Higgs relaxation after inflation

Abstract

We show that the mechanism of cosmological relaxation of the electroweak scale can take place independently of the inflation mechanism, thus relieving burdens from the original relaxion proposal. What eventually stops the (fast-rolling) relaxion field during its cosmological evolution is the production of particles whose mass is controlled by the Higgs vacuum expectation value. We first show that Higgs particle production does not work for that purpose as the Higgs field does not track the minimum of its potential in the regime where Higgs particles get efficiently produced through their coupling to the relaxion. We then focus on gauge boson production. We provide a detailed analysis of the scanning and stopping mechanism and determine the parameter space for which the relaxion mechanism can take place after inflation, while being compatible with cosmological constraints, such as the relaxion dark matter overabundance and Big Bang Nucleosynthesis. We find that the cutoff scale can be as high as two hundreds of TeV. In this approach, the relaxion sector is responsible for reheating the visible sector. The stopping barriers of the periodic potential are large and Higgs-independent, facilitating model-building. The allowed relaxion mass ranges from 200 MeV up to the weak scale. In this scenario, the relaxion field excursion is subplanckian, and is thus many orders of magnitude smaller than in the original relaxion proposal.

Chiral anomaly, Schwinger effect, Euler-Heisenberg Lagrangian and application to axion inflation

“…The (spontaneously) C P -violating nature of this coupling moreover makes it a promising candidate to implement baryogenesis, either by a direct coupling of the inflaton (or SM Higgs) to the fermion current [58][59][60][61][62], or by sourcing a baryon asymmetry from the generated C P -violating background of gauge fields [27][28][29][30][31][32][33]. At much lower energy scales, the same coupling to the Chern Simons term can play a crucial role in explaining the smallness of the electroweak scale [34][35][36][37].…”

“…In the presence of a magnetic field on top of the chiral imbalance, a separation of electric charge is induced by the chiral magnetic effect [14][15][16][17][18][19], which is a signature of the local P -/C P -violation [20][21][22]. Turning to cosmology, strong helical gauge fields appear in models of axion inflation [23][24][25], are postulated to permeate intergalactic voids [26], may play a crucial role in baryogenesis [27][28][29][30][31][32][33] and also appear in some implementations of the relaxion model [34][35][36][37], constructed to address the hierarchy problem in the Standard Model (SM) of particle physics.…”

Relaxion dark matter

“…We will assume that relaxation takes place during inflation, and refer the reader to Ref. [20] for an analysis of the case in which relaxation happens after inflation. The Lagrangian is [2]:…”

Out-of-the-box baryogenesis during relaxation

“…Here we focus on models with Hubble friction; for alternative models involving particle production see Ref. [16,17] and Ref. [18] where the latter also implements leptogenesis in this scenario.…”