Instanton - like transitions at high energies in (1+1) dimensional scalar models. II.Classically allowed induced vacuum decay

We consider classical Minkowskian solutions to the field equation in the (1+1) dimensional scalar model with the exponential interaction that describe the unsuppressed false vacuum decay induced by $n$ initial particles. We find that there is a critical value of $n$ below which there are no such solutions, i.e., the vacuum decay is always suppressed. For the number of initial particles larger than this value the vacuum decay is unsuppressed at high enough energies.Comment: 18 pages, 2 figures, LaTex, figures in PS, INR-T-94/

Birth of the Brane World

Birth of the brane world is studied using the Hamiltonian approach. It is shown that an inflating brane world can be created from nothing. The wave function of the universe obtained from the Wheeler de-Witt equation and the time-dependent Schr$\ddot{o}$dinger equation for quantized scalar fields on the brane are the same as in the conventional 4-dimensional quantum cosmology if the bulk is exactly the Anti-de Sitter spacetime. The effect of the massive objects in the bulk is also discussed. This analysis tells us the presence of the extra dimension imprints a nontrivial effect on the quantum cosmology of the brane world. This fact is important for the analysis of the quantum fluctuations in the inflationary scenario of the brane world.Comment: 14 pages, no figure, to appear in Phys. Lett.

Cosmology

In these lectures we first concentrate on the cosmological problems which, hopefully, have to do with the new physics to be probed at the LHC: the nature and origin of dark matter and generation of matter-antimatter asymmetry. We give several examples showing the LHC cosmological potential. These are WIMPs as cold dark matter, gravitinos as warm dark matter, and electroweak baryogenesis as a mechanism for generating matter-antimatter asymmetry. In the remaining part of the lectures we discuss the cosmological perturbations as a tool for studying the epoch preceeding the conventional hot stage of the cosmological evolution.Comment: 47 pages, set of lectures given at the 2011 European School of High-Energy Physics, Cheile Gradistei, Romania, 7-20 Sep 2011, edited by C. Grojean, M. Mulder

Large and infinite extra dimensions

The emphasis in the developmet of theories with more than three spatial dimensions has recently shifted towards ``brane world'' picture, which assumes that ordinary matter (with possible exceptions of gravitons and other, hypothetic, particles which interact very weakly with matter) is trapped to a three-dimensional submanifold --- brane --- embedded in fundamental multi-dimensional space. In the brane world scenario, extra dimensions may be large, and even infinite; they may have effects, directly observable in current or fothcoming experiments. On the basis of simple field-theoretic models, various ideas in this direction are exposed at a non-expert level.Comment: 55 pages, 10 figures Several references and figures added. Journal version, to appear in Uspekhi Fiz. Nau