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Slow-roll inflation is a successful paradigm. However we find that even a
small coupling of the inflaton to other light fields can dramatically alter the
dynamics and predictions of inflation. As an example, the inflaton can
generically have an axion-like coupling to gauge bosons. Even relatively small
couplings will automatically induce a thermal bath during inflation. The
thermal friction from this bath can easily be stronger than Hubble friction,
significantly altering the usual predictions of any particular inflaton
potential. Thermal effects suppress the tensor-to-scalar ratio $r$
significantly, and predict unique non-gaussianities. This axion-like coupling
provides a minimal model of warm inflation which avoids the usual problem of
thermal backreaction on the inflaton potential. As a specific example, we find
that hybrid inflation with this axion-like coupling can easily fit the current
cosmological data.
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