A Simple Remark on Fields of Definition


  • Ruben A. Hidalgo Universidad Técnica Federico Santa María.




Algebraic curves, field of moduli, field of definition, curvas algebraicas, campo de módulos, campo de definición.


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 π : X → Y be a non-constant morphism, defined over L. If we assume that K 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.


Author Biography

Ruben A. Hidalgo, Universidad Técnica Federico Santa María.

Departamento de Matemática.


[1] M. de Franchis. Un teorema sulle involutioni irrationali. Rend. Circ. Mat. Palermo 36 (1913), 368.

[2] G. González-Diez. Variations on Belyi’s Theorem. Quart. J. Math. 57 (2006), 339-354.

[3] H. Hammer and F Herrlich. A Remark on the Moduli Field of a Curve. Arch. Math. 81 (2003), 5-10.

[4] I. Tsai. Dominating the varieties of general type. J. Reine Angew. Math. 483 (1997), 197-219.



How to Cite

R. A. Hidalgo, “A Simple Remark on Fields of Definition”, Proyecciones (Antofagasta, On line), vol. 31, no. 1, pp. 25-28, Jan. 2012.