QCD axion window and low-scale inflation

Takahashi, Fuminobu; Yin, Wen; Guth, Alan H.

doi:10.1103/physrevd.98.015042

Cited by 160 publications

(177 citation statements)

References 92 publications

(99 reference statements)

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“…The typical e-folds in this model is large enough for various light scalars such the QCD axion to reach the Bunch-Davies distribution [34]. For instance, the required e-folds for the axion to reach the so-called Bunch-Davies distribution is N 10 26 (H inf /100MeV) 2 /(m a /10 −5 eV) 2 [2,3]. 3 For comparison, we also show the result for the usual case with the negative mass-squared, where the averaged efolding number decreases as expected.…”

Section: Example Modelmentioning

confidence: 95%

“…From the observational point of view, the total number of e-folds, N , must be larger than ∼ 50-60, which weakly depends on the inflation scale and thermal history after inflation. On the other hand, an extremely long duration of inflation is often required in certain scenarios, e.g., the relaxion model [1], the stochastic axion scenario [2][3][4][5], etc. The purpose of this Letter is to provide a simple single-field, slow-roll inflation model whose typical number of e-folds is extremely large.…”

Section: Introductionmentioning

confidence: 99%

“…By adding a linear term[32] or the Coleman-Weinberg correction[33], one can increase ns to give a better fit to observation 3. The typical e-folds can be even larger if one considers a lower inflation scale.…”

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confidence: 99%

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Stochastic inflation with an extremely large number of e-folds

2020

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We propose a class of single-field, slow-roll inflation models in which a typical number of efolds can be extremely large. The key point is to introduce a very shallow local minimum near the top of the potential in a hilltop inflation model. In particular, a typical number of e-folds is enhanced if classical behavior dominates around the local minimum such that the inflaton probability distribution is drifted to the local minimum as a whole. After the inflaton escapes from the local minimum due to the stochastic dynamics, the ordinary slow-roll inflation follows and it can generate the primordial density perturbation consistent with observation. Interestingly, our scenario inherits the advantages of the old and new inflation: the typical e-folds can be extremely large as in the old inflation, and slow-roll inflation naturally follows after the stochastic regime as in the new inflation. In our numerical example, the typical number of e-folds can be as large as 10 10 8 , which is large enough for various light scalars such the QCD axion to reach the Bunch-Davies distribution.

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Section: Example Modelmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Stochastic inflation with an extremely large number of e-folds

2020

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“…For fields with m ∼ H * the spectrum can have a non-trivial scale dependence; see Refs. [31,32] in the context of axions and Refs. [115,116] for a more general case.…”

Section: Axion Isocurvature Fluctuationsmentioning

confidence: 99%

Axion dark matter from Higgs inflation with an intermediate H_*

Tenkanen

Visinelli

2019

J. Cosmol. Astropart. Phys.

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In order to accommodate the QCD axion as the dark matter (DM) in a model in which the Peccei-Quinn (PQ) symmetry is broken before the end of inflation, a relatively low scale of inflation has to be invoked in order to avoid bounds from DM isocurvature fluctuations, H * O(10 9 ) GeV. We construct a simple model in which the Standard Model Higgs field is non-minimally coupled to Palatini gravity and acts as the inflaton, leading to a scale of inflation H * ∼ 10 8 GeV. When the energy scale at which the PQ symmetry breaks is much larger than the scale of inflation, we find that in this scenario the required axion mass for which the axion constitutes all DM is m 0 0.05 µeV for a quartic Higgs self-coupling λ φ = 0.1, which correspond to the PQ breaking scale v σ 10 14 GeV and tensor-to-scalar ratio r ∼ 10 −12 . Future experiments sensitive to the relevant QCD axion mass scale can therefore shed light on the physics of the Universe before the end of inflation.

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“…Larger f a is possible if θ i is (much) smaller than unity. This can be realized by fine-tuning based on the anthropic argument [14][15][16], or very low-scale inflation [17,18]. 1 On the other hand, smaller f a is possible if the initial position of the QCD axion is close to the hilltop of the potential, i.e., θ i ≈ π.…”

Section: Introductionmentioning

confidence: 99%

QCD axion on hilltop by a phase shift of π.

Takahashi

Yin

2019

J. High Energ. Phys.

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We show that the initial misalignment angle of the QCD axion (or axion-like particles) can be set very close to π, if the QCD axion has a mixing with another heavy axion which induces the phase shift ≈ π after inflation. In the simplest case, the heavy axion plays the role of the inflaton, and we call such inflation as "πnflation." The basic idea was first proposed by Daido and the present authors in Ref.[1] in 2017 and more recently discussed in Ref. [2]. We show that the QCD axion with a decay constant f a 3 × 10 9 GeV can explain dark matter by the πnflation mechanism. A large fraction of the parameter region has an overlap with the projected sensitivity of ORGAN, MADMAX, TOORAD and IAXO. We also study implications for the effective neutrino species and isocurvature perturbations. The πnflation can provide an initial condition for the hilltop inflation in the axion landscape, and in a certain set-up, a chain of the hilltop inflation may take place. 1 arXiv:1908.06071v2 [hep-ph] 3 Oct 2019 5 The mass and kinetic mixings between the QCD axion and another axion were discussed in e.g. Refs. [41][42][43][44][45], where the level crossing between the two axions can reduce the axion abundance. The mixing can also induce the DM decay [1,46,47]. Also the mixing between axions plays an important role in inflation model building [48][49][50][51][52][53] 6 The axion isocurvature perturbations can be suppressed in this case [58]. See e.g. Refs. [14,26,[59][60][61][62][63][64][65][66][67][68][69][70][71][72][73] for other scenarios to suppress the axion isocurvature.

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QCD axion window and low-scale inflation

Cited by 160 publications

References 92 publications

Stochastic inflation with an extremely large number of e-folds

Stochastic inflation with an extremely large number of e-folds

Axion dark matter from Higgs inflation with an intermediate H_*

QCD axion on hilltop by a phase shift of π.

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QCD axion window and low-scale inflation

Cited by 160 publications

References 92 publications

Stochastic inflation with an extremely large number of e-folds

Stochastic inflation with an extremely large number of e-folds

Axion dark matter from Higgs inflation with an intermediate H*

QCD axion on hilltop by a phase shift of π.

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Axion dark matter from Higgs inflation with an intermediate H_*