On decays of Z' into unparticle stuff

We study the decay of a Z' - boson into U -unparticle and a photon. The extended Landau-Yang theorem is used. The clear photon signal would make the decay Z' \rightarrow \gamma U as an additional contribution mode for study of unparticle physics.Comment: 11 pages, 3 figures, paper accepted for publication by Advances in High Energy Physics journa

Rolling in the Higgs Model and Elliptic Functions

Asymptotic methods in nonlinear dynamics are used to improve perturbation theory results in the oscillations regime. However, for some problems of nonlinear dynamics, particularly in the case of Higgs (Duffing) equation and the Friedmann cosmological equations, not only small oscillations regime is of interest but also the regime of rolling (climbing), more precisely the rolling from a top (climbing to a top). In the Friedman cosmology, where the slow rolling regime is often used, the rolling from a top (not necessary slow) is of interest too. In the present work a method for approximate solution to the Higgs equation in the rolling regime is presented. It is shown that in order to improve perturbation theory in the rolling regime turns out to be effective not to use an expansion in trigonometric functions as it is done in case of small oscillations but use expansions in hyperbolic functions instead. This regime is investigated using the representation of the solution in terms of elliptic functions. An accuracy of the corresponding approximation is estimated.Comment: Latex, 36 Pages, 8 figures, typos correcte

Radiative Losses in Plasma Accelerators

We investigate the dynamics of a relativistic electron in a strongly nonlinear plasma wave in terms of classical mechanics by taking into account the action of the radiative reaction force. The two limiting cases are considered. In the first case where the energy of the accelerated electrons is low, the electron makes many betatron oscillations during the acceleration. In the second case where the energy of the accelerated electrons is high, the betatron oscillation period is longer than the electron residence time in the accelerating phase. We show that the force of radiative friction can severely limit the rate of electron acceleration in a plasma accelerator.Comment: 17 pages, 5 figure

Exciton correlations in coupled quantum wells and their luminescence blue shift

In this paper we present a study of an exciton system where electrons and holes are confined in double quantum well structures. The dominating interaction between excitons in such systems is a dipole - dipole repulsion. We show that the tail of this interaction leads to a strong correlation between excitons and substantially affects the behavior of the system. Making use of qualitative arguments and estimates we develop a picture of the exciton - exciton correlations in the whole region of temperature and concentration where excitons exist. It appears that at low concentration degeneracy of the excitons is accompanied with strong multi-particle correlation so that the system cannot be considered as a gas. At high concentration the repulsion suppresses the quantum degeneracy down to temperatures that could be much lower than in a Bose gas with contact interaction. We calculate the blue shift of the exciton luminescence line which is a sensitive tool to observe the exciton - exciton correlations.Comment: 27 pages in PDF and DVI format, 8 figure

Comment on "Correlation of the Highest-Energy Cosmic Rays with Nearby Extragalactic Objects"

We argue that the data published by the Pierre Auger Collaboration (arXiv:0711.2256) disfavor at 99% confidence level their hypothesis that most of the highest-energy cosmic rays are protons from nearby astrophysical sources, either Active Galactic Nuclei or other objects with a similar spatial distribution.Comment: 1000 words, 2 figures, scicite.st

Upper limit on the ultra-high-energy photon flux from AGASA and Yakutsk data

We present the interpretation of the muon and scintillation signals of ultra-high-energy air showers observed by AGASA and Yakutsk extensive air shower array experiments. We consider case-by-case ten highest energy events with known muon content and conclude that at the 95% confidence level (C.L.) none of them was induced by a primary photon. Taking into account statistical fluctuations and differences in the energy estimation of proton and photon primaries, we derive an upper limit of 36% at 95% C.L. on the fraction of primary photons in the cosmic-ray flux above 10^20 eV. This result disfavors the Z-burst and superheavy dark-matter solutions to the GZK-cutoff problem.Comment: revtex, 8 pages, 4 figure

FRW Cosmology with Non-positively Defined Higgs Potentials

We discuss the classical aspects of dynamics of scalar models with non-positive Higgs potentials in the FRW cosmology. These models appear as effective local models in non-local models related with string field theories. After a suitable field redefinition these models have the form of local Higgs models with a negative extra cosmological term and the total Higgs potential is non-positively defined and has rather small coupling constant. The non-positivity of the potential leads to the fact that on some stage of evolution the expansion mode gives place to the mode of contraction, due to that the stage of reheating is absent. In these models the hard regime of inflation gives place to inflation near the hill top and the area of the slow roll inflation is very small. Meanwhile one can obtain enough e-foldings before the contraction to make the model under consideration admissible to describe inflation.Comment: 40 pages, 20 figures, typos correcte

The Lorentz Integral Transform (LIT) method and its applications to perturbation induced reactions

The LIT method has allowed ab initio calculations of electroweak cross sections in light nuclear systems. This review presents a description of the method from both a general and a more technical point of view, as well as a summary of the results obtained by its application. The remarkable features of the LIT approach, which make it particularly efficient in dealing with a general reaction involving continuum states, are underlined. Emphasis is given on the results obtained for electroweak cross sections of few--nucleon systems. Their implications for the present understanding of microscopic nuclear dynamics are discussed.Comment: 83 pages, 31 figures. Topical review. Corrected typo