5,157 research outputs found
Linearized Weyl-Weyl Correlator in a de Sitter Breaking Gauge
We use a de Sitter breaking graviton propagator to compute the tree order
correlator between noncoincident Weyl tensors on a locally de Sitter
background. An explicit, and very simple result is obtained, for any spacetime
dimension D, in terms of a de Sitter invariant length function and the tensor
basis constructed from the metric and derivatives of this length function. Our
answer does not agree with the one derived previously by Kouris, but that
result must be incorrect because it not transverse and lacks some of the
algebraic symmetries of the Weyl tensor. Taking the coincidence limit of our
result (with dimensional regularization) and contracting the indices gives the
expectation value of the square of the Weyl tensor at lowest order. We propose
the next order computation of this as a true test of de Sitter invariance in
quantum gravity.Comment: 31 pages, 2 tables, no figures, uses LaTex2
Some Inconvenient Truths
A recent paper by Fr\"ob employs the linearized Weyl-Weyl correlator to
construct the tensor power spectrum. Although his purpose was to argue that
infrared divergences and secular growth in the graviton propagator are gauge
artefacts, a closer examination of the problem leads to the opposite
conclusion. The analogies with the BMS symmetries of graviton scattering on a
flat background, and with the Aharonov-Bohm effect of quantum mechanics,
suggest that de Sitter breaking secular growth is likely to be observable in
graviton loop effects. And a recent result for the vacuum polarization does
seem to show it.Comment: 14 pages, uses LaTeX2
Light Cone QED in a Homogeneous Electric Background
I present an exact solution for the Heisenberg picture, Dirac electron in the
presence of an electric field which depends arbitrarily upon the light cone
time parameter . This is the largest class of background
fields for which the mode functions have ever been obtained. The solution
applies to electrons of any mass and in any spacetime dimension. The
traditional ampiguity at is explicitly resolved. It turns out that
the initial value operators include not only at
but also at . Pair creation
is a discrete and instantaneous event on the light cone, so one can compute the
particle production rate in real time. In dimensions one can also see
the anomaly. Another novel feature of the solution is that the expectation
value of the currents operators depends non-analytically upon the background
field. This seems to suggest a new, strong phase of QED.Comment: 9 pages, 2 figures, LaTeX 2 epsilon, talk given at the 6th Workshop
on Non-Perturbative QCD, Paris, France, June 5-9, 200
- …