Energy Density in Expanding Universes as Seen by Unruh's Detector

We consider the response of an Unruh detector to scalar fields in an expanding space-time. When combining transition elements of the scalar field Hamiltonian with the interaction operator of detector and field, one finds at second order in time-dependent perturbation theory a transition amplitude, which actually dominates in the ultraviolet over the first order contribution. In particular, the detector response faithfully reproduces the particle number implied by the stress-energy of a minimally coupled scalar field, which is inversely proportional to the energy of a scalar mode. This finding disagrees with the contention that in de Sitter space, the response of the detector drops exponentially with particle energy and therefore indicates a thermal spectrum.Comment: 15 pages, 1 figur

Lamb Shift of Unruh Detector Levels

We argue that the energy levels of an Unruh detector experience an effect similar to the Lamb shift in Quantum Electrodynamics. As a consequence, the spectrum of energy levels in a curved background is different from that in flat space. As examples, we consider a detector in an expanding Universe and in Rindler space, and for the latter case we suggest a new expression for the local virtual energy density seen by an accelerated observer. In the ultraviolet domain, that is when the space between the energy levels is larger than the Hubble rate or the acceleration of the detector, the Lamb shift quantitatively dominates over the thermal response rate.Comment: 20 page

Baryogenesis from the amplification of vacuum fluctuations during inflation

We propose that the baryon asymmetry of the Universe may originate from the amplification of quantum fluctuations of a light complex scalar field during inflation. CP-violation is sourced by complex mass terms, which are smaller than the Hubble rate, as well as non-standard kinetic terms. We find that, when assuming 60 e-folds of inflation, an asymmetry in accordance with observation can result for models where the energy scale of inflation is of the order of 10^16 GeV. Lower scales may be achieved when assuming substantially larger amounts of e-folds.Comment: 18 page

Unruh response functions for scalar fields in de Sitter space

We calculate the response functions of a freely falling Unruh detector in de Sitter space coupled to scalar fields of different coupling to the curvature, including the minimally coupled massless case. Although the responses differ strongly in the infrared as a consequence of the amplification of superhorizon modes, the energy levels of the detector are thermally populated.Comment: 16 pages, 1 figure, accepted for publication by Classical and Quantum Gravit

Self-consistent solitons for vacuum decay in radiatively generated potentials

We use a Green’s function approach in order to develop a method for calculating the tunneling rate between radiatively generated nondegenerate vacua. We apply this to a model that exhibits spontaneous symmetry breaking via the Coleman-Weinberg mechanism, where we determine the self-consistent tunneling configuration and illustrate the impact of gradient effects that arise from accounting for the underlying space-time inhomogeneity

Right-handed Sneutrinos as Nonthermal Dark Matter

When the minimal supersymmetric standard model is augmented by three right-handed neutrino superfields, one generically predicts that the neutrinos acquire Majorana masses. We postulate that all supersymmetry (SUSY) breaking masses as well as the Majorana masses of the right-handed neutrinos are around the electroweak scale and, motivated by the smallness of neutrino masses, assume that the lightest supersymmetric particle (LSP) is an almost-pure right-handed sneutrino. We discuss the conditions under which this LSP is a successful dark matter candidate. In general, such an LSP has to be nonthermal in order not to overclose the universe, and we find the conditions under which this is indeed the case by comparing the Hubble expansion rate with the rates of the relevant thermalizing processes, including self-annihilation and co-annihilation with other SUSY and standard model particles.Comment: 17 pages v.2: References adde

Textures and Semi-Local Strings in SUSY Hybrid Inflation

Global topological defects may account for the large cold spot observed in the Cosmic Microwave Background. We explore possibilities of constructing models of supersymmetric F-term hybrid inflation, where the waterfall fields are globally SU(2)-symmetric. In contrast to the case where SU(2) is gauged, there arise Goldstone bosons and additional moduli, which are lifted only by masses of soft-supersymmetry breaking scale. The model predicts the existence of global textures, which can become semi-local strings if the waterfall fields are gauged under U(1)_X. Gravitino overproduction can be avoided if reheating proceeds via the light SU(2)-modes or right-handed sneutrinos. For values of the inflaton- waterfall coupling >=10^-4, the symmetry breaking scale imposed by normalisation of the power spectrum generated from inflation coincides with the energy scale required to explain the most prominent of the cold spots. In this case, the spectrum of density fluctuations is close to scale-invariant which can be reconciled with measurements of the power spectrum by the inclusion of the sub-dominant component due to the topological defects.Comment: 29 page

Accelerated detectors in Dirac vacuum: the effects of horizon fluctuations

We consider an Unruh-DeWitt detector interacting with a massless Dirac field. Assuming that the detector is moving along an hyperbolic trajectory, we modeled the effects of fluctuations in the event horizon using a Dirac equation with random coefficients. First, we develop the perturbation theory for the fermionic field in a random media. Further we evaluate corrections due to the randomness in the response function associated to different model detectors.Comment: 19 pages, 1 figur

D-term inflation in non-minimal supergravity

D-term inflation is one of the most interesting and versatile models of inflation. It is possible to implement naturally D-term inflation within high energy physics, as for example SUSY GUTs, SUGRA, or string theories. D-term inflation avoids the $\eta$-problem, while in its standard form it always ends with the formation of cosmic strings. Given the recent three-year WMAP data on the cosmic microwave background temperature anisotropies, we examine whether D-term inflation can be successfully implemented in non-minimal supergravity theories. We show that for all our choices of K\"ahler potential, there exists a parameter space for which the predictions of D-term inflation are in agreement with the measurements. The cosmic string contribution on the measured temperature anisotropies is always dominant, unless the superpotential coupling constant is fine tuned; a result already obtained for D-term inflation within minimal supergravity. In conclusion, cosmic strings and their r\^ole in the angular power spectrum cannot be easily hidden by just considering a non-flat K\"ahler geometry.Comment: 29 pages, 9 figures; minor changes to match publihed versio

Resonant decay of flat directions

We study preheating, i.e., non-perturbative resonant decay, of flat direction fields, concentrating on MSSM flat directions and the right handed sneutrino. The difference between inflaton preheating and flaton preheating, is that the potential is more constraint in the latter case. The effects of a complex driving field, quartic couplings in the potential, and the presence of a thermal bath are important and cannot be neglected. Preheating of MSSM flat directions is typically delayed due to out-of-phase oscillations of the real and imaginary components and may be preceded by perturbative decay or $Q$-ball formation. Particle production due to the violation of adiabaticity is expected to be inefficient due to back reaction effects. For a small initial sneutrino VEV, $\lesssim m_N/h$ with $m_N$ the mass of the right handed sneutrino and $h$ a yakawa coupling, there are tachyonic instabilities. The $D$-term quartic couplings do not generate an effective mass for the tachyonic modes, making it an efficient decay channel. It is unclear how thermal scattering affects the resonance.Comment: 20 pages, 4 figure