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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