60 research outputs found
On the generalized minimal massive gravity
No full textIn this paper we study the Generalized Minimal Massive Gravity (GMMG) in asymptotically AdS3 background. The generalized minimal massive gravity theory is realized by adding the CS deformation term, the higher derivative deformation term, and an extra term to pure Einstein gravity with a negative cosmological constant. We study the linearized excitations around the AdS3 background and find that at special point (tricritical) in parameter space the two massive graviton solutions become massless and they are replaced by two solutions with logarithmic and logarithmic-squared boundary behavior. So it is natural to propose that GMMG model could also provide a holographic description for a 3-rank Logarithmic Conformal Field Theory (LCFT). We calculate the energy of the linearized gravitons in AdS3 background, and show that the theory is free of negative-energy bulk modes. Then we obtain the central charges of the CFT dual explicitly and show GMMG also avoids the aforementioned “bulk-boundary unitarity clash”. After that we show that General Zwei–Dreibein Gravity (GZDG) model can reduce to GMMG model. Finally by a Hamiltonian analysis we show that the GMMG model has no Boulware–Deser ghosts and this model propagates only two physical modes
The Heisenberg algebra as near horizon symmetry of the black flower solutions of Chern–Simons-like theories of gravity
No full textAbstractIn this paper we study the near horizon symmetry algebra of the non-extremal black hole solutions of the Chern–Simons-like theories of gravity, which are stationary but are not necessarily spherically symmetric. We define the extended off-shell ADT current which is an extension of the generalized ADT current. We use the extended off-shell ADT current to define quasi-local conserved charges such that they are conserved for Killing vectors and asymptotically Killing vectors which depend on dynamical fields of the considered theory. We apply this formalism to the Generalized Minimal Massive Gravity (GMMG) and obtain conserved charges of a spacetime which describes near horizon geometry of non-extremal black holes. Eventually, we find the algebra of conserved charges in Fourier modes. It is interesting that, similar to the Einstein gravity in the presence of negative cosmological constant, for the GMMG model also we obtain the Heisenberg algebra as the near horizon symmetry algebra of the black flower solutions. Also the vacuum state and all descendants of the vacuum have the same energy. Thus these zero energy excitations on the horizon appear as soft hairs on the black hole
Black hole entropy in the Chern–Simons-like theories of gravity and Lorentz-diffeomorphism Noether charge
No full textAbstractIn the first order formalism of gravity theories, there are some theories which are not Lorentz-diffeomorphism covariant. In the framework of such theories we cannot apply the method of conserved charge calculation used in Lorentz-diffeomorphism covariant theories. In this paper we firstly introduce the total variation of a quantity due to an infinitesimal Lorentz-diffeomorphism transformation. Secondly, in order to obtain the conserved charges of Lorentz-diffeomorphism non-covariant theories, we extend the Tachikawa method [1]. This extension includes not only Lorentz gauge transformation but also the diffeomorphism. We apply this method to the Chern–Simons-like theories of gravity (CSLTG) and obtain a general formula for the entropy of black holes in those theories. Finally, some examples on CSLTG are provided and the entropy of the BTZ black hole is calculated in the context of the examples
Visualizing the Intellectual Structure of Iranian Physicists in Scisearch during 1990-2009: An Author Co-Citation Analysis (ACA)
No full textThe purpose of this paper was to study and map the intellectual structure of Iranian physicists using author co-citation technique during 1990-2009. The results of the study showed that Iranian physicists have produced 6290 documents indexed in Science Citation Index (SciSearch) during the studied period. Publication counts have grown at an approximate rate of 24/70 % per year. Setare M.R. with 121 documents was the most productive Iranian author in this study. Applied Physics, with1564 documents was the most interesting subject area for the Iranian physicists. We identified 42 Iranian and international physicists who were highly co-cited in 6290 documents during the studied period. Using principal components analysis, 8 subject factors were extracted. The subject areas of factors were in: "Physics, Particles & Fields", "Astronomy & Astrophysics", “Physics, Mathematical", “Physics, Multidisciplinary", "Physics, Nuclear", "Cosmology", "Physics, Atomic, Molecular & Chemical", and "Physics, Fluids & Plasmas". The PFNet map of the intellectual structure of Iranian physicists in SciSearch during 1990-2009 showed a central subject area in "Physics, Particles & Field" with Witten E. as its focal author. The other clusters were rooted in this essential cluster
Surface vacuum energy and stresses for a brane in de Sitter spacetime
No full textAbstractVacuum expectation values of the surface energy–momentum tensor is investigated for a massless scalar field obeying mixed boundary condition on a brane in de Sitter bulk. To generate the corresponding vacuum surface densities we use the conformal relation between de Sitter and Rindler spacetimes
Generalized second law of thermodynamics in quintom dominated universe
No full textAbstractIn this Letter we will investigate the validity of the generalized second law of thermodynamics for the quintom model of dark energy. Reviewing briefly the quintom scenario of dark energy, we will study the conditions of validity of the generalized second law of thermodynamics in three cases: quintessence dominated, phantom dominated and transition from quintessence to phantom will be discussed
Bouncing cosmological solutions due to the self-gravitational corrections and their stability
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