arXiv subjects

P. K. Panda

Publications and source records attributed to P. K. Panda.

At least 19 recordsLinked to original sources

arXiv2018

Neutron star matter with strange interactions in a relativistic quark model

The effect of strange interactions in neutron star matter and the role of the strange meson-hyperon couplings are studied in a relativistic quark model where the confining interaction for quarks inside a baryon is represented by a phenomenological average potential in an equally mixed scalar-vector harmonic form. The hadron-hadron interaction in nuclear matter is then realized by introducing additional quark couplings to $σ$, $ω$, $ρ$, $σ^*$ and $ϕ$ mesons through mean-field approximations. The meson-baryon couplings are fixed through the SU(6) spin-flavor symmetry and the SU(3) flavor symmetry to determine the hadronic equation of state (EoS). We find that the SU(3) coupling set gives the potential depth between $Λ$s around $-5$ MeV and favours a stiffer EoS.The radius for the canonical neutron star lies within a range of $12.7$ to $13.1$ km.

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arXiv2017

$Δ$ isobars in hyperon stars in a modified quark meson coupling model

The possibility of the appearance of $Δ$ isobars in neutron star matter and the so called {\it $Δ$ puzzle} is studied in a modified quark meson coupling model where the confining interaction for quarks inside a baryon is represented by a phenomenological average potential in an equally mixed scalar-vector harmonic form. The hadron-hadron interaction in nuclear matter is then realized by introducing additional quark couplings to $σ$, $ω$, and $ρ$ mesons through mean-field approximations. The couplings of the $Δ$ to the meson fields are fixed from available constraints while the hyperon couplings are fixed from the optical potential values. It is observed that within the constraints of the mass of the precisely measured massive pulsars, PSR J0348+0432 and PSR J1614-2230, neutron stars with a composition of both $Δ$ isobars and hyperons is possible. It is also observed that with an increase in the vector coupling strength of the $Δ$ isobars there is a decrease in the radius of the neutron stars.

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arXiv2016

Hyperon star in a modified quark meson coupling model

We determine the equation of state (EOS) of nuclear matter with the inclusion of hyperons in a self-consistent manner by using a Modified Quark Meson Coupling Model (MQMC) where the confining interaction for quarks inside a baryon is represented by a phenomenological average potential in an equally mixed scalar-vector harmonic form. The hadron-hadron interaction in nuclear matter is then realized by introducing additional quark couplings to $σ$, $ω$, and $ρ$ mesons through mean-field approximations. The effect of a nonlinear $ω$-$ρ$ term on the equation of state is studied. The hyperon couplings are fixed from the optical potential values and the mass-radius curve is determined satisfying the maximum mass constraint of $2$~M$_{\odot}$ for neutron stars, as determined in recent measurements of the pulsar PSR J0348+0432. We also observe that there is no significant advantage of introducing the nonlinear $ω$-$ρ$ term in the context of obtaining the star mass constraint in the present set of parametrizations.

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arXiv2015

Nuclear symmetry energy in a modified quark meson coupling model

We study nuclear symmetry energy and the thermodynamic instabilities of asymmetric nuclear matter in a self-consistent manner by using a modified quark-meson coupling model where the confining interaction for quarks inside a nucleon is represented by a phenomenologically averaged potential in an equally mixed scalar-vector harmonic form. The nucleon-nucleon interaction in nuclear matter is then realized by introducing additional quark couplings to $σ$, $ω$, and $ρ$ mesons through mean-field approximations. We find an analytic expression for the symmetry energy ${\cal E}_{sym}$ as a function of its slope $L$. Our result establishes a linear correlation between $L$ and ${\cal E}_{sym}$. We also analyze the constraint on neutron star radii in $(pn)$ matter with $β$ equilibrium.

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arXiv2013

Nuclear equation of state in a relativistic independent quark model with chiral symmetry and variation with quark masses

We have calculated the properties of nuclear matter in a self-consistent manner with quark-meson coupling mechanism incorporating structure of nucleons in vacuum through a relativistic potential model; where the dominant confining interaction for the free independent quarks inside a nucleon, is represented by a phenomenologically average potential in equally mixed scalar-vector harmonic form. Corrections due to spurious centre of mass motion as well as those due to other residual interactions such as the one gluon exchange at short distances and quark-pion coupling arising out of chiral symmetry restoration; have been considered in a perturbation manner to obtain the nucleon mass in vacuum. The nucleon-nucleon interaction in nuclear matter is then realized by introducing additional quark couplings to sigma and omega mesons through mean field approximations. The relevant parameters of the interaction are obtained self consistently while realizing the saturation properties such as the binding energy, pressure and compressibility of the nuclear matter. We also discuss some implications of chiral symmetry in nuclear matter along with the nucleon and nuclear sigma term and the sensitivity of nuclear matter binding energy with variations in the light quark mass.

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arXiv2012

The effect of isoscalar-isovector coupling in infinite nuclear matter

Working on the framework of Relativistic Mean Field theory, we exposed the effect of nonlinear isoscalar-isovector coupling on G2 parameter set on the density dependence of nuclear symmetry energy in infinite nuclear matter. The observables like symmetric energy and few related coefficients are studied systematically. We presented the results of stiff symmetry energy at sub-saturation densities and a soft variation at normal densities. Correlation between the symmetric energy and the isoscalar-isovector coupling parameter fully demonstrated for wide range of density. The work further extended to the octet system and showed the effect of coupling over the equation of state.

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arXiv2011

Warm and dense stellar matter under strong magnetic fields

We investigate the effects of strong magnetic fields on the equation of state of warm stellar matter as it may occur in a protoneutron star. Both neutrino free and neutrino trapped matter at a fixed entropy per baryon are analyzed. A relativistic mean field nuclear model, including the possibility of hyperon formation, is considered. A density dependent magnetic field with the magnitude $10^{15}$ G at the surface and not more than $3\times 10^{18}$ G at the center is considered. The magnetic field gives rise to a neutrino suppression, mainly at low densities, in matter with trapped neutrinos. It is shown that an hybrid protoneutron star will not evolve to a low mass blackhole if the magnetic field is strong enough and the magnetic field does not decay. However, the decay of the magnetic field after cooling may give rise to the formation of a low mass blackhole.

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arXiv2009

Quark matter nucleation in hot hadronic matter

We study the quark deconfinement phase transition in hot $β$-stable hadronic matter. Assuming a first order phase transition, we calculate the enthalpy per baryon of the hadron-quark phase transition. We calculate and compare the nucleation rate and the nucleation time due to thermal and quantum nucleation mechanisms. We compute the crossover temperature above which thermal nucleation dominates the finite temperature quantum nucleation mechanism. We next discuss the consequences for the physics of proto-neutron stars. We introduce the concept of limiting conversion temperature and critical mass $M_{cr}$ for proto-hadronic stars, and we show that proto-hadronic stars with a mass $M < M_{cr}$ could survive the early stages of their evolution without decaying to a quark star.

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arXiv2009

Pion correlations in Nuclear Matter

The saturation properties of the nuclear matter taking pion correlations into account is studied. We construct a Bogoliubov transformations for the pion pair operators and calculate the energy associated with the pion pairs. The pion dispersion relation is investigated. We next study the correlation energy due to one pion exchange in nuclear matter and neutron matter at random phase approximation using the generator coordinate method. The techniques of the charged pion correlations are discussed in the neutron matter calculations. We observe that there is no sign of the pion condensation in this model.

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arXiv2009

Quark-hadron phase transition in a neutron star under strong magnetic fields

We study the effect of a strong magnetic field on the properties of neutron stars with a quark-hadron phase transition. It is shown that the magnetic field prevents the appearance of a quark phase, enhances the leptonic fraction, decreases the baryonic density extension of the mixed phase and stiffens the total equation of state, including both the stellar matter and the magnetic field contributions. Two parametrisations of a density dependent static magnetic field, increasing, respectively, fast and slowly with the density and reaching $2-4\times 10^{18}$G in the center of the star, are considered. The compact stars with strong magnetic fields have maximum mass configurations with larger masses and radius and smaller quark fractions. The parametrisation of the magnetic field with density has a strong influence on the star properties.

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arXiv2009

Particle Production within the Quark Meson Coupling Model

Quark meson coupling (QMC) models can be successfully applied to the description of compact star properties in nuclear astrophysics as well as to nuclear matter. In the regime of hot hadronic matter very few calculations exist using the QMC model, in particular when applied to particle yields in heavy ion collisions. In the present work, we identify the free energy of the bag with the effective mass of the baryons and we calculate the particle production yields on a Au+Au collision at RHIC with the QMC model and compare them with results obtained previously with other relativistic models. A smaller temperature for the fireball, T=132 MeV, is obtained due to the smaller effective baryon masses predicted by QMC. QMC was also applied to the description of particle yields at SPS in Pb+Pb collisions.

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arXiv2008

Asymmetric nuclear matter : a variational approach

We discuss here a self-consistent method to calculate the properties of the cold asymmetric nuclear matter. In this model, the nuclear matter is dressed with s-wave pion pairs and the nucleon-nucleon (N-N) interaction is mediated by these pion pairs, $ω$ and $ρ$ mesons. The parameters of these interactions are calculated self-consistently to obtain the saturation properties like equilibrium binding energy, pressure, compressibility and symmetry energy. The computed equation of state is then used in the Tolman- Oppenheimer-Volkoff (TOV) equation to study the mass and radius of a neutron star in the pure neutron matter limit.

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arXiv2008

Metastability of hadronic compact stars

Pure hadronic compact stars, above a threshold value of their gravitational mass (central pressure), are metastable to the conversion to quark stars (hybrid or strange stars). In this paper, we present a systematic study of the metastability of pure hadronic compact stars using different relativistic models for the equation of state (EoS). In particular, we compare results for the quark-meson coupling (QMC) model with those for the Glendenning--Moszkowski parametrization of the non-linear Walecka model (NLWM). For QMC model, we find large values ($M_{cr} = 1.6$ -- $1.9 M_\odot$) for the critical mass of the hadronic star sequence and we find that the formation of a quark star is only possible with a soft quark matter EoS. For the Glendenning--Moszkowski parametrization of the NLWM, we explore the effect of different hyperon couplings on the critical mass and on the stellar conversion energy. We find that increasing the value of the hyperon coupling constants shifts the bulk transition point for quark deconfinement to higher densities, increases the stellar metastability threshold mass and the value of the critical mass, and thus makes the formation of quark stars less likely. For the largest values of the hyperon couplings we find a critical mass which may be as high as 1.9 - 2.1 $M_\odot$. These stellar configurations, which contain a large central hyperon fraction ($f_{Y,cr} \sim 30 %$), would be able to describe highly-massive compact stars, such as the one associated to the millisecond pulsars PSR B1516+02B with a mass $M = 1.94^{+ 0.17}_{- 0.19} M_{\odot}$.

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arXiv2007

Asymmetric Nuclear Matter with Pion Dressing

We discuss a self-consistent method to calculate the properties of cold asymmetric nuclear matter which is dressed with isoscalar scalar pion condensates. The nucleon-nucleon interaction is mediated by these pion pairs, omega- and rho- mesons. The parameters of these interactions are evaluated self-consistently using the saturation properties of nuclear matter like binding energy, pressure, compressibility and symmetry energy. The computed equation of state of pure neutron matter (PNM) is used to calculate mass and radius of a pure neutron star.

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arXiv2007

Neutron star matter in an effective model

We study the equation of state (EOS) for dense matter in the core of the compact star with hyperons and calculate the star structure in an effective model in the mean field approach. With varying incompressibility and effective nucleon mass, we analyse the resulting EOS with hyperons in beta equilibrium and its underlying effect on the gross properties of the compact star sequences. The results obtained in our analysis are compared with predictions of other theoretical models and observations. The maximum mass of the compact star lies in the range $1.21-1.96 ~M_{\odot}$ for the different EOS obtained, in the model.

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arXiv2006

Phase transition and properties of compact star

We investigate the phase transition to a deconfined phase and the consequences in the formation of neutron stars. We use the recently proposed effective field theory motivated relativistic mean field theory for hadron and the MIT Bag model and color-flavor locked (CFL) phase for the quark matter in order to get the appropriate equation of state. The properties of star are then calculated. The differences between unpaired and CFL quark matter are discussed.

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arXiv2006

Short range correlations in relativistic nuclear matter models

Short range correlations are introduced using unitary correlation method in a relativistic approach to the equation of state of the infinite nuclear matter in the framework of the Hartree-Fock approximation. It is shown that the correlations give rise to an extra node in the ground-state wave-function in the nucleons, contrary to what happens in non-relativistic calculations with a hard core. The effect of the correlations in the ground state properties of the nuclear matter and neutron matter is studied. The nucleon effective mass and equation of state (EOS) are very sensitive to short range correlations. In particular, if the pion contact term is neglected a softening of the EOS is predicted. Correlations have also an important effect on the neutron matter EOS which presents no binding but only a very shallow minimum contrary to the Walecka model.

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arXiv2006

Rotating compact star with superconducting quark matter

A compact star with superconducting quark core, the hadron crust and the mixed phase between the two is considered. The quark meson coupling model for hadron matter and the color flavor locked quark model for quark matter is used in order to construct the equation of state for the compact star. The effect of pairing of quarks in the color flavor locked phase and the mixed phase on the mass, radius, and period of the rotating star is studied.

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