119229799
Cosmological parameter estimation from CMB and X-ray cluster after Planck
. We investigate constraints on cosmological parameters in three 8-parameter models with the summed neutrino mass as a free parameter, by a joint analysis of CCCP X-ray cluster data, the newly released Planck CMB data as well as some external data sets including baryon acoustic oscillation measurements from the 6dFGS, SDSS DR7 and BOSS DR9 surveys, and Hubble Space Telescope Ho measurement. We find that the combined data strongly favor a non-zero neutrino masses at more than 3 sigma confidence level in these non-vanilla models. Allowing the CMB lensing amplitude A(L) to vary, we find A(L) > 1 at 3 sigma confidence level. For dark energy with a constant equation of state w, we obtain w < -1 at 3 sigma confidence level. The estimate of the matter power spectrum amplitude 08 is discrepant with the Planck value at 2 sigma confidence level, which reflects some tension between X-ray cluster data and Planck data in these non-vanilla models. The tension can be alleviated by adding a 9% systematic shift in the cluster mass function.
15707844
Holography, UV/IR Relation, Causal Entropy Bound, and Dark Energy
The constraint on the total energy in a given spatial region is given from holography by the mass of a black hole that just fits in that region, which leads to an UV/IR relation: the maximal energy density in that region is propotional to M(p)(2)/L(2), wher M(p) is the Planck mass and L is the spatial scale of that region under consideration. Assuming that maximal black hole in the universe is formed through gravitational collapse of perturbations in the universe, then the "Jeans" scale of the perturbations gives a causal connection scale R(CC). For gravitational perturbations, R(CC)(-2) = Max ((H) over dot + 2H(2), -(H) over dot) for a flat universe. We study the cosmological dynamics of the corresponding vacuum energy density by choosing the causal connection scale as the IR cutoff in the UV/IR relation, in the cases of the vacuum energy density as an independently conserved energy component and an effective dynamical cosmological constant, respectively. It turns out that only the case with the choice R(CC)(-2) = (H) over dot + 2H(2), could be consistent with the current cosmological observations when the vacuum density appears as an independently conserved energy component. In this case, the model is called holographic Ricci scalar dark energy model in the literature.
118528998
Note on self-gravitating radiation in AdS spacetime
Recently Vaganov and Hammersley investigated independently the equilibrium self-gravitating radiation in higher (d >= 4)-dimensional, spherically symmetric anti-de Sitter space. It was found that in 4 = 11, the temperature, mass, and entropy of the self-gravitating configuration are monotonic functions of the central energy density, asymptoting to their maxima as the central density goes to infinity. In this paper we investigate the equilibrium self-gravitating radiation in higher-dimensional, plane-symmetric anti-de Sitter space. We find that there exist essential differences from the spherically syrnmetric case: In each dimension (d >= 4), there are maximal mass (density), maximal entropy (density), and maximal temperature configurations; they do not appear at the same central energy density; the oscillation behavior appearing in the spherically symmetric case does not happen in this case; and the mass (density), as a function of the central energy density, increases first and reaches its maximum at a certain central energy density and then decreases monotonically in 4 = 8, besides the maximum, the mass (density) of the equilibrium configuration has a minimum: the mass (density) first increases and reaches its maximum, then decreases to its minimum, and then increases to its asymptotic value monotonically. The reason causing the difference is discussed.
118029650
Future CMB integrated-Sachs-Wolfe-lensing bispectrum constraints on modified gravity in the parametrized post-Friedmann formalism
We forecast the constraints on both Hu-Sawicki model and Bertschinger-Zukin model of modified gravity within the Parameterized Post-Friedmann (PPF) formalism for the Planck satellite experiment by performing the joint analysis of ISW-Lensing bispectrum and CMB power spectrum. We find that, even considering the temperature-temperature mode of CMB power spectrum only, Planck data are expected to reduce the error bars on the modified gravity parameter $B_0$ (related to the present value of Compton wavelength of the extra scalar degree of freedom) at least one order magnitude compared with WMAP. The spectrum-bispectrum joint analysis can further improve the results by a factor ranging from 1.14 to 5.32 depending on the specific modified gravity model. One of our main results is that the cross-correlation between ISW-Lensing bispectrum and power spectrum can be safely neglected when performing the joint analysis. For simplicity, we only investigate the likelihood of one parameter ({$B_0$}) and fix all other cosmological parameters to their best-fit values in WMAP7yr results.
119185851
Timelike vector field dynamics in the early universe
We study the dynamics of a timelike vector field when the background spacetime is in an accelerating phase in the early universe. With a timelike vector field, an inflationary phase is shown to be difficult to realize, so we investigate the evolution of a vector field within a scalar field-driven inflation model. Also, we calculate the power spectrum of the vector field without considering the metric perturbations. While the time component of the vector field perturbations provides a scale invariant spectrum when ζ = 0, where ζ is a nonminimal coupling parameter, both the longitudinal and the transverse perturbations give a scale invariant spectrum when ζ = 1/6 in the absence of the coupling terms. The deviation of the power spectrum due to the coupling terms is calculated by use of the Greens’ function.
118657913
Constraining models of f(R) gravity with Planck and WiggleZ power spectrum data
In order to explain cosmic acceleration without invoking "dark" physics, we consider f(R) modified gravity models, which replace the standard Einstein-Hilbert action in General Relativity with a higher derivative theory. We use data from the WiggleZ Dark Energy survey to probe the formation of structure on large scales which can place tight constraints on these models. We combine the large-scale structure data with measurements of the cosmic microwave background from the Planck surveyor. After parameterizing the modification of the action using the Compton wavelength parameter B0, we constrain this parameter using ISiTGR, assuming an initial non-informative log prior probability distribution of this cross-over scale. We find that the addition of the WiggleZ power spectrum provides the tightest constraints to date on B0 by an order of magnitude, giving log10(B0) < -4.07 at 95% confidence limit. Finally, we test whether the effect of adding the lensing amplitude ALens and the sum of the neutrino mass ∑mν is able to reconcile current tensions present in these parameters, but find f(R) gravity an inadequate explanation.
122768225
Nonequilibrium inflaton dynamics and reheating: Back reaction of parametric particle creation and curved spacetime effects
We present a detailed and systematic analysis of the nonperturbative, nonequilibrium dynamics of a quantum field in the reheating phase of inflationary cosmology, including full back reactions of the quantum field on the curved spacetime, as well as the fluctuations on the mean field. We use the O(N) field theory with unbroken symmetry in a spatially flat Friedmann-Robertson-Walker (FRW) universe to study the dynamics of the inflaton in the post-inflation, preheating stage. Oscillations of the inflaton{close_quote}s zero mode induce parametric amplification of quantum fluctuations, resulting in a rapid transfer of energy to the inhomogeneous modes of the inflaton field. The large-amplitude oscillations of the mean field, as well as stimulated emission effects require a nonperturbative formulation of the quantum dynamics, while the nonequilibrium evolution requires a statistical field theory treatment. We adopt the coupled nonperturbative equations for the mean field and variance derived in a preceding paper [S. A. Ramsey and B. L. Hu, this issue, Phys. Rev. D {bold 56}, 661 (1997)] by means of a two-particle-irreducible (2PI), closed-time-path (CTP) effective action for curved spacetimes while specialized to a dynamical FRW background, up to leading order in the 1/N expansion. Adiabatic regularization is employed to yield a covariantly conserved,more » renormalized energy-momentum tensor. The renormalized dynamical equations are evolved numerically from initial data which are generic to the end state of slow roll in many inflationary cosmological scenarios. The initial conditions consist of a large-amplitude, quasiclassical, oscillating mean field {l_angle}{Phi}{r_angle} with variance {l_angle}{Phi}{sup 2}{r_angle}{minus}{l_angle}{Phi}{r_angle}{sup 2} around the de Sitter-invariant vacuum. (Abstract Truncated)« less
119019834
Statistical mechanics and quantum cosmology
ABSTRACT Statistical mechanical concepts and processes such as decoherence, correlation, and dissipation can prove to be of basic importance to understanding some fundamental issues of quantum cosmology and theoretical physics such as the choice of initial states, quantum to classical transition and the emergence of time. Here we summarize our effort in 1) constructing a unified theoretical framework using techniques in interacting quantum field theory such as influence functional and coarse-grained effective action to discuss the interplay of noise, fluctuation, dissipation and decoherence; and 2) illustrating how these concepts when applied to quantum cosmology can alter the conventional views on some basic issues. Two questions we address are 1) the validity of minisuperspace truncation, which is usually assumed without proof in most discussions, and 2) the relevance of specific initial conditions, which is the prevailing view of the past decade. We also mention how some current ideas in chaotic dynamics, dissipative collective dynamics and complexity can alter our view of the quantum nature of the universe.
119214934
A Master Equation for Gravitational Decoherence: Probing the Textures of Spacetime
We give a first principles derivation of a master equation for the evolution of a quantum matter field in a linearly perturbed Minkowski spacetime, based solely on quantum field theory and general relativity. We make no additional assumptions nor introduce extra ingredients, as is often done in alternative quantum theories. When the quantum matter field is projected to a one-particle state, the master equation for a non-relativistic quantum particle in a weak gravitational field predicts decoherence in the energy basis, in contrast to most existing theories of gravitational decoherence. We point out the gauge nature of time and space reparameterizations in matter–gravity couplings, and warn that ‘intrinsic’ decoherence or alternative quantum theories invoking stochastic dynamics arising from temporal or spatial fluctuations violate this fundamental symmetry of classical general relativity. Interestingly we find that the decoherence rate depends on extra parameters other than the Planck scale, an important feature of gravitational decoherence. This is similar to the dependence of the decoherence rate of a quantum Brownian particle to the temperature and spectral density of the environment it interacts with. The corresponding features when gravity acts as an environment in decohering quantum objects are what we call the ‘textures’ of spacetime. We point out the marked difference between the case when gravity is represented as a background spacetime versus the case when gravity acts like a thermodynamic bath to quantum particles. This points to the possibility of using gravitational decoherence measurements to discern whether gravity is intrinsically elemental or emergent.
116099863
Wigner Function and Quantum Liouville Equation in Curved Spacetime
123110822
Corrections to scaling for period doubling
We have studied a multiple scaling which describes corrections to scaling. For the period doubling in one-dimensional dissipative maps, two-dimensional areapreserving maps, and four-dimensional symplectic maps, the multiple scaling is seen to be well-obeyed, and new scaling factors have been found. The multiple scaling is also seen to be a very powerful tool for searching for scaling behavior.