On the cyclicity of a Galois module in local fields. D.S. Dummit (1983) Journal für die reine und angewandte Mathematik
On the main invariant of an element over a local field. Popescu, N., Zaharescu, A. (1997) Portugaliae Mathematica
On the p adic nearby cycles of log smooth families Takeshi Tsuji (2000) Bulletin de la Société Mathématique de France