Prasanta Kumar Tripathy

Geroch;s solution-generating method is extended to the case of Einstein spaces, which possess a Killing vector and are thus asymptotically (locally) (anti) de Sitter. This includes the reduction to a three-dimensional coset space, the description of the dynamics in terms of a sigma-model and its transformation properties under the SL (2, ℝ) group, and the reconstruction of new four-dimensional Einstein spaces. The detailed analysis of the space of solutions is performed using the Hamilton-Jacobi method in the instance where the three-dimensional coset space is conformal to ℝ × S2. The cosmological constant appears in this framework as a constant of motion and transforms under SL (2, ℝ).

In this paper we consider a massive vector field in the background of a space-time obtained by certain Z2 quotient of the Banados-Teitelboim-Zanelli black hole. We analyze the backreaction of the matter field on the space-time geometry up to first order in metric perturbation. The expectation value of the stress-energy tensor can be computed exactly by considering its pullback onto the covering space. Upon a suitable choice of the boundary condition on the vector field around a noncontractible cycle of the quotient manifold it is possible to obtain the average energy on a null geodesic to be negative there by resulting a traversable wormhole.

We study four dimensional non-supersymmetric attractors in type IIA string theory in the presence of sub-leading corrections to the prepotential. For a given Calabi- Yau manifold, the D0-D4 system admits an attractor point in the moduli space which is uniquely specified by the black hole charges. The perturbative corrections to the prepotential do not change the number of massless directions in the black hole effective potential. We further study non-supersymmetric D0 - D6 black holes in the presence of sub-leading corrections. In this case the space of attractor points define a hypersurface in the moduli space. © SISSA 2011.

In this paper we consider the Klebanov-Tseytlin background and its non-Abelian T-dual geometry along a suitably chosen SU(2) subgroup of isometries. We analyze the Penrose limits along various null geodesics of both geometries. We observe that the Klebanov-Tseytlin geometry does not admit any pp-wave solutions. However, the T-dual background gives rise to a pp-wave solution upon taking the Penrose limit along some appropriate null geodesic. We comment on the possible gauge theory dual for our pp-wave background.

Abstract: In this paper we study spherically symmetric single-centered attractors in (Formula presented.) supergravity in four dimensions. The attractor points are obtained by extremising the effective black hole potential in the moduli space. Both supersymmetric as well as non-supersymmetric attractors exist in mutually exclusive domains of the charge lattice. We construct axion free supersymmetric as well as non-supersymmetric multiple attractors in a simple two parameter model. We further obtain explicit examples of two distinct non-supersymmetric attractors in type IIA string theory compactified on K3 × T2 carrying D0 − D4 − D6 charges. We compute the entropy of these attractors and analyse their stability in detail.

In this paper we consider the non-Abelian T-dual geometry of the type IIB supergravity theory on AdS3×S3×T4 background along a convenient SU(2) subgroup of the SO(4) R-symmetry. We examine various null geodesics of the resulting massive type IIA supergravity theory and investigate the Penrose limits along these geodesics. We find that one of the resulting backgrounds admits pp-wave geometry in the neighborhood of a suitable null geodesic. We carry out the supersymmetry analysis of the resulting pp-wave geometry and observe that it preserves sixteen supercharges. Further we comment on the possible gauge theory dual of the resulting pp-wave background.

In this article we briefly review the attractor mechanism in the context of N= 2 supergravity theories arising from the compactification of type-. IIA string theory on a Calabi-Yau manifold. We find non-supersymmetric attractors and discuss their stability. We further discuss the generalization of the attractor mechanism to N= 2 gauged supergravity and explicitly construct configurations corresponding to Bianchi attractors. © 2014 Elsevier B.V.

We study extremal solutions arising in M-theory compactifications on Calabi-Yau threefolds, focussing on non-BPS attractors for their importance in relation to the Weak Gravity Conjecture (WGC); M2 branes wrapped on two-cycles give rise to black holes, whereas M5 branes wrapped on four-cycles result in black strings. In the low-energy/field theory limit one obtains minimal N = 2, D = 5 supergravity coupled to Abelian vector multiplets. By making use of the effective black hole potential formalism with Lagrange multipliers and of the Attractor Mechanism, we obtain the explicit expressions of the attractor moduli for BPS and non-BPS solutions, and we compute the Bekenstein-Hawking black hole entropy and the black string tension. Furthermore, by focussing on one modulus complete intersection (CICY) or toric hypersurface (THCY) Calabi-Yau threefolds, we investigate the possible non-uniqueness of the attractor solutions, as well as the stability of non-BPS black holes and black strings (restricting to doubly-extremal solutions, for simplicity’s sake). In all models taken into consideration, we find that both BPS and non-BPS extremal black hole attractors are always unique for a given, supporting electric charge configuration; moreover, non-BPS black holes are always unstable, and thus they decay into constituent BPS/anti-BPS pairs: this confirms the WGC, for which macroscopic non-supersymmetric solutions are bound to decay. For what concerns extremal black strings, it is well known they are unique in the BPS case; we confirm uniqueness also for non-BPS strings in one-modulus CICY models. On the other hand, we discover multiple non-BPS extremal black string attractors (with different tensions) in most of the one-modulus THCY models, and we determine the corresponding magnetic configurations supporting them; this indicates the existence of volume-minimizing representatives in the same homology class having different values of their local minimal volume. Moreover, we find that non-BPS (doubly-) extremal black strings, both for single and multiple solutions, are kinematically stable against decay into their constituent BPS/anti-BPS pairs; in Calabi-Yau geometry, this means that the volume of the representative corresponding to the black string is less than the volume of the minimal piecewise-holomorphic representative, predicting recombination for those homology classes and thus leading to stable, non-BPS string solutions, which for the WGC are microscopic with small charges.

In this paper, we analyse the stability of extremal black brane horizons with homogeneous symmetry in the spatial directions in five dimensional gauged supergravity, under the fluctuations of the scalar fields about their attractor values. We examine the scalar fluctuation equations at the linearised level and demand that the fluctuations vanish as one approaches the horizon. Imposing certain restrictions on the Killing vectors used for gauging we find that the necessary conditions for stability are satisfied only by a subclass of the Bianchi metrics whose symmetry group factorises into a two dimensional Lifshitz symmetry and any homogeneous symmetry group given by the Bianchi classification. We apply these results to a simple example of a gauged supergravity model with one vector multiplet to find the stable attractors.

We study non-supersymmetric attractors obtained in Type IIA compactifications on Calabi Yau manifolds. Determining if an attractor is stable or unstable requires an algebraically complicated analysis in general. We show using group theoretic techniques that this analysis can be considerably simplified and can be reduced to solving a simple example like the STU model. For attractors with DO -DA brane charges, determining stability requires expanding the effective potential to quartic order in the massless fields. We obtain the full set of these terms. For attractors with DO -D6 brane charges, we find that there is a moduli space of solutions and the resulting attractors are stable. Our analysis is restricted to the two derivative action. © SISSA 2007.