CUSPIDAL Q-RATIONAL TORSION SUBGROUP OF J(Gamma) OF LEVEL P

Abstract

For p > 3 an odd prime, let Gamma be a congruence subgroup between Gamma(1)(p) and Gamma(0)(p). In this article, we give an explicit basis for the group of modular units on X(Gamma) that have divisors defined over Q. As an application, we determine the order of the cuspidal Q-rational torsion subgroup of J(Gamma) generated by the divisor classes of cuspidal divisors of degree 0 defined over Q.