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Tel Aviv University
The cosmological relaxation of the electroweak scale has been proposed as a mechanism to address the hierarchy problem of the Standard Model. A field, the relaxion, rolls down its potential and, in doing so, scans the squared mass parameter of the Higgs. In the original proposal, the rolling takes place in the background of inflation, which provides constant Hubble friction. In this work, we promote the relaxion to an inflaton, and in addition we couple it to Abelian gauge bosons. This introduces a new dissipation mechanism, crucial to slow down the field in the last stages, and allows for reheating at the end of inflation. The reheating mechanism proceeds via the vacuum production of electron-positron pairs, due to the presence of strong electric and magnetic fields. For the simultaneous success of relaxation and reheating, we couple the relaxion to a dark photon, which has a small mixing with the visible photon. We discuss the cosmological dynamics of the model and the phenomenological constraints from CMB and other experiments.