The recent multi-messenger observation campaign of event GW170817, attributed to merging neutron stars, opens exciting new possibilities to test fundamental laws of nature ranging from general relativity to nuclear physics. Deriving a single consistent model explaining the observed gravitational waves and electromagnetic counterparts is, however, a very complex undertaking. A key element in...

Using the quasinormal mode formalism, we study the ringdown phase of gravitational waves emitted from neutron stars. We consider several alternative models of gravity that include additional scalar degrees of freedom in the action. As a result, in these theories the compact objects are typically surrounded by a non-trivial scalar field. An analysis of the quasinormal modes of these objects...

We discuss the emission process of GW echoes from ultracompact strange stars. Strange stars are extremely compact, and exotic, objects consisting of deconfined quark matter. If in the merging of two neutron stars a strange star is formed, the GW emission process should result in a GW echo at a frequency of the order of tens of kHz. This would allow to (indirectly) probe the equation of state...

We consider special classes of massive tensor-multi-scalar theories of gravity whose target space metric admits Killing field(s) with a periodic flow. For such tensor-multi-scalar theories we show that there exist mixed configurations of tenor-multi-scalar solitons and neutron stars. The influence of the curvature of the target space on the structure of the mixed configurations is studied...

Neutron stars (NSs) in low-mass X-ray binaries have an accreted crust, whose equation of state and composition differs from that in isolated NSs. To determine it, one usually makes a number of simplifying assumptions regarding both thermodynamics and kinetics of crust matter. We critically revise some of these assumptions and propose new thermodynamically consistent derivation of the crust...

We study bulk viscosity arising from weak current Urca processes in dense baryonic matter at and beyond nuclear saturation density. We consider the temperature regime where neutrinos are trapped and therefore have non-zero chemical potential. We model the nuclear matter in a relativistic density functional approach, taking in to account the trapped neutrino component. We find that the resonant...

We contribute a publicly available set of tables and code to provide Equations of State (EoS) for matter at neutron star densities. Our EoS's are constrained only by input from hadron physics and fundamental principles, without feedback from neutron star observations, and so without relying on General Relativity. They can therefore be used to test General Relativity itself, as well as modified...

In this talk I discuss elastic properties of neutron star crust within model of static Coulomb crystal (ions are treated as point charges; electron screening and ion motion are neglected). I start from discussion of the elasticity tensor of the perfect crystal and demonstrate that it has additional symmetry, which do not depend on the actual crystalline structure and composition. As a...

We construct a simplified reaction network model for calculating the multicomponent composition of accreted neutron star crust and apply it to probe the sensitivity of the composition to the choice of the theoretical atomic mass model. Following Haensel & Zdunik [A&A 229 (1990) 117], our approach considers the evolution of matter with increasing pressure and employs Gibbs energy formalism to...

I will review the heat transport mechanisms that are most important for

thermal structure of neutron stars and thermal radiation from

neutron-star surfaces. The effects of the heat transport on thermal

evolution and thermal states of different classes of neutron stars will

be highlighted. Special attention will be given to the effects of strong

magnetic fields, to recent developments in the...

We discuss the contribution of the chiral separation effect, which is proportional to the mean spin of plasma, to the system of anomalous MHD equations. It is found that the chiral imbalance in inhomogeneous matter gets supported by the chiral separation effect versus its washing out by spin flipping collisions in plasma. Thus, the magnetic field instability, driven by the chiral magnetic...

We revisit the Polyakov Loop coupled Nambu-Jona-Lasinio model that maintains the Polyakov loop dynamics in the limit of zero temperature. This is of interest for astrophysical applications in the interior of neutron stars. For this purpose we re-examine the form of the potential for the deconfinement order parameter at finite baryonic densities. Since the modification of this potential at any...

I will review the current constraints on the neutron star properties from multi-messenger astrophysical observations. I will then discuss if and how they complement the constraints from nuclear experiments and calculations.

The rapid advance of the neutron star observations offers unprecedented opportunities to test different modification of general relativity. Our talk focuses on a variety of solutions describing neutron stars in alternatives theories of gravity, as well as their astrophysical implications. A special emphasis is made on the gravitational wave emission after neutron star mergers and the possible...