83 research outputs found
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 and
an exterior Schwarzschild geometry of arbitrary total mass is constructed.
These are separated by a shell with a small but finite proper thickness
of fluid with equation of state , 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 , instead of the Bekenstein-Hawking entropy
formula, . Hence unlike black holes, the
new solution is thermodynamically stable and has no information paradox.Comment: 17 pages, LaTeX fil
Gravitational Condensate Stars: An Alternative to Black Holes
A new solution for the endpoint of gravitational collapse is proposed. By
extending the concept of Bose-Einstein condensation to gravitational systems, a
cold, compact object with an interior de Sitter condensate phase and an
exterior Schwarzschild geometry of arbitrary total mass M is constructed. These
are separated by a phase boundary with a small but finite thickness of fluid
with eq. 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, instead of the
Bekenstein-Hawking entropy. Unlike black holes, a collapsed star of this kind
is thermodynamically stable and has no information paradox.Comment: Four Pages, Two-Column RevTeX, uses title2.tex Title, Abstract,
Introduction slightly rewritten to comply with referee suggestions.
Conclusions and References adde
- …