Let p be a prime number, B_p,∞ the cyclotomic Z_p-extension of the rational number field Q, B_p,n the n-th layer of B_p,∞/Q and h_p,n the class number of B_p,n. We obtained the following:Let p be a prime number which is not congruent to 1 or -1 mo...

We studied the Noether's Problem, which asks the rationality of the fixed field of the rational function field of several variables over a given field, with respect to a given finite subgroup G of the Cremona group. We solved this problem affirmat...

We construct certain algebraic integers αm as special values of two variable theta functions in the ray class field of a certain quartic field modulo 2m, and study a property of prime i deals which appear in αm in connection to the relationships b...

Thanks to the current Grant-in-Aid, we were able to organize seven research workshops inviting the most active mathematicians on this field, through which we had many discussions on our subjects.
This enabled us to make a considerable developments...

In 1976, Coates and Wiles gave large improvement to Birch-Swinnerton-Dyer conjecture for some elliptic curves with complex multiplication by using elliptic units in abelian extensions of imaginary quadratic fields. Main purpose of car investigatio...