290 research outputs found
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Sitter background which was originally made by Boran, Kahya and Park [1-3].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
Explaining Large Electromagnetic Logarithms from Loops of Inflationary Gravitons
Recent progress on nonlinear sigma models on de Sitter background has
permitted the resummation of large inflationary logarithms by combining a
variant of Starobinsky's stochastic formalism with a variant of the
renormalization group. We reconsider single graviton loop corrections to the
photon wave function, and to the Coulomb potential, in light of these
developments. Neither of the two 1-loop results have a stochastic explanation,
however, the flow of a curvature-dependent field strength renormalization
explains their factors of . We speculate that the factor of
in the Coulomb potential should not be considered as a leading logarithm
effect.Comment: 22 pages, uses LaTeX2e, slightly revised for publicatio
VennDiagramWeb: a web application for the generation of highly customizable Venn and Euler diagrams.
BackgroundVisualization of data generated by high-throughput, high-dimensionality experiments is rapidly becoming a rate-limiting step in computational biology. There is an ongoing need to quickly develop high-quality visualizations that can be easily customized or incorporated into automated pipelines. This often requires an interface for manual plot modification, rapid cycles of tweaking visualization parameters, and the generation of graphics code. To facilitate this process for the generation of highly-customizable, high-resolution Venn and Euler diagrams, we introduce VennDiagramWeb: a web application for the widely used VennDiagram R package. VennDiagramWeb is hosted at http://venndiagram.res.oicr.on.ca/ .ResultsVennDiagramWeb allows real-time modification of Venn and Euler diagrams, with parameter setting through a web interface and immediate visualization of results. It allows customization of essentially all aspects of figures, but also supports integration into computational pipelines via download of R code. Users can upload data and download figures in a range of formats, and there is exhaustive support documentation.ConclusionsVennDiagramWeb allows the easy creation of Venn and Euler diagrams for computational biologists, and indeed many other fields. Its ability to support real-time graphics changes that are linked to downloadable code that can be integrated into automated pipelines will greatly facilitate the improved visualization of complex datasets. For application support please contact [email protected]
Graviton Propagator in a 2-Parameter Family of de Sitter Breaking Gauges
We formulate the graviton propagator on de Sitter background in a 2-parameter
family of simple gauges which break de Sitter invariance. Explicit results are
derived for the first order perturbations in each parameter. These results
should be useful in computations to check for gauge dependence of graviton loop
corrections.Comment: 23 pages, 1 table, uses LaTeX2e, version 2 slightly revised for
publicatio
Breaking of scaling symmetry by massless scalar on de Sitter
We study the response of a classical massless minimally coupled scalar to a
static point scalar charge on de Sitter. By considering explicit solutions of
the problem we conclude that -- even though the dynamics formally admits
dilatation (scaling) symmetry -- the physical scalar field profile necessarily
breaks the symmetry. This is an instance of symmetry breaking in classical
physics due to large infrared effects. The gravitational backreaction, on the
other hand, does respect dilatation symmetry, making this an example of
symmetry non-inheritance phenomenon.Comment: 10 page
One-loop Graviton Corrections to Conformal Scalars on a de Sitter Background
We exploit a recent computation of one graviton loop corrections to the
self-mass [1] to quantum-correct the field equation for a massless, conformally
coupled scalar on a de Sitter background. With the obvious choice for the
finite part of the counterterm, we find that neither plane wave
mode functions nor the response to a point source acquires large infrared
logarithms. However, we do find a decaying logarithmic correction to the mode
function and a short distance logarithmic running of the potential in addition
to the power-law effect inherited from flat space.Comment: 25 pages, 2 figures; published versio
Vacuum properties of nonsymmetric gravity in de Sitter space
We consider quantum effects of a massive antisymmetric tensor field on the
dynamics of de Sitter space-time. Our starting point is the most general,
stable, linearized Lagrangian arising in nonsymmetric gravitational theories
(NGTs), where part of the antisymmetric field mass is generated by the
cosmological term. We construct a renormalization group (RG) improved effective
action by integrating out one loop vacuum fluctuations of the antisymmetric
tensor field and show that, in the limit when the RG scale goes to zero, the
Hubble parameter -- and thus the effective cosmological constant -- relaxes
rapidly to zero. We thus conclude that quantum loop effects in de Sitter space
can dramatically change the infrared sector of the on-shell gravity, making the
expansion rate insensitive to the original (bare) cosmological constant.Comment: 32 pages, 2 eps figure
Classical approximation to quantum cosmological correlations
We investigate up to which order quantum effects can be neglected in
calculating cosmological correlation functions after horizon exit. As a toy
model, we study theory on a de Sitter background for a massless
minimally coupled scalar field . We find that for tree level and one loop
contributions in the quantum theory, a good classical approximation can be
constructed, but for higher loop corrections this is in general not expected to
be possible. The reason is that loop corrections get non-negligible
contributions from loop momenta with magnitude up to the Hubble scale H, at
which scale classical physics is not expected to be a good approximation to the
quantum theory. An explicit calculation of the one loop correction to the two
point function, supports the argument that contributions from loop momenta of
scale are not negligible. Generalization of the arguments for the toy model
to derivative interactions and the curvature perturbation leads to the
conclusion that the leading orders of non-Gaussian effects generated after
horizon exit, can be approximated quite well by classical methods. Furthermore
we compare with a theorem by Weinberg. We find that growing loop corrections
after horizon exit are not excluded, even in single field inflation.Comment: 44 pages, 1 figure; v2: corrected errors, added references,
conclusions unchanged; v3: added section in which we compare with stochastic
approach; this version matches published versio
- …