Cosmological relaxation from dark fermion production

In implementations of the electroweak scale cosmological relaxation mechanism proposed so far, the effect of the quantum fluctuations of the homogeneous relaxion field has been ignored. We show that they can grow during the classical cosmological evolution of the relaxion field passing through its many potential barriers. The resulting production of relaxion particles can act as an efficient stopping mechanism for the relaxion. We revisit the original relaxion proposal and determine under which conditions inflation may no longer be needed as a source of friction. We review alternative stopping mechanisms and determine in detail the allowed parameter space for each of them (whether happening before, during and after inflation), also considering and severely constraining the case of friction from electroweak gauge boson production in models with large and Higgs-independent barriers.

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“…In [8] a potential instability is introduced to stop the field. Finally, friction from the production of dark fermions is discussed in [9].…”

Section: Introductionmentioning

confidence: 99%

Relaxion fluctuations (self-stopping relaxion) and overview of relaxion stopping mechanisms

Fonseca

Morgante

Sato

et al. 2020

J. High Energ. Phys.

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“…The appearance of the barriers as the Higgs mass scans through the origin and triggers a non-zero EW vacuum expectation value (VEV) acts as the trigger that stops the relaxion field, with Hubble friction and a small, technically natural slope ensuring the correct EW VEV is not overshot. Issues with the original model were addressed in [25] and alternative stopping mechanisms using, e.g., friction from the tachyonic production of EW gauge bosons [26][27][28][29], 1 friction from parametric resonance due to the Higgs zero mode [31], potential instabilities [32], fermion production [33], and dark photon production [34,35] have also been considered. The general idea of solving the hierarchy problem by means of the cosmological evolution has been the subject of a number of recent studies, see e.g.…”

Section: Jhep12(2021)037mentioning

confidence: 99%

Axion fragmentation on the lattice

Morgante

Ratzinger

Sato

et al. 2021

J. High Energ. Phys.

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We analyze the phenomenon of axion fragmentation when an axion field rolls over many oscillations of a periodic potential. This is particularly relevant for the case of relaxion, in which fragmentation provides the necessary energy dissipation to stop the field evolution. We compare the results of a linear analysis with the ones obtained from a classical lattice simulation, finding an agreement in the stopping time of the zero mode between the two within an $$ \mathcal{O}(1) $$ O 1 difference. We finally speculate on the generation of bubbles with different VEVs of the axion field, and discuss their cosmological consequences.

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“…A similar hierarchy is required for different models that exploit different mechanisms to dissipate away relaxion kinetic energy (124)(125)(126)(127)(128)(129)(130). Here we consider two examples in which dissipation is dominated by bosonic particle production (125,130).…”

Section: Coupling Hierarchy For the Relaxionmentioning

confidence: 99%

Recent Progress in the Physics of Axions and Axion-Like Particles

Choi

Shin

2021

Annu. Rev. Nucl. Part. Sci.

125

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The axion is a light pseudoscalar particle postulated to solve issues with the Standard Model, including the strong CP problem and the origin of dark matter. In recent years, there has been remarkable progress in the physics of axions in several directions. An unusual type of axion-like particle termed the relaxion was proposed as a new solution to the weak scale hierarchy problem. There are also new ideas for laboratory, astrophysical, or cosmological searches for axions; such searches can probe a wide range of model parameters that were previously inaccessible. On the formal theory side, the weak gravity conjecture indicates a tension between quantum gravity and a trans-Planckian axion field excursion. Many of these developments involve axions with hierarchical couplings. In this article, we review recent progress in axion physics, with particular attention paid to hierarchies between axion couplings. We emphasize that the parameter regions of hierarchical axion couplings are the most accessible experimentally. Moreover, such regions are often where important theoretical questions in the field are addressed, and they can result from simple model-building mechanisms. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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Cosmological relaxation from dark fermion production

Cited by 11 publications

References 68 publications

Relaxion fluctuations (self-stopping relaxion) and overview of relaxion stopping mechanisms

Relaxion fluctuations (self-stopping relaxion) and overview of relaxion stopping mechanisms

Axion fragmentation on the lattice

Recent Progress in the Physics of Axions and Axion-Like Particles

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