Domain Walls in AdS-Einstein-scalar Gravity

In this note, we will show that the supergravity theory which is dual to ABJM field theory can be consistently reduced to scalar-coupled AdS-Einstein gravity and then consider the reflection symmetric domain wall and its small fluctuation. This domain wall solution is none other than dimensional reduction of M2-brane configuration.Comment: 14 pages, v2: minor change

Pulsating Strings in Deformed Backgrounds

This is a brief summary on pulsating strings in beta deformed backgrounds found recently.Comment: 8 pages. Talk presented at Quantum Theory and Symmetries 7, Prague, August 7-13, 201

Inhomogeneous tachyon condensation

We investigate the spacetime-dependent condensation of the tachyon in effective field theories. Previous work identified singularities in the field which appear in finite time: infinite gradients at the kinks, and (in the eikonal approximation) caustics near local minima. By performing a perturbation analysis, and with numerical simulations, we demonstrate and explain key features of the condensation process: perturbations generically freeze, and minima develop singular second derivatives in finite time (caustics). This last has previously been understood in terms of the eikonal approximation to the dynamics. We show explicitly from the field equations how this approximation emerges, and how the caustics develop, both in the DBI and BSFT effective actions. We also investigate the equation of state parameter of tachyon matter showing that it is small, but generically non-zero. The energy density tends to infinity near field minima with a charateristic profile. A proposal to regulate infinities by modifying the effective action is also studied. We find that although the infinities at the kinks are successfully regularised in the time-dependent case, caustics still present.Comment: 4 figures,19p

Dual Spikes; New Spiky String Solutions

We find a new class of spiky solutions for closed strings in flat, $AdS_3\subset AdS_5$ and $R\times S^2(\subset S^5)$ backgrounds. In the flat case the new solutions turn out to be T-dual configurations of spiky strings found by Kruczenski hep-th/0410226. In the case of solutions living in $AdS$, we make a semi classical analysis by taking the large angular momentum limit. The anomalous dimension for these dual spikes is similar to that for rotating and pulsating circular strings in AdS with angular momentum playing the role of the level number. This replaces the well known logarithmic dependence for spinning strings. For the dual spikes living on sphere we find that no large angular momentum limit exists.Comment: Added reference

D-Brane Effective Actions and Particle Production near the Beginning of the Tachyon Condensation

In this paper we will study the quantum field theory of fluctuation modes around the classical solution that describes tachyon condensation on unstable D-brane.We will calculate the number of particle produced near the beginning of the rolling tachyon process. We will perform this calculation for different tachyon effective actions and we will find that the rate of the particle production strongly depends on the form of the effective action used for the description of the early stage of the tachyon condensation.Comment: 21 page

On open superstring partition function in inhomogeneous rolling tachyon background

We consider open superstring partition function Z on the disc in time-dependent tachyon background T= f(x_i) e^{m x_0} where the profile function f depends on spatial coordinates. We compute Z to second order in derivatives of f and compare the result with some previously suggested effective actions depending only on the first derivatives of the tachyon field. We also compute the target-space stress-energy tensor in this background and demonstrate its conservation in the ``on-shell'' case of the linear profile f= f_0 + q_i x_i corresponding to a marginal perturbation. We comment on the role of the rolling tachyon with linear spatial profile in the decay of an unstable D-brane.Comment: 32p, latex, v2: introduction revised to expand and correct comments on the paper by Kutasov and Niarchos, v3: corrected typos and formulas in section 4, final version to appear in JHE

Pulsating Strings in Lunin-Maldacena Backgrounds

We consider pulsating strings in Lunin-Maldacena backgrounds, specifically in deformed Minkowski spacetime and deformed AdS_5xS^5. We find the relation between the energy and the oscillation number of the pulsating string when the deformation is small. Since the oscillation number is an adiabatic invariant it can be used to explore the regime of highly excited string states. We then quantize the string and look for such a sector. For the deformed Minkowski background we find a precise match with the classical results if the oscillation number is quantized as an even number. For the deformed AdS_5xS^5 we find a contribution which depends on the deformation parameter.Comment: 16 pages, 2 figures, typos fixe

Bosonic D-brane Effective Action in Linear Dilaton Background

In this paper we will study tachyon effective action for Dp-brane in bosonic string theory in the linear dilaton background. We obtain the tachyon effective Lagrangian from boundary state coeficient of Dp-brane in the linear dilaton background and compare it with tachyon effective Lagrangians that were proposed in previous papers.Comment: 16 pages, Typos correcte

A Toy Model of Closed String Tachyon Effective Action

In this paper we propose the toy model of the closed string tachyon effective action that has marginal tachyon profile as its exact solution in case of constant or linear dilaton background. Then we will apply this model for description of two dimensional bosonic string theory. We will find that the background configuration with the spatial dependent linear dilaton, flat spacetime metric and marginal tachyon profile is the exact solution of our model even if we take into account backreaction of tachyon on dilaton and metric.Comment: 17 page

On the pulsating strings in AdS_5 x T^{1,1}

We study the class of pulsating strings in AdS_5 x T^{1,1}. Using a generalized ansatz for pulsating string configurations we find new solutions of this class. Further we semiclassically quantize the theory and obtain the first correction to the energy. The latter, due to AdS/CFT correspondence, is supposed to give the anomalous dimensions of operators in the dual N=1 superconformal gauge field theory.Comment: 12 pages, improvements made, references adde