Radoslav Rashkov

Flavoured large N gauge theory in an external magnetic field

We consider a D7-brane probe of AdS5 × S5 in the presence of pure gauge B-field. In the dual gauge theory, the B-field couples to the fundamental matter introduced by the D7-brane and acts as an external magnetic field. The B-field supports a 6-form Ramond-Ramond potential on the D7-branes world volume that breaks the supersymmetry and enables the dual gauge theory to develop a non-zero fermionic condensate. We explore the dependence of the fermionic condensate on the bare quark mass mq and show that at zero bare quark mass a chiral symmetry is spontaneously broken. A study of the meson spectrum reveals a coupling between the vector and scalar modes, and in the limit of weak magnetic field we observe Zeeman splitting of the states. We also observe the characteristic √mq dependence of the ground state corresponding to the Goldstone boson of spontaneously broken chiral symmetry.

Dp-brane tension from tachyons and aBfield in vacuum string field theory

We consider tachyonic string-field fluctuations about a Dp-brane background in the geometrical (CFT) formulation of Vacuum String Field Theory. We then extend this analysis to the case of a background B-field. We find that the standard results for D-brane tension are reproduced in both cases.

Semiclassical analysis of string-gauge duality on noncommutative space

We use semiclassical methods to study closed strings in the modified AdS{sub 5}xS{sup 5} background with constant B fields. The pointlike closed strings and the stretched closed strings rotating around the big circle of S{sup 5} are considered. Quantization of these closed string leads to a time-dependent string spectrum, which we argue corresponds to the renormalization-group flow of the dual noncommutative Yang-Mills theory.

Entanglement entropy and Fisher information metric for closed bosonic strings in homogeneous plane wave background

We derive the extended renormalized entanglement entropy (EREE) and the Fisher information metric in the case of closed bosonic strings in homogeneous plane wave background. Our investigations are conducted within the framework of Thermo Field Dynamics (TFD). The formalism is also illustrated on the example of some particular models in condensed matter physics and the non-equilibrium case for system with dissipations.