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Presentation
Quasi-platonic actions of some simple groups on Riemann surfaces and their dessins d’enfant
Joint Mathematics Meetings, Session on Higher Genus Curves (2016)
  • Sean A Broughton
Abstract
A quasi-platonic action of the group G on the Riemann surface S is a conformal action of G on S such that S/G is a sphere and the projection S -> S/G is branched over {0,1,infinity}/. The action is induced by a triple of (a, b, c) in G^3, generating G, with abc = 1: The quasi-platonic action induces a regular dessin d'enfant on S, and S is de fined over a number field. The absolute Galois group Gal(Q/Q) acts on dessins, hence quasi-platonic actions, by acting on the coefficients of a de fining equation of S. The action of f in Gal(Q/Q) on triples is (a,b,c)-> (ua^tu^(-1), vb^tv^(-1),wa^tw^(-1)), for some (u,v,w) in G^3, according to the branch cycle argument. The integer t is characterized by the action of f on cyclotomic subfi elds of Q, and (u,v,w) is determined by the action of  f  away from cyclotomic subfieelds. In this talk we discuss the action of the absolute Galois group on quasi-platonic actions on some simple groups. In particular, we show that the Galois action on quasi-platonic actions of PSL2(q) depends only the action on cyclotomic sub fields.
Keywords
  • Riemann surface,
  • dessin d'enfant,
  • simple group
Publication Date
January 8, 2016
Location
Seattle, WA
Citation Information
Sean A Broughton. "Quasi-platonic actions of some simple groups on Riemann surfaces and their dessins d’enfant" Joint Mathematics Meetings, Session on Higher Genus Curves (2016)
Available at: http://works.bepress.com/allen_broughton/57/
Creative Commons License
Creative Commons License
This work is licensed under a Creative Commons CC_BY-NC-SA International License.