arXiv subjects

Violetta Sagun

Publications and source records attributed to Violetta Sagun.

25 records · Page 2Linked to original sources

arXiv2022

How does dark matter affect compact star properties and high density constraints of strongly interacting matter

We study the impact of asymmetric bosonic dark matter on neutron star properties, including possible changes of tidal deformability, maximum mass, radius, and matter distribution inside the star. The conditions at which dark matter particles tend to condensate in the star's core or create an extended halo are presented. We show that dark matter condensed in a core leads to a decrease of the total gravitational mass and tidal deformability compared to a pure baryonic star, which we will perceive as an effective softening of the equation of state. On the other hand, the presence of a dark matter halo increases those observable quantities. Thus, observational data on compact stars could be affected by accumulated dark matter and, consequently, constraints we put on strongly interacting matter at high densities. To confirm the presence of dark matter in the compact star's interior, and to break the degeneracy between the effect of accumulated dark matter and strongly interacting matter properties at high densities, several astrophysical and GW tests are proposed.

astro-ph.HE↗

arXiv2022

Colliding and Fixed Target Mode in a Single Experiment -- A Novel Approach to Study the Matter under New Extreme Conditions

Here, we propose a novel approach to experimentally and theoretically study the properties of QCD matter under new extreme conditions, namely having an initial temperature over 300~MeV and baryonic charge density over three times the values of the normal nuclear density. According to contemporary theoretical knowledge, such conditions were not accessible during the early Universe evolution and are not accessible now in the known astrophysical phenomena. To achieve these new extreme conditions, we proposed performing high-luminosity experiments at LHC or other colliders by means of scattering the two colliding beams at the nuclei of a solid target that is fixed at their interaction region. Under plausible assumptions, we estimate the reaction rate for the p+C+p and Pb+Pb+Pb reactions and discuss the energy deposition into the target and possible types of fixed targets for such reactions. To simulate the triple nuclear collisions, we employed the well-known UrQMD 3.4 model for the beam center-of-mass collision energies 2.76 TeV. As a result of our modeling, we found that, in the most central and simultaneous triple nuclear collisions, the initial baryonic charge density is approximately three times higher than the one achieved in the ordinary binary nuclear collisions at this energy.

hep-ph↗

arXiv2022

Numerical Simulations of Dark Matter Admixed Neutron Star Binaries

Multi-messenger observations of compact binary mergers provide a new way to constrain the nature of dark matter that may accumulate in and around neutron stars. In this article, we extend the infrastructure of our numerical-relativity code BAM to enable the simulation of neutron stars that contain an additional mirror dark matter component. We perform single star tests to verify our code and the first binary neutron star simulations of this kind. We find that the presence of dark matter reduces the lifetime of the merger remnant and favors a prompt collapse to a black hole. Furthermore, we find differences in the merger time for systems with the same total mass and mass ratio, but different amounts of dark matter. Finally, we find that electromagnetic signals produced by the merger of binary neutron stars admixed with dark matter are very unlikely to be as bright as their dark matter free counterparts. Given the increasing sensitivity of multi-messenger facilities, our analysis gives a new perspective on how to probe the presence of dark matter.

gr-qc↗

arXiv2022

Bosonic Dark Matter in Neutron Stars and its Effect on Gravitational Wave Signal

We study an impact of self-interacting bosonic dark matter (DM) on various observable properties of neutron stars (NSs). The analysis is performed for asymmetric DM with masses from few MeV to GeV, the self-coupling constant of order $\mathcal{O}(1)$ and various DM fractions. Allowing a mixture between DM and baryonic matter, the formation of a dense DM core or an extended dark halo have been explored. We find that both distribution regimes crucially depend on the mass and fraction of DM for sub-GeV boson masses in the strong coupling regime. From the combined analysis of the mass-radius relation and the tidal deformability of compact stars including bosonic DM, we set a stringent constraint on DM fraction. We conclude that observations of 2$M_{\odot}$ NSs together with $Λ_{1.4}\leq580$ constraint, set by LIGO/Virgo Collaboration, favour sub-GeV DM particles with low fractions below $\sim 5 \%$.

astro-ph.HE↗

arXiv2021

Tidal Deformability as a Probe of Dark Matter in Neutron Stars

The concept of boson stars (BSs) was first introduced by Kaup and Ruffini-Bonazzola in the 1960s. Following this idea, we investigate an effect of self-interacting asymmetric bosonic dark matter (DM) according to Colpi et al. model for BSs (1986) on different observable properties of neutron stars (NSs). In this paper, the bosonic DM and baryonic matter (BM) are mixed together and interact only through gravitational force. The presence of DM as a core of a compact star or as an extended halo around it is examined by applying different boson masses and DM fractions for a fixed coupling constant. The impact of DM core/halo formations on a DM admixed NS properties is probed through the maximum mass and tidal deformability of NSs. Thanks to the recent detection of Gravitational-Waves (GWs) and the latest X-ray observations, the DM admixed NS's features are compared to LIGO/Virgo and NICER results.

astro-ph.HE↗

arXiv2021

Thermal production of sexaquarks in heavy-ion collisions

We present new results on the thermal production yield of a hypothetical state made of six quarks $uuddss$ assuming its production in heavy-ion collisions at the CERN LHC. A state with this quark content and mass low enough to be stable against decay in timescales of the order of the age of the Universe, has been hypothesized by one of us (G.F.) and has been discussed as a possible dark matter candidate. In this work we address for the first time the thermal production rate that can be expected for this state in heavy-ion collisions at colliders. For this estimate we use a thermal model which has been shown to describe accurately the production of hadrons and nuclei in heavy-ion collisions at LHC energy. This estimate is of great relevance for sexaquark searches at colliders as well as for its consideration as a dark matter candidate and for the composition of neutron stars.

hep-ph↗

arXiv2020

Neutron star cooling within the equation of state with induced surface tension

We study the thermal evolution of neutron stars described within the equation of state with induced surface tension (IST) that reproduces properties of normal nuclear matter, fulfills the proton flow constraint, provides a high-quality description of hadron multiplicities created during the nuclear-nuclear collision experiments, and it is equally compatible with the constraints from astrophysical observations and the GW170817 event. The model features strong direct Urca processes for the stars above $1.91~M_{\odot}$. The IST equation of state shows very good agreement with the available cooling data, even without introducing nuclear pairing. We also analysed the effect of the singlet proton/neutron and triplet neutron pairing on the cooling of neutron stars of different mass. We show that the description of the compact object in the center of the Cassiopeia A does not necessarily require an inclusion of neutron superfluidity and/or proton superconductivity. Our results indicate that data of Cassiopeia A can be adequately well reproduced by a $1.66~M_{\odot}$ star with an atmosphere of light elements. Moreover, the IST EoS reproduces each of the observational datasets for the surface temperature of Cassiopeia A either by a rapidly cooling $\sim$ $1.955~M_{\odot}$ star with paired and unpaired matter or by a $1.91~M_{\odot}$ star with the inclusion of neutron and proton pairings in the singlet channel.

astro-ph.HE↗