  We propose the first model of warm inflation in which the particle production
emerges directly from coupling the inflaton to Standard Model particles. Warm
inflation, an early epoch of sustained accelerated expansion at finite
temperature, is a compelling alternative to cold inflation, with distinct
predictions for inflationary observables such as the amplitude of fluctuations,
the spectral tilt, the tensor-to-scalar ratio, and non-gaussianities. In our
model a heavy QCD axion acts as the warm inflaton whose coupling to Standard
Model gluons sources the thermal bath during warm inflation. Axion-like
couplings to non-Abelian gauge bosons have been considered before as a
successful microphysical theory with emerging thermal friction that can
maintain finite temperature during inflation via sphaleron heating. However,
the presence of light fermions charged under the non- Abelian group suppresses
particle production, hindering a realization of warm inflation by coupling to
QCD. We point out that the Standard Model quarks can be heavy during warm
inflation if the Higgs field resides in a high-energy second minimum which
restores efficient sphaleron heating. A subsequent large reheating temperature
is required to allow the Higgs field to relax to its electroweak minimum.
Exploring a scenario in which hybrid inflation provides the large reheating
temperature, we show that future collider and beam dump experiments have
discovery potential for a heavy QCD axion taking the role of the minimal warm
inflaton.
