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Reduction of abstract homomorphisms of lattices mod p and rigidity

Chandrashekhar Khare·Dipendra Prasad
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Abstract

In this paper we pose and answer the following question in a few different contexts: Given a homomorphism f:L_1 --> L_2 of a ``lattices'' that ``reduces mod p'' for almost all primes p, is f ``algebraic''? For instance the lattices may be the Mordell-Weil lattices of rational points of abelian varieties over Q, or arithmetic groups etc. Implicit in an affirmative answer to the question for Mordell-Weil lattices is a novel criterion for abelian varities to be isogenous.

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Chandrashekhar Khare, Dipendra Prasad. 2002-02-13. Reduction of abstract homomorphisms of lattices mod p and rigidity. https://arxiv.org/abs/math/0202310

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