Zariski density and finite quotients of mapping class groups

Louis Funar

Published 2011-06-21, updated 2012-02-13Version 3

Our main result is that the image of the quantum representation of a central extension of the mapping class group of the genus $g\geq 3$ closed orientable surface at a prime $p\geq 5$ is a Zariski dense discrete subgroup of some higher rank algebraic semi-simple Lie group $\mathbb G_p$ defined over $\Q$. As an application we find that, for any prime $p\geq 5$ a central extension of the genus $g$ mapping class group surjects onto the finite groups $\mathbb G_p(\Z/q\Z)$, for all but finitely many primes $q$. This method provides infinitely many finite quotients of a given mapping class group outside the realm of symplectic groups.