On the Theory of Fermionic Preheating

In inflationary cosmology, the particles constituting the Universe are created after inflation due to their interaction with moving inflaton field(s) in the process of preheating. In the fermionic sector, the leading channel is out-of equilibrium particle production in the non-perturbative regime of parametric excitation, which respects Pauli blocking but differs significantly from the perturbative expectation. We develop theory of fermionic preheating coupling to the inflaton, without and with expansion of the universe, for light and massive fermions, to calculate analytically the occupation number of created fermions, focusing on their spectra and time evolution. In the case of large resonant parameter $q$ we extend for rermions the method of successive parabolic scattering, earlier developed for bosonic preheating. In an expanding universe parametric excitation of fermions is stochastic. Created fermions very quickly, within tens of inflaton oscillations, fill up a sphere of radius $\simeq q^{1/4}$ in monetum space. We extend our formalism to the production of superheavy fermions and to `instant' fermion creation.Comment: 14 pages, latex, 12 figures, submitted for publicatio

Dynamics of Symmetry Breaking and Tachyonic Preheating

We reconsider the old problem of the dynamics of spontaneous symmetry breaking using 3d lattice simulations, and develop a theory of tachyonic preheating, which occurs due to the spinodal instability of the scalar field. Tachyonic preheating is so efficient that symmetry breaking typically completes within a single oscillation of the field distribution as it rolls towards the minimum of its effective potential. As an application of this theory we consider preheating in the hybrid inflation scenario, including SUSY-motivated F-term and D-term inflationary models. We show that preheating in hybrid inflation is typically tachyonic and the stage of oscillations of a homogeneous component of the scalar fields driving inflation ends after a single oscillation. Our results may also be relevant for the theory of the formation of disoriented chiral condensates in heavy ion collisions.Comment: 7 pages, 6 figures. Higher quality figures and computer generated movies in gif format illustrating our results can be found at http://physics.stanford.edu/gfelder/hybri

Spinors, Inflation, and Non-Singular Cyclic Cosmologies

We consider toy cosmological models in which a classical, homogeneous, spinor field provides a dominant or sub-dominant contribution to the energy-momentum tensor of a flat Friedmann-Robertson-Walker universe. We find that, if such a field were to exist, appropriate choices of the spinor self-interaction would generate a rich variety of behaviors, quite different from their widely studied scalar field counterparts. We first discuss solutions that incorporate a stage of cosmic inflation and estimate the primordial spectrum of density perturbations seeded during such a stage. Inflation driven by a spinor field turns out to be unappealing as it leads to a blue spectrum of perturbations and requires considerable fine-tuning of parameters. We next find that, for simple, quartic spinor self-interactions, non-singular cyclic cosmologies exist with reasonable parameter choices. These solutions might eventually be incorporated into a successful past- and future-eternal cosmological model free of singularities. In an Appendix, we discuss the classical treatment of spinors and argue that certain quantum systems might be approximated in terms of such fields.Comment: 12 two-column pages, 3 figures; uses RevTeX

Sine-Gordon Parametric Resonance

We consider the instability of fluctuations in an oscillating scalar field which obeys the Sine-Gordon equation. We present simple closed-form analytic solutions describing the parametric resonance in the Sine-Gordon model. The structure of the resonance differs from that obtained with the Mathieu equation which is usually derived with the small angle approximation to the equation for fluctuations. The results are applied to axion cosmology, where the oscillations of the classical axion field, with a Sine-Gordon self-interaction potential, constitute the cold dark matter of the universe. When the axion misalignment angle at the QCD epoch, $\theta_0$, is small, the parametric resonance of the axion fluctuations is not significant. However, in regions of larger $\theta_0$ where axion miniclusters would form, the resonance may be important. As a result, axion miniclusters may disintegrate into finer, denser clumps. We also apply the theory of Sine-Gordon parametric resonance to reheating in the Natural Inflation scenario. The decay of the inflaton field due to the self-interaction alone is ineffective, but a coupling to other bosons can lead to preheating in the broad resonance regime. Together with the preheating of fermions, this can alter the reheating scenario for Natural Inflation.Comment: LaTex 12 pages, 6 figs, submitted for publicatio

Supergravity Inflation Free from Harmful Relics

We present a realistic supergravity inflation model which is free from the overproduction of potentially dangerous relics in cosmology, namely moduli and gravitinos which can lead to the inconsistencies with the predictions of baryon asymmetry and nucleosynthesis. The radiative correction turns out to play a crucial role in our analysis which raises the mass of supersymmetry breaking field to intermediate scale. We pay a particular attention to the non-thermal production of gravitinos using the non-minimal Kahler potential we obtained from loop correction. This non-thermal gravitino production however is diminished because of the relatively small scale of inflaton mass and small amplitudes of hidden sector fields.Comment: 10 pages, revtex, 1 eps figure, references added, conclusion section expande

The Sloan Digital Sky Survey Reverberation Mapping Project: Technical Overview

The Sloan Digital Sky Survey Reverberation Mapping project (SDSS-RM) is a dedicated multi-object RM experiment that has spectroscopically monitored a sample of 849 broad-line quasars in a single 7 deg$^2$ field with the SDSS-III BOSS spectrograph. The RM quasar sample is flux-limited to i_psf=21.7 mag, and covers a redshift range of 0.1<z<4.5. Optical spectroscopy was performed during 2014 Jan-Jul dark/grey time, with an average cadence of ~4 days, totaling more than 30 epochs. Supporting photometric monitoring in the g and i bands was conducted at multiple facilities including the CFHT and the Steward Observatory Bok telescopes in 2014, with a cadence of ~2 days and covering all lunar phases. The RM field (RA, DEC=14:14:49.00, +53:05:00.0) lies within the CFHT-LS W3 field, and coincides with the Pan-STARRS 1 (PS1) Medium Deep Field MD07, with three prior years of multi-band PS1 light curves. The SDSS-RM 6-month baseline program aims to detect time lags between the quasar continuum and broad line region (BLR) variability on timescales of up to several months (in the observed frame) for ~10% of the sample, and to anchor the time baseline for continued monitoring in the future to detect lags on longer timescales and at higher redshift. SDSS-RM is the first major program to systematically explore the potential of RM for broad-line quasars at z>0.3, and will investigate the prospects of RM with all major broad lines covered in optical spectroscopy. SDSS-RM will provide guidance on future multi-object RM campaigns on larger scales, and is aiming to deliver more than tens of BLR lag detections for a homogeneous sample of quasars. We describe the motivation, design and implementation of this program, and outline the science impact expected from the resulting data for RM and general quasar science.Comment: 25 pages, submitted to ApJS; project website at http://www.sdssrm.or

Microwave Electrodynamics of Electron-Doped Cuprate Superconductors

We report microwave cavity perturbation measurements of the temperature dependence of the penetration depth, lambda(T), and conductivity, sigma(T) of Pr_{2-x}Ce_{x}CuO_{4-delta} (PCCO) crystals, as well as parallel-plate resonator measurements of lambda(T) in PCCO thin films. Penetration depth measurements are also presented for a Nd_{2-x}Ce_{x}CuO_{4-delta} (NCCO) crystal. We find that delta-lambda(T) has a power-law behavior for T<T_c/3, and conclude that the electron-doped cuprate superconductors have nodes in the superconducting gap. Furthermore, using the surface impedance, we have derived the real part of the conductivity, sigma_1(T), below T_c and found a behavior similar to that observed in hole-doped cuprates.Comment: 4 pages, 4 figures, 1 table. Submitted to Physical Review Letters revised version: new figures, sample characteristics added to table, general clarification give