High Energy Theory Seminar
17 September 2010
Federico Piazza
(Perimeter Institute)
Modifying gravity in the Infra
Red by imposing an "ultra-strong" equivalence principle
Abstract:
The standard framework "gravity + matter fields" deals with some
difficulties which already appear at low energy and therefore are
likely to be detached from its UV completion. I will give account
of a recent attempt to modify General Relativity (GR) in the infra-red
(IR) and address those difficulties. The proposed modification does not
contain any adjustable parameter as it is effective at length scales
comparable with the inverse curvature. The guiding line for this
modification is a recently proposed "ultra-strong" version of the
equivalence principle, according to which the vacuum expectation value
of the (bare) energy momentum tensor is exactly the same as in flat
space: constant everywhere and quartically divergent with the cut-off.
It is possible to work out explicitly the first IR-corrections to GR in
the case of a Friedman Robertson Walker Universe. I will show that, for
a matter dominated universe, the proposed modification goes in the
direction of an effective positive acceleration, but it is too mild to
explain, on its own, supernovae data.
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