Math 847: padic Hodge Theory
Bryden Cais
Tu, Th, 11:0012:15 am, Van Vleck B 129
One of the central aims of modern algebraic number theory is to understand the absolute Galois group G of the rational numbers.
The main approach to this end is the study of (continuous) representations of G, an important class of which consists of
representations on vector spaces over a padic field (henceforth called padic representations). Since G is (topologically)
generated by the decomposition subgroups G_{l} at primes l, it is enough to restrict attention to (continuous) padic
representations of these simpler groups. For l not equal to p, such representations are mostly understood as in these cases
the continuity requirement drastically limits the kinds of representations one can have. For l = p, however, the situation
turns out to be much more subtle and interesting.
The goal of padic Hodge theory is to classify and study padic representations of G_{p} (i.e. l = p above)
and to this end padic Hodge theory is astonishingly successful. Much of the theory has been motivated by Galois
representations coming from geometry (via etale cohomology) so it should be no surprise that padic Hodge theory
has many spectacular applications in number theory. Indeed, the recent proof of Serre's conjecture on modular forms
and Kisin's refinements of the TaylorWiles method for proving Fermat's Last Theorem both rely heavily on padic
Hodge theory, and many questions about padic Lfunctions have been fruitfully analyzed via the comparison isomorphisms of padic Hodge theory.
In this course, we will develop padic Hodge theory from the beginning and will provide complete proofs of many of the key
results and theorems. We assume only a good understanding of linear algebra and familiarity with padic fields and Galois
theory (though we will review padic fields in the first few classes). Some exposure to algebraic geometry in the form of
etale cohomology and de Rham cohomology will be useful for motivation but is neither required nor necessary.
We will closely follow the
excellent lecture notes of Olivier Brinon and Brian Conrad throughout the course.
