$F$-rationality of two-dimensional graded rings with a rational singularity

Abstract

It is known that a two-dimensional $F$-rational ring has a rational singularity. However a two-dimensional ring with a rational singularity is not $F$-rational in general. In this paper, we investigate $F$-rationality of a two-dimensional graded ring with a rational singularity in terms of the multiplicity. Moreover, we determine when a two-dimensional graded ring with a rational singularity and a small multiplicity is $F$-rational.

33 pages, I have slightly modified the proof of Theorem 4.5 and added Lemma 4.3 to support it