arXiv subjects

D. N. Voskresensky

Publications and source records attributed to D. N. Voskresensky.

At least 37 records · Page 2Linked to original sources

arXiv2017

Charged $ρ$-meson condensation in neutron stars

We extend relativistic mean-field models with hadron masses and meson-baryon coupling constants dependent on the scalar field $σ$, including hyperons and $Δ(1232)$ baryons, to incorporate a possibility of the charged $ρ$ meson condensation in neutron star matter. The influence of the $ρ^-$ condensation on the equation of state proves to be strongly model dependent. In our models of one type (KVORcut-based ones) the $ρ^-$ condensation arises by a second-order phase transition above a critical density and the maximum value of the neutron star mass diminishes only slightly. The matter composition changes more significantly. In our models of other type (MKVOR*-based ones), if the system is considered at fixed density, the $ρ^-$ condensation arises by a second-order phase transition at the baryon density $n=n_{c,ρ}^{(\rm II)}$ and at a slightly higher density $n=n_{c,ρ}^{(\rm I)}$ there occurs a first-order phase transition. In a neutron star matter starting with a density $n<n_{c,ρ}^{(\rm II)}$ there appears a region of a mixed phase, or the system is described by Maxwell construction, that results in a substantial decrease of the value of the maximum neutron star mass. Nevertheless in the models under consideration the observational constraint on the maximum neutron star mass is fulfilled. Besides, in MKVOR*-based models the appearance of the $ρ^-$ condensate is accompanied by a strong rearrangement of the matter composition. Dependence of the results on a choice of the $ρ$ meson scaling functions for the effective $ρ$ meson mass and coupling constants is also investigated.

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arXiv2017

Fluctuations in non-ideal pion gas with dynamically fixed particle number

We consider a non-ideal hot pion gas with the dynamically fixed number of particles in the model with the $λϕ^4$ interaction. The effective Lagrangian for the description of such a system is obtained after dropping the terms responsible for the change of the total particle number. Reactions $π^+π^-\leftrightarrowπ^0π^0$, which determine the isospin balance of the medium, are permitted. Within the self-consistent Hartree approximation we compute the effective pion mass, thermodynamic characteristics of the system and the variance of the particle number at temperatures above the critical point of the induced Bose-Einstein condensation when the pion chemical potential reaches the value of the effective pion mass. We analyze conditions for the condensate formation in the process of thermalization of an initially non-equilibrium pion gas. The normalized variance of the particle number increases with a temperature decrease but remains finite in the critical point of the Bose-Einstein condensation. This is due to the non-perturbative account of the interaction and is in contrast to the ideal-gas case. In the kinetic regime of the condensate formation the variance is shown to stay finite also.

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arXiv2017

Cooling of neutron stars with stiff stellar matter

Recent evidence for high masses ($\sim 2~ M_\odot$) pulsars PSR J1614-2230 and PSR J0348-0432 requires neutron star matter to have a stiff equation of state (EoS). The thermal evolution of compact stars (CS) with stiff hadronic EoS necessitates the application of the "nuclear medium cooling" scenario with a selection of appropriate proton gap profiles together with in-medium effects (like pion softening) on cooling mechanisms in order to achieve a satisfactory explanation of all existing observational data for the temperature-age relation of CS. Here we focus on two examples from \cite{Grigorian:2016leu} for a stiff hadronic EoS without (DD2 EoS) and with (DD2vex) excluded volume correction.

astro-ph.HE↗

arXiv2016

Scalar quanta in Fermi liquids: zero sounds, instabilities, Bose condensation, and a metastable state in dilute nuclear matter

Spectrum of bosonic scalar-mode excitations in a normal Fermi liquid with a local scalar interaction is investigated for various values and momentum dependence of the scalar Landau parameter $f_0$ in the particle-hole channel. For $f_0 >0$ the conditions are found when the phase velocity on the spectrum of the zero sound acquires a minimum at a non-zero momentum. For $-1 0$. We also argue that in peripheral heavy-ion collisions the Pomeranchuk instability may occur already for $f_0 >-1$.

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arXiv2016

Condensate of excitations in moving superfluids

A possibility of the condensation of excitations with a non-zero momentum in rectilinearly moving and rotating superfluid bosonic and fermionic (with Cooper pairing) media is considered in terms of a phenomenological order-parameter functional at zero and non-zero temperature. The results might be applicable to the description of bosonic systems like superfluid $^4$He, ultracold atomic Bose gases, charged pion and kaon condensates in rotating neutron stars, and various superconducting fermionic systems with pairing, like proton and color-superconducting components in compact stars, metallic superconductors, and neutral fermionic systems with pairing, like the neutron component in compact stars and ultracold atomic Fermi gases. Order parameters of the "mother" condensate in the superfluid and the new condensate of excitations, corresponding energy gains, critical temperatures and critical velocities are found.

cond-mat.quant-gas↗

arXiv2016

The effect of inclusion of $Δ$ resonances in relativistic mean-field model with scaled hadron masses and coupling constants

Knowledge of the equation of state of the baryon matter plays a decisive role in the description of neutron stars. With an increase of the baryon density the filling of Fermi seas of hyperons and $Δ$ isobars becomes possible. Their inclusion into standard relativistic mean-field models results in a strong softening of the equation of state and a lowering of the maximum neutron star mass below the measured values. We extend a relativistic mean-field model with scaled hadron masses and coupling constants developed in our previous works and take into account now not only hyperons but also the $Δ$ isobars. We analyze available empirical information to put constraints on coupling constants of $Δ$s to mesonic mean fields. We show that the resulting equation of state satisfies majority of presently known experimental constraints.

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arXiv2016

Delta isobars in relativistic mean-field models with $σ$-scaled hadron masses and couplings

We extend the relativistic mean-field models with hadron masses and meson-baryon coupling constants dependent on the scalar $σ$ field, studied previously to incorporate $Δ(1232)$ baryons. Available empirical information is analyzed to put constraints on the couplings of $Δ$s with meson fields. Conditions for the appearance of $Δ$s are studied. We demonstrate that with inclusion of the $Δ$s our equations of state continue to fulfill majority of known empirical constraints including the pressure-density constraint from heavy-ion collisions, the constraint on the maximum mass of the neutron stars, the direct Urca and the gravitational-baryon mass ratio constraints.

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arXiv2016

Relativistic Mean-Field Models with Scaled Hadron Masses and Couplings: Hyperons and Maximum Neutron Star Mass

An equation of state of cold nuclear matter with an arbitrary isotopic composition is studied within a relativistic mean-field approach with hadron masses and coupling constants depending self-consistently on the scalar mean-field. All hadron masses decrease universally with the scalar field growth, whereas meson-nucleon coupling constants can vary differently. More specifically we focus on two modifications of the KVOR model studied previously. One extension of the model (KVORcut) demonstrates that the equation of state stiffens if the increase of the scalar-field magnitude with the density is bounded from above at some value for baryon densities above the saturation nuclear density. This can be realized if the nucleon vector-meson coupling constant changes rapidly as a function of the scalar field slightly above the desired value. The other version of the model (MKVOR) utilizes a smaller value of the nucleon effective mass at the nuclear saturation density and a saturation of the scalar field in the isospin asymmetric matter induced by a strong variation of the nucleon isovector-meson coupling constant as function of the scalar field. A possibility of hyperonization of the matter in neutron star interiors is incorporated. Our equations of state fulfill majority of known empirical constraints including the pressure-density constraint from heavy-ion collisions, direct Urca constraint, gravitational-baryon mass constraint for the pulsar J0737-3039B, and the constraint on the maximum mass of the neutron stars.

astro-ph.HE↗

arXiv2016

Influence of the stiffness of the equation of state and in-medium effects on the cooling of compact stars

Measurements demonstrate the existence of compact stars with masses in a broad range from 1.2 to 2 $M_\odot$. The most massive of these objects might be hybrid stars. To fulfill the constraint $M_{\rm max}>2~M_{\odot}$ with a reserve we exploit the stiff DD2 hadronic equation of state (EoS) without and with excluded volume (DD2vex) correction, which produce maximum neutron star masses of $M_{\rm max} = 2.43~M_{\odot}$ and $2.70~M_{\odot}$, respectively. We show that the stiffness of the EoS does not preclude an explanation of the whole set of cooling data within "nuclear medium cooling" scenario for compact stars by a variation of the star masses. We select appropriate proton gap profiles from those exploited in the literature and allow for a variation of the effective pion gap controlling the efficiency of the medium modified Urca process. However, we suppress the possibility of pion condensation. In general, the stiffer the EoS the steeper a decrease with density of the effective pion gap is required. Results are compared with previously obtained ones for the HDD EoS for which $M_{\rm max} =2.06~M_{\odot}$. The cooling of the compact star in the supernova remnant Cassiopeia A (Cas A) is explained mainly by an efficient medium modified Urca process. With the DD2vex EoS and using an effective pion gap steeper decreasing with the density and/or a proton gap shifted to smaller densities we are also able to reproduce both a strong decline compatible with ACIS-S data and HRC-S instrument data. The mass of Cas A is estimated as $1.6 - 1.9~M_{\odot}$, above the value $1.5~M_{\odot}$, which we have evaluated with the softer HDD equation of state. Different mass choices for the hottest object XMMU J173203.3-344518 are discussed. We make general remarks also on hybrid star cooling and on its dependence on the stiffness of the hadronic EoS.

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arXiv2015

Making a soft relativistic mean-field equation of state stiffer at high density

We study relativistic mean-field (RMF) models including nucleons interacting with scalar, vector and iso-vector mean fields and self- and cross- mean-field interaction terms. Usually, in such a models the magnitude of the scalar field increases monotonically with the nucleon density, and the nucleon effective mass decreases. We demonstrate that the latter quantity stops to decrease and the equation of state stiffens, provided the mean-field self-interaction potential rises sharply in a narrow vicinity of the values of mean fields corresponding to nucleon densities $n> n_{*}>n_0$, where $n_0$ is the nuclear saturation density. As the result the limiting neutron star mass increases. This procedure offers a simple way to stiffen the equation of state at densities above $n_{*}$ without altering it at densities $n\le n_{0}$. The developed scheme allows an application to neutron stars of the RMF models, which are well fitted to finite nuclei but do not fulfill the experimental constraint on the limiting neutron star mass. The exemplary application of the method to the well-known FSUGold model allows us to increase the limiting neutron star mass from $1.72~M_\odot$ to $M \geq 2.01~M_\odot$.

astro-ph.HE↗

arXiv2015

Hyperon puzzle and the RMF model with scaled hadron masses and coupling constants

The equation of state of cold baryonic matter is studied within a relativistic mean-field model with hadron masses and coupling constants depending on a scalar field. We demonstrate that if the effective nucleon mass stops to decrease with a density increase at densities $n>n_*>n_0$, where $n_0$ is the nuclear saturation density, the equation of state stiffens for these densities and the limiting neutron star mass increases. The stabilization of the nucleon mass can be realised if in the equation of motion for the scalar mean-field there appear a term sharply varying in a narrow vicinity of the field value corresponding to the density $n_*$. We show several possible realizations of this mechanism getting sufficiently stiff equations of state. The appearance of hyperons in dense neutron star interiors is accounted for. The obtained equations of state remain sufficiently stiff if the reduction of the $ϕ$ meson mass is incorporated. Thereby, the hyperon puzzle can be resolved.

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arXiv2015

Solution of the Hyperon Puzzle within a Relativistic Mean-Field Model

The equation of state of cold baryonic matter is studied within a relativistic mean-field model with hadron masses and coupling constants depending on the scalar field. All hadron masses undergo a universal scaling, whereas the coupling constants are scaled differently. The appearance of hyperons in dense neutron star interiors is accounted for, however the equation of state remains sufficiently stiff if a reduction of the $ϕ$ meson mass is included. Our equation of state matches well the constraints known from analyses of the astrophysical data and the particle production in heavy-ion collisions.

astro-ph.HE↗

arXiv2015

Pomeranchuk instability and Bose condensation of scalar quanta in a Fermi liquid

We study excitations in a normal Fermi liquid with a local scalar interaction. Spectrum of bosonic scalar-mode excitations is investigated for various values and momentum dependence of the scalar Landau parameter $f_0$ in the particle-hole channel. For $f_0 >0$ the conditions are found when the phase velocity on the spectrum of the zero sound acquires a minimum at a non-zero momentum. For $-1 0$.

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arXiv2015

Cooling of neutron stars and hybrid stars with a stiff hadronic EoS

Within the "nuclear medium cooling" scenario of neutron stars all reliably known temperature - age data, including those of the central compact objects in the supernova remnants of Cassiopeia A and XMMU-J1732, can be comfortably explained by a set of cooling curves obtained by variation of the star mass within the range of typical observed masses. The recent measurements of the high masses of the pulsars PSR J1614-2230 and PSR J0348-0432 on the one hand, and of the low masses for PSR J0737-3039B and the companion of PSR J1756-2251 on the other, provide independent proof for the existence of neutron stars with masses in a broad range from $\sim 1.2$ to 2 $M_\odot$. The values $M>2 M_{\odot}$ call for sufficiently stiff equations of state for neutron star matter. We investigate the response of the set of neutron star cooling curves to a stiffening of the nuclear equation of state so that maximum masses of about $2.4 M_\odot$ would be accessible and to a deconfinement phase transition from such stiff nuclear matter in the outer core to color superconducting quark matter in the inner core. Without readjustment of cooling inputs the mass range required to cover all cooling data for the stiff DD2 equation of state should include masses of $2.426 M_\odot$ for describing the fast cooling of CasA while the existence of a quark matter core accelerates the cooling so that CasA cooling data are described with a hybrid star of mass $1.674 M_\odot$.

astro-ph.HE↗

arXiv2015

Viscosity of neutron star matter and $r$-modes in rotating pulsars

We study viscosity of the neutron star matter and $r$-mode instability in rotating neutron stars. Contributions to the shear and bulk viscosities from various processes are calculated with account of in-medium modifications of the nucleon-nucleon interaction. A softening of the pion mode and a possibility of the pion condensation are included. The nucleon pairing is incorporated. In the shear viscosity we include the lepton contribution calculated with account of the Landau damping in the photon exchange, the nucleon contribution described by the medium-modified one pion exchange, and other terms, such as the novel phonon contribution in the 1S$_0$ superfluid neutron phase, and the neutrino term in the neutrino opacity region. The nucleon shear viscosity depends on the density rather moderately and proves to be much less than the lepton term. Among the terms contributing to the bulk viscosity, the term from the medium modified Urca reactions possesses strongest density dependence because of the pion softening. Contributions to the bulk viscosity arising from other reactions induced by charged weak currents are included. The radiative bulk viscosity induced by charged and neutral weak currents in the region of the neutrino transparency of the star is also calculated with account for in-medium effects. The computed frequency boundary of the $r$-mode stability for the stars with the mass $\ge 1.8 M_{\odot}$ proves to be above the frequencies of all rotating young pulsars. To explain the stability of rapid rotation of old pulsars in X-ray binaries we propose a novel efficient mechanism associated with appearance of condensates of low-lying modes of bosonic excitations with finite momentum and/or with an enhancement of the inhomogeneous pion/kaon condensates in some parts of the star, if the angular velocity exceeds a critical value.

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arXiv2015

Multistrangeness in Heavy-Ion Collisions

We discuss strangeness production in heavy-ion collisions in the broad energy range --- from SIS energies through AGS-SPS-RHIC and upto LHC energies. On several examples we demonstrate how the strange particle production can reveal information about the collision dynamics and about possible modifications of particle properties in medium. In particular the production of hadrons containing two and more strange quarks, like $Ξ$ and $Ω$ baryons, or a $ϕ$ meson is of interest. We conduct our discussion in the framework of the minimal statistical model, in which the total strangeness yield is fixed by the $K^+$ multiplicity. It is emphasized that in collisions with a small number of produced strange particles, the exact strangeness conservation in each collision event must be explicitly preserved.

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arXiv2015

Running condensate in moving superfluid

A possibility of the condensation of excitations with non-zero momentum in moving superfluid media is considered in terms of the Ginzburg-Landau model. The results might be applicable to the superfluid $^4$He, ultracold atomic Bose gases, various superconducting and neutral systems with pairing, like ultracold atomic Fermi gases and the neutron component in compact stars. The order parameters, the energy gain, and critical velocities are found.

cond-mat.quant-gas↗

arXiv2014

Mechanism of r-mode stability in young rapidly rotating pulsars

We demonstrate that stability of r-modes in young rapidly rotating pulsars might be explained if one takes into account strong medium modifications of the nucleon-nucleon interaction because of the softening of pionic degrees of freedom in dense nucleon matter. Presence of the efficient direct Urca processes is not required. Within our model the most rapidly rotating observed young pulsar PSR J0537-6910 should have the mass $\geq 1.8M_{\odot}$.

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