High-scale axions without isocurvature from inflationary dynamics

Kearney, John; Orlofsky, Nicholas; Pierce, Aaron

doi:10.1103/physrevd.93.095026

Cited by 24 publications

(14 citation statements)

References 107 publications

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“…If, for instance, f instead oscillates around its final value f 0 , then the axion perturbations may get a "kick" during the first oscillation, and be enhanced much stronger than in the cases analyzed in this paper. The oscillations of f could further induce resonant amplifications of the sub-horizon axion perturbations [25,26,27,28,29,21]. We also note that, for the evolution of f to take place not too far from the QCD phase transition, a relatively light degree of freedom is required.…”

Section: Discussionmentioning

confidence: 91%

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Cosmological perturbations of axion with a dynamical decay constant

Kobayashi

Takahashi

2016

J. Cosmol. Astropart. Phys.

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A QCD axion with a time-dependent decay constant has been known to be able to accommodate high-scale inflation without producing topological defects or too large isocurvature perturbations on CMB scales. We point out that a dynamical decay constant also has the effect of enhancing the small-scale axion isocurvature perturbations. The enhanced axion perturbations can even exceed the periodicity of the axion potential, and thus lead to the formation of axionic domain walls. Unlike the well-studied axionic walls, the walls produced from the enhanced perturbations are not bounded by cosmic strings, and thus would overclose the universe independently of the number of degenerate vacua along the axion potential.Here the lower bound is set by astrophysical arguments of star cooling [4], while the upper bound comes from the requirement that the abundance of the axion be less than or equal to that of cold dark matter (CDM) without fine-tuning the initial misalignment angle [5,6,7].Cosmological considerations further set bounds on a combination of the decay constant f a and the inflationary Hubble scale H inf . Firstly, f a should be larger than H inf , otherwise the PQ symmetry breaking would happen after inflation and thus would produce domain walls which overclose the universe. An exception to this statement is when the number of degenerate vacua along the bottom of the PQ scalar's Mexican hat potential (the so-called domain wall number) is N = 1; then the walls are bounded by cosmic strings without being connected to other walls, and such walls of finite size can annihilate soon after the QCD phase transition [8,9,10,11].

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Section: Discussionmentioning

confidence: 91%

“…(See also e.g. [21,26,38] for explicit models of axions with dynamical decay constants.) Let us now study the axion dynamics with a dynamical f , at very early times when the axion potential is absent.…”

Section: Qcd Axion With a Dynamical Decay Constantmentioning

confidence: 99%

Cosmological perturbations of axion with a dynamical decay constant

Kobayashi

Takahashi

2016

J. Cosmol. Astropart. Phys.

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“…(7.34), such that both DW and the isocurvature problems are avoided. This solution has been studied in the context of axion DM [166,[192][193][194][195][196][197]. In Sec.…”

Section: Solutionmentioning

confidence: 99%

Kination cosmology from scalar fields and gravitational-wave signatures

Gouttenoire¹,

Servant²,

Simakachorn³

2021

Preprint

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Kination denotes an era in the cosmological history corresponding to an equation of state ω = +1 such that the total energy density of the universe redshifts as the sixth inverse power of the scale factor. This arises if the universe is dominated by the kinetic energy of a scalar field. It has often been motivated in the literature as an era following inflation, taking place before the radiation era. In this paper, we review instead the possibility that kination is disconnected from primordial inflation and occurs much later, inside the Standard Model radiation era. We study the implications on all main sources of primordial gravitational waves. We show how this leads to very distinctive peaked spectra in the stochastic background of long-lasting cosmological sources of gravitational waves, namely the irreducible gravitational waves from inflation, and gravitational waves from cosmic strings, both local and global, with promising observational prospects. We present model-independent signatures and detectability predictions at LIGO, LISA, ET, CE, BBO, as a function of the energy scale and duration of the kination era. We then argue that such intermediate kination era is in fact symptomatic in a large class of axion models. We analyse in details the scalar field dynamics, the working conditions and constraints in the underlying models. We present the gravitational-wave predictions as a function of particle physics parameters. We derive the general relation between the gravitational-wave signal and the axion dark matter abundance as well as the baryon asymmetry. We investigate the predictions for the special case of the QCD axion. The key message is that gravitational-waves of primordial origin represent an alternative experimental probe of axion models.

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“…See also[24][25][26][27] for other realization of dynamics which solves the domain wall and the isocurvature problems. The solutions in the context of the axion predicted in the string theory[28][29][30] have also been discussed, where the axion dark matter abundance is suppressed dynamically[31,32].…”

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confidence: 99%

Dynamical solution to the axion domain wall problem

et al. 2020

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The domain wall problem and the isocurvature problem restrict possible combinations of axion models and inflation models. In this paper, we considered a new mechanism which solves those problems by dynamics of multiple scalar fields during/after inflation. The mechanism makes axion models with a non-trivial domain wall number compatible with inflation models with a large Hubble parameter, H I 10 7-8 GeV. The mechanism also avoids the isocurvature problem. This mechanism increases the freedom of choice of combinations of axion models and inflation models. *

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High-scale axions without isocurvature from inflationary dynamics

Cited by 24 publications

References 107 publications

Cosmological perturbations of axion with a dynamical decay constant

Cosmological perturbations of axion with a dynamical decay constant

Kination cosmology from scalar fields and gravitational-wave signatures

Dynamical solution to the axion domain wall problem

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