constant and the mass scaling, with respect to causality and various possible upper mass limits and the dimensionless tidal deformability $Λ_{1.4}$. In particular, we pay special attention on two main phenomenological parameters of the X17, the one is related to the coupling constant $\mathrm{g}$ that it has with hadrons or quarks and the other with the in-medium effects through the regulator $\mathrm{C}$. Both are very crucial concerning the contribution on the total energy density and pressure. In the case of considering the X17 as a carrier of nuclear force in Relativistic Mean Field (RMF) theory, an admixture into vector boson segment was constrained by 20\% and 30\%. In our investigation, we came to the general conclusion that the effect of the hypothetical X17 both on neutron and QSs constrained mainly by the causality limit, which is a specific property of each EoS. Moreover, it depends on the interplay between the main two parameters that is the interaction coupling $\mathrm{g}$ and the in-medium effects regulator $\mathrm{C}$. These effects are more pronounced in the case of QSs concerning all the bulk properties.

nucl-th↗

arXiv2023

Identification of medium mass (A=60-80) ejectiles from 15 MeV/nucleon peripheral heavy-ion collisions with the MAGNEX large-acceptance spectrometer

An approach to identify medium-mass ejectiles from peripheral heavy-ion reactions in the energy region of 15 MeV/nucleon is developed for data obtained with a large acceptance magnetic spectrometer. This spectrometer is equipped with a focal plane multidetector, providing position, angle, energy loss and residual energy of the ions along with measurement of the time-of-flight. Ion trajectory reconstruction is performed at high order and ion mass is obtained with a resolution of better than 1/150. For the unambiguous particle identification however, the reconstruction of both the atomic number Z and the ionic charge q of the ions is critical and it is suggested, within this work, to be performed prior to mass identification. The new proposed method was successfully applied to MAGNEX spectrometer data, for identifying neutron-rich ejectiles related to multinucleon transfer generated in the 70Zn+ 64Ni collision at 15 MeV/nucleon. This approach opens up the possibility of employing heavy-ion reactions with medium-mass beams below the Fermi energy (i.e., in the region 15-25 MeV/nucleon) in conjunction with large acceptance ray tracing spectrometers, first, to study the mechanism(s) of nucleon transfer in these reactions and, second, to produce and study very neutron-rich or even new nuclides in previously unexplored regions of the nuclear landscape.

physics.ins-det↗

arXiv2022

A path to the Nuclear Equation of State within the frameworks of Mean-Field and Fermionic Dynamics

The nuclear Equation of State (EoS) lies in the center of the nuclear N-body problem as it describes the properties of the Nuclear Matter (NM) and determines the parameters of the nuclear interaction. In this work, we propose a theoretical description of the EoS of both Symmetric (SNM) and Asymmetric (ANM) nuclear matter within the framework of Fermionic Dynamics. With this description we produce several new semi-hard EoS with density dependent effective mass. Finally, we transform the aforementioned theory in order to be consistent with Mean-Field dynamics. We use this approach to accurately calculate the binding energies and charge radii of nuclei in the A= 40--238 region with the Skyrme Hartree Fock (SHF) model.

nucl-th↗

arXiv2022

Investigating Possible Existence of Hyper-Heavy Nuclei in Neutron Star Environment

The synthesis of hyper-heavy elements is investigated under conditions simulating neutron star environment. The Constrained Molecular Dynamics (CoMD) approach is used to simulate low energy collisions of extremely n-rich nuclei. A new type of the fusion barrier due to a "neutron wind" is observed when the effect of neutron star environment (screening of Coulomb interaction) is introduced implicitly. When introducing also a background of surrounding nuclei, the nuclear fusion becomes possible down to temperatures of 10$^{8}$ K and synthesis of extremely heavy and n-rich nuclei appears feasible. A possible existence of hyper-heavy nuclei in a neutron star environment could provide a mechanism of extra coherent neutrino scattering or an additional mechanism, resulting in X-ray burst or a gravitational wave signal and, thus, becoming another crucial process adding new information to the suggested models on neutron star evolution.

nucl-th↗

arXiv2021

Anomaly in decay of 8Be and 4He -- can an observed light boson mediate low energy nucleon-nucleon interactions ?

We present a hypothesis that the anomaly in the folding angle distribution of electron-positron pairs, emitted in the decay of the excited levels of nucleus $^{8}$Be and $^{4}$He can be related to the cluster structure of the decaying state. Furthermore, we present a hypothesis that the potentially observed boson with re st mass $m_{X}$=17 MeV can mediate the nucleon-nucleon interaction at the low-energy regime of QCD, in particular in the weakly bound cluster state p+$^{7}$Li,$^{3}$H. We present a possible equations of state of symmetric nuclear matter corresponding to the vector meson mass $m_{v}$=17 MeV, obtained using relativistic mean field theory of nuclear force, QHD-I in particular, with physically relevant incompessibility K$_{0}$=240-260 MeV and the values of couplings $g_{v}$, $g_{s}$ lower than unity. Based on concepts of chiral symmetry breaking, we show that reduction of the rest mass of pseudoscalar particle from physical value $m_π$=135 MeV to $m_{X}$=17 MeV is equivalent to reduction of the quark mass from dynamical value around 310 MeV down to current quark mass around 5 MeV ($\frac{m_{X}^2} {m_{q,curr}} \simeq \frac{m_π^2} {m_{q,dyn}}$). Corresponding version of Goldberger-Treiman relation leads to the value of coupling close to the results from relativistic mean field theory of nuclear force. Both model approaches thus point towards apparent restoration of chiral symmetry in nucleon-nucleon interaction at large distances, possibly via bounce into false instanton vacuum. Observation of boson with rest mass $m_{X}$=17 MeV in the decay of high lying excited states of $^{8}$Be and $^{4}$He can possibly resolve one of the longest lasting open questions in nuclear physics.

nucl-th↗

arXiv2021

Production cross sections and angular distributions of neutron-rich rare isotopes from 15 MeV/nucleon Kr-induced collisions: toward the r-process path

We present our recent study of cross sections and angular distributions of projectile fragments from heavy-ion reactions at beam energy of 15 MeV/nucleon. We studied the production cross sections and the angular distributions of neutron-rich nuclides from collisions of a 86 Kr (15 MeV/nucleon) beam with heavy targets ( 64 Ni, 124 Sn and 238 U). Experimental data from our previous work at Texas A & M were compared with model calculations. Our calculations were based on a two-step approach: the dynamical stage of the collision was described with, first, the phenomenological Deep-Inelastic Transfer model (DIT) and, alternatively, with the microscopic Constrained Molecular Dynamics model (CoMD). The de-excitation of the hot heavy projectile fragments was performed with the Statistical Multifragmentation Model (SMM). An overall good discription of the available data was obtained with the models employed. Furthermore, we performed calculations with a radioactive beam of 92 Kr (15 MeV/nucleon) interacting with a target of 238 U. We observed that the multinucleon transfer mechanism leads to extremely neutron-rich nuclides toward and beyond the astrophysical r-process path.

nucl-ex↗

arXiv2021

Momentum Distributions of Projectile Fragments from Heavy-ion Peripheral Collisions at 15 MeV/nucleon with Emphasis on Trans-Projectile Isotopes

This paper presents our recent efforts to study the momentum distributions as well as the production of neutron-rich rare isotopes with heavy-ion beams in the energy region of 15 MeV/nucleon. Experimental cross sections of neutron-rich nuclides from collisions of a 86 Kr (15 MeV/nucleon) beam with 64 Ni and 58 Ni targets are presented. Experimental data were obtained from the previous work of our group with the MARS mass spectrometer at the Cyclotron Institute of Texas A&M University. On that note, detailed calculations of yields and momentum distributions of neutron-rich projectile-like fragments are presented for the interaction of 86 Kr with 64 Ni and compared with the aforementioned experimental data. The calculations were based on a two-step general approach: the dynamical stage of the primary interaction was described with the phenomenological deep-inelastic transfer model (DIT) and the microscopic constrained molecular dynamics model (CoMD); the deexcitation stage of the excited projectile fragments was described with the statistical binary-decay model GEMINI. The experimental data show an enhancement in the production of neutron-rich isotopes close to the projectile, and interestingly of heavier than the projectile neutron-rich nuclei. The behaviour of the data is relative to the predictions of the CoMD/GEMINI calculation. The study of the momentum distributions offers a novel route to study the reaction mechanism that dominates the production of the fragments of interest in peripheral heavy-ion collisions at intermediate energies. In the future, we plan to analyze experimental data that were obtained from the MAGNEX spectometer at the INFN-LNS in Catania, Italy.

nucl-ex↗

arXiv2019

Simulation of fusion and quasi-fission in nuclear reactions leading to production of superheavy elements using the Constrained Molecular Dynamics model

Fusion dynamics and the onset of quasi-fission in reactions, leading to production of superheavy nuclei are investigated using the constrained molecular dynamics model. Constraints on the parameters of the nuclear equation of state are derived from experimental fusion probabilities. The obtained constraint on the modulus of incompressibility of nuclear matter K0 = 240 - 260 MeV is consistent with the results of previous study using the Boltzmann-Uehling-Uhlenbeck equation and also with constraints derived using the recent neutron star binary collision event GW170817. Unlike the modulus of incompressibility of symmetric nuclear matter, the stiffness of the density-dependence of symmetry energy influences the fusion probability only weakly.

nucl-th↗

arXiv2018

Microscopic description of proton-induced spallation reactions with the Constrained Molecular Dynamics (CoMD) Model

We studied the complete dynamics of the proton-induced spallation process with the microscopic framework of the Constrained Molecular Dynamics (CoMD) Model. We performed calculations of proton-induced spallation reactions on 181Ta, 208Pb, and 238U targets with the CoMD model and compared the results with a standard two-step approach based on an intranuclear cascade model (INC) followed by a statistical deexcitation model. The calculations were also compared with recent experimental data from the literature. Our calculations showed an overall satisfactory agreement with the experimental data and suggest further improvements in the models. We point out that this CoMD study represents the first complete dynamical description of spallation reactions with a microscopic N-body approach and may lead to advancements in the physics-based modelling of the spallation process.

nucl-th↗

arXiv2018

Neutron-rich rare isotope production with stable and radioactive beams in the mass range A=40-60 at beam energy around 15 MeV/nucleon

We studied the production of neutron-rich nuclides in multinucleon transfer collisions of stable and radioactive beams in the mass range A=40-60. We first presented our experimental cross section data of projectile fragments from the reaction of 40Ar(15 MeV/nucleon) with 64Ni, 58Ni and 27Al. We then compared them with calculations based on either the deep-inelastic transfer (DIT) model or the constrained molecular dynamics (CoMD) model, followed by the statistical multifragmentation model (SMM). An overall good agreement of the calculations with the experimental data is obtained. We continued with calculations of the reaction of 40Ar (15 MeV/nucleon) with 238U target and then with reactions of 48Ca (15 MeV/nucleon) with 64Ni and 238U targets. In these reactions, neutron-rich rare isotopes with large cross sections are produced. These nuclides, in turn, can be assumed to form radioactive beams and interact with a subsequent target (preferably 238U), leading to the production of extremely neutron-rich and even new isotopes (e.g. 60Ca) in this mass range. We conclude that multinucleon transfer reactions with stable or radioactive beams at the energy of around 15 MeV/nucleon offer an effective route to access extremely neutron-rich rare isotopes for nuclear structure or reaction studies.

nucl-ex↗

arXiv2016

Thermal and transport properties in central heavy-ion reactions around a few hundred MeV/nucleon

Thermalization process of nuclear matter in central fireball region of heavy-ion collisions is investigated by employing an extension model of Boltzmann-Uehling-Uhlenbeck, namely the Van der Waals Boltzmann-Uehling-Uhlenbeck (VdWBUU) model. Temperature ($T$) is extracted by the quantum Fermion fluctuation approach and other thermodynamic quantities, such as density ($ρ$), entropy density ($s$), shear viscosity ($η$), isospin diffusivity ($D_{I}$) and heat conductivity ($κ$), are also deduced. The liquid-like and gas-like phase signs are discussed through the behavior of shear viscosity during heavy-ion collisions process with the VdWBUU model.

nucl-th↗