Gravitational Waves from a Rolling Axion Monodromy. (arXiv:2005.10280v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ozsoy_O/0/1/0/all/0/1">Ogan Özsoy</a>
In string theory inspired models of axion-like fields, sub-leading
non-perturbative effects, if sufficiently large, can introduce steep cliffs and
gentle plateaus onto the underlying scalar potential. During inflation, the
motion of a spectator axion $sigma$ in this potential becomes temporarily
fast, leading to exponential amplification of one helicity state of gauge
fields. In this model, the axion-gauge field sector interacts gravitationally
with the inflaton, therefore the resulting sourced scalar and tensor
fluctuations are produced only through gravitational interactions. Due to the
temporary speeding up of $sigma$ in the cliff-like regions, the tensor and
scalar correlators sourced by the gauge fields exhibit a localized bump in
momentum space corresponding to the modes that exit the horizon while the roll
of $sigma$ is significant. Thanks to the gravitational coupling of gauge
fields with the visible sector and the localized nature of particle production,
this model can generate observable gravitational wave signal at CMB scales
while satisfying the current limits on scalar perturbations. The resulting
gravitational wave signal breaks parity and exhibit sizeable non-Gaussianity
that can be probed by future CMB B-mode missions. Depending on the initial
conditions on $sigma$ and model parameters, the roll of the spectator axion
can also generate an observably large GW signature at interferometer scales
while respecting the bounds on the scalar fluctuations from primordial black
hole limits.
In string theory inspired models of axion-like fields, sub-leading
non-perturbative effects, if sufficiently large, can introduce steep cliffs and
gentle plateaus onto the underlying scalar potential. During inflation, the
motion of a spectator axion $sigma$ in this potential becomes temporarily
fast, leading to exponential amplification of one helicity state of gauge
fields. In this model, the axion-gauge field sector interacts gravitationally
with the inflaton, therefore the resulting sourced scalar and tensor
fluctuations are produced only through gravitational interactions. Due to the
temporary speeding up of $sigma$ in the cliff-like regions, the tensor and
scalar correlators sourced by the gauge fields exhibit a localized bump in
momentum space corresponding to the modes that exit the horizon while the roll
of $sigma$ is significant. Thanks to the gravitational coupling of gauge
fields with the visible sector and the localized nature of particle production,
this model can generate observable gravitational wave signal at CMB scales
while satisfying the current limits on scalar perturbations. The resulting
gravitational wave signal breaks parity and exhibit sizeable non-Gaussianity
that can be probed by future CMB B-mode missions. Depending on the initial
conditions on $sigma$ and model parameters, the roll of the spectator axion
can also generate an observably large GW signature at interferometer scales
while respecting the bounds on the scalar fluctuations from primordial black
hole limits.
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