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.
We investigate the impacts of interaction between dark matter and dark energy in the context of two dark energy models, holographic and ghost dark energy. In fact, using the dynamical system analysis, we obtain the cosmological consequence of several interactions, considering all relevant component of universe, i.e. matter (Dark and luminous), radiation and dark energy. Studying the phase space for all interactions in detail, we show the existence of unstable matter dominated and stable dark energy dominated phases. We also show that linear interactions suffer from the absence of standard radiation dominated epoch. Interestingly, this failure resolved by adding the non-linear interactions to the models. We find an upper bound for the value of the coupling constant of the interaction between dark matter and dark energy as b < 0.57 in the case of holographic model, and b < 0.61 in the case of ghost dark energy model, to result in a cosmological viable matter dominated epoch. More specifically, this bound is vital to satisfy instability and deceleration of matter dominated epoch.
In this paper we investigate ghost dark energy model in the presence of non-linear interaction between dark energy and dark matter. We also extend the analysis to the so called generalized ghost dark energy (GGDE) which ρ D = αH +βH 2 . The model contains three free parameters as Ω D , ζ(= ) and b 2 (the coupling coefficient of interactions). We propose three kinds of non-linear interaction terms and discuss the behavior of equation of state, deceleration and dark energy density parameters of the model. We also find the squared sound speed and search for signs of stability of the model. To compare the interacting GGDE model with observational data sets, we use more recent observational outcomes, namely SNIa from JLA catalog, Hubble parameter, baryonic acoustic oscillation and the most relevant CMB parameters including, the position of acoustic peaks, shift parameters and redshift to recombination. For GGDE with the first non-linear interaction, the joint analysis indicates that Ω D = 0.7192 ± 0.0062, b 2 = 0.146
In this paper, we check the universality of the entropy product for some black hole and black ring solutions. Applying the asymptotic symmetry group (ASG) analysis, we also find the central charges of the dual CFTs for these solutions. It has been observed [16] that if the entropy product for a solution is universal, it is possible to read the central charges of the dual CFTs from the entropy product as cwhere N i is a conserved charge of the solution like angular momentum or electric charge. In this work we consider some other families of solutions and we check that the same behavior is valid for them. Moreover, in the case of solutions containing the conical singularity, we find the central charges using the ASG analysis. We show that the central charges receive a contribution from the conical characteristic κ of the solution, however it is still possible to read the central charges from the entropy product.
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