VIVEK THAPA - Academia.edu (original) (raw)

Papers by VIVEK THAPA

arXiv (Cornell University), Feb 12, 2022

We study the implications of the recent development in nuclear symmetry energy constraints from P... more We study the implications of the recent development in nuclear symmetry energy constraints from PREX-2 data on dense matter equation of state and its impact on dURCA threshold density. In this work, we construct the equation of state within the framework of covariant density functional theory implementing coupling schemes of non-linear and density-dependent models and exploring the coupling parameter space of isovector-vector meson to baryons constrained by the isospin asymmetry parameter values deduced from recent PREX-2 data. The modified parameter sets are applied to evaluate the dense matter properties. We find that the updated data suggests the occurence of dURCA process within neutron star even with mass as low as one solar mass.

Physical review, Mar 22, 2023

Compact stars (CS) are stellar remnants of massive stars. Inside CSs the density is so high that ... more Compact stars (CS) are stellar remnants of massive stars. Inside CSs the density is so high that matter is in subatomic form composed of nucleons. With increase of density of matter towards the centre of the objects other degrees of freedom like hyperons, heavier non-strange baryons, meson condensates may appear. Not only that at higher densities, the nucleons may get decomposed into quarks and form deconfined strange quark matter (SQM). If it is so then CSs may contain SQM in the core surrounded by nucleonic matter forming hybrid stars (HSs). However, the nature and composition of matter inside CSs can only be inferred from the astrophysical observations of these CSs. Recent astrophysical observations in terms of CS mass-radius (M-R) relation and gravitational wave (GW) observation indicate that the matter should be soft in the intermediate density range and stiff enough at higher density range to attain the maximum possible mass above 2 M which is not compatible with pure hadronic equation of states (EOSs). Consequently, we study the HS properties with different models of SQM and find that within vector bag model considering density dependent bag parameter, the model goes well with the astrophysical observations so far.

Physical Review C

The nuclear symmetry energy and its behaviour with density has been recently evaluated with enhan... more The nuclear symmetry energy and its behaviour with density has been recently evaluated with enhanced value by PREX-2 experiment. This new values enables direct Urca neutrino emission process to be functioning in the dense matter inside neutron stars. With this new outlook we study the cooling rate of canonical mass neutron stars and compare with available observational cooling data. We find most of the isolated neutron star thermal profile is compatible with the cooling of canonical mass star including superfluidity suppression.

arXiv (Cornell University), Feb 22, 2023

Physical Review C

Recent observations of several massive pulsars, with masses near and above 2 M , point towards th... more Recent observations of several massive pulsars, with masses near and above 2 M , point towards the existence of matter at very high densities, compared to normal matter that we are familiar with in our terrestrial world. This leads to the possibility of appearance of exotic degrees of freedom other than nucleons inside the core of the neutrons stars (NS). Another significant property of NSs is the presence of high surface magnetic field, with highest range of the order of ∼ 10 16 G. We study the properties of highly dense matter with the possibility of appearance of heavier strange and non-strange baryons, and kaons in presence of strong magnetic field. We find that the presence of a strong magnetic field stiffens the matter at high density, delaying the kaon appearance and, hence, increasing the maximum attainable mass of NS family.

Physical Review D

Compact stars (CS) are stellar remnants of massive stars. Inside CSs the density is so high that ... more Compact stars (CS) are stellar remnants of massive stars. Inside CSs the density is so high that matter is in subatomic form composed of nucleons. With increase of density of matter towards the centre of the objects other degrees of freedom like hyperons, heavier non-strange baryons, meson condensates may appear. Not only that at higher densities, the nucleons may get decomposed into quarks and form deconfined strange quark matter (SQM). If it is so then CSs may contain SQM in the core surrounded by nucleonic matter forming hybrid stars (HSs). However, the nature and composition of matter inside CSs can only be inferred from the astrophysical observations of these CSs. Recent astrophysical observations in terms of CS mass-radius (M-R) relation and gravitational wave (GW) observation indicate that the matter should be soft in the intermediate density range and stiff enough at higher density range to attain the maximum possible mass above 2 M which is not compatible with pure hadronic equation of states (EOSs). Consequently, we study the HS properties with different models of SQM and find that within vector bag model considering density dependent bag parameter, the model goes well with the astrophysical observations so far.

EPJ Web of Conferences

Recently an improved value of neutron skin thickness of 208Pb was reported in Lead Radius EXperim... more Recently an improved value of neutron skin thickness of 208Pb was reported in Lead Radius EXperiment-2 (PREX-2) to be Rskin = Rn Rp = (0.283 0.071) fm which corresponds to high estimations of nuclear symmetry energy (Esym) and its slope (Lsym). The updated values of Esym and Lsym commensurating to the neutron star observable estimations lie exterior to the astrophysical observed range. The higher values of Lsym at n0 deduced from recent PREX-2 data correlates to matter being easily deformable (yielding higher radius values) around intermediate matter densities leading to higher values of Λ̃ creating a tension between the terrestrial and astrophysical observations. In this study, we exploit this tension to constrain the Δ-scalar meson coupling parameter space.

Springer proceedings in physics, 2022

arXiv (Cornell University), Feb 15, 2023

arXiv (Cornell University), Oct 26, 2022

Recent observations of several massive pulsars, with masses near and above 2 M , point towards th... more Recent observations of several massive pulsars, with masses near and above 2 M , point towards the existence of matter at very high densities, compared to normal matter that we are familiar with in our terrestrial world. This leads to the possibility of appearance of exotic degrees of freedom other than nucleons inside the core of the neutrons stars (NS). Another significant property of NSs is the presence of high surface magnetic field, with highest range of the order of ∼ 10 16 G. We study the properties of highly dense matter with the possibility of appearance of heavier strange and non-strange baryons, and kaons in presence of strong magnetic field. We find that the presence of a strong magnetic field stiffens the matter at high density, delaying the kaon appearance and, hence, increasing the maximum attainable mass of NS family.

arXiv (Cornell University), Feb 12, 2022

We study the implications of the recent development in nuclear symmetry energy constraints from P... more We study the implications of the recent development in nuclear symmetry energy constraints from PREX-2 data on dense matter equation of state and its impact on dURCA threshold density. In this work, we construct the equation of state within the framework of covariant density functional theory implementing coupling schemes of non-linear and density-dependent models and exploring the coupling parameter space of isovector-vector meson to baryons constrained by the isospin asymmetry parameter values deduced from recent PREX-2 data. The modified parameter sets are applied to evaluate the dense matter properties. We find that the updated data suggests the occurence of dURCA process within neutron star even with mass as low as one solar mass.

Monthly Notices of the Royal Astronomical Society

We investigate the properties of stars participating in double compact star merger events conside... more We investigate the properties of stars participating in double compact star merger events considering interacting model of stable strange quark matter. We model the matter making it compatible with the recent astrophysical observations of compact star mass–radius and gravitational wave events. In this context, we consider modified MIT bag model and vector bag model with and without self-interaction. We find new upper bound on tidal deformability of 1.4,rmModot1.4\, {\rm M}_\odot1.4,rmModot strange star corresponding to the upper bound of effective tidal deformability inferred from gravitational wave event. Range of compactness of 1.4,rmModot1.4\, {\rm M}_\odot1.4,rmModot strange star is obtained as 0.175 ≤ C1.4 ≤ 0.199. Radius range of 1.5,rmModot1.5\, {\rm M}_\odot1.5,rmModot primary star is deduced to be 10.57 km ≤ R1.5 ≤ 12.04 km, following stringent GW170817 constraints. GW190425 constraints provide with upper limit on radius of 1.7 solar mass strange star that it should be less than 13.41,textkm13.41\, \text{km}13.41,textkm.

In this work, we study the effects of nuclear symmetry energy slope on neutron star dense matter ... more In this work, we study the effects of nuclear symmetry energy slope on neutron star dense matter equation of state and its impact on neutron star observables (mass-radius, tidal response). We construct the equation of state within the framework of covariant density functional theory implementing coupling schemes of non-linear and density-dependent models with viability of heavier non-nucleonic degrees of freedom. The slope of symmetry energy parameter (L_sym) is adjusted following density-dependence of isovector meson coupling to baryons. We find that smaller values of L_sym at saturation favour early appearance of Δ-resonances in comparison to hyperons leading to latter's threshold at higher matter densities. We also investigate the dependence of L_sym on tidal deformability and compactness parameter of a 1.4 M_⊙ neutron star for different equation of states and observe similar converging behaviour for larger L_sym values.

In this work, we study the effects of nuclear symmetry energy slope on neutron star dense matter ... more In this work, we study the effects of nuclear symmetry energy slope on neutron star dense matter equation of state and its impact on neutron star observables (mass-radius, tidal response). We construct the equation of state within the framework of covariant density functional theory implementing coupling schemes of non-linear and density-dependent models with viability of heavier non-nucleonic degrees of freedom. The slope of symmetry energy parameter (Lsym) is adjusted following density-dependence of isovector meson coupling to baryons. We find that smaller values of Lsym at saturation favour early appearance of ∆-resonances in comparison to hyperons leading to latter's threshold at higher matter densities. We also investigate the dependence of Lsym on tidal deformability and compactness parameter of a 1.4 M neutron star for different equation of states and observe similar converging behaviour for larger Lsym values.

Monthly Notices of the Royal Astronomical Society, 2021

The detection of gravitational waves (GWs) from the merger of binary neutron star (NS) events (GW... more The detection of gravitational waves (GWs) from the merger of binary neutron star (NS) events (GW170817 and GW190425) and subsequent estimations of tidal deformability play a key role in constraining the behaviour of dense matter. In addition, massive NS candidates (∼2 M⊙) along with NICER mass–radius measurements also set sturdy constraints on the dense matter equation of state. Strict bounds from GWs and massive NS observations constrain the theoretical models of nuclear matter comportment at large density regimes. On the other hand, model parameters providing the highly dense matter response are bounded by nuclear saturation properties. This work analyses coupling parametrizations from two classes based on covariant density functional models: non-linear and density-dependent schemes. Considering these constraints together, we study possible models and parametrization schemes with the feasibility of exotic degrees of freedom in dense matter which go well with the astrophysical obs...

Physical Review D, 2020

Recent measurements of neutron star mass from several candidates (PSR J1614 − 2230, PSR J0348 + 0... more Recent measurements of neutron star mass from several candidates (PSR J1614 − 2230, PSR J0348 + 0432, MSP J0740 + 6620) set the lower bound on the maximum possible mass for this class of compact objects ∼ 2 M. Existence of stars with high mass brings the possibility of existence of exotic matter (hyperons, meson condensates) at the core region of the objects. In this work, we investigate the (anti)kaon (K − ,K 0) condensation in β−equilibrated nuclear matter within the framework of covariant density functional theory. The functionals in the kaonic sector are constrained by the experimental studies on K − atomic, kaon-nucleon scattering data fits. We find that the equation of state softens with the inclusion of (anti)kaon condensates, which lowers the maximum mass of neutron star. In one of the density-independent coupling cases, the K − condensation is through a first-order phase transition type, which produces a 2 M neutron star. The first-order phase transition results in mixed phase region in the inner core of the stars. Whilē K 0 condensation appears via second-order phase transition for all the models we consider here.

Physical Review D, 2021

In this work, we study the effect of (anti)kaon condensation on the properties of compact stars t... more In this work, we study the effect of (anti)kaon condensation on the properties of compact stars that develop hypernuclear cores with and without an admixture of ∆-resonances. We work within the covariant density functional theory with the parameters adjusted to K-atomic and kaon-nucleon scattering data in the kaonic sector. The density-dependent parameters in the hyperonic sector are adjusted to the data on Λ and Ξ − hypernuclei data. The ∆-resonance couplings are tuned to the data obtained from their scattering off nuclei and heavy-ion collision experiments. We find that (anti)kaon condensate leads to a softening of the equation of state and lower maximum masses of compact stars than in the absence of the condensate. Both the K − andK 0-condensations occur through a second-order phase transition, which implies no mixed-phase formation. For large values of (anti)kaon and ∆-resonance potentials in symmetric nuclear matter, we observe that condensation leads to an extinction of Ξ −,0 hyperons. We also investigate the influence of inclusion of additional hidden-strangeness σ * meson in the functional and find that it leads to a substantial softening of the equation of state and delay in the onset of (anti)kaons.

arXiv (Cornell University), Feb 12, 2022

We study the implications of the recent development in nuclear symmetry energy constraints from P... more We study the implications of the recent development in nuclear symmetry energy constraints from PREX-2 data on dense matter equation of state and its impact on dURCA threshold density. In this work, we construct the equation of state within the framework of covariant density functional theory implementing coupling schemes of non-linear and density-dependent models and exploring the coupling parameter space of isovector-vector meson to baryons constrained by the isospin asymmetry parameter values deduced from recent PREX-2 data. The modified parameter sets are applied to evaluate the dense matter properties. We find that the updated data suggests the occurence of dURCA process within neutron star even with mass as low as one solar mass.

Physical review, Mar 22, 2023

Compact stars (CS) are stellar remnants of massive stars. Inside CSs the density is so high that ... more Compact stars (CS) are stellar remnants of massive stars. Inside CSs the density is so high that matter is in subatomic form composed of nucleons. With increase of density of matter towards the centre of the objects other degrees of freedom like hyperons, heavier non-strange baryons, meson condensates may appear. Not only that at higher densities, the nucleons may get decomposed into quarks and form deconfined strange quark matter (SQM). If it is so then CSs may contain SQM in the core surrounded by nucleonic matter forming hybrid stars (HSs). However, the nature and composition of matter inside CSs can only be inferred from the astrophysical observations of these CSs. Recent astrophysical observations in terms of CS mass-radius (M-R) relation and gravitational wave (GW) observation indicate that the matter should be soft in the intermediate density range and stiff enough at higher density range to attain the maximum possible mass above 2 M which is not compatible with pure hadronic equation of states (EOSs). Consequently, we study the HS properties with different models of SQM and find that within vector bag model considering density dependent bag parameter, the model goes well with the astrophysical observations so far.

Physical Review C

The nuclear symmetry energy and its behaviour with density has been recently evaluated with enhan... more The nuclear symmetry energy and its behaviour with density has been recently evaluated with enhanced value by PREX-2 experiment. This new values enables direct Urca neutrino emission process to be functioning in the dense matter inside neutron stars. With this new outlook we study the cooling rate of canonical mass neutron stars and compare with available observational cooling data. We find most of the isolated neutron star thermal profile is compatible with the cooling of canonical mass star including superfluidity suppression.

arXiv (Cornell University), Feb 22, 2023

Physical Review C

Recent observations of several massive pulsars, with masses near and above 2 M , point towards th... more Recent observations of several massive pulsars, with masses near and above 2 M , point towards the existence of matter at very high densities, compared to normal matter that we are familiar with in our terrestrial world. This leads to the possibility of appearance of exotic degrees of freedom other than nucleons inside the core of the neutrons stars (NS). Another significant property of NSs is the presence of high surface magnetic field, with highest range of the order of ∼ 10 16 G. We study the properties of highly dense matter with the possibility of appearance of heavier strange and non-strange baryons, and kaons in presence of strong magnetic field. We find that the presence of a strong magnetic field stiffens the matter at high density, delaying the kaon appearance and, hence, increasing the maximum attainable mass of NS family.

Physical Review D

Compact stars (CS) are stellar remnants of massive stars. Inside CSs the density is so high that ... more Compact stars (CS) are stellar remnants of massive stars. Inside CSs the density is so high that matter is in subatomic form composed of nucleons. With increase of density of matter towards the centre of the objects other degrees of freedom like hyperons, heavier non-strange baryons, meson condensates may appear. Not only that at higher densities, the nucleons may get decomposed into quarks and form deconfined strange quark matter (SQM). If it is so then CSs may contain SQM in the core surrounded by nucleonic matter forming hybrid stars (HSs). However, the nature and composition of matter inside CSs can only be inferred from the astrophysical observations of these CSs. Recent astrophysical observations in terms of CS mass-radius (M-R) relation and gravitational wave (GW) observation indicate that the matter should be soft in the intermediate density range and stiff enough at higher density range to attain the maximum possible mass above 2 M which is not compatible with pure hadronic equation of states (EOSs). Consequently, we study the HS properties with different models of SQM and find that within vector bag model considering density dependent bag parameter, the model goes well with the astrophysical observations so far.

EPJ Web of Conferences

Recently an improved value of neutron skin thickness of 208Pb was reported in Lead Radius EXperim... more Recently an improved value of neutron skin thickness of 208Pb was reported in Lead Radius EXperiment-2 (PREX-2) to be Rskin = Rn Rp = (0.283 0.071) fm which corresponds to high estimations of nuclear symmetry energy (Esym) and its slope (Lsym). The updated values of Esym and Lsym commensurating to the neutron star observable estimations lie exterior to the astrophysical observed range. The higher values of Lsym at n0 deduced from recent PREX-2 data correlates to matter being easily deformable (yielding higher radius values) around intermediate matter densities leading to higher values of Λ̃ creating a tension between the terrestrial and astrophysical observations. In this study, we exploit this tension to constrain the Δ-scalar meson coupling parameter space.

Springer proceedings in physics, 2022

arXiv (Cornell University), Feb 15, 2023

arXiv (Cornell University), Oct 26, 2022

Recent observations of several massive pulsars, with masses near and above 2 M , point towards th... more Recent observations of several massive pulsars, with masses near and above 2 M , point towards the existence of matter at very high densities, compared to normal matter that we are familiar with in our terrestrial world. This leads to the possibility of appearance of exotic degrees of freedom other than nucleons inside the core of the neutrons stars (NS). Another significant property of NSs is the presence of high surface magnetic field, with highest range of the order of ∼ 10 16 G. We study the properties of highly dense matter with the possibility of appearance of heavier strange and non-strange baryons, and kaons in presence of strong magnetic field. We find that the presence of a strong magnetic field stiffens the matter at high density, delaying the kaon appearance and, hence, increasing the maximum attainable mass of NS family.

arXiv (Cornell University), Feb 12, 2022

We study the implications of the recent development in nuclear symmetry energy constraints from P... more We study the implications of the recent development in nuclear symmetry energy constraints from PREX-2 data on dense matter equation of state and its impact on dURCA threshold density. In this work, we construct the equation of state within the framework of covariant density functional theory implementing coupling schemes of non-linear and density-dependent models and exploring the coupling parameter space of isovector-vector meson to baryons constrained by the isospin asymmetry parameter values deduced from recent PREX-2 data. The modified parameter sets are applied to evaluate the dense matter properties. We find that the updated data suggests the occurence of dURCA process within neutron star even with mass as low as one solar mass.

Monthly Notices of the Royal Astronomical Society

We investigate the properties of stars participating in double compact star merger events conside... more We investigate the properties of stars participating in double compact star merger events considering interacting model of stable strange quark matter. We model the matter making it compatible with the recent astrophysical observations of compact star mass–radius and gravitational wave events. In this context, we consider modified MIT bag model and vector bag model with and without self-interaction. We find new upper bound on tidal deformability of 1.4,rmModot1.4\, {\rm M}_\odot1.4,rmModot strange star corresponding to the upper bound of effective tidal deformability inferred from gravitational wave event. Range of compactness of 1.4,rmModot1.4\, {\rm M}_\odot1.4,rmModot strange star is obtained as 0.175 ≤ C1.4 ≤ 0.199. Radius range of 1.5,rmModot1.5\, {\rm M}_\odot1.5,rmModot primary star is deduced to be 10.57 km ≤ R1.5 ≤ 12.04 km, following stringent GW170817 constraints. GW190425 constraints provide with upper limit on radius of 1.7 solar mass strange star that it should be less than 13.41,textkm13.41\, \text{km}13.41,textkm.

In this work, we study the effects of nuclear symmetry energy slope on neutron star dense matter ... more In this work, we study the effects of nuclear symmetry energy slope on neutron star dense matter equation of state and its impact on neutron star observables (mass-radius, tidal response). We construct the equation of state within the framework of covariant density functional theory implementing coupling schemes of non-linear and density-dependent models with viability of heavier non-nucleonic degrees of freedom. The slope of symmetry energy parameter (L_sym) is adjusted following density-dependence of isovector meson coupling to baryons. We find that smaller values of L_sym at saturation favour early appearance of Δ-resonances in comparison to hyperons leading to latter's threshold at higher matter densities. We also investigate the dependence of L_sym on tidal deformability and compactness parameter of a 1.4 M_⊙ neutron star for different equation of states and observe similar converging behaviour for larger L_sym values.

In this work, we study the effects of nuclear symmetry energy slope on neutron star dense matter ... more In this work, we study the effects of nuclear symmetry energy slope on neutron star dense matter equation of state and its impact on neutron star observables (mass-radius, tidal response). We construct the equation of state within the framework of covariant density functional theory implementing coupling schemes of non-linear and density-dependent models with viability of heavier non-nucleonic degrees of freedom. The slope of symmetry energy parameter (Lsym) is adjusted following density-dependence of isovector meson coupling to baryons. We find that smaller values of Lsym at saturation favour early appearance of ∆-resonances in comparison to hyperons leading to latter's threshold at higher matter densities. We also investigate the dependence of Lsym on tidal deformability and compactness parameter of a 1.4 M neutron star for different equation of states and observe similar converging behaviour for larger Lsym values.

Monthly Notices of the Royal Astronomical Society, 2021

The detection of gravitational waves (GWs) from the merger of binary neutron star (NS) events (GW... more The detection of gravitational waves (GWs) from the merger of binary neutron star (NS) events (GW170817 and GW190425) and subsequent estimations of tidal deformability play a key role in constraining the behaviour of dense matter. In addition, massive NS candidates (∼2 M⊙) along with NICER mass–radius measurements also set sturdy constraints on the dense matter equation of state. Strict bounds from GWs and massive NS observations constrain the theoretical models of nuclear matter comportment at large density regimes. On the other hand, model parameters providing the highly dense matter response are bounded by nuclear saturation properties. This work analyses coupling parametrizations from two classes based on covariant density functional models: non-linear and density-dependent schemes. Considering these constraints together, we study possible models and parametrization schemes with the feasibility of exotic degrees of freedom in dense matter which go well with the astrophysical obs...

Physical Review D, 2020

Recent measurements of neutron star mass from several candidates (PSR J1614 − 2230, PSR J0348 + 0... more Recent measurements of neutron star mass from several candidates (PSR J1614 − 2230, PSR J0348 + 0432, MSP J0740 + 6620) set the lower bound on the maximum possible mass for this class of compact objects ∼ 2 M. Existence of stars with high mass brings the possibility of existence of exotic matter (hyperons, meson condensates) at the core region of the objects. In this work, we investigate the (anti)kaon (K − ,K 0) condensation in β−equilibrated nuclear matter within the framework of covariant density functional theory. The functionals in the kaonic sector are constrained by the experimental studies on K − atomic, kaon-nucleon scattering data fits. We find that the equation of state softens with the inclusion of (anti)kaon condensates, which lowers the maximum mass of neutron star. In one of the density-independent coupling cases, the K − condensation is through a first-order phase transition type, which produces a 2 M neutron star. The first-order phase transition results in mixed phase region in the inner core of the stars. Whilē K 0 condensation appears via second-order phase transition for all the models we consider here.

Physical Review D, 2021

In this work, we study the effect of (anti)kaon condensation on the properties of compact stars t... more In this work, we study the effect of (anti)kaon condensation on the properties of compact stars that develop hypernuclear cores with and without an admixture of ∆-resonances. We work within the covariant density functional theory with the parameters adjusted to K-atomic and kaon-nucleon scattering data in the kaonic sector. The density-dependent parameters in the hyperonic sector are adjusted to the data on Λ and Ξ − hypernuclei data. The ∆-resonance couplings are tuned to the data obtained from their scattering off nuclei and heavy-ion collision experiments. We find that (anti)kaon condensate leads to a softening of the equation of state and lower maximum masses of compact stars than in the absence of the condensate. Both the K − andK 0-condensations occur through a second-order phase transition, which implies no mixed-phase formation. For large values of (anti)kaon and ∆-resonance potentials in symmetric nuclear matter, we observe that condensation leads to an extinction of Ξ −,0 hyperons. We also investigate the influence of inclusion of additional hidden-strangeness σ * meson in the functional and find that it leads to a substantial softening of the equation of state and delay in the onset of (anti)kaons.