Sanjay Siwach

Spin 3/2 baryons and form factors in AdS/QCD

We study the 5D Rarita-Schwinger fields to describe spin 3/2 baryons in AdS/QCD. We calculate the spectrum of spin 3/2 baryons ({delta} resonances) and their form factors, together with meson-baryon couplings from AdS/QCD. The transition form factors between {delta} and nucleon are evaluated. Both pion and rho meson couplings have the same origin in the bulk and hence are unified. The numerical values for the meson-baryon transition couplings are roughly consistent with the values obtained from other methods. We also predict the numerical values of some new couplings associated with {delta} resonances.

The electric dipole moment of the nucleons in holographic QCD

We introduce the strong CP-violation in the framework of AdS/QCD model and calculate the electric dipole moments of nucleons as well as the CP-violating pion-nucleon coupling. Our holographic estimate of the electric dipole moments gives for the neutron dn = 1.08 × 10−16 e⋅cm , which is comparable with previous estimates. We also predict that the electric dipole moment of the proton should be precisely the minus of the neutron electric dipole moment, thus leading to a new sum rule on the electric dipole moments of baryons.

1 / 2 BPS geometries of M2 giant gravitons

We construct the general 1/2 BPS M2 giant graviton solutions asymptotic to the 11-dimensional maximally supersymmetric plane-wave background, based on the recent work of Lin, Lunin, and Maldacena. The solutions have null singularity and we argue that it is unavoidable to have null singularity in the proposed framework, although the solutions are still physically relevant. They involve an arbitrary function F(x) which is shown to have a correspondence to the 1/2 BPS states of the Berenstein-Maldacena-Nastase (BMN) matrix model. A detailed map between the 1/2 BPS states of both sides is worked out.

Time-dependent supergravity solutions in null dilaton background

Abstract A class of time dependent pp-waves with NS–NS flux in type IIA string theory is considered. The background preserves 1/4 supersymmetry and may provide a toy model of Big Bang cosmology with nontrivial flux. At the Big Bang singularity in early past, the string theory is strongly coupled and matrix string model can be used to describe the dynamics. We also construct some time dependent supergravity solutions for D-branes and analyze their supersymmetry properties.

Deformed conformal and super-Poincaré symmetries in the non-(anti-) commutative spaces

Generators of the super-Poincaré algebra in the non- (anti-) commutative superspace are represented using appropriate higher derivative operators defined in this quantum superspace. Also discussed are the analogous representations of the conformal and superconformal symmetry generators in the deformed spaces. This construction is obtained by generalizing the recent work of Wess et al. on the Poincaré generators in the θ-deformed Minkowski space, or by using the substitution rules we derived on the basis of the phase-space structures of non- (anti-) commutative-space variables. Even with the non-zero deformation parameters the algebras remain unchanged although the comultiplication rules are deformed. The transformation of the fields under deformed symmetry is also discussed. Our construction can be used for systematic development of field theories in the deformed spaces.

Brane solutions with/without rotation in pp-wave spacetime

Abstract We present two classes of brane solutions in pp-wave spacetime. The first class of branes with a rotation parameter are constructed in an exact string background with NS–NS and R–R flux. The spacetime supersymmetry is analyzed by solving the standard Killing spinor equations and is shown to preserve the same amount of supersymmetry as the case without the rotation. This class of branes do not admit regular horizon. The second class of brane solutions are constructed by applying a null Melvin twist to the brane solutions of flat spacetime supergravity. These solutions admit regular horizon. We also comment on some thermodynamic properties of this class of solutions.

THERMODYNAMICS OF SOFT WALL AdS/QCD AT FINITE CHEMICAL POTENTIAL

We study the thermodynamics of soft wall model in AdS/QCD framework. The low temperature phase of QCD is described by thermal AdS and high temperature phase by AdS black hole solution of five-dimensional gravity with negative cosmological constant. The chemical potential is introduced via the solution of U(1) vector field in the bulk. The difference of action densities in two phases is studied and the results are compared with hard wall model. The quark number susceptibility is also calculated in both models.

DC conductivity with external magnetic field in hyperscaling violating geometry

We investigate the holographic dc conductivity of (2+1) dimensional systems while considering hyperscaling violating geometry in the bulk. We consider Einstein-Maxwell-Dilaton system with two gauge fields and Liouville type potential for dilaton. We also consider axionic fields in the bulk in order to introduce momentum relaxation in the system. We apply an external magnetic field to study the response of the system and obtain analytic expressions for dc conductivity, Hall angle and (thermo)electric conductivity.

ON ATTRACTOR FLOW AND SMALL BLACK HOLES

We study the attractor flow and near horizon geometry of two-charge small black holes in heterotic string theory. The Hessian of Sens entropy function with respect to the moduli fields has standard attractor properties and shows the interesting factorization at the attractor fixed points. We notice that the stability conditions are preserved under arbitrary α′-corrections to the black hole solutions.

RG flow of AC conductivity in soft wall model of QCD

We study the Renormalization Group (RG) flow of AC conductivity in soft wall model of holographic QCD. We consider the charged black hole metric and the explicit form of AC conductivity is obtained at the cut-off surface. We plot the numerical solution of conductivity flow as a function of radial co-ordinate. The equation of gauge field is also considered and the numerical solution is obtained for AC conductivity as a function of frequency. The results for AC conductivity are also obtained for different values of chemical potential and Gauss-Bonnet couplings.