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Sheikh Shajidul Haque

Publications and source records attributed to Sheikh Shajidul Haque.

7 recordsLinked to original sources
arXiv2013

Cosmology or Catastrophe? A non-minimally coupled scalar in an inhomogeneous universe

A non-minimally coupled scalar field can have, in principle, a negative effective Planck mass squared which depends on the scalar field. Surprisingly, an isotropic and homogeneous cosmological universe with a non-minimally coupled scalar field is perfectly smooth as the rolling scalar field causes the effective Planck mass to change sign and pass through zero. However, we show that any small deviations from homogeneity diverge as the effective Planck mass vanishes, with catastrophic consequences for the cosmology. The physical origin of the divergence is due to the presence of non-zero scalar anisotropic stress from the non-minimally coupled scalar field. Thus, while the homogeneous and isotropic cosmology appears surprisingly sensible when the effective Planck mass vanishes, inhomogeneities tell a different story.

hep-th↗
arXiv2010

Towards Classical de Sitter Solutions in String Theory

We investigate the type II string effective potential at tree-level and derive necessary ingredients for having de Sitter solutions in orientifold models with fluxes. Furthermore, we examine some explicit O6 compactifications in IIA supergravity on manifolds with SU(3)-structure in the limit where the orientifold sources are smeared. In particular, we use a simple ten-dimensional Ansatz for four-dimensional de Sitter solutions and find the explicit criteria in terms of the torsion classes such that these de Sitter solutions solve the equations of motion. We have verified these torsion conditions for the cosets and the Iwasawa manifold and it turns out that the conditions cannot be fulfilled for these spaces. However, this investigation allows us to find new non-supersymmetric AdS solutions for some cosets. It remains an open question whether there exist SU(3)-structure manifolds that satisfy the conditions on the torsion classes for these simple de Sitter solutions to exist.

hep-th↗
arXiv2009

Mass-spin relation for quark anti-quark bound states in non-commutative Yang-Mills theory

We investigate the relationship between mass and spin of quark anti-quark bound state in non-commutative gauge theory with N=4 supersymmetry. In the large N and large 't Hooft coupling limit, these bound states correspond to rotating open strings ending on a D-brane embedded into the supergravity background dual of the non-commutative field theory. Although the physical configuration of the open strings are drastically deformed by the non-commutativity, we find that the relation between the energy and the angular momentum of the bound state is unaffected by the non-commutativity parameter. We also clarify the holographic interpretation of quark anti-quark potential in non-commutative gauge theories.

hep-th↗
arXiv2009

Minimal Simple de Sitter Solutions

We show that the minimal set of necessary ingredients to construct explicit, four-dimensional de Sitter solutions from IIA string theory at tree-level are O6-planes, non-zero Romans mass parameter, form fluxes, and negative internal curvature. To illustrate our general results, we construct such minimal simple de Sitter solutions from an orientifold compactification of compact hyperbolic spaces. In this case there are only two moduli and we demonstrate that they are stabilized to a sufficiently weakly coupled and large volume regime. We also discuss generalizations of the scenario to more general metric flux constructions.

hep-th↗
arXiv2008

Microscopic Formulation of Puff Field Theory

We describe a generalization of Puff Field Theory to p+1 dimensions where 0 \le p \le 5. We then focus on the case of p=0, ``Puff Quantum Mechanics,'' and construct a formulation independent of string theory.

hep-th↗