Hill-top inflation from Dai-Freed anomaly in the standard model — a solution to the iso-curvature problem of the axion dark matter

Abstract

Abstract The discrete symmetry Z 4 in the standard model (SM) with three right-handed neutrinos is free from the Dai-Freed anomaly. Motivated by this Z 4 symmetry, we constructed a topological inflation model consistent with all known constraints and observations. However, we assumed a specific inflaton potential in the previous work. In this paper we extend the inflaton potential in a more general form allowed by the discrete Z 4 gauge symmetry and show that consistent hilltop inflation is realized.We find that the Hubble parameter H_inf can be smaller than ≃ 109 GeV so that the isocurvature fluctuations of the axion dark matter are sufficiently suppressed. Furthermore, the running of the spectral index can be as large as dns /ln k ≃ 0.0018 which will be tested in future CMB observations. Since this discrete Z 4 acts on the SM, the inflaton can couple to pairs of the right-handed neutrinos and hence the reheating temperature can be high as ∼ 1010 GeV, producing the cosmic baryon asymmetry naturally through the thermal leptogenesis.