In this paper we study Prym varieties and their moduli space using the
well-known techniques of the infinite Grassmannian. There are three m
ain results of this paper: a new definition of the BKP hierarchy over
an arbitrary base field (that generalizes the classical one over C); a
characterization of Prym varieties in terms of dynamical systems, and
explicit equations for the moduli space of (certain) Prym varieties.
For all of these problems the language of the infinite Grassmannian, i
n its algebro-geometric version, allows us to deal with these problems
from the same point of view.