Supriya Kar

Tunneling between de Sitter and anti de Sitter black holes in a noncommutative D 3 -brane formalism

We obtain de Sitter (dS) and anti-de Sitter (AdS) generalized Reissner-Nordstrom\char21{}like black hole geometries in a curved

Brane production and the neutrino nucleon cross-section at ultrahigh-energies in low scale gravity models

{\mathrm{D}}_{3}

BLACK HOLE GEOMETRIES IN NONCOMMUTATIVE STRING THEORY

-brane framework, underlying a noncommutative gauge theory on the brane world. The noncommutative scaling limit is explored to investigate a possible tunneling of an AdS vacuum in string theory to dS vacuum in its low energy gravity theory. The Hagedorn transition is invoked into its self-dual gauge theory to decouple the gauge nonlinearity from the dS geometry, which in turn is shown to describe a pure dS vacuum.

Discrete torsion, de Sitter tunneling vacua and AdS brane: U(1) gauge theory on D4-brane and an effective curvature

The observed ultrahigh energy cosmic rays (UHECR) might require a modification of the basic laws of physics. In low scale gravity models, where the neutrino–nucleon cross section rises to typical hadronic values at energies above 1020 eV, the neutrino becomes a candidate for the primary that initiates these showers. We calculate the neutrino–nucleon cross section at ultrahigh energies by assuming that it is dominated by the production of p-branes. We show, using a generalized Randall–Sundrum model, that the neutrino–nucleon cross-section at neutrino energies of 1020 eV is of the order of 100 mb, which is required for explaining the UHECR events. Similar results also follow in other models such as the Lykken–Randall model.

Noncommutative brane-world, (Anti) de Sitter vacua and extra dimensions

We obtain a generalized Schwarzschild (GS) and a generalized Reissner–Nordstrom (GRN) black hole geometries in 3+1 dimensions, in a noncommutative string theory. In particular, we consider an effective theory of gravity on a curved D3-brane in presence of an electromagnetic (EM) field. Two different length scales, inherent in its noncommutative counterpart, are exploited to obtain a theory of effective gravity coupled to an U(1) noncommutative gauge theory to all orders in Θ. It is shown that the GRN-black hole geometry, in the Planckian regime, reduces to the GS-black hole. However in the classical regime it may be seen to govern both the Reissner–Nordstrom and the Schwarzschild geometries. The emerging notion of 2D black holes evident in the framework are analyzed. It is argued that the D-string in the theory may be described by the near horizon 2D black hole geometry, in the gravity decoupling limit. Finally, our analysis explains the nature of the effective force derived from the nonlinear EM-field and accounts for the Hawking radiation phenomenon in the formalism.

D-branes and twelve dimensions

A bstractThe U(1) gauge dynamics on a D4-brane is revisited, with a two form, to construct an effective curvature theory in a second order formalism. We exploit the local degrees in a two form, and modify its dynamics in a gauge invariant way, to incorporate a non-perturbative metric fluctuation in an effective D4-brane. Interestingly, the near horizon D4-brane is shown to describe an asymptotic Anti de Sitter (AdS) in a semi-classical regime. Using Weyl scaling(s), we obtain the emergent rotating geometries leading to primordial de Sitter (dS) and AdS vacua in a quantum regime. Under a discrete transformation, we re-arrange the mixed dS patches to describe a Schwazschild-like dS (SdS) and a topological-like dS (TdS) black holes. We analyze SdS vacuum for Hawking radiations to arrive at Nariai geometry, where a discrete torsion forms a condensate. We perform thermal analysis to identify Nariai vacuum with a TdS. Investigation reveals an AdS patch within a thermal dS brane, which may provide a clue to unfold dS/CFT. In addition, the role of dark energy, sourced by a discrete torsion, in the dS vacua is investigated using Painleve geometries. It is argued that a D-instanton pair is created by a discrete torsion, with a Big Bang/Crunch, at the past horizon in a pure dS. Nucleation, of brane/anti-brane pair(s), is qualitatively analyzed to construct an effective space-time on a D4-brane and its anti brane. Analysis re-assures the significant role played by a non-zero mode, of NS-NS two form, to generalize the notion of branes within a brane.

S duality and cosmological constant in string theory

We investigate a curved brane-world, inspired by a noncommutative D3-brane, in a type IIB string theory. We obtain, an axially symmetric and a spherically symmetric, (anti) de Sitter black holes in 4D. The event horizons of these black holes possess a constant curvature and may be seen to be governed by different topologies. The extremal geometries are explored, using the noncommutative scaling in the theory, to reassure the attractor behavior at the black hole event horizon. The emerging two dimensional, semi-classical, black hole is analyzed to provide evidence for the extra dimensions in a curved brane-world. It is argued that the gauge nonlinearity in the theory may be redefined by a potential in a moduli space. As a result, D=11 and D=12 dimensional geometries may be obtained at the stable extrema of the potential.

Quantum Kerr tunneling vacua on a

We study the D-brane solutions to a type IIB superstring in ten dimensions and find an interpretation in terms of the compactification of a twelve-dimensional three-brane of (a specific) F-theory on torus T2. In this framework, there also exists a two-brane which may be argued to be equivalent to the three-brane by utilizing the electric-magnetic duality in eleven dimensions. In this context, we propose the existence of an isometry in one of the transverse directions to the three-brane in F-theory. As a consequence the two-brane may be identified with the three-brane in twelve dimensions. The twelve-dimensional picture of D-branes in type IIB theory suggests the reformulation of the type IIB superstring in terms of the three-brane of F-theory.

(D{\bar D})_4

Abstract The S -duality invariance of the equations of motion of four dimensional string effective action with cosmological constant, Λ, is studied. It is demonstrated that the S -duality symmetry of the field equations are broken for nonzero Λ. The “naturalness” hypothesis is invoked to argue that Λ should remain small since exact S -duality symmetry will force the cosmological constant to vanish in the string effective action.

-brane: An emergent Kerr black hole in five dimensions

Abstract A non-perturbation formalism underlying a quantum theory of gravity is revisited by exploiting a two form in a non-linear U ( 1 ) gauge theory on a D 4 -brane. In particular, we explore two different gauge choices for a two form underlying the dynamics of a higher dimensional geometric torsion in a second order formalism. We obtain two non-extremal quantum Kerr geometries in five dimensions on a pair of ( D D ¯ ) 4 -brane in a type IIA superstring theory. In the gauge choice, the quantum vacua may seen to underlie a non-propagating torsion on a non-BPS brane. It is argued that the quantum Kerr vacua undergo tunneling and lead to a five dimensional Einstein Kerr black hole in a low energy limit.