A simple remark on fields of definition

Let K< L be an extension of fields, in characteristic zero, with L algebraically closed and let ¯K < L be the algebraic closure of K in L. Let X and Y be irreducible projective algebraic varieties, X defined over ¯K and Y defined over L, and let &#960; : X &#8594;Y be a non-constant mo...

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Autor principal: Hidalgo,Rubén
Lenguaje:English
Publicado: Universidad Católica del Norte, Departamento de Matemáticas 2012
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Acceso en línea:http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-09172012000100003
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Sumario:Let K< L be an extension of fields, in characteristic zero, with L algebraically closed and let ¯K < L be the algebraic closure of K in L. Let X and Y be irreducible projective algebraic varieties, X defined over ¯K and Y defined over L, and let &#960; : X &#8594;Y be a non-constant morphism, defined over L. If we assume that ¯K &#8800; L, then one may wonder if Y is definable over ¯K. In the case that K = Q, L = C and that X and Y are smooth curves, a positive answer was obtained by Gonzalez-Diez. In this short note we provide simple conditions to have a positive answer to the above question. We also state a conjecture for a class of varieties of general type.