Leptogenesis in cosmological relaxation with particle production

Abstract

Cosmological relaxation of the electroweak scale is improved by using particle production to trap the relaxion. We combine leptogenesis with such a relaxion model that has no extremely small parameters or large e-foldings. Scanning happens after inflation-now allowed to be at a high scale-over a sub-Planckian relaxion field range for a cutoff scale of new physics up to O(100) TeV. Particle production by the relaxion also reheats the universe and generates the baryonic matterantimatter asymmetry. We propose a realisation in which out-of-equilibrium leptons, produced by the relaxion, scatter with the thermal bath through interactions that violate CP and lepton number via higher-dimensional operators. Such a minimal effective field theory setup, with no new physics below the cutoff, naturally decouples new physics while linking leptogenesis to relaxion particle production; the baryon asymmetry of the universe can thus be intrinsically tied to a weak scale hierarchy.

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

“…The stopping mechanism is qualitatively different as the potential barriers are Higgs-independent and relaxation starts in the EW broken phase. The idea of using the tachyonic production of Standard Model gauge boson as a source of friction to slow down and stop the relaxion evolution was introduced in [3], and further studied in various aspects in [4,14,27,31]. Here we will only summarize the model and its constraints, referring the reader to [3,4] for further details.…”

Higgs relaxation after inflation

“…It might also be possible that the relaxion itself generates the baryon asymmetry through the φF F coupling with a mechanism similar to [41,42]. As this work is being completed, a recent proposal appeared in [40] that is constrained by the bounds we derive in the following sections.…”

Relaxion dark matter

“…This paradigm shift fits in the interface between particle physics and early universe cosmology and gave rise to a varied literature, including studies on the model building challenges [3][4][5][6][7][8][9][10][11][12], concerns about the inflationary and reheating sectors [13][14][15][16][17][18], alternatives to inflation [2,19,20], UV completions [21][22][23][24], developments on the model building front [25][26][27][28][29][30][31][32][33][34][35][36], baryogenesis [37,38], experimental signatures [39][40][41][42][43], and cosmological implications [44,45].…”