Irina Ya. Aref'eva

Time evolution in superstring field theory on non-BPS brane 1. Rolling tachyon and energy-momentum conservation

We derive equations of motion for the tachyon field living on an unstable non-BPS D-brane in the level truncated open cubic superstring field theory in the first non-trivial approximation. We construct a special time dependent solution to this equation which describes a rolling tachyon. It starts from the perturbative vacuum and approaches one of stable vacua in infinite time. We investigate conserved energy functional and show that its different parts dominate in different stages of the evolution. We show that the pressure for this solution has its minimum at zero time and goes to minus energy at infinite time.We derive equations of motion for the tachyon field living on an unstable non-BPS D-brane in the level truncated open cubic superstring field theory in the first non-trivial approximation. We construct a special time dependent solution to this equation which describes the rolling tachyon. It starts from the perturbative vacuum and approaches one of stable vacua in infinite time. We investigate conserved energy functional and show that its different parts dominate in different stages of the evolution. We show that the pressure for this solution has its minimum at zero time and goes to minus energy at infinite time.

Nonlocal String Tachyon as a Model for Cosmological Dark Energy

There are many different phenomenological models describing the cosmological dark energy and accelerating Universe by choosing adjustable functions. In this paper we consider a specific model of scalar tachyon field which is derived from the NSR string field theory and study its cosmological applications. We find that in the effective field theory approximation the equation of state parameter w < −1, i.e. one has a phantom Universe. It is shown that due to nonlocal effects there is no quantum instability that the usual phantom models suffer from. Moreover due to a flip effect of the potential the Universe does not enter to a future singularity.

Bouncing and accelerating solutions in nonlocal stringy models

A general class of cosmological models driven by a nonlocal scalar field inspired by string field theories is studied. In particular cases the scalar field is a string dilaton or a string tachyon. A distinguished feature of these models is a crossing of the phantom divide. We reveal the nature of this phenomena showing that it is caused by an equivalence of the initial nonlocal model to a model with an infinite number of local fields some of which are ghosts. Deformations of the model that admit exact solutions are constructed. These deformations contain locking potentials that stabilize solutions. Bouncing and accelerating solutions are presented.

Cosmic acceleration and crossing of w = −1 barrier in non-local Cubic Superstring Field Theory model

We show that the rolling of the Cubic Superstring Field Theory (CSSFT) non-local tachyon in the FRW Universe leads to a cosmic acceleration with a periodic crossing of the w = −1 barrier at large time. An asymptotic solution for the tachyon field and Hubble parameter is constructed explicitly linearizing non-local equations of motion. For a small Hubble parameter a period of oscillations is a number entirely determined by parameters of the CSSFT action.

Dynamics in nonlocal linear models in the Friedmann–Robertson–Walker metric

A general class of cosmological models driven by a nonlocal scalar field inspired by string field theory is studied. Using the fact that the considering linear nonlocal model is equivalent to an infinite number of local models we have found an exact special solution of the nonlocal Friedmann equations. This solution describes a monotonically increasing universe with the phantom dark energy.

Stringy Model of Cosmological Dark Energy

A string field theory (SFT) nonlocal model of the cosmological dark energy providing w<−1 is briefly surveyed. We summarize recent developments and open problems, as well as point out some theoretical issues related with others applications of the SFT nonlocal models in cosmology, in particular, in inflation and cosmological singularity.

Analytic black branes in Lifshitz-like backgrounds and thermalization

A bstractUsing black brane solutions in 5d Lifshitz-like backgrounds with arbitrary dynamical exponent ν, we construct the Vaidya geometry, asymptoting to the Lifshitz-like spacetime, which represents a thin shell infalling at the speed of light. We apply the new Lifshitz-Vaidya background to study the thermalization process of the quark-gluon plasma via the thin shell approach previously successfully used in several backgrounds. We find that the thermalization depends on the chosen direction because of the spatial anisotropy. The plasma thermalizes thus faster in the transversal direction than in the longitudinal one. To probe the system described by the Lifshitz-like backgrounds, we also calculate the holographic entanglement entropy for the subsystems delineated along both transversal and longitudinal directions. We show that the entropy has some universality in the behavior for both subsystems. At the same time, we find that certain characteristics strongly depend on the critical exponent ν.

QGP time formation in holographic shock waves model of heavy ion collisions

We estimate the thermalization time in two colliding shock waves holographic model of heavy-ion collisions. For this purpose we model the process by the Vaidya metric with a horizon defined by the trapped surface location. We consider two bottom-up AdS/QCD models that give, within the colliding shock waves approach, the dependence of multiplicity on the energy compatible with RHIC and LHC results. One model is a bottom-up AdS/QCD confining model and the other is related to an anisotropic thermalization. We estimate the thermalization time and show that increasing the confining potential decreases the thermalization time as well as an anisotropy accelerates the thermalization.

Descent relations in cubic superstring field theory

The descent relations between string field theory (SFT) vertices are characteristic relations of the operator formulation of SFT and they provide self-consistency of this theory. The descent relations V2|V1 and V3|V1 in the NS fermionic string field theory in the κ and discrete bases are established. Different regularizations and schemes of calculations are considered and relations between them are discussed.

Holographic Wilson loops in spacetimes with spatial anisotropy

In this note we study Wilson loops in an anisotropic black brane background within the holographic framework. The anisotropy is controlled by the so called critical exponent. We calculate time-, space- and light-like static Wilson loops for different orientations of rectangular contours. The first two cases allow us to estimate behaviours of potential and pseudopotential of interquark interaction. We observe that the potential has a similar behaviour comparing to the potential for the isotropic (AdS) case, while the pseudopotential for a certain configuration of the contour has screened Coulomb and linear parts. For the light-like case we derive an analytic expression for the Nambo-Goto action for arbitrary values of the critical exponent.