arXiv subjects

O. Ivanytskyi

Publications and source records attributed to O. Ivanytskyi.

8 recordsLinked to original sources

arXiv2025

Primordial black-hole formation and heavy r-process element synthesis from the cosmological QCD transition. Two aspects of an inhomogeneous early Universe

We review the role of primordial black holes (PBHs) for illuminating the dark ages of the cosmological evolution and as dark matter candidates. We elucidate the role of phase transitions for primordial black hole formation in the early Universe and focus our attention to the cosmological QCD phase transition within a recent microscopical model. We explore the impact of physics beyond the Standard Model on the cosmic equation of state and the probability distribution for the formation of primordial black holes which serve as dark matter (DM) candidates. We argue that besides primordial black holes also droplet-like quark-gluon plasma inhomogeneities may become gravitationally stabilized for a sufficiently long epoch to distill baryon number and form nuclear matter droplets which upon their evaporation may enrich the cosmos locally with heavy $r$-process elements already in the early Universe.

hep-ph↗

arXiv2023

Thermodynamics of quark matter with multiquark clusters in an effective Beth-Uhlenbeck type approach

We describe multiquark clusters in quark matter within a Beth-Uhlenbeck approach in a background gluon field coupled to the underlying chiral quark dynamics using the Polyakov gauge which establishes the center symmetry of color SU(3) that suppresses colored states as an aspect of confinement. Quark confinement is modeled by a large quark mass in vacuum motivated by a confining density functional approach. A multiquark cluster containing $n$ quarks and antiquarks is described as a binary composite of smaller subclusters $n_1$ and $n_2$ ($n_1+n_2=n$). It has a spectrum consisting of a bound state and a scattering state continuum. For the corresponding cluster-cluster phase shifts we discuss simple ans\"atze that capture the Mott dissociation of clusters as a function of temperature and chemical potential. We go beyond the simple "step-up-step-down" model that ignores continuum correlations and introduce an improved model that includes them in a generic form. In order to explain the model, we restrict ourselves here to the cases where the cluster size is $1 \le n \le 6$. A striking result is the suppression of the abundance of colored multiquark clusters at low temperatures by the coupling to the Polyakov loop and their importance for a quantitative description of lattice QCD thermodynamics at non-vanishing baryochemical potentials. An important ingredient are Polyakov-loop generalized distribution functions of $n$-quark clusters which are derived here for the first time. Within our approach we calculate thermodynamic properties such as baryon density and entropy. We demonstrate that the limits of a hadron resonance gas at low temperatures and $\mathcal{O}(g^2)$ perturbative QCD at high temperatures are correctly reproduced. A comparison with lattice calculations shows that our model is able to give a unified, systematic approach to describe properties of the quark-gluon-hadron system.

nucl-th↗

arXiv2022

Quark deconfinement in compact stars through sexaquark condensation

In this contribution, we present for the first time a scenario according to which early quark deconfinement in compact stars is triggered by the Bose-Einstein condensation (BEC) of a light sexaquark (S) with a mass $m_S<2054$ MeV, that has been suggested as a candidate particle to explain the baryonic dark matter in the Universe. The onset of S BEC marks the maximum mass of hadronic neutron stars and it occurs when the condition for the baryon chemical potential $\mu_b=m_S/2$ is fulfilled in the center of the star, corresponding to $M_{\rm onset}\lesssim 0.7~M_\odot$. In the gravitational field of the star the density of the BEC of the S increases until a new state of the matter is attained, where each of the S-states got dissociated into a triplet of color-flavor-locked (CFL) diquark states. These diquarks are the Cooper pairs in the color superconducting CFL phase of quark matter, so that the developed scenario corresponds to a BEC-BCS transition in strongly interacting matter. For the description of the CFL phase, we develop here for the first time the three-flavor extension of the density-functional formulation of a chirally symmetric Lagrangian model of quark matter where confining properties are encoded in a divergence of the scalar self-energy at low densities and temperatures.

nucl-th↗

arXiv2021

Constraints on the fermionic dark matter from observations of neutron stars

We study an impact of asymmetric fermionic dark matter on neutron star properties, including tidal deformability, mass, radius, etc. We present the conditions at which dark matter particles tend to form a compact structure in a core of the star or create an extended halo around it. We show that compact core of dark matter leads to a decrease of the total gravitational mass and tidal deformability compared to a pure baryonic star, while presence of a dark matter halo increases those observable quantities. By imposing an existing astrophysical and gravitational wave constraints set by LIGO/Virgo Collaboration together with the recent results on the spatial distribution of dark matter in the Milky Way we determine a new upper limit on the mass and fraction of dark matter particles inside compact stars. Furthermore, we show that the formation of an extended halo around a NS is incompatible with the GW170817 tidal deformability constraint.

astro-ph.HE↗

arXiv2021

Statistical Multifragmentation Model Within the Extended Morphological Thermodynamics Approach

On the basis of morphological thermodynamics we develop an exactly solvable version of statistical mutifragmentation model for the nuclear liquid-gas phase transition. It is shown that the hard-core repulsion between spherical nuclei generates only the bulk (volume), surface and curvature parts of the free energy of the nucleus, while the Gaussian curvature one does not appear in the derivation. The phase diagram of nuclear liquid-gas phase transition is studied for a truncated version of the developed model.

nucl-th↗

arXiv2019

Neutron stars: new constraints on asymmetric dark matter

We study an impact of asymmetric dark matter on properties of the neutron stars and their ability to reach the two solar masses limit, which allows us to present a new range of masses of dark matter particles and their fractions inside the star. Our analysis is based on the observational fact of the existence of two pulsars reaching this limit and on the theoretically predicted reduction of the neutron star maximal mass caused by the accumulation of dark matter in its interior. We also demonstrate that light dark matter particles with masses below 0.2 GeV can create an extended halo around the neutron star leading not to decrease, but to increase of its visible gravitational mass. By using recent results on the spatial distribution of dark matter in the Milky Way, we present an estimate of its fraction inside the neutron stars located in the Galaxy center. We show how the detection of a 2 Msun neutron star in the most central region of the Galaxy will impose an upper constraint on the mass of dark matter particles of ~ 60 GeV. Future high precision measurements of the neutron stars maximal mass near the Galactic center, will put a more stringent constraint on the mass of the dark matter particle. This last result is particularly important to prepare ongoing, and future radio and x-ray surveys.

astro-ph.HE↗

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

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↗