Hodge groups of certain superelliptic jacobians

Suppose that $K$ is a field of characteristic 0, $p$ is an odd prime, $r$ a positive integer, $q=p^r$ a prime power. Suppose that $f(x)$ is a polynomial of degree $n > 4$ with coefficients in $K$ and without multiple roots. Let us consider the superelliptic curve $C: y^q=f(x)$ and its jacobian $J(C)$. Assuming that $K$ is a subfield of the field of complex numbers, we study the (connected reductive algebraic) Hodge group $Hdg$ of the corresponding complex abelian variety $J(C)$. In our previous paper (arXiv:0907.1563 [math.AG]) we studied the center of $Hdg. In this paper we study the semisimple part (commutator subgroup) of$Hdg$. Assuming that$p$does not divide$n$and$n-1$is not divisible by$q$, the Galois group of$f(x)$over$K$is either the full symmetric group$S_n$or the alternating group$A_n$, we prove that the semisimple part of$Hdg$ is "as large as possible".

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