Conformal Invariance, Dynamical Dark Energy and the CMB

General Relativity receives quantum corrections relevant at cosmological distance scales from the conformal scalar degrees of freedom required by the trace anomaly of the quantum stress tensor in curved space. In the theory including the trace anomaly terms, the cosmological "constant" becomes dynamical and hence potentially dependent upon both space and time. The fluctuations of these anomaly scalars may also influence the spectrum and statistics of the Cosmic Microwave Background. Under the hypothesis that scale invariance should be promoted to full conformal invariance, an hypothesis supported by the exact equivalence of the conformal group of three dimensions with the de Sitter group SO(4,1), the form of the CMB bispectrum can be fixed, and the trispectrum constrained. The non-Gaussianities predicted by conformal invariance differ from those suggested by simple models of inflation.Comment: 8 pages, Latex2e, uses moriond.sty file. Talk given at "2010 Cosmology," March 13-20, 2010, La Thuile, Aosta, Ital

Gauge Invariance in 2PI Effective Actions

The problem of maintaining gauge invariance in the 2PI formulation of QED is discussed. A modified form of the 2PI effective action is suggested in which Ward identities for external (background field) and internal (quantum field) gauge transformations are both satisfied, but in different manners. The residual gauge-fixing dependence in this modified 2PI formulation vanishes in a certain low momentum limit, which allows it to be used reliably for calculating quantities such as transport coeffcients and soft field relaxation in hot gauge theories.Comment: Talk given at Strong and Electroweak Matter 2002, Oct. 4, 2002 in Heidelberg, Germany; Five pages, uses World Scientific style file, ws-procs9x6.cls. To be published in the Proceedings of SEWM 2002 by World Scientific Publishing C

Scalar Gravitational Waves in the Effective Theory of Gravity

As a low energy effective field theory, classical General Relativity receives an infrared relevant modification from the conformal trace anomaly of the energy-momentum tensor of massless, or nearly massless, quantum fields. The local form of the effective action associated with the trace anomaly is expressed in terms of a dynamical scalar field that couples to the conformal factor of the spacetime metric, allowing it to propagate over macroscopic distances. Linearized around flat spacetime, this semi-classical EFT admits scalar gravitational wave solutions in addition to the transversely polarized tensor waves of the classical Einstein theory. The amplitude of the scalar wave modes, as well as their energy and energy flux which are positive and contain a monopole moment, are computed. Astrophysical sources for scalar gravitational waves are considered, with the excited gluonic condensates in the interiors of neutron stars in merger events with other compact objects likely to provide the strongest burst signals.Comment: 43 pages, Final published version, including all corrections. Sec. VI on energy and power radiated in scalar gravitational waves replaces previous version Sec. V and two Appendice

The Trace Anomaly and Dynamical Vacuum Energy in Cosmology

The trace anomaly of conformal matter implies the existence of massless scalar poles in physical amplitudes involving the stress-energy tensor. These poles may be described by a local effective action with massless scalar fields, which couple to classical sources, contribute to gravitational scattering processes, and can have long range gravitational effects at macroscopic scales. In an effective field theory approach, the effective action of the anomaly is an infrared relevant term that should be added to the Einstein-Hilbert action of classical General Relativity to take account of macroscopic quantum effects. The additional scalar degrees of freedom contained in this effective action may be understood as responsible for both the Casimir effect in flat spacetime and large quantum backreaction effects at the horizon scale of cosmological spacetimes. These effects of the trace anomaly imply that the cosmological vacuum energy is dynamical, and its value depends on macroscopic boundary conditions at the cosmological horizon scale, rather than sensitivity to the extreme ultraviolet Planck scale.Comment: Invited Talk at the Ninth Conference on Quantum Field Theory under the Influence of External Conditions, The University of Oklahoma, Norman, OK, September 21-25, 2009, To appear in the Proceedings of QFEXT09, 22 pages, 1 figur

Systematics of High Temperature Perturbation Theory: The Two-Loop Electron Self-Energy in QED

In order to investigate the systematics of the loop expansion in high temperature gauge theories beyond the leading order hard thermal loop (HTL) approximation, we calculate the two-loop electron proper self-energy in high temperature QED. The two-loop bubble diagram contains a linear infrared divergence. Even if regulated with a non-zero photon mass M of order of the Debye mass, this infrared sensitivity implies that the two-loop self-energy contributes terms to the fermion dispersion relation that are comparable to or even larger than the next-to-leading-order (NLO) contributions at one-loop. Additional evidence for the necessity of a systematic restructuring of the loop expansion comes from the explicit gauge parameter dependence of the fermion damping rate at both one and two-loops. The leading terms in the high temperature expansion of the two-loop self-energy for all topologies arise from an explicit hard-soft factorization pattern, in which one of the loop integrals is hard, nested inside a second loop integral which is soft. There are no hard-hard contributions to the two-loop Sigma at leading order at high T. Provided the same factorization pattern holds for arbitrary ell loops, the NLO high temperature contributions to the electron self-energy come from ell-1 hard loops factorized with one soft loop integral. This hard-soft pattern is both a necessary condition for the resummation over ell to coincide with the one-loop self-energy calculated with HTL dressed propagators and vertices, and to yield the complete NLO correction to the self-energy at scales ~eT, which is both infrared finite and gauge invariant. We employ spectral representations and the Gaudin method for evaluating finite temperature Matsubara sums, which facilitates the analysis of multi-loop diagrams at high T.Comment: 63 pages, 10 figures. Published version. Main differences from v1: (1) Gaudin method explained in more detail; (2) Full expression (3.9) for Two-Loop Bubble Self-Energy with no need to expand in M; (3) Appendix C eliminated and incorporated in Secs. 4 and 5; (4) Examples of the breakdown of HTL resummation added to summary and Discussion in Sec.

Gravitational Vacuum Condensate Stars

A new final state of gravitational collapse is proposed. By extending the concept of Bose-Einstein condensation to gravitational systems, a cold, dark, compact object with an interior de Sitter condensate $p_{_V} = -\rho_{_V}$ and an exterior Schwarzschild geometry of arbitrary total mass $M$ is constructed. These are separated by a shell with a small but finite proper thickness $\ell$ of fluid with equation of state $p=+\rho$, replacing both the Schwarzschild and de Sitter classical horizons. The new solution has no singularities, no event horizons, and a global time. Its entropy is maximized under small fluctuations and is given by the standard hydrodynamic entropy of the thin shell, which is of order $k_{_B}\ell Mc/\hbar$, instead of the Bekenstein-Hawking entropy formula, $S_{_{BH}}= 4\pi k_{_B} G M^2/\hbar c$. Hence unlike black holes, the new solution is thermodynamically stable and has no information paradox.Comment: 17 pages, LaTeX fil