Values of character sums for finite unitary groups

A known result for the finite general linear group GL(n,Fq) and for the finite unitary group U(n,Fq2) posits that the sum of the irreducible character degrees is equal to the number of symmetric matrices in the group. Fulman and Guralnick extended this result by considering sums of irreducible characters evaluated at an arbitrary conjugacy class of GL(n,Fq). We develop an explicit formula for the value of the permutation character of U(2n,Fq2) over Sp(2n,Fq) evaluated at an arbitrary conjugacy class and use results concerning Gelfand–Graev characters to obtain an analogous formula for U(n,Fq2) in the case where q is an odd prime. These results are also given as probabilistic statements.