The masses of weakly-coupled scalar fields in the early universe.

Lyth, David H. and Moroi, Takeo (2004) The masses of weakly-coupled scalar fields in the early universe. Journal of High Energy Physics, 2004 (5). 004.

Abstract

We consider the effective mass-squared in the early Universe, of a scalar field which has only Planck-suppressed couplings with light fields and whose true mass is less than the Hubble parameter H. A detailed investigation shows that the effective mass-squared generically is of order ±H2 during inflation and matter-domination, but much smaller during radiation domination. We consider the special circumstances under which the mass-squared may be much bigger or much smaller than the generic value.