Primordial magnetic fields in the $f^{2}FF$ model in large field inflation under de Sitter and power law expansion

Abstract

We use the $f^{2}FF$ model to study the generation of primordial magnetic fields (PMF) in the context of large field inflation (LFI), described by the potential, $V \sim M \phi^{p}$. We compute the magnetic and electric spectra for all possible values of the model parameters under de Sitter and power law expansion. We show that scale invariant PMF are not obtained in LFI to first order in the slow roll approximation, if we impose the constraint $V(\phi=0)\sim 0$. Alternatively, if these constraints are relaxed, the scale invariant PMF can be generated. The associated electric field energy can fall below the energy density of inflation, $\rho_{\rm{Inf}}$ for the ranges of comoving wavenumbers, $ k > 8 \times 10^{-7} \rm{Mpc^{-1}}$ and $ k > 4 \times 10^{-6} \rm{Mpc^{-1}}$ in de Sitter and power law (PL) expansion. Further, it can drop below $\rho_{\rm{Inf}}$ on the ranges, e-foldings $N > 51$, $p<1.66$, $p >2.03$, $l_0 > 3 \times 10^5 {M_{\rm{Pl}}}^{-1} (H_i < 3.3 \times 10^{-6} M_{\rm{Pl}})$, and $M > 2.8 \times 10^{-3} M_{\rm{Pl}}$. All of the above ranges fit with the observational constraints.