Armen Sedrakian

Physics of Neutron Star Interiors

Microscopic Theory of the Nuclear Equation of State and Neutron Star Structure.- Superfluidity in Neutron Star Matter.- Relativistic Superfluid Models for Rotating Neutron Stars.- The Tensor Virial Method and Its Applications to Self-Gravitating Superfluids.- Neutron Star Crusts.- Kaon Condensation in Neutron Stars.- Phases of QCD at High Baryon Density.- Diquarks in Dense Matter.- Color Superconductivity in Compact Stars.- Strange Quark Stars: Structural Properties and Possible Signatures for Their Existence.- Phase Diagram for Spinning and Accreting Neutron Stars.- Signal of Quark Deconfinement in Millisecond Pulsars and Reconfinement in Accreting X-ray Neutron Stars.- Supernova Explosions and Neutron Star Formation.- Evolution of a Neutron Star from Its Birth to Old Age.- Neutron Star Kicks and Asymmetric Supernovae.- Spin and Magnetism in Old Neutron Stars.- Neutrino Cooling of Neutron Stars: Medium Effects.

Composition and stability of hybrid stars with hyperons and quark color-superconductivity

The recent measurement of a

Precession of Isolated Neutron Stars. I. Effects of Imperfect Pinning

1.97\pm 0.04

The physics of dense hadronic matter and compact stars

solar-mass pulsar places a stringent lower bound on the maximum mass of compact stars and therefore challenges the existence of any agents that soften the equation of state of ultra-dense matter. We investigate whether hyperons and/or quark matter can be accommodated in massive compact stars by constructing an equation of state based on a combination of phenomenological relativistic hyper-nuclear density functional and an effective model of quantum chromodynamics (the Nambu-Jona-Lasinio model). Stable configurations are obtained with

Type-I superconductivity and neutron star precession

M \ge 1.97 M_{\sun}

Constraining hypernuclear density functional with Λ-hypernuclei and compact stars

featuring hyper-nuclear and quark matter in color superconducting state if the equation of state of nuclear matter is stiff above the saturation density, the transition to quark matter takes place at a few times the nuclear saturation density, and the repulsive vector interactions in quark matter are substantial.

Transition from BCS pairing to Bose-Einstein condensation in low density asymmetric nuclear matter

We consider the precession of isolated neutron stars in which superfluid is not pinned to the stellar crust perfectly. In the case of perfect pinning, Shaham showed that there are no slowly oscillatory, long-lived modes. When the assumption of perfect pinning is relaxed, new modes are found that can be long lived but are expected to be damped rather than oscillatory, unless the drag force on moving superfluid vortex lines has a substantial component perpendicular to the direction of relative motion. The response of a neutron star to external torques, such as the spin-down torque, is also treated. We find that when computing the response of a star to perturbations, assuming perfect coupling of superfluid to normal matter from the start can miss some effects.

Thermodynamics of a n-p condensate in asymmetric nuclear matter

This review describes the properties of hadronic phases of dense matter in compact stars. The theory is developed within the method of real-time Greens functions and is applied to study of baryonic matter at and above the saturation density. The non-relativistic and covariant theories based on continuum Greens functions and the T-matrix and related approximations to the self-energies are reviewed. The effects of symmetry energy, onset of hyperons and meson condensation on the properties of stellar configurations are demonstrated on specific examples. Neutrino interactions with baryonic matter are introduced within a kinetic theory. We concentrate on the classification, analysis and first principle derivation of neutrino radiation processes from unpaired and superfluid hadronic phases. We then demonstrate how neutrino radiation rates from various microscopic processes affect the macroscopic cooling of neutron stars and how the observed X-ray fluxes from pulsars constrain the properties of dense hadronic matter.

Equation of state of hypernuclear matter: Impact of hyperon–scalar-meson couplings

Type-I proton superconducting cores of neutron stars break up in a magnetic field into alternating domains of superconducting and normal fluids. We examine two channels of superfluid-normal fluid friction where (i) rotational vortices are decoupled from the nonsuperconducting domains and the interaction is due to the strong force between protons and neutrons; (ii) the nonsuperconducting domains are dynamically coupled to the vortices and the vortex motion generates transverse electric fields within them, causing electronic current flow and Ohmic dissipation. The obtained dissipation coefficients are consistent with the Eulerian precession of neutron stars.

EMMI rapid reaction task force meeting on quark matter in compact stars

Abstract We present a simultaneous calculation of heavy single-Λ hypernuclei and compact stars containing hypernuclear core within a relativistic density functional theory based on a Lagrangian which includes the hyperon octet and lightest isoscalar-isovector mesons which couple to baryons with density-dependent couplings. The corresponding density functional allows for SU(6) symmetry breaking and mixing in the isoscalar sector, whereby the departures in the σ–Λ and σ–Σ couplings away from their values implied by the SU(3) symmetric model are used to adjust the theory to the laboratory and astronomical data. We fix σ–Λ coupling using the data on the single-Λ hypernuclei and derive an upper bound on the σ–Σ from the requirement that the lower bound on the maximum mass of a compact star is 2 M ⊙ .