Bouncing of gravitons emitted from the brane to the bulk back to the brane

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 non-static 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.Comment: LaTeX2e, 12 pages. Refs. added. arXiv admin note: text overlap with arXiv:1204.235

Nonabelian Fields in Exact String Solutions

Within the framework of "anomalously gauged" Wess-Zumino-Witten (WZW) models, we construct solutions which include nonabelian fields. Both compact and noncompact groups are discussed. In the case of compact groups, as an example of background containing nonabelian fields, we discuss conformal theory on the $SO(4)/SO(3)$ coset, which is the natural generalization of the 2D monopole theory corresponding to the $SO(3)/SO(2)$ coset. In noncompact case, we consider examples with $SO(2,1)/SO(1,1)$ and $SO(3,2)/SO(3,1)$ cosets.Comment: 15 pages, Late

Quantum field theory with a fundamental length: A general mathematical framework

We review and develop a mathematical framework for nonlocal quantum field theory (QFT) with a fundamental length. As an instructive example, we reexamine the normal ordered Gaussian function of a free field and find the primitive analyticity domain of its n-point vacuum expectation values. This domain is smaller than the usual future tube of local QFT, but we prove that in difference variables, it has the same structure of a tube whose base is the (n-1)-fold product of a Lorentz invariant region. It follows that this model satisfies Wightman-type axioms with an exponential high-energy bound which does not depend on n, contrary to the claims in the literature. In our setting, the Wightman generalized functions are defined on test functions analytic in the complex l-neighborhood of the real space, where l is an n-independent constant playing the role of a fundamental length, and the causality condition is formulated with the use of an analogous function space associated with the light cone. In contrast to the scheme proposed by Bruning and Nagamachi [J. Math. Phys. 45 (2004) 2199] in terms of ultra-hyperfunctions, the presented theory obviously becomes local as l tends to zero.Comment: 25 pages, v2: updated to match J. Math. Phys. versio

String-Loop Corrected Magnetic Black Holes

We discuss the form of the string-loop-corrected effective action obtained by compactification of the heterotic string theory on the manifold $K3\times T^2$ or on its orbifold limit and the loop-corrected magnetic black hole solutions of the equations of motion. Effective 4D theory has N=2 local supersymmetry. Using the string-loop-corrected prepotential of the N=2 supersymmetric theory, which receives corrections only from the string world sheets of torus topology, we calculate the loop corrections to the tree-level gauge couplings and solve the loop-corrected equations of motion. At the string-tree level, the effective gauge couplings decrease at small distances from the origin, and in this region string-loop corrections to the gauge couplings become important. A possibility of smearing the singularity of the tree-level supersymmetric solution with partially broken supersymmetry by quantum corrections is discussed.Comment: Improved version. Mixing of the dilaton with other moduli properly taken into account. Explanatory notes adde

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 ${}^4 He$ 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.Comment: 21 pages, 4 figure