493 research outputs found
Lamb Shift of Unruh Detector Levels
We argue that the energy levels of an Unruh detector experience an effect
similar to the Lamb shift in Quantum Electrodynamics. As a consequence, the
spectrum of energy levels in a curved background is different from that in flat
space. As examples, we consider a detector in an expanding Universe and in
Rindler space, and for the latter case we suggest a new expression for the
local virtual energy density seen by an accelerated observer. In the
ultraviolet domain, that is when the space between the energy levels is larger
than the Hubble rate or the acceleration of the detector, the Lamb shift
quantitatively dominates over the thermal response rate.Comment: 20 page
Deducing Cosmological Observables from the S-matrix
We study one loop quantum gravitational corrections to the long range force
induced by the exchange of a massless scalar between two massive scalars. The
various diagrams contributing to the flat space S-matrix are evaluated in a
general covariant gauge and we show that dependence on the gauge parameters
cancels at a point considerably {\it before} forming the full S-matrix, which
is unobservable in cosmology. It is possible to interpret our computation as a
solution to the effective field equations --- which could be done even in
cosmology --- but taking account of quantum gravitational corrections from the
source and from the observer.Comment: 28 pages, 5 figures, uses LaTeX2
The Graviton Tail almost Completely Wags the Dog
One graviton loop corrections to the vacuum polarization on de Sitter show
two interesting infrared effects: a secular enhancement of the photon electric
field strength and a long range running of the Coulomb potential. We show that
the first effect derives solely from the "tail" term of the graviton
propagator, but that the second effect does not. Our result agrees with the
earlier observation that the secular enhancement of massless fermion mode
functions derives from solely from the tail term. We discuss the implications
this has for the important project of generalizing to quantum gravity the
Starobinsky technique for summing the series of leading infrared effects from
inflationary quantum field theory.Comment: 17 pages, 1 figure, uses LaTeX2
Graviton Loop Corrections to Vacuum Polarization in de Sitter in a General Covariant Gauge
We evaluate the one-graviton loop contribution to the vacuum polarization on
de Sitter background in a 1-parameter family of exact, de Sitter invariant
gauges. Our result is computed using dimensional regularization and fully
renormalized with BPHZ counterterms, which must include a noninvariant owing to
the time-ordered interactions. Because the graviton propagator engenders a
physical breaking of de Sitter invariance two structure functions are needed to
express the result. In addition to its relevance for the gauge issue this is
the first time a covariant gauge graviton propagator has been used to compute a
noncoincident loop. A number of identities are derived which should facilitate
further graviton loop computations.Comment: 61 pages, 1 figure, 11 tables, version 2 (63 pages) revised for
publication in CQ
One loop graviton corrections to dynamical photons in de Sitter
We employ a recent, general gauge computation of the one loop graviton
contribution to the vacuum polarization on de Sitter to solve for one loop
corrections to the photon mode function. The vacuum polarization takes the form
of a gauge independent, spin 2 contribution and a gauge dependent, spin 0
contribution. We show that the leading secular corrections derive entirely from
the spin 2 contribution.Comment: 41 pages, no figures, uses LaTeX2
Single Graviton Loop Contribution to the Self-Mass of a Massless, Conformally Coupled Scalar on de Sitter Background
We use a simplified formalism to re-compute the single graviton loop
contribution to the self-mass of a massless, conformally coupled scalar on de
Sitter background which was originally made by Boran, Kahya and Park [1-3]. Our
result resolves the problem with the flat space correspondence limit that was
pointed out by Fr\"ob [4]. We discuss how this computation will be used in a
long-term project to purge the linearized effective field equation of gauge
dependence.Comment: 26 pages, 1 figure, uses LaTeX 2e. Version 2 revised slightly for
publicatio
Quantum backreaction in evolving FLRW spacetimes
Quantum fluctuations of a nonminimally coupled scalar field in D-dimensional
homogeneous and isotropic background are calculated within the operator
formalism in curved models with time evolutions of the scale factor that allow
smooth transitions between contracting and expanding and between decelerating
and accelerating regimes. The coincident propagator is derived and used to
compute the one-loop backreaction from the scalar field. The inflationary
infrared divergences are absent in Bunch-Davies vacuum when taking into account
a preceding cosmological era or spatial curvature which can be either positive
or negative. It is found that asymptotically, the backreaction energy density
in the minimally coupled case grows logarithmically with the scale factor in
quasi-de Sitter space, and in a class of models decays in slow-roll inflation
and grows as a power-law during super-inflation. The backreaction increases
generically in a contracting phase or in the presence of a negative nonminimal
coupling. The effects of the coupling and renormalization scale upon the
quantum fluctuations together with the novel features due to nontrivial time
evolution and spatial curvature are clarified with exact solutions and
numerical examples.Comment: 23 pages, 6 figure
A Simple Operator Check of the Effective Fermion Mode Function during Inflation
We present a relatively simple operator formalism which reproduces the
leading infrared logarithm of the one loop quantum gravitational correction to
the fermion mode function on a locally de Sitter background. This rule may
serve as the basis for an eventual stochastic formulation of quantum gravity
during inflation. Such a formalism would not only effect a vast simplification
in obtaining the leading powers of at fixed loop orders, it would also
permit us to sum the series of leading logarithms. A potentially important
point is that our rule does not seem to be consistent with any simple infrared
truncation of the fields. Our analysis also highlights the importance of spin
as a gravitational interaction that persists even when kinetic energy has
redshifted to zero.Comment: 39 pages, no figuire.(1) New version has clarified the ultimate
motivation by adding sentences to the abstract and to the penultimate
paragraph of the introduction. (2) By combining a number of references and
equations we have managed to reduce the length by 2 page
On the One Loop Corrections to Inflation II: The Consistency Relation
In this paper we extend our previous treatment of the one-loop corrections to
inflation. Previously we calculated the one-loop corrections to the background
and the two-point correlation function of inflaton fluctuations in a specific
model of chaotic inflation. We showed that the loop corrections depend on the
total number of e-foldings and estimated that the effect could be as large as a
few percent in a lambda-phi-four model of chaotic inflation. In the present
paper we generalize the calculations to general inflationary potentials. We
find that effect can be as large as 70% in the simplest model of chaotic
inflation with a quadratic inflationary potential. We discuss the physical
interpretation of the effect in terms of the tensor-to-scalar consistency
relation. Finally, we discuss the relation to the work of Weinberg on quantum
contributions to cosmological correlators.Comment: 21 pages, 4 figures. v2: IR approximation corrected, references
added. v3: typos correcte
- …