Session U9: Cosmology

Effects of Conformally Invariant Quantum Fields on Future Singularities - Part I

The effects of conformally invariant quantum fields on universes with future singularities are investigated. It is assumed that these singularities are caused by dark energy in the form of a perfect fluid with a known equation of state. The sign of the coefficient of the $\Box R$ term in the trace of the semi-classical backreaction equations determines the behavior of the universe. For one sign, the universe must expand forever, driving it inevitably to the singularity in all cases. For the other sign, the universe will inevitably reach a maximum size, avoiding a future singularity, for big rip (type I) and little rip cosmologies, while it may or may not reach a maximum size before encountering the singularity for type III, II, or IV singularities depending on initial conditions. Though the approach or avoidance of said singularities may occur on the Planck scale, this can be avoided if the coefficient of $\Box R$ is sufficiently large, possibly due the presence of large numbers of quantum fields.   

Effects of Conformally Invariant Quantum Fields on Future Singularities - Part II

The effects of conformally invariant quantum fields on universes with future singularities are numerically investigated. It is assumed that these singularities are caused by dark energy in the form of a perfect fluid with a known equation of state. Comparison is made between the behaviors of the universe for a purely classical analysis, an order reduced quantum analysis, and a fully self-consistent semiclassical backreaction analysis. Numerical results for big rip (type I) and little rip cosmologies are presented. It is found, consistent with theory, that for one sign of the coefficient of $\Box R$ term in the trace of the semi-classical backreaction equations, the future singularity is always avoided, and the universe achieves a maximum size before recontracting, while for the other sign the universe is inevitably driven to expand forever, driving it to the singularity.   

Effects of Conformally Invariant Quantum Fields on Future Singularities - Part III

The effects of conformally invariant quantum fields on universes with future singularities are numerically investigated. It is assumed that these singularities are caused by dark energy in the form of a perfect fluid with a known equation of state. Numerical results for type III, type II, and type IV singularities are presented. It is found that for one sign of the coefficient of $\Box R$ term in the trace of the semi-classical backreaction equations, the future singularity may or may not be reached, depending on the initial conditions, while for the other sign, the singularity is always reached. However, in every case where the singularity is reached, quantum effects apparently cancel or partially cancel the divergences caused by the classical dark energy.   

Natural vacuum state for quantum fields in an initially radiation dominated universe and its relationship to the Bunch-Davies state

It is shown that if the universe is initially radiation dominated, then for a scalar field with arbitrary mass and curvature coupling there is a natural vacuum state. The evolution of scalar fields in this vacuum state is investigated for a simple model where the presence of a cosmological constant causes the universe to expand exponentially at late times and thus to be asymptotically de Sitter. The question of whether the vacuum state approaches the Bunch-Davies state at late times is addressed.   

Quantum instability of global de Sitter space

Global de Sitter space is an exact solution to the semiclassical backreaction equations when the quantum fields are in the Bunch-Davies state. For massive scalar fields it is shown that perturbations of the Bunch-Davies state result in deviations of the energy density from its value in the Bunch-Davies state which grow exponentially during the early part of the contraction phase. During the expansion phase the sizes of these deviations decrease. However, in many cases the deviations become large enough to significantly alter the evolution of the universe before the expanding phase is reached.   

Generalizing the Faddeev-Jackiw Technique to Curved Spacetimes to Study Bose-Einstein Condensates in Space

Motivated by the desire to fully understand Bose-Einstein condensates in curved spacetimes, we present a generalization of the Faddeev-Jackiw technique for constraint reduction that simplifies calculating the Poisson brackets for gauge field theories in curved backgrounds. The Faddeev-Jackiw technique is a symplectic approach to phase space coordinate reduction on singular Lagrangians which offers an alternative to the Dirac technique. This approach was generalized by Barcelos-Nieto and Wotzasek to make its application easier. We find that the technique is a useful tool that avoids some of the subtle complications of the Dirac approach to constraints. A major difference between our work and previous formulations is that we do not explicitly construct the symplectic matrix, as that is not necessary. We apply this formulation to the Ginzburg-Landau action and calculate its Poisson brackets in a curved spacetime. We sketch out steps to apply the technique to a Bose field in the gauge theory General Relativity.   

An Early Cyclic Universe

We provide a comprehensive numerical study of the Emergent Cyclic Inflation scenario. This is a scenario where instead of traditional monotonic slow roll inflation, the universe expands over numerous short asymmetric cycles due to the production of entropy via interactions among different species. This is one of the very few scenarios of inflation which provides a nonsingular geodesically complete space-time and does not require any ``reheating'' mechanism.   

Cosmology at z~2.4 from the Baryon Acoustic Oscillations measured in the SDSS/DR11 BOSS-LyA quasar sample

The Baryon Acoustic Oscillation (BAO) scale, imprinted in the distribution of matter in the Universe, can be used to study the geometry of the Universe as a function of redshift (or cosmic time). Using a total of 160 000 high-redshift quasar spectra at z $>$ 2.15 from the Sloan Digital Sky Survey III (SDSS-III) Data Release 11 (DR11), we are able to measure the BAO scale at high redshift (z~2.4), both in the auto-correlation of the transmitted flux fraction of the observed flux of a quasar in the Lyman alpha forest region (Delubac et al., in preparation) and in its cross-correlation with the density of quasars (Font-Ribera et al. 2013). From the measurement of the BAO scale along and across the line of sight, we are able to measure the Hubble parameter and the angular diameter distance at z~2.4 with an accuracy better than 3\%.   

DESI and other Dark Energy experiments in the era of neutrino mass measurements

We present projections for future cosmological parameter measurements, including neutrino masses, Dark Energy, curvature, modified gravity, the inflationary perturbation spectrum, non-Gaussianity, and dark radiation. We focus on DESI and generally redshift surveys (BOSS, HETDEX, eBOSS, Euclid, and WFIRST), but also include CMB (Planck) and weak gravitational lensing (DES and LSST) constraints. The goal is to present a consistent set of projections, for concrete experiments, which are otherwise scattered throughout many papers and proposals. We include neutrino mass as a free parameter in most projections, as it will inevitably be relevant -- DESI and other experiments can measure the sum of neutrino masses to $\sim 0.02$ eV or better, while the minimum possible sum is $\sim 0.06$ eV.