Normalized solutions to mass supercritical Schroedinger equations with negative potential

We study the existence of positive solutions with prescribed L-2-norm for the mass supercritical Schrodinger equation -delta u+lambda u - V(x)u = |u|(p-2)u u is an element of H-1(R-N), lambda is an element of R, where V >= 0, N >= 1 and p is an element of(2+4/N, 2*), 2*: = 2N/N-2 if N >= 3 and 2* : = +infinity if N = 1,2. We treat two cases. Firstly, under an explicit smallness assumption on V and no condition on the mass, we prove the existence of a mountain pass solution at positive energy level, and we exclude the existence of solutions with negative energy. Secondly, requiring that the mass is smaller than some explicit bound, depending on V, and that V is not too small in a suitable sense, we find two solutions: a local minimizer with negative energy, and a mountain pass solution with positive energy. Moreover, a nonexistence result is proved.