Cosmological Relaxation through the Dark Axion Portal

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.

Gauge-field production during axion inflation in the gradient expansion formalism

“…For a recent application in the context of cosmological relaxation as a solution to the hierarchy problem, see also Ref. [89].…”

Early-Universe Model Building

“…[1608] was subsequently eroded by constraints from relaxion fragmentation and requiring naturally photophobic relaxion couplings [1627,1628]. Furthermore the Schwinger effect involving SM fermions had been neglected, which suppresses the necessary dissipation [1625]. The latest particle production model of cosmological relaxation introduced in Ref.…”

“…The latest particle production model of cosmological relaxation introduced in Ref. [1625] overcomes these issues by instead making use of the Schwinger effect as a backreaction mechanism.…”

Theory Closing Talk

“…There has been growing interest in the idea that the Higgs mass may not be a rigid parameter but a dynamical variable determined by selection criteria related to the evolution of the universe [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Like every other theorist in the world, I am particularly excited about my own work and I will highlight here an idea [16] developed in this context together with Matthew McCullough and Tevong You.…”

“…Like every other theorist in the world, I am particularly excited about my own work and I will highlight here an idea [16] developed in this context together with Matthew McCullough and Tevong You. Interestingly, a related but independent framework was recently put forward by Justin Khoury and collaborators [18,19].…”