Cosmological Relaxation through the Dark Axion Portal

Article
Report number	arXiv:2108.11295 ; CERN-TH-2021-125
Title	Cosmological Relaxation through the Dark Axion Portal
Author(s)	Domcke, Valerie (CERN ; Ecole Polytechnique, Lausanne) ; Schmitz, Kai (CERN) ; You, Tevong (CERN ; Cambridge U., DAMTP ; Cambridge U.)
Publication	2022-07-20
Imprint	2021-08-25
Number of pages	36
Note	36 pages, 9 figures. Matches published version
In:	JHEP 2207 (2022) 126
DOI	10.1007/JHEP07(2022)126
Subject category	astro-ph.CO ; Astrophysics and Astronomy ; hep-ph ; Particle Physics - Phenomenology
Abstract	The dark axion portal is a coupling of an axion-like particle to a dark photon kinetically mixed with the visible photon. We show how this portal, when applied to the relaxion, can lead to cosmological relaxation of the weak scale using dark photon production. The key backreaction mechanism involves the Schwinger effect: As long as electroweak symmetry is unbroken, Schwinger production of massless Standard Model fermions, which carry dark millicharges, suppresses the dark photon production. Once the electroweak symmetry is broken, the fermions acquire mass and the suppression is lifted. An enhanced dark photon dissipation then traps the relaxion at a naturally small weak scale. Our model thus provides a novel link between the phenomenological dark axion portal, dark photons, and the hierarchy problem of the Higgs mass.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) Publication: (License: CC-BY-4.0), sponsored by SCOAP³

$Cartoon sketch of the relaxion potential in the model with a vev-dependent periodic potential (left) and with particle production (right). The vev-dependent periodic potential height grows linearly or quadratically with $\phi$ after passing the critical point $\phi_c = -M/\epsilon$, trapping the relaxion as shown by the red point. In the particle production mechanism, particle production is triggered after the critical point, indicated by dashed red lines, which introduces extra friction to trap the relaxion.$ $Cartoon sketch of the relaxion potential in the model with a vev-dependent periodic potential (left) and with particle production (right). The vev-dependent periodic potential height grows linearly or quadratically with $\phi$ after passing the critical point $\phi_c = -M/\epsilon$, trapping the relaxion as shown by the red point. In the particle production mechanism, particle production is triggered after the critical point, indicated by dashed red lines, which introduces extra friction to trap the relaxion.$ $Upper bound on gauge field production including backreaction from SM leptons with unit charge (left) and millicharge $\theta_D = 0.1$ (right). The black contour corresponds to a vanishing Higgs vev, including the backreaction of all three massless SM charged leptons on the gauge field production. The coloured contours correspond to a Higgs vev of 246 GeV for different values of the Hubble parameter $H$, with the dotted red line indicating the limit $H \rightarrow \infty$. Here we include only the electron as the lightest charged SM particle. The dashed lines show our analytical approximations, given by Eq.~\eqref{eq:EBexp} (green), \eqref{eq:EBm0} (grey) and \eqref{eq:EB} (purple) with $\beta = 1$ and $\tilde \beta = 3$.$ Show more plots

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Journalen skapades 2021-08-27, och modifierades senast 2023-10-04

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