Mikhail Z. Iofa

Cosmological constraints on parameters of one-brane models with extra dimension

We study some aspects of cosmologies in 5D models with one infinite extra dimension. Matter is confined to the brane, gravity extends to the bulk. Models with positive and negative tension of the brane are considered. Cosmological evolution of the 4D world is described by warped solutions of the generalized Friedmann equation. Cosmological solutions on the brane are obtained with the input of the present-time observational cosmological parameters. We estimate the age of the Universe and abundance of

Statistical entropy of Calabi-Yau black holes

{}^4 He

CONNECTION BETWEEN TWO FORMS OF EXTRA DIMENSIONAL METRIC REVISITED

produced in primordial nucleosynthesis in different models. Using these estimates we find constraints on dimensionless combinations of the 5D gravitational scale, scale of the warp factor and coupling at the 4D curvature term in the action.We study some aspects of cosmologies in 5D models with one infinite extra dimension. Matter is confined to the brane, gravity extends to the bulk. Models with positive and negative tension of the brane are considered. Cosmological evolution of the 4D world is described by warped solutions of the generalized Friedmann equation. Cosmological solutions on the brane are obtained with the input of the present-time observational cosmological parameters. We estimate the age of the Universe and abundance of 4He produced in primordial nucleosynthesis in different models. Using these estimates we find constraints on dimensionless combinations of the 5D gravitational scale, scale of the warp factor and coupling at the 4D curvature term in the action.

BOUNCE OF GRAVITONS EMITTED FROM THE BRANE TO THE BULK BACK TO THE BRANE

We computed the statistical entropy of nonextremal 4D and extremal 5D Calabi-Yau black holes and found exact agreement with the Bekenstein-Hawking entropy. The computation is based on the fact that the near-horizon geometry of equivalent representations contains as a factor the Ba\~nados-Teitelboim-Zanelli black hole and on subsequent use of Stromingers proposal generalizing the statistical count of microstates of the BTZ black hole due to Carlip.

Graviton emission from the brane in the bulk in a model with extra dimension

5D cosmological model with 3-brane with matter is considered. The brane divides the bulk in two AdS half-spaces. Geometry of the model can be described by two types of coordinate systems: in the first setting the metric is static and the brane is moving in the bulk, in the second approach the metric is time-dependent and the brane is located at a fixed position in the bulk. Coordinate transformation connecting two coordinate systems is constructed.

CONSTRAINTS ON PARAMETERS OF MODELS WITH EXTRA DIMENSION FROM PRIMORDIAL NUCLEOSYNTHESIS

Solutions of geodesic equations describing propagation of gravitons in the bulk are studied in a cosmological model with one extra dimension. Brane with matter is embedded in the bulk. It is shown that in the period of early cosmology gravitons emitted from the brane to the bulk under certain conditions can return back to the brane. The model is discussed in two alternative approaches: (i) brane with static metric moving in the AdS space, and (ii) brane located at a fixed position in extra dimension with nonstatic metric. Transformation of coordinates from the one picture to another is performed. In both approaches, conditions for gravitons emitted to the bulk to come back to the brane are found.

N=2 SUPERSYMMETRY AND STRING-LOOP CORRECTED MAGNETIC BLACK HOLES

In a model of 3-brane embedded in 5D space-time we calculate the graviton emission from the brane to the bulk. Matter is confined to the brane, gravitons produced in reactions of matter on the brane escape to the bulk. The Einstein equations which are modified by the terms due to graviton production are solved perturbatively, the leading order being that without the graviton production. In the period of late cosmology, in which in the generalized Friedmann equation the term linear in the energy density of matter is dominant, we calculate the spectrum of gravitons (of the tower of Kaluza-Klein states) and the collision integral in the Boltzmann equation. We find the energy-momentum tensor of the emitted gravitons in the bulk, and using it show that corrections due to graviton production to the leading-order terms in the Einstein equations are small, and the perturbative approach is justified. We calculate the difference of abundances of 4He produced in primordial nucleosynthesis in the models with and without the graviton production, and find that the difference is a very small number, much smaller than that estimated previously.

STATISTICAL ENTROPY OF MAGNETIC BLACK HOLES FROM NEAR-HORIZON GEOMETRY

5D models with one 3D brane and one infinite extra dimension are studied. Matter is confined to the brane, gravity extends to the bulk. Models with positive and negative tension of the brane are studied. Cosmological solutions on the brane are obtained by solving the generalized Friedmann equation. As the input in cosmological solutions we use the present-time observational cosmological parameters. We find constraints on dimensionless combinations of scales of 5D models which follow from the requirement that the models reproduce the data on production of 4He in primordial nucleosynthesis.

Thermal Hawking radiation of black hole with supertranslation field

We study string-loop corrections to magnetic black hole. Four-dimensional theory is obtained by compactification of the heterotic string theory on the manifold K3×T2 or on a suitable orbifold yielding N=1 supersymmetry in 6D. The resulting 4D theory has N=2 local supersymmetry. Prepotential of this theory receives only one-string-loop correction. The tree-level gauge couplings are proportional to the inverse effective string coupling and decrease at small distances from the center of magnetic black hole, so that loop corrections to the gauge couplings are important in this region. We solve the system of Killing spinor equations (conditions for the supersymmetry variations of the fermions to vanish) and Maxwell equations. At the string-tree level, we reproduce the magnetic black hole solution which can also be obtained by solving the system of the Einstein–Maxwell equations and the equations of motion for the moduli. String-loop corrections to the tree-level solution are calculated in the first order in string coupling. The resulting corrections to the metric and dilaton are large at small distances from the center of the black hole. Possible smearing of the singularity at the origin by quantum corrections is discussed.

Density matrix of radiation of a black hole with a fluctuating horizon

Abstract Four-dimensional magnetic black holes including dilaton and abelian gauge fields which are solutions of supergravity can also be obtained by dimensional reduction of the Einstein-Maxwell gravity in five dimensions. In the extremal case the five-dimensional solutions have horizon and their near-horizon geometry is AdS 3 × S 2 . In the non-extremal case the near-horizon geometry is shown to be the product of the three-dimensional Banados-Teitelboim-Zanelli black hole and S 2 . This allows to perform microscopic counting of statistical entropy of magnetic black holes. Exact agreement with the geometric entropy is found. The microstates responsible for statistical entropy are located in the near-horizon region.