Dipartimento di Matematica, Università di Siena, Via del Capitano 15, 53100 Siena, Italy ; Dipartimento di Matematica, Università di Roma Tre, Largo San Leonardo Murialdo 1, 00146 Roma, Italy
Abstract:
In this article we apply the classical method of focal loci of families to give a lower bound for the genus of curves lying on general surfaces. First we translate and reprove Xu's result that any curve on a general surface in of degree has geometric genus . Then we prove a similar lower bound for the curves lying on a general surface in a given component of the Noether-Lefschetz locus in and on a general projectively Cohen-Macaulay surface in .