Irregular hypergeometric systems associated with a singular monomial curve

Abstract

In this paper we study irregular hypergeometric systems defined by one row. Specifically, we calculate slopes of such systems. In the case of reduced semigroups, we generalize the case studied by Castro and Takayama. In all the cases we find that there always exists a slope with respect to a hyperplane of this system. Only in the case of an irregular system defined by a 1 × 2 1\times 2 integer matrix we might need a change of coordinates to study slopes at infinity. In the other cases slopes are always at the origin, defined with respect to a hyperplane. We also compute all the L L -characteristic varieties of the system, so we have a section of the Gröbner fan of the module defined by the hypergeometric system.