Massive Neutron Stars with Antikaon Condensates in a Density Dependent Hadron Field Theory

The measurement of $1.97 \pm 0.04 M_{solar}$ for PSR J1614-2230 and $2.01 \pm 0.04M_{solar}$ for PSR J0348+0432 puts a strong constraint on the neutron star equation of state and its exotic composition at higher densities. In this paper, we investigate the possibility of exotic equation of state within the observational mass constraint of $2M_{solar}$ in the framework of relativistic mean field model with density-dependent couplings. We particularly study the effect of antikaon condensates in the presence of hyperons on the mass-radius relationship of the neutron star.Comment: 6 figures, submitted to Phy. Rev.

Critical temperature of antikaon condensation in nuclear matter

We investigate the critical temperature of Bose-Einstein condensation of $K^-$ mesons in neutron star matter. This is studied within the framework of relativistic field theoretical models at finite temperature where nucleon-nucleon and (anti)kaon-nucleon interactions are mediated by the exchange of mesons. The melting of the antikaon condensate is studied for different values of antikaon optical potential depths. We find that the critical temperature of antikaon condensation increases with baryon number density. Further it is noted that the critical temperature is lowered as antikaon optical potential becomes less attractive. We also construct the phase diagram of neutron star matter with $K^-$ condensate.Comment: LaTeX; 18 pages including 7 figures; two new figures are added and section III is modified; accepted for publication in Physical Review

A Comparative study of hyperon equations of state in supernova simulations

A comparative study of the $\Lambda$ hyperon equations of state of Banik, Hempel and Banyopadhyay (BHB) \citep{bhb} and \citet{shen11} (denoted as HShen $\Lambda$) for core collapse supernova (CCSN) simulations is carried out in this work. The dynamical evolution of a protoneutron star (PNS) into a black hole is investigated in core collapse supernova simulations in the general relativistic one dimensional code using the BHB$\Lambda \phi$ and HShen $\Lambda$ equation of state (EoS) tables and different progenitor models from Woosley and Heger \citep{Woos}. Radial profiles of the mass fractions of baryons, the density as well as the temperature in the PNS at different moments in time, are compared for both EoS tables. The behaviour of the central density of the PNS with time is demonstrated for those two $\Lambda$ hyperon EoS tables and compared with their corresponding nuclear EoS tables. It is observed that the black hole formation time is higher in the BHB$\Lambda \phi$ case than in the HShen $\Lambda$ EoS for the entire set of progenitor models adopted here, because the repulsive $\Lambda$-$\Lambda$ interaction makes the BHB$\Lambda \phi$ EoS stiffer. Neutrino emission with the $\Lambda$ hyperon EoS ceases earlier than that of its nuclear counterpart. The long duration evolution of the shock radius and gravitational mass of the PNS after a successful supernova explosion with enhanced neutrino heating are studied with the BHB$\Lambda \phi$ EoS and $s$20WH07 progenitor model. The PNS is found to remain stable for 4 s and might evolve into a cold neutron star.Comment: LaTeX; 25 pages including two tables and 10 figures; to be published in the Astrophysical Journa

New Hyperon Equations of State for Supernovae and Neutron Stars in Density-dependent Hadron Field Theory

We develop new hyperon equation of state (EoS) tables for core-collapse supernova simulations and neutron stars. These EoS tables are based on a density-dependent relativistic hadron field theory where baryon-baryon interaction is mediated by mesons, using the parameter set DD2 from Typel et al. (2010) for nucleons. Furthermore, light and heavy nuclei along with the interacting nucleons are treated in the nuclear statistical equilibrium model of Hempel and Schaffner-Bielich which includes excluded volume effects. Of all possible hyperons, we consider only the contribution of $\Lambda$s. We have developed two variants of hyperonic EoS tables: in the np$\Lambda \phi$ case the repulsive hyperon-hyperon interaction mediated by the strange $\phi$ meson is taken into account, and in the np$\Lambda$ case it is not. The EoS tables for the two cases encompass wide range of density ($10^{-12}$ to $\sim$ 1 fm$^{-3}$), temperature (0.1 to 158.48 MeV), and proton fraction (0.01 to 0.60). The effects of $\Lambda$ hyperons on thermodynamic quantities such as free energy per baryon, pressure, or entropy per baryon are investigated and found to be significant at high densities. The cold, $\beta$-equilibrated EoS (with the crust included self-consistently) results in a 2.1 M$_{\odot}$ maximum mass neutron star for the np$\Lambda \phi$ case, whereas that for the np$\Lambda$ case is 1.95 M$_{\odot}$. The np$\Lambda \phi$ EoS represents the first supernova EoS table involving hyperons that is directly compatible with the recently measured 2 M$_{\odot}$ neutron stars.Comment: 39 pages, 9 figures, 11 tables; matches published version, only minor additions and editorial change