Very low scale Coleman-Weinberg inflation with nonminimal coupling

We study viable small-field Coleman-Weinberg (CW) inflation models with the help of nonminimal coupling to gravity. The simplest small-field CW inflation model (with a low-scale potential minimum) is incompatible with the cosmological constraint on the scalar spectral index. However, there are possibilities to make the model realistic. First, we revisit the CW inflation model supplemented with a linear potential term. We next consider the CW inflation model with a logarithmic nonminimal coupling and illustrate that the model can open a new viable parameter space that includes the model with a linear potential term. We also show parameter spaces where the Hubble scale during the inflation can be as small as 10-4 GeV, 1 GeV, 104 GeV, and 108 GeV for the number of e-folds of 40, 45, 50, and 55, respectively, with other cosmological constraints being satisfied. © 2018 authors. Published by the American Physical Society2211Nsciescopu