Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPhase Transitions in an Expanding Universe: Stochastic Gravitational Waves in Standard and Non-Standard Histories
69
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We undertake a careful analysis of stochastic gravitational wave production from cosmological phase transitions in an expanding universe, studying both a standard radiation as well as a matter dominated history. We analyze in detail the dynamics of the phase transition, including the false vacuum fraction, bubble lifetime distribution, bubble number density, mean bubble separation, etc., for an expanding universe. We also study the full set of differential equations governing the evolution of plasma and the scalar field during the phase transition and generalize results obtained in Minkowski spacetime. In particular, we generalize the sound shell model to the expanding universe and determine the velocity field power spectrum. This ultimately provides an accurate calculation of the gravitational wave spectrum seen today for the dominant source of sound waves. For the amplitude of the gravitational wave spectrum visible today, we find a suppression factor arising from the finite lifetime of the sound waves and compare with the commonly used result in the literature, which corresponds to the asymptotic value of our suppression factor. We point out that the asymptotic value is only applicable for a very long lifetime of the sound waves, which is highly unlikely due to the onset of shocks, turbulence and other damping processes. We also point out that features of the gravitational wave spectral form may hold the tantalizing possibility of distinguishing between different expansion histories using phase transitions.
rate research
Read More
We study the tensorial modes of the two-fluid model, where one of this fluids has an equation of state $p = - rho/3$ (variable cosmological constant, cosmic string fluid, texture) or $p = - rho$ (cosmological constant), while the other fluid is an ordinary matter (radiation, stiff matter, incoherent matter). In the first case, it is possible to have a closed Universe whose dynamics can be that of an open Universe providing alternative solutions for the age and horizon problems. This study of the gravitational waves is extended for all values of the effective curvature $k_{eff}=k-frac{8pi G}{3}rho_{0s}$, that is, positive, negative or zero, $k$ being the curvature of the spacelike section. In the second case, we restrict ourselves to a flat spatial section. The behaviour of gravitational waves have, in each case, very particular features, that can be reflected in the anisotropy spectrum of Cosmic Microwave Background Radiation. We make also some considerations of these models as candidate to dark matter models.
This report summarizes the present status of neutrino non-standard interactions (NSI). After a brief overview, several aspects of NSIs are discussed, including connection to neutrino mass models, model-building and phenomenology of large NSI with both light and heavy mediators, NSI phenomenology in both short- and long-baseline neutrino oscillation experiments, neutrino cross-sections, complementarity of NSI with other low- and high-energy experiments, fits with neutrino oscillation and scattering data, DUNE sensitivity to NSI, effective field theory of NSI, as well as the relevance of NSI to dark matter and cosmology. We also discuss the open questions and interesting future directions that can be pursued by the community at large. This report is based on talks and discussions during the Neutrino Theory Network NSI workshop held at Washington University in St. Louis from May 29-31, 2019 (https://indico.cern.ch/event/812851/)
In this paper, we revisit the estimation of the spectrum of primordial gravitational waves originated from inflation, particularly focusing on the effect of thermodynamics in the Standard Model of particle physics. By collecting recent results of perturbative and non-perturbative analysis of thermodynamic quantities in the Standard Model, we obtain the effective degrees of freedom including the corrections due to non-trivial interaction properties of particles in the Standard Model for a wide temperature interval. The impact of such corrections on the spectrum of primordial gravitational waves as well as the damping effect due to free-streaming particles is investigated by numerically solving the evolution equation of tensor perturbations in the expanding universe. It is shown that the reevaluation of the effects of free-streaming photons and neutrinos gives rise to some additional damping features overlooked in previous studies. We also observe that the continuous nature of the QCD crossover results in a smooth spectrum for modes that reenter the horizon at around the epoch of the QCD phase transition. Furthermore, we explicitly show that the values of the effective degrees of freedom remain smaller than the commonly used value 106.75 even at temperature much higher than the critical temperature of the electroweak crossover, and that the amplitude of primordial gravitational waves at a frequency range relevant to direct detection experiments becomes $mathcal{O}(1),%$ larger than previous estimates that do not include such corrections. This effect can be relevant to future high-sensitivity gravitational wave experiments such as ultimate DECIGO. Our results on the temperature evolution of the effective degrees of freedom are made available as tabulated data and fitting functions, which can also be used in the analysis of other cosmological relics.
A notable feature of UV freeze-in is that the relic density is strongly dependent on the highest temperatures of the thermal bath, and a common assumption is that the relevant highest temperature should be the reheating temperature after inflation $T_text{RH}$. However, the temperature of the thermal bath can be significantly higher in certain scenarios, reaching a value denoted T max , a fact which is only apparent away from the instantaneous decay approximation. Interestingly, it has been shown that if the operators are of sufficiently high mass dimension then the dark matter abundance can be enhanced by a boost factor depending on ($T_text{max}/T_text{RH}$) relative to naive estimates assuming instantaneous reheating. We highlight here that in non-standard cosmological histories the critical mass dimension of the operator above at which the instantaneous decay approximation breaks down, and the exponent of the boost factor, depend on the equation of state $omega$ prior to reheating. We highlight four examples in which the dark matter abundance receives a significant enhancement in the context of gravitino dark matter, the moduli portal, the Higgs portal, and the spin-2 portal (as might arise in bimetric gravity models). We comment on the transition from kination domination to radiation domination as a motivated example of non-standard cosmologies.
Cosmological phase transitions in the primordial universe can produce anisotropic stochastic gravitational wave backgrounds (GWB), similar to the cosmic microwave background (CMB). For adiabatic perturbations, the fluctuations in GWB follow those in the CMB, but if primordial fluctuations carry an isocurvature component, this need no longer be true. It is shown that in non-minimal inflationary and reheating settings, primordial isocurvature can survive in GWB and exhibit significant non-Gaussianity (NG) in contrast to the CMB, while obeying current observational bounds. While probing such NG GWB is at best a marginal possibility at LISA, there is much greater scope at future proposed detectors such as DECIGO and BBO. It is even possible that the first observations of inflation-era NG could be made with gravitational wave detectors as opposed to the CMB or Large-Scale Structure surveys.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
