Giant Pulsar Glitches and the Inertia of Neutron-Star Crusts

Giant pulsar frequency glitches as detected in the emblematic Vela pulsar have long been thought to be the manifestation of a neutron superfluid permeating the inner crust of a neutron star. However, this superfluid has been recently found to be entrained by the crust, and as a consequence it does not carry enough angular momentum to explain giant glitches. The extent to which pulsar-timing observations can be reconciled with the standard vortex-mediated glitch theory is studied considering the current uncertainties on dense-matter properties. To this end, the crustal moment of inertia of glitching pulsars is calculated employing a series of different unified dense-matter equations of state.Comment: 11 pages, 6 figures, submitted to PR

Elementary excitations in homogeneous superfluid neutron star matter: Role of the proton component

The thermal evolution of neuron stars depends on the elementary excitations affecting the stellar matter. In particular, the low-energy excitations, whose energy is proportional to the transfered momentum, can play a major role in the emission and propagation of neutrinos. In this paper, we focus on the density modes associated with the proton component in the homogeneous matter of the outer core of neutron stars (at density between one and three times the nuclear saturation density, where the baryonic constituants are expected to be neutrons and protons). In this region, it is predicted that the protons are superconductor. We study the respective roles of the proton pairing and Coulomb interaction in determining the properties of the modes associated with the proton component. This study is performed in the framework of the Random Phase Approximation, generalized in order to describe the response of a superfluid system.The formalism we use ensures that the Generalized Ward's Identities are satisfied. An important conclusion of this work is the presence of a pseudo-Goldstone mode associated with the proton superconductor in neutron-star matter. Indeed, the Goldstone mode, which characterizes a pure superfluid, is suppressed in usual superconductors due to the long-range Coulomb interaction, which only allows a plasmon mode. However, for the proton component of stellar matter, the Coulomb field is screened by the electrons and a pseudo-Goldstone mode occurs, with a velocity increased by the Coulomb interaction.Comment: Submitted for publicatio

Cluster formation in compact stars: relativistic versus Skyrme models

We present various properties of nuclear and compact-star matter, comparing the predictions from two kinds of phenomenological approaches: relativistic models (both with constant and density-dependent couplings) and non-relativistic Skyrme-type interactions. We mainly focus on the liquid-gas instabilities that occur at sub-saturation densities, leading to the decomposition of the homogeneous matter into a clusterized phase. Such study is related to the description of neutron-star crust (at zero temperature) and of supernova dynamics (at finite temperature)

Phase diagram of neutron-rich nuclear matter and its impact on astrophysics

Dense matter as it can be found in core-collapse supernovae and neutron stars is expected to exhibit different phase transitions which impact the matter composition and equation of state, with important consequences on the dynamics of core-collapse supernova explosion and on the structure of neutron stars. In this paper we will address the specific phenomenology of two of such transitions, namely the crust-core solid-liquid transition at sub-saturation density, and the possible strange transition at super-saturation density in the presence of hyperonic degrees of freedom. Concerning the neutron star crust-core phase transition at zero and finite temperature, it will be shown that, as a consequence of the presence of long-range Coulomb interactions, the equivalence of statistical ensembles is violated and a clusterized phase is expected which is not accessible in the grand-canonical ensemble. A specific quasi-particle model will be introduced to illustrate this anomalous thermodynamics and some quantitative results relevant for the supernova dynamics will be shown. The opening of hyperonic degrees of freedom at higher densities corresponding to the neutron stars core modifies the equation of state. The general characteristics and order of phase transitions in this regime will be analyzed in the framework of a self-consistent mean-field approach.Comment: Invited Talk given at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

Elementary excitations in homogeneous neutron star matter

We study the collective density modes which can affect neutron-star thermodynamics in the baryonic density range between nuclear saturation ($\rho_0$) and $3\rho_0$. In this region, the expected constituents of neutron-star matter are mainly neutrons, protons and electrons ($npe$ matter), under the constraint of beta equilibrium. The elementary excitations of this $npe$ medium are studied in the RPA framework. We emphasize the effect of Coulomb interaction, in particular the electron screening of the proton plasmon mode. For the treatment of the nuclear interaction, we compare two modern Skyrme forces and a microscopic approach. The importance of the nucleon effective mass is observed.Comment: misprint corrected in Eq. (1

Numerical investigation of the interaction between laminar to turbulent transition and the wake of an airfoil

The objective of this work is to investigate numerically the different physical mechanisms of the transition to turbulence of a separated boundary-layer flow over an airfoil at low angle of attack. In this study, the spectral elements code Nek5000 is used to simulate the flow over a SD7003 wing section at an angle of attack of α = 4 ◦ . Several laminar cases are first studied from Re = 2000 to Re = 10000, and a gradual increase of the Reynolds number is then performed in order to investigate one transitional case at Re = 20000. Computations are compared with measurements where the instability mechanisms in the separated zone and near wake zone have been analyzed. The mechanism of transition is investigated, where the DMD (Dynamic Mode Decomposition) is used in order to extract the main physical modes of the flow and to highlight the interaction between the transition and the wake flow. The results suggest that the transition process appears to be physically independent of the wake flow, while the LSB shedding process is locked-in with the von Kármán instability and acts as a sub-harmonic

Phase transitions of hadronic to quark matter at finite T and \mu_B

The phase transition of hadronic to quark matter and the boundaries of the mixed hadron-quark coexistence phase are studied within the two Equation of State (EoS) model. The relativistic effective mean field approach with constant and density dependent meson-nucleon couplings is used to describe hadronic matter, and the MIT Bag model is adopted to describe quark matter. The boundaries of the mixed phase for different Bag constants are obtained solving the Gibbs equations. We notice that the dependence on the Bag parameter of the critical temperatures (at zero chemical potential) can be well reproduced by a fermion ultrarelativistic quark gas model, without contribution from the hadron part. At variance the critical chemical potentials (at zero temperature) are very sensitive to the EoS of the hadron sector. Hence the study of the hadronic EoS is much more relevant for the determination of the transition to the quark-gluon-plasma at finite baryon density and low-T. Moreover in the low temperature and finite chemical potential region no solutions of the Gibbs conditions are existing for small Bag constant values, B < (135 MeV)^4. Isospin effects in asymmetric matter appear relevant in the high chemical potential regions at lower temperatures, of interest for the inner core properties of neutron stars and for heavy ion collisions at intermediate energies.Comment: 24 pages and 16 figures (revtex4

Plasmon excitations in homogeneous neutron star matter

We study the possible collective plasma modes which can affect neutron-star thermodynamics and different elementary processes in the baryonic density range between nuclear saturation ($\rho_0$) and $3\rho_0$. In this region, the expected constituents of neutron-star matter are mainly neutrons, protons, electrons and muons ($npe\mu$ matter), under the constraint of beta equilibrium. The elementary plasma excitations of the $pe\mu$ three-fluid medium are studied in the RPA framework. We emphasize the relevance of the Coulomb interaction among the three species, in particular the interplay of the electron and muon screening in suppressing the possible proton plasma mode, which is converted into a sound-like mode. The Coulomb interaction alone is able to produce a variety of excitation branches and the full spectral function shows a rich structure at different energy. The genuine plasmon mode is pushed at high energy and it contains mainly an electron component with a substantial muon component, which increases with density. The plasmon is undamped for not too large momentum and is expected to be hardly affected by the nuclear interaction. All the other branches, which fall below the plasmon, are damped or over-damped.Comment: misprint corrected in Eq. (1

Lattice QCD Constraints on the Nuclear Equation of State

Based on the quasi-particle description of the QCD medium at finite temperature and density we formulate the phenomenological model for the equation of state that exhibits crossover or the first order deconfinement phase transition. The models are constructed in such a way to be thermodynamically consistent and to satisfy the properties of the ground state nuclear matter comply with constraints from intermediate heavy--ion collision data. Our equations of states show quite reasonable agreement with the recent lattice findings on temperature and baryon chemical potential dependence of relevant thermodynamical quantities in the parameter range covering both the hadronic and quark--gluon sectors. The model predictions on the isentropic trajectories in the phase diagram are shown to be consistent with the recent lattice results. Our nuclear equations of states are to be considered as an input to the dynamical models describing the production and the time evolution of a thermalized medium created in heavy ion collisions in a broad energy range from SIS up to LHC.Comment: 13 pages, 11 figure

Higher order bulk characteristic parameters of asymmetric nuclear matter

The bulk parameters characterizing the energy of symmetric nuclear matter and the symmetry energy defined at normal nuclear density $\rho_0$ provide important information on the equation of state (EOS) of isospin asymmetric nuclear matter. While significant progress has been made in determining some lower order bulk characteristic parameters, such as the energy $E_0(\rho_0)$ and incompressibility $K_0$ of symmetric nuclear matter as well as the symmetry energy $E_{sym}(\rho_0)$ and its slope parameter $L$, yet the higher order bulk characteristic parameters are still poorly known. Here, we analyze the correlations between the lower and higher order bulk characteristic parameters within the framework of Skyrme Hartree-Fock energy density functional and then estimate the values of some higher order bulk characteristic parameters. In particular, we obtain $J_0=-355 \pm 95$ MeV and $I_0=1473 \pm 680$ MeV for the third-order and fourth-order derivative parameters of symmetric nuclear matter at $\rho_0$ and $K_{sym} = -100 \pm 165$ MeV, $J_{sym} = 224 \pm 385$ MeV, $I_{sym} = -1309 \pm 2025$ MeV for the curvature parameter, third-order and fourth-order derivative parameters of the symmetry energy at $\rho_0$, using the empirical constraints on $E_0(\rho_0)$, $K_0$, $E_{sym}(\rho_0)$, $L$, and the isoscalar and isovector nucleon effective masses. Furthermore, our results indicate that the three parameters $E_0(\rho_0)$, $K_0$, and $J_0$ can reasonably characterize the EOS of symmetric nuclear matter up to $2\rho_0$ while the symmetry energy up to $2\rho_0$ can be well described by $E_{sym}(\rho_0)$, $L$, and $K_{sym}$.Comment: 6 pages, 7 figures. Typos fixed. Contribution to a special issue in Science China: Physics, Mechanics & Astronom