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Rolling axions during inflation: perturbativity and signatures
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abstract
The motion of a pseudo-scalar field $X$ during inflation naturally induces a significant amplification of the gauge fields to which it is coupled. The amplified gauge fields can source characteristic scalar and tensor primordial perturbations. Several phenomenological implications have been discussed in the cases in which (i) $X$ is the inflation, and (ii) $X$ is a field different from the inflation, that experiences a temporary speed up during inflation. In this second case, visible sourced gravitational waves (GW) can be produced at the CMB scales without affecting the scalar perturbations, even if the scale of inflation is several orders of magnitude below what is required to produce a visible vacuum GW signal. Perturbativity considerations can be used to limit the regime in which these results are under perturbative control. We revised limits recently claimed for the case (i), and we extend these considerations to the case (ii). We show that, in both cases, these limits are satisfied by the applications that generate signals at CMB scales. Applications that generate gravitational waves and primordial black holes at much smaller scales are at the limit of the validity of this perturbativity analysis, so we expect those results to be valid up to possibly order one corrections.
Forward citations
Cited by 8 Pith papers
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Axion Inflation: Perturbative control in the strong backreaction regime
Axion inflation with strong gauge-field backreaction is generically non-perturbative for ξ ≳ 2.5, yet a newly found steady 'mild backreaction' phase at large β can stay perturbatively controlled.
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High-frequency gravitational waves from axion inflation in the weak-backreaction regime
Even in the weak-backreaction regime, axion inflation produces high-frequency primordial gravitational waves many orders of magnitude above the vacuum spectrum, peaking around MHz–GHz.
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Axion USR Inflation
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Cosmic string gravitational wave backgrounds at LISA: I. Signal survey, template reconstruction, and model comparison
As provided, the manuscript body (random lasing) does not correspond to the abstract (cosmic string gravitational wave backgrounds at LISA), leaving the abstract's quantitative claims unsupported by any accessible text.
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CMB constraints on $U(1)$ axion warm inflation
Axion-driven warm inflation with U(1) gauge fields is constrained with CMB data and remains viable for sub-Planckian decay constants, but requires large Chern-Simons couplings.
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