On non-solvable Camina pairs

In this paper we study non-solvable and non-Frobenius Camina pairs (G,N). It is known [D. Chillag, A. Mann, C. Scoppola, Generalized Frobenius groups II, Israel J. Math. 62 (1988) 269–282] that in this case N is a p-group. Our first result (Theorem 1.3) shows that the solvable residual of G/Op(G) is isomorphic either to SL(2,pe),p is a prime or to SL(2,5), SL(2,13) with p=3, or to SL(2,5) with p⩾7.Our second result provides an example of a non-solvable and non-Frobenius Camina pair (G,N) with |Op(G)|=55 and G/Op(G)≅SL(2,5). Note that G has a character which is zero everywhere except on two conjugacy classes. Groups of this type were studies by S.M. Gagola [S.M. Gagola, Characters vanishing on all but two conjugacy classes, Pacific J. Math. 109 (1983) 363–385]. To our knowledge this group is the first example of a Gagola group which is non-solvable and non-Frobenius.