Parabolic induction in characteristic p

Singularities in characteristic 0 and characteristic p

1 Characteristic 0 We start with a basic question: given a polynomial f ∈ C[z1, · · · , zn] with a singularity at 0, how can we measure the “singularness” of this polynomial in a precise way? In other words: we can look at various singularities and see intuitively that some singularities are worse than others. For instance, it feels like a transverse self-intersection is probably not as bad as ...

Polynomial iteration in characteristic p ∗ †

Let f(x) = ∑d s=0 asx s ∈ Z[x] be a polynomial with ad 6≡ 0 mod p. Take z ∈ Fp and let Oz = {fi(z)}i∈Z+ ⊂ Fp be the orbit of z under f , where fi(z) = f(fi−1(z)) and f0(z) = z. For M < |Oz|, we study the diameter of the partial orbit Oz,M = {z, f(z), f2(z), . . . , fM−1(z)} and prove that diam Oz,M & min { M c log logM , Mp , M 1 2p 1 2 } , where ‘diameter’ is naturally defined in Fp and c depe...

Chapter 1 Characteristic p methods in characteristic zero via ultraproducts

Characteristic p methods in characteristic zero via ultraproducts

In recent decades, by exploiting the algebraic properties of the Frobenius in positive characteristic, many so-called homological conjectures and intersection conjectures have been established, culminating into the powerful theory of tight closure and big Cohen–Macaulay algebras. In the present article, I give a survey of how these methods also can be applied directly in characteristic zero by ...

On the geometry of p-typical covers in characteristic p

For p a prime, a p-typical cover of a connected scheme on which p = 0 is a finite étale cover whose monodromy group (i.e., the Galois group of its normal closure) is a p-group. The geometry of such covers exhibits some unexpectedly pleasant behaviors; building on work of Katz, we demonstrate some of these. These include a criterion for when a morphism induces an isomorphism of the p-typical quo...