No abstract

We have examined the momentum expansion of the disk level S-matrix element of two tachyons and two gauge fields to find, up to on-shell ambiguity, the couplings of these fields in the world volume theory of N coincident non-BPS D-branes to all order of $\alpha'$. Using the proposal that the action of D-brane-anti-D-brane is given by the projection of the action of two non-BPS D-branes with $(-1)^{F_L}$, we find the corresponding couplings in the world volume theory of the brane-anti-brane system. Using these infinite tower of couplings, we then calculate the massless pole of the scattering amplitude of one RR field, two tachyons and one gauge field in the brane-anti-brane theory. We find that the massless pole of the field theory amplitude is exactly equal to the massless pole of the disk level S-matrix element of one RR, two tachyons and one gauge field to all order of $\alpha'$.Comment: 22 pages, 1 figure, latex file, V2: minor change in notatio

In this paper we study traversable wormholes in the context of f (R) gravity. Exact solutions of traversable wormholes are found by imposing the nonconstant Ricci scalar. These solutions asymptotically match spherical, flat and hyperbolic FRW metric. By choosing some static f (R) gravity models, we verify the standard energy conditions for the asymptotically spherical, flat and hyperbolic wormhole solutions. Unlike the Einstein gravity, we find that in the context of f (R) modified gravity, the asymptotically spherical, flat and hyperbolic wormhole solutions can respect the null energy condition (NEC) at the wormhole throat and near that. We find that in some static f (R) models, asymptotically flat and hyperbolic wormholes respect the weak energy condition (WEC) through the whole space.

In this paper we continue our analysis of arXiv:1308.1478 and study in detail the parameter space of three families of doubly spinning black ring solutions: balanced black ring, unbalanced ring and dipole-charged balanced black rings. In all these three families the Extremal Vanishing Horizon (EVH) ring appears in the vanishing limit of the dimensionful parameter of the solution which measures the ring size. We study the near horizon limit of the EVH black rings and for all three cases we find a (pinching orbifold) AdS 3 throat with the AdS 3 radius ℓ 2 = 8G 5 M/(3π) where M is the ring mass and G 5 is the 5d Newton constant. We also discuss the near horizon limit of near-EVH black rings and show that the AdS 3 factor is replaced with a generic BTZ black hole. We use these results to extend the EVH/CFT correspondence for black rings, a 2d CFT dual to near-EVH black rings.

It has been observed that the area product of horizons for many black hole solutions is mass independent and satisfy the universality relation A + A − = (8π) 2 N , where N is related to the quantized charges of the solution as angular momentum and electric charge. In this work the same analysis is done for black hole and black ring solutions with conical singularity. We find that the area product is still mass independent and regardless of the horizon topology, the conical characteristic (κ) of the solutions, appears in the universality relation as κA + A − = (8π) 2 N . We also check that the first law of black hole inner mechanics is satisfied for these solutions.