Phase transition and stiffer core fluid in neutron stars: Effects on stellar configurations, dynamical stability, and tidal deformability

In this work, we investigate the influence of the phase transition and a stiffer fluid in neutron stars' cores on the static equilibrium configuration, dynamical stability, and tidal deformability. For this aim, it is taken into account that the fluid in the core and the envelope follow the relativistic polytropic equation of state. We find that the phase transition and a stiffer fluid in the core will reflect in the total mass, radius, speed of sound, core radius, radial stability with a slow and rapid conversion at the interface, and tidal deformability. We also investigate the dimensionless tidal deformability $\Lambda_1$ and $\Lambda_2$ for a binary neutron stars system with chirp mass equal to GW$170817$. Finally, we contrast our results with observational data to show the role that phase transition and a stiffer core fluid could play in the study of neutron stars.Comment: To appear in EPJ

Dark matter effects on hybrid star properties

In the present work we investigate the effects of dark matter (DM) on hybrid star properties. We assume that dark matter is mixed with both hadronic and quark matter and interact with them through the exchange of a Higgs boson. The hybrid star properties are obtained from equations of state calculated with a Maxwell prescription. For the hadronic matter we use the NL3* parameter set and for the quark matter, the MIT bag model with a vector interaction. We see that dark matter does not influence the phase transition points (pressure and chemical potential) but shifts the discontinuity on the energy density, which ultimately reduces the minimum mass star that contains a quark core. Moreover, it changes considerably the star family mass-radius diagrams and moves the merger polarizability curves inside the confidence lines. Another interesting feature is the influence of DM in the quark core of the hybrid stars constructed. Our results show an increase of the core radius for higher values of the dark particle Fermi momentum

Astrophysics from data analysis of spherical gravitational wave detectors

The direct detection of gravitational waves will provide valuable astrophysical information about many celestial objects. Also, it will be an important test to general relativity and other theories of gravitation. The gravitational wave detector SCHENBERG has recently undergone its first test run. It is expected to have its first scientific run soon. In this work the data analysis system of this spherical, resonant mass detector is tested through the simulation of the detection of gravitational waves generated during the inspiralling phase of a binary system. It is shown from the simulated data that it is not necessary to have all six transducers operational in order to determine the source's direction and the wave's amplitudes.Comment: 8 pages and 3 figure

High-spin states in 212Po above the α-decaying (18+) isomer

The nucleus Po has been produced through the fragmentation of a U primary beam at 1 GeV/nucleon at GSI, separated with the FRagment Separator, FRS, and studied via isomer γ-decay spectroscopy with the RISING setup. Two delayed previously unknown γ rays have been observed. One has been attributed to the E3 decay of a 21 isomeric state feeding the α-emitting 45-s (18) high-spin isomer. The other γ-ray line has been assigned to the decay of a higher-lying 23 metastable state. These are the first observations of high-spin states above the Po (18) isomer, by virtue of the selectivity obtained via ion-by-ion identification of U fragmentation products. Comparison with shell-model calculations points to shortfalls in the nuclear interactions involving high-j proton and neutron orbitals, to which the region around Z∼100 is sensitive.This work was partially supported by the Ministry of Science, and Generalitat Valenciana, Spain, under the Grants SEV-2014-0398, FPA2017-84756-C4, PID2019-104714GB-C21, PROMETEO/2019/005 and by the EU FEDER funds. The support of the UK STFC, of the Swedish Research Council under Contract No. 2008-4240 and No. 2016-3969 and of the DFG (EXC 153) is also acknowledged. The experimental activity has been partially supported by the EU under the FP6-Integrated Infras-tructure Initiative EURONS, Contract No. RII3-CT-2004-506065 and FP7-Integrated Infrastructure Initiative ENSAR, Grant No. 262010

Isospin dependence of electromagnetic transition strengths among an isobaric triplet

Electric quadrupole matrix elements, M, for the J=2→0, ΔT=0, T=1 transitions across the A=46 isobaric multiplet Cr-V-Ti have been measured at GSI with the FRS-LYCCA-AGATA setup. This allows direct insight into the isospin purity of the states of interest by testing the linearity of M with respect to T. Pairs of nuclei in the T=1 triplet were studied using identical reaction mechanisms in order to control systematic errors. The M values were obtained with two different methodologies: (i) a relativistic Coulomb excitation experiment was performed for Cr and Ti; (ii) a “stretched target” technique was adopted here, for the first time, for lifetime measurements in V and Ti. A constant value of M across the triplet has been observed. Shell-model calculations performed within the fp shell fail to reproduce this unexpected trend, pointing towards the need of a wider valence space. This result is confirmed by the good agreement with experimental data achieved with an interaction which allows excitations from the underlying sd shell. A test of the linearity rule for all published data on complete T=1 isospin triplets is presented.Peer Reviewe

Quark confinement in an equiparticle quark model: Application to stellar matter

International audienceWe perform an improvement in a thermodynamical consistent model with density-dependent quark masses (mu,d,s′) by introducing effects of quark confinement/deconfinement phase transition, at high-density regime and zero temperature, by means of the traced Polyakov loop (Φ). We use realistic values for the current quark masses, provided by the Particle Data Group, and replace the constants of the interacting part of mu,d,s′ by functions of Φ, leading to a first-order phase-transition structure, for symmetric and stellar quark matter, with Φ being the order parameter. We show that the improved model points out the direction of the chiral-symmetry restoration due to the emergence of a deconfined phase. In another application, we construct quark star mass-radius profiles, obtained from this new model, and show to be possible to satisfy recent astrophysical observational data coming from the LIGO and Virgo Collaboration, and the Neutron star Interior Composition Explorer (NICER) mission concerning the millisecond pulsars PSR J0030+0451 and PSR J0740+6620