Radiation can never again dominate Matter in a Vacuum Dominated Universe

We demonstrate that in a vacuum-energy-dominated expansion phase, surprisingly neither the decay of matter nor matter-antimatter annihilation into relativistic particles can ever cause radiation to once again dominate over matter in the future history of the universe.Comment: updated version, as it will appear in Phys. Rev D. Title change, and some other minor alteration

Thermal effects on slow-roll dynamics

A description of the transition from the inflationary epoch to radiation domination requires the understanding of quantum fields out of thermal equilibrium, particle creation and thermalisation. This can be studied from first principles by solving a set of truncated real-time Schwinger-Dyson equations, written in terms of the mean field (inflaton) and the field propagators, derived from the two-particle irreducible effective action. We investigate some aspects of this problem by considering the dynamics of a slow-rolling mean field coupled to a second quantum field, using a \phi^2\chi^2 interaction. We focus on thermal effects. It is found that interactions lead to an earlier end of slow-roll and that the evolution afterwards depends on details of the heatbath.Comment: 25 pages, 11 eps figures. v2: paper reorganized, title changed, conclusions unchanged, to appear in PR

Scattering of Dirac and Majorana Fermions off Domain Walls

We investigate the interaction of fermions having both Dirac and left-handed and right-handed Majorana mass terms with vacuum domain walls. By solving the equations of motion in thin-wall approximation, we calculate the reflection and transmission coefficients for the scattering of fermions off walls.Comment: 6 pages, 1 figure, some typos corrected, one reference added, major revisions, title changed, version accepted for publication in Phys. Rev.

Leptogenesis with Dirac Neutrinos

We describe a "neutrinogenesis" mechanism whereby, in the presence of right-handed neutrinos with sufficiently small pure Dirac masses, (B+L)-violating sphaleron processes create the baryon asymmetry of the Universe, even when B=L=0 initially. It is shown that the resulting neutrino mass constraints are easily fulfilled by the neutrino masses suggested by current experiments. We present a simple toy model which uses this mechanism to produce the observed baryon asymmetry of the Universe. (PostScript Errors corrected in latest Version).Comment: 4 pages, Latex (using amsmath,feynmp,graphicx), 4 figure

Resonant decay of parity odd bubbles in hot hadronic matter

We investigate the decay of metastable states with broken CP-symmetry which have recently been proposed by Kharzeev, Pisarski and Tytgat to form in hot hadronic matter. We consider the efficiency of the amplification of the $\eta'$-field via parametric resonance, taking the backreaction into account. For times of the order $t\approx 10 fm$, we find a particle density of about $0.7/fm^3$ and a correlation length of $\xi_{max}\approx 2.5 fm$. The corresponding momentum spectra show a non-thermal behaviour.Comment: 11 pages latex file with 4 gif - figures. Uses elsart.cls (included

Potentially Large One-loop Corrections to WIMP Annihilation

We compute one-loop corrections to the annihilation of non--relativistic particles $\chi$ due to the exchange of a (gauge or Higgs) boson $\phi$ with mass $\mu$ in the initial state. In the limit $m_\chi \gg \mu$ this leads to the "Sommerfeld enhancement" of the annihilation cross section. However, here we are interested in the case \mu \lsim m_\chi, where the one--loop corrections are well--behaved, but can still be sizable. We find simple and accurate expressions for annihilation from both $S-$ and $P-$wave initial states; they differ from each other if $\mu \neq 0$. In order to apply our results to the calculation of the relic density of Weakly Interacting Massive Particles (WIMPs), we describe how to compute the thermal average of the corrected cross sections. We apply this formalism to scalar and Dirac fermion singlet WIMPs, and show that the corrections are always very small in the former case, but can be very large in the latter. Moreover, in the context of the Minimal Supersymmetric Standard Model, these corrections can decrease the relic density of neutralinos by more than 1%, if the lightest neutralino is a strongly mixed state.Comment: 25 pages, 8 figures. Added an appendix showing that the approximation works well in a scalar toy model. To be published in PRD

On the Influence of Eccentricities on Flux Linkages of Permanent Magnet Synchronous Machines

The noise behavior of electrical machines is influenced by tolerances. Eccentricities in particular lead to poorer noise behavior. However, the measurement of NVH quantities is usually very complex. Therefore, it is of interest to be able to detect such tolerances also by other measurands. In this paper, the influence of eccentricities on the flux linkages is investigated. For this purpose, detailed investigations were carried out using FEA. In a further step, these are compared with the results obtained from a test rig measurement. Prior to this, a methodology is presented with which the angle-dependent flux linkages can be determined. It is shown that eccentricities cause only slight changes in the harmonic components of the flux linkages. Due to the symmetry properties of the investigated machine, the changes in the flux linkage caused by the different air gap lengths cancel each other out. This could also be confirmed in the experiment

Transverse-Mass Spectra in Heavy-Ion Collisions at energies E_{lab} = 2--160 GeV/nucleon

Transverse-mass spectra of protons, pions and kaons produced in collisions of heavy nuclei are analyzed within the model of 3-fluid dynamics. It was demonstrated that this model consistently reproduces these spectra in wide ranges of incident energies E_{lab}, from 4A GeV to 160A GeV, rapidity bins and centralities of the collisions. In particular, the model describes the "step-like" dependence of kaon inverse slopes on the incident energy. The key point of this explanation is interplay of hydrodynamic expansion of the system with its dynamical freeze-out.Comment: 13 pages, 16 figures, summary is extended, version accepted by Phys. Rev.

New Upper Limits on the Tau Neutrino Mass from Primordial Helium Considerations

In this paper we reconsider recently derived bounds on $MeV$ tau neutrinos, taking into account previously unaccounted for effects. We find that, assuming that the neutrino life-time is longer than $O(100~sec)$, the constraint $N_{eff}<3.6$ rules out $\nu_{\tau}$ masses in the range $0.5~(MeV)<m_{\nu_\tau}<35~(MeV)$ for Majorana neutrinos and $0.74~(MeV)<m_{\nu_\tau}<35~(MeV)$ for Dirac neutrinos. Given that the present laboratory bound is 35 MeV, our results lower the present bound to $0.5$ and $0.74$ for Majorana and Dirac neutrinos respectively.Comment: 9 pages (2 figures available upon request), UM-AC-93-0

Dramatic reductions of in feed medication via immunization against enteric pathogens

The use of in-feed antimicrobials is coming under increased pressure in food animal production. Five field studies examined the impact of vaccines to stimulate protective immunity against pathogens commonly controlled with in-feed antimicrobials (Lawsonia intracellularis, a common enteric pathogen causing ileitis). Grow-finish pigs were immunized and various levels of in-feed antimicrobials used to control or prevent Lawsonia were removed