Inflationary magnetogenesis with reheating phase from higher curvature coupling

We investigate the generation of magnetic fields from inflation, which occurs via breakdown of the conformal invariance of the electromagnetic (EM) field, when coupled with the Ricci scalar and the Gauss-Bonnet invariant. For the case of instantaneous reheating, the resulting strength of the magnetic field at present is too small and violates the observational constraints. However, the problem is solved provided there is a reheating phase with a non-zero e-fold number. During reheating, the energy density of the magnetic field is seen to evolve as (a(3)H)(-2) and, after that, as a(-4) up to the present epoch (here a is the scale factor and H the Hubble parameter). It is found that this reheating phase -characterized by a certain e-fold number, a constant value of the equation of state parameter, and a given reheating temperature- renders the magnetogenesis model compatible with the observational constraints. The model provides, in turn, a viable way of constraining the reheating equation of state parameter, from data analysis of the cosmic microwave background radiation.

Automated summary

The generation of magnetic fields during inflation is studied in relation to the breakdown of the conformal invariance of the electromagnetic field coupled with the Ricci scalar and Gauss-Bonnet invariant. It is found that a reheating phase with a non-zero e-fold number can solve the problem of the magnetic field strength being too small. The evolution of the energy density of the magnetic field during reheating allows the magnetogenesis model to be compatible with observational constraints.