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[1008.5157]
Higgs inflation: consistency and generalisations

Authors:  F. Bezrukov, A. Magnin, M. Shaposhnikov, S. Sibiryakov 
Abstract:  We analyse the selfconsistency of inflation in the Standard Model, where the
Higgs field has a large nonminimal coupling to gravity. We determine the
domain of energies in which this model represents a valid effective field
theory as a function of the background Higgs field. This domain is bounded
above by the cutoff scale which is found to be higher than the relevant
dynamical scales throughout the whole history of the Universe, including the
inflationary epoch and reheating. We present a systematic scheme to take into
account quantum loop corrections to the inflationary calculations within the
framework of effective field theory. We discuss the additional assumptions that
must be satisfied by the ultraviolet completion of the theory to allow
connection between the parameters of the inflationary effective theory and
those describing the lowenergy physics relevant for the collider experiments.
A class of generalisations of inflationary theories with similar properties is
constructed. 

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Syksy Rasanen
Joined: 02 Mar 2005 Posts: 128 Affiliation: University of Helsinki

Posted: September 17 2010 


This is the most recent analysis of the validity of effective field theory and stability under quantum corrections in the very interesting proposal by Bezrukov and Shaposhnikov (0710.3755) of using the Standard Model Higgs as the inflaton.
The model relies on a large nonminimal coupling of the Higgs field to gravity, ξ˜10^{4}. It has been argued that this means that the cutoff scale of the model is below the Planck scale by the factor 1 / ξ, and that the model is therefore not valid at the high energy scales where inflation occurs. Similarly, since the model involves gravity, it is nonrenormalisable, and it has been argued that this spoils the predictivity of the model (0902.4465, 0903.0355, 1002.2730).
Bezrukov et al analyse the situation by identifying a lower limit on the breakdown scale from the suppression coefficients of nonrenormalisable operators, and do the analysis both in the Einstein and Jordan frames. The key feature is that the cutoff scale depends on the field value, since the background is timedependent. They conclude that the cutoff scale remains above the scales of interest. However, they find that the connection between the inflationary parameters and the lowenergy parameters accessible to collider experiments is sensitive to the quantum corrections, so connecting cosmological measurements and LHC measurements requires extra assumptions.
This model brings home the fact that while conformal transformations don't change the content of a classical scalar theory in curved space, quantising and changing conformal frame do not commute. This is of course also true for inflationary models which are written in the Einstein frame to begin with: how do you know which is the correct frame?
One question is that the motivation for the SM Higgs potential plus a nonminimal coupling comes from arguments about renormalisation, but since the model is nonrenormalisable anyway, I'm not sure about the strength of that starting assumption. 

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