1,721,006 research outputs found
Introduction to cosmology
No full textAn introductory lectures on cosmology at ITEP Winter School for students specializing in particle physics are presented. Many important subjects are not covered because of lack of time and space but hopefully the lectures may serve as a starting point for further studies
Problems of cosmological constant, dark energy and possible adjustment mechanism
No full textVacuum and dark energy energy problems are reviewed. Cosmology with non-zero vacuum energy is discussed. The astronomical data which indicate that the universe is filled with an anti-gravitating state of matter are described. The mechanisms which may lead to cancellation of almost infinite vacuum energy down to the astronomically observed value are enumerated with an emphasis to dynamical adjustment
Evaporation of charged bosonic condensate in cosmology
No full textCosmological evolution of equilibrium plasma with a condensate of U(1)-charged bosonic field is considered. It is shown that the evaporation of the condensate is very much different from naive expectations, discussed in the literature, as well as from evaporation of non-equilibrium neutral condensate. The charged condensate evaporates much slower than the decay of the corresponding bosons. The evaporation rate is close to that of the cosmological expansion. The plasma temperature, in contrast, drops much faster than usually, namely as the third power of the cosmological scale factor. As a result the universe becomes very cold and the cosmological charge asymmetry reaches a huge value
Baryogenesis by R-parity violating top quark decays and neutron-antineutron oscillations
No full textGeneration of the cosmological baryon asymmetry in SUSY based model with broken R-parity and low scale gravity is considered. The model allows for a long-life time or even stable proton and observable neutron-antineutron oscillations
Antimatter in the Milky Way
No full textObservational signatures of existence of antimatter objects in the Galaxy are discussed. We focus on point-like sources of gamma radiation, diffuse galactic gamma ray background and anti-nuclei in cosmic rays
Do neutrino flavor oscillations forbid large lepton asymmetry of the universe?
No full textIt is shown that hypothetical neutrino-majoron coupling can suppress neutrino flavor oscillations in the early universe, in contrast to the usual weak interaction case. This reopens a window for a noticeable cosmological lepton asymmetry which is forbidden for the large mixing angle solution in the case of standard interactions of neutrinos
Cosmological model with dynamical cancellation of vacuum energy and dark energy
No full textWe propose a model with a compensating scalar field whose back reaction to the cosmological curvature cancels possible vacuum energy density down to the terms of the order of the time-dependent critical energy density. Thus, the model simultaneously solves the mystery of the compensation of vacuum energy with an accuracy of 120 orders of magnitude and explains the existence of the observed dark energy. At an early stage, the suggested cosmological model might experience exponential expansion without an additional inflaton field. However, the solution found is unstable with respect to small perturbations. The stability can be ensured by introducing nonanalytical terms depending upon the absolute value of the curvature scalar R. Unfortunately, stable solutions do not describe realistic cosmology at the matter-dominated stage
Antimatter in the universe
No full textThe models leading to a high abundance of antimatter in the universe are discussed. Special attention is payed to the model of antimatter creation in the form of compact stellar-like objects. Such objects can contribute significantly to the cosmological dark matter. Observational signatures of antimatter in the Galaxy are discussed. © 2011 Pleiades Publishing, Ltd
Scalar field instability in de Sitter space-time
No full textStarting from the equation of motion of the quantum operator of a real scalar field φ in de Sitter space-time, a simple differential equation is derived which describes the evolution of quantum fluctuations 〈φ2〉 of this field. Full de Sitter invariance is assumed and no ad hoc infrared cutoff is introduced. This equation is solved explicitly and in massive case our result agrees with the standard one. In massless case the large time behavior of our solution differs by sign from the expression found in earlier papers. A possible cause of discrepancy may be a spontaneous breaking of de Sitter invariance
Photon mass and electrogenesis.
No full textWe show that if photon possesses a tiny but non-vanishing mass the universe cannot be electrically neutral. Cosmological electric asymmetry could be generated either at an early stage by different evaporation rates of primordial black holes with respect to positively and negatively charged particles or by predominant capture of protons in comparison to electrons by heavy galactic black holes in contemporary universe. An impact of this phenomenon on the generation of large scale magnetic fields and on the universe acceleration is considered
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