Quark matter in compact stars: astrophysical implications and possible signatures

After a brief non technical introduction of the basic properties of strange quark matter (SQM) in compact stars, we consider some of the late important advances in the field, and discuss some recent astrophysical observational data that could shed new light on the possible presence of SQM in compact stars. We show that above a threshold value of the gravitational mass a neutron star (pure hadronic star) is metastable to the decay (conversion) to an hybrid neutron star or to a strange star. We explore the consequences of the metastability of "massive" neutron stars and of the existence of stable compact "quark" stars (hybrid neutron stars or strange stars) on the concept of limiting mass of compact stars, and we give an extension of this concept with respect to the "classical" one given in 1939 by Oppenheimer and Volkoff.Comment: Invited talk at "the Eleventh Marcel Grossman Meeting on General Relativity", Berlin 200

Quark deconfinement and neutrino trapping in compact stars

We study the role played by neutrino trapping on the hadron star (HS) to quark star (QS) conversion mechanism proposed recently by Berezhiani and collaborators. We find that the nucleation of quark matter drops inside hadron matter, and therefore the conversion of a HS into a QS, is strongly inhibit by the presence of neutrinos.Comment: 3 pages, 3 figures. Talk given at the VIII International Conference on Strangeness in Quark Matter. Cape Town, South Africa, Septembre 200

Spin-orbit and tensor interactions in homogeneous matter of nucleons: accuracy of modern many-body theories

We study the energy per particle of symmetric nuclear matter and pure neutron matter using realistic nucleon--nucleon potentials having non central tensor and spin--orbit components, up to three times the empirical nuclear matter saturation density, $\rho_0=0.16$ fm$^{-3}$. The calculations are carried out within the frameworks of the Brueckner--Bethe--Goldstone (BBG) and Correlated Basis Functions (CBF) formalisms, in order to ascertain the accuracy of the methods. The two hole--line approximation, with the continuous choice for the single particle auxiliary potential, is adopted for the BBG approach, whereas the variational Fermi Hypernetted Chain/Single Operator Chain theory, corrected at the second order perturbative expansion level, is used in the CBF one. The energies are then compared with the available Quantum and Variational Monte Carlo results in neutron matter and with the BBG, up to the three hole--line diagrams. For neutron matter and potentials without spin--orbit components all methods, but perturbative CBF, are in reasonable agreement up to $\rho\sim$ 3 $\rho_0$. After the inclusion of the LS interactions, we still find agreement around $\rho_0$, whereas it is spoiled at larger densities. The spin--orbit potential lowers the energy of neutron matter at $\rho_0$ by $\sim$ 3--4 MeV per nucleon. In symmetric nuclear matter, the BBG and the variational results are in agreement up to $\sim$ 1.5 $\rho_0$. Beyond this density, and in contrast with neutron matter, we find good agreement only for the potential having spin--orbit components.Comment: 18 pages, 4 tables. Accepted in PL

Microscopic calculations of spin polarized neutron matter at finite temperature

The properties of spin polarized neutron matter are studied both at zero and finite temperature within the framework of the Brueckner--Hartree--Fock formalism, using the Argonne v18 nucleon-nucleon interaction. The free energy, energy and entropy per particle are calculated for several values of the spin polarization, densities and temperatures together with the magnetic susceptibility of the system. The results show no indication of a ferromagnetic transition at any density and temperature.Comment: 19 pages, 5 figure

Quark matter nucleation in hot hadronic matter

We study the quark deconfinement phase transition in hot $\beta$-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

Comparison of dynamical multifragmentation models

Multifragmentation scenarios, as predicted by antisymmetrized molecular dynamics (AMD) or momentum-dependent stochastic mean-field (BGBD) calculations are compared. While in the BGBD case fragment emission is clearly linked to the spinodal decomposition mechanism, i.e. to mean-field instabilities, in AMD many-body correlations have a stronger impact on the fragmentation dynamics and clusters start to appear at earlier times. As a consequence, fragments are formed on shorter time scales in AMD, on about equal footing of light particle pre-equilibrium emission. Conversely, in BGBD pre-equilibrium and fragment emissions happen on different time scales and are related to different mechanisms