Neven Bilic

Unification of dark matter and dark energy: The Inhomogeneous Chaplygin gas

Abstract We extend the world model of Kamenshchik et al. to large perturbations by formulating a Zeldovich-like approximation. We sketch how this model unifies dark matter with dark energy in a geometric setting reminiscent of M-theory.

Born?Infeld phantom gravastars

We construct new gravitational vacuum star solutions with a Born–Infeld phantom replacing the de Sitter interior. The model allows for a wide range of masses and radii required by phenomenology, and can be motivated from low energy string theory.

Gravitational phase transition of fermionic matter

Abstract We study the phase transition of a system of self-gravitating weakly interacting massive fermions in the presence of a large radiation-density background in the framework of the Thomas-Fermi model. We show that by cooling a nondegenerate gas of weakly interacting massive fermions below some critical temperature, a condensed phase emerges, consisting of quasidegenerate supermassive fermion stars. These compact dark objects could play an important role in structure formation in the early universe, as they might in fact provide seeds for galactic nuclei and quasistellar objects.

Pauli interference effect in D+ lifetime

We estimate the interference effect on the D+ decay rate in terms of the matrix elements of an effective 4-quark operator calculated in quark models which are particularly successful in describing D-mesons. In the relativistic bag model, the interference effect reduces the hadronic rate of D+ by 40 per cent. Our results are consistent with recent experimental data on the semileptonic branching ratio and the lifetime of D+.

Dark Matter, Dark Energy and the Chaplygin Gas

We formulate a Zeľdovich-like approximation for the Chaplain gas equation of state P = -A/ρ, and sketch how this model unifies dark matter with dark energy in a geometric setting reminiscent of M-theory.

Thermodynamics of k-essence

We discuss thermodynamic properties of dark energy using the formalism of field theory at finite temperature. In particular, we apply our formalism to a purely kinetic type of k-essence. We show quite generally that the entropy associated with dark energy is always equal or greater than zero. Hence, contrary to often stated claims, a violation of the null energy condition (phantom dark energy) does not necessarily yield a negative entropy. In addition, we find that the thermal fluctuations of a k-essence field may be represented by a free boson gas with an effective number of degrees of freedom equal to c −3 s .

Stars and halos of degenerate relativistic heavy-neutrino and neutralino matter

Rudjer Boˇskovi´c Institute, 10000 Zagreb, Croatia(February 5, 2008)Heavy-neutrino (or neutralino) stars are studied using the general relativistic equations of hy-drostatic equilibrium and the relativistic equation of state for degenerate fermionic matter. TheTolman-Oppenheimer-Volkoff equations are then generalized to include a system of degenerate neu-trino and neutralino matter that is gravitationally coupled. The properties and implications of suchan interacting astrophysical system are discussed in detail.04.40.-b, 04.40.Dg, 97.20.Rp, 95.35.+d, 97.60.Jd, 98.35.JkI. INTRODUCTION

One-dimensional QCD with finite chemical potential

Abstract We consider a one-dimensional SU( N ) model with Kogut-Susskind fermions in order to investigate the effects of finite chemical potential. We calculate the chiral condensate exactly and compare it with the quenched approximation.

{QCD} Calculation of

AbstractWe calculate theB parameter for