Calculation of Particle Production by Nambu Goldstone Bosons with Application to Inflation Reheating and Baryogenesis

A semiclassical calculation of particle production by a scalar field in a potential is performed. We focus on the particular case of production of fermions by a Nambu-Goldstone boson $\theta$. We have derived a (non)local equation of motion for the $\theta$-field with the backreaction of the produced particles taken into account. The equation is solved in some special cases, namely for purely Nambu-Goldstone bosons and for the tilted potential $U(\theta ) \propto m^2 \theta^2$. Enhanced production of bosons due to parametric resonance is investigated; we argue that the resonance probably disappears when the expansion of the universe is included. Application of our work on particle production to reheating and an idea for baryogenesis in inflation are mentioned.Comment: Submitted to Physical Review {\rm D}: October 4, 1994 21 page, UM-AC 94-3

Multiband Description of Optical Conductivity in Ferropnictide Superconductors

We study optical properties of the multiband superconductors with an s± order parameter symmetry. By comparing results of our theory with experimental data on optical conductivity for Ba0.68K0.32Fe2As2 single crystals, we show that satisfactory description of the novel superconductors can be obtained only considering a strong electron-boson coupling. We reexamine the effect of disorder and demonstrate that multiband superconductors are more robust with respect to it than naively expected by simple analogy with paramagnetic impurities in single-band superconductors. Moreover, disorder may give rise to new effects, in particular to a phase transition s±→s++. We discuss how the systematic study of disorder impact on the density of states and the optical conductivity may provide information on the underlying order parameter structur

Baryogenesis During Reheating in Natural Inflation and Comments on Spontaneous Baryogenesis

We calculate the baryon asymmetry created by the decay of a pseudo Nambu-Goldstone boson whose interactions violate baryon number conservation. Our results are in disagreement with previous results in the original spontaneous baryogenesis models for the asymmetry produced by the decay of an oscillating scalar field with B number violating derivative couplings; we find that the net baryon number density is proportional to $\th_i^3$, where $\th_i$ is the amplitude of the PNGB-field in natural inflation at the onset of reheating. We also discuss our disagreement with the interpretation of $\dot\theta$ as an effective chemical potential for baryon number in spontaneous baryogenesis models. While our calculation of the asymmetry is carried out in the context of natural inflation our approach is generally valid for baryogenesis models using decaying classical fields. In the Appendices, we include a complete derivation of the number density of particles produced by the decay of a classical scalar field; this number density is proportional to the integral over momenta of the one pair production amplitude.Comment: 22 pages, TeX, no figures. Submitted to Physical Review

Screening of Long-Range Leptonic Forces by Cosmic Background Neutrinos

The absence of dispersion effects of the SN~1987A neutrino pulse has been used to constrain novel long-range forces between neutrinos and galactic baryonic or non-baryonic matter. If these forces are mediated by vector bosons, screening effects by the cosmic neutrino background invalidate the SN~1987A limits and other related arguments.Comment: REVTeX 3.0 document, 6 pages, no figures

The Price of Neutrino Superluminality continues to rise

We revisit the model building challenges that one faces when trying to reconcile the OPERA claim of neutrino superluminality with other observational constraints. The severity of the supernova bound and of the kinematical constraints of Cohen-Glashow type lead us to focus on scenarios where all types of particles are superluminal inside matter. In contrast to the Dvali-Vikman proposal, this matter effect needs to be very short-ranged to avoid constraints from experiments on the Earth's surface in low-density environments. Due to this short range, the interaction underlying such a matter effect would have to be far stronger than permitted by fifth-force bounds. As a conceivable way out we suggest to make the matter effect "binary", i.e., dense matter does not directly trigger superluminality, but merely induces the transition to a different phase of some weakly coupled hidden sector. This phase exhibits spontaneous Lorentz violation or at least a stronger than usual mediation of some residual Lorentz violation to all matter. The effect has not been observed before since we have never before been able to measure the velocity of high-energy particles in dense matter with sufficient precision.Comment: 5 pages, 1 figure, references adde

Stability of Closed Timelike Curves in a Galileon Model

Recently Burrage, de Rham, Heisenberg and Tolley have constructed eternal, classical solutions with closed timelike curves (CTCs) in a Galileon model coupled to an auxiliary scalar field. These theories contain at least two distinct metrics and, in configurations with CTCs, two distinct notions of locality. As usual, globally CTCs lead to pathologies including nonlocal constraints on the initial Cauchy data. Locally, with respect to the gravitational metric, we use a WKB approximation to explicitly construct small, short-wavelength perturbations without imposing the nonlocal constraints and observe that these perturbations do not grow and so do not lead to an instability.Comment: 10 pages, no figure

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

Introduction to particle cosmology: the standard model of cosmology and its open problems

This book introduces the basic concepts of particle cosmology and covers all the main aspects of the Big Bang Model (expansion of the Universe, Big Bang Nucleosynthesis, Cosmic Microwave Background, large scale structures) and the search for new physics (inflation, baryogenesis, dark matter, dark energy). It also includes the majority of recent discoveries, such as the precise determination of cosmological parameters using experiments like WMAP and Planck, the discovery of the Higgs boson at LHC, the non-discovery to date of supersymmetric particles, and the search for the imprint of gravitational waves on the CMB polarization by Planck and BICEP.   This textbook is based on the authors’ courses on Cosmology, and aims at introducing Particle Cosmology to senior undergraduate and graduate students. It has been especially written to be accessible even for those students who do not have a strong background in General Relativity and quantum field theory. The content of this book is organized in an easy-to-use style and students will find it a helpful research guide