Bounding Picard numbers of surfaces using p-adic cohomology
Abstract
Motivated by an application to LDPC (low density parity check) algebraic geometry codes described by Voloch and Zarzar, we describe a computational procedure for establishing an upper bound on the arithmetic or geometric Picard number of a smooth projective surface over a finite field, by computing the Frobenius action on p-adic cohomology to a small degree of p-adic accuracy. We have implemented this procedure in Magma; using this implementation, we exhibit several examples, such as smooth quartics over F_2 and F_3 with arithmetic Picard number 1, and a smooth quintic over F_2 with geometric Picard number 1. We also produce some examples of smooth quartics with geometric Picard number 2, which by a construction of van Luijk also have trivial geometric automorphism group.
Keywords
Cite
@article{arxiv.math/0601508,
title = {Bounding Picard numbers of surfaces using p-adic cohomology},
author = {Timothy G. Abbott and Kiran S. Kedlaya and David Roe},
journal= {arXiv preprint arXiv:math/0601508},
year = {2007}
}
Comments
34 pages; v2: refereed version, to appear in proceedings "Arithmetic, Geometry, and Coding Theory (AGCT-10)"