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Critically separable rational maps in families

Published online by Cambridge University Press:  12 October 2012

Clayton Petsche*
Department of Mathematics, Oregon State University, Corvallis OR 97331, USA (email:
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Given a number field K, we consider families of critically separable rational maps of degree d over K possessing a certain fixed-point and multiplier structure. With suitable notions of isomorphism and good reduction between rational maps in these families, we prove a finiteness theorem which is analogous to Shafarevich’s theorem for elliptic curves. We also define the minimal critical discriminant, a global object which can be viewed as a measure of arithmetic complexity of a rational map. We formulate a conjectural bound on the minimal critical discriminant, which is analogous to Szpiro’s conjecture for elliptic curves, and we prove that a special case of our conjecture implies Szpiro’s conjecture in the semistable case.

Research Article
Copyright © Foundation Compositio Mathematica 2012


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