Eikonal Amplitude in the Gravireggeon Model at Superplanckian Energies

The gravity effects in high-energy scattering, described by a four-dimensional eikonal amplitude related to gravireggeons induced by compact extra dimensions are studied. It is demonstrated that the real part of the eikonal (with a massless mode subtracted) dominates its imaginary part at both small and large impact parameters, in contrast to the usual case of hadronic high-energy behavior. The real part of the scattering amplitude exhibits an exponential falloff at large momentum transfer, similar to that of the imaginary part of the amplitude.Comment: 21 pages, LaTeX2e, no figure

Quark-antiquark pair production in space-time dependent fields

Fermion-antifermion pair-production in the presence of classical fields is described based on the retarded and advanced fermion propagators. They are obtained by solving the equation of motion for the Dirac Green's functions with the respective boundary conditions to all orders in the field. Subsequently, various approximation schemes fit for different field configurations are explained. This includes longitudinally boost-invariant forms. Those occur frequently in the description of ultrarelativistic heavy-ion collisions in the semiclassical limit. As a next step, the gauge invariance of the expression for the expectation value of the number of produced fermion-antifermion pairs as a functional of said propagators is investigated in detail. Finally, the calculations are carried out for a longitudinally boost-invariant model-field, taking care of the last issue, especially.Comment: 32 pages, 8 figures, revised versio

Poliomyelitis surveillance report number 18, May 20, 1955

Dr. Edwin Lennette, Virus Laboratory, California Department of Public Health, reports isolation of type 1 virus from the stool of case PSU No. Cal-21. He also reports isolation of type 1 virus from the stool of a third \uc2\ub0th contact of non-paralytic case PSU No. Cal-14. Isolations from 2 other contacts of this case were previously reported.Dr. Werner Henle, Children\ue2\u20ac\u2122s Hospital, Philadelphia, reports isolation of type 1 poliomyelitis virus from Case PSU No. Pa-2. This is the first isolation from a case receiving Wyeth Vaccine. This case had first paralysis at the same site as inoculation.One new case was accepted today from West Virginia. This seven-year-old female developed bulbar signs 26 days after inoculation with Lilly Vaccine. Vaccinated cases total 79 at 12:00 noon 5-20-55 (Table l)

Relativistic Turbulence: A Long Way from Preheating to Equilibrium

We study, both numerically and analytically, the development of equilibrium after preheating. We show that the process is characterised by the appearance of Kolmogorov spectra and the evolution towards thermal equilibrium follows self-similar dynamics. Simplified kinetic theory gives values for all characteristic exponents which are close to what is observed in lattice simulations. The resulting time for thermalization is long, and temperature at thermalization is low, $T \sim 100$ eV in the simple $\lambda \Phi^4$ inflationary model. Our results allow a straightforward generalization to realistic models.Comment: 4 pages, 3figures, LaTe

Standard Model Neutrinos as Warm Dark Matter

Standard Model neutrinos are not usually considered plausible dark matter candidates because the usual treatment of their decoupling in the early universe implies that their mass must be sufficiently small to make them ``hot'' dark matter. In this paper we show that decoupling of Standard Model neutrinos in low reheat models may result in neutrino densities very much less than usually assumed, and thus their mass may be in the keV range. Standard Model neutrinos may therefore be warm dark matter candidates.Comment: 5 pages, 5 figures, LaTeX file uses revtex packag

Decaying neutralino dark matter in anomalous U(1)HU(1)_H models

In supersymmetric models extended with an anomalous $U(1)_H$ different R-parity violating couplings can yield an unstable neutralino. We show that in this context astrophysical and cosmological constraints on neutralino decaying dark matter forbid bilinear R-parity breaking neutralino decays and lead to a class of purely trilinear R-parity violating scenarios in which the neutralino is stable on cosmological scales. We have found that among the resulting models some of them become suitable to explain the observed anomalies in cosmic-ray electron/positron fluxes.Comment: 19 pages, 3 figures. References added, typos corrected, accepted version in Phys Rev

Semistable Higgs bundles on Calabi-Yau manifolds

We provide a partial classification of semistable Higgs bundles over a simply connected Calabi-Yau manifolds. Applications to a conjecture about a special class of semistable Higgs bundles are given. In particular, the conjecture is proved for K3 and Enriques surfaces, and some related classes of surfaces

Searching for Dark Matter with Future Cosmic Positron Experiments

Dark matter particles annihilating in the Galactic halo can provide a flux of positrons potentially observable in upcoming experiments, such as PAMELA and AMS-02. We discuss the spectral features which may be associated with dark matter annihilation in the positron spectrum and assess the prospects for observing such features in future experiments. Although we focus on some specific dark matter candidates, neutralinos and Kaluza-Klein states, we carry out our study in a model independent fashion. We also revisit the positron spectrum observed by HEAT.Comment: 19 pages, 33 figure