4,200 research outputs found
Leading Log Solution for Inflationary Yukawa
We generalize Starobinskii's stochastic technique to the theory of a
massless, minimally coupled scalar interacting with a massless fermion in a
locally de Sitter geometry. The scalar is an ``active'' field that can engender
infrared logarithms. The fermion is a ``passive'' field that cannot cause
infrared logarithms but which can carry them, and which can also induce new
interactions between the active fields. The procedure for dealing with passive
fields is to integrate them out, then stochastically simplify the resulting
effective action following Starobinski\u{\i}. Because Yukawa theory is
quadratic in the fermion this can be done explicitly using the classic solution
of Candelas and Raine. We check the resulting stochastic formulation against an
explicit two loop computation. We also derive a nonperturbative, leading log
result for the stress tensor. Because the scalar effective potential induced by
fermions is unbounded below, back-reaction from this model might dynamically
cancel an arbitrarily large cosmological constant.Comment: 35 pages, LaTeX 2epsilon, 4 figures (using axodraw), version 2 has an
updated reference lis
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
Causality Implies Inflationary Back-Reaction
There is a widespread belief among inflationary cosmologists that a local
observer cannot sense super-horizon gravitons. The argument goes that a local
observer would subsume super-horizon gravitons into a redefinition of his
coordinate system. We show that adopting this view for pure gravity on de
Sitter background leads to time variation in the Hubble parameter measured by a
local observer. It also leads to a violation of the gravitational field
equation because that equation is obeyed by the full metric,
rather than the one which has been cleansed of super-horizon modes.Comment: 20 pages, 2 figures, uses LaTeX2e, version 2 slightly revised for
publicatio
Chronic pain as the result of traumatic injury: A group counseling model for survivors
Millions of Americans live with chronic pain as the result of traumatic injury. These individuals face countless challenges as they attempt to cope with daily pain and grieve the many losses caused by their injuries. The physical and emotional stresses associated with chronic pain and traumatic injury place these survivors at significant psychological risk and contribute to the perpetuation of their chronic pain. Group counseling with a grief model emphasis is a cost effective way to meet the specific needs of survivors living with chronic pain. These needs include: the establishment of a social support system, an opportunity to grieve losses since the injury, the development of self-care skills, and the learning of skills and strategies to move through pain and grief toward empowerment and self-esteem. An eight week psychoeducational support group is described
The Graviton Propagator in de Donder Gauge on de Sitter Background
We construct the graviton propagator on de Sitter background in exact de
Donder gauge. We prove that it must break de Sitter invariance, just like the
propagator of the massless, minimally coupled scalar. Our explicit solutions
for its two scalar structure functions preserve spatial homogeneity and
isotropy so that the propagator can be used within the larger context of
inflationary cosmology, however, it is simple to alter the residual symmetry.
Because our gauge condition is de Sitter invariant (although no solution for
the propagator can be) renormalization should be simpler using this propagator
than one based on a noncovariant gauge. It remains to be seen how other
computational steps compare.Comment: 39 pages, no figures, uses LaTeX2
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