On eigenvalues of the Schr\"odinger operator with an even complex-valued   polynomial potential
  In this paper, we generalize several results of the article "Analytic continuation of eigenvalues of a quartic oscillator" of A. Eremenko and A. Gabrielov.   We consider a family of eigenvalue problems for a Schr\"odinger equation with even polynomial potentials of arbitrary degree d with complex coefficients, and k<(d+2)/2 boundary conditions. We show that the spectral determinant in this case consists of two components, containing even and odd eigenvalues respectively.   In the case with k=(d+2)/2 boundary conditions, we show that the corresponding parameter space consists of infinitely many connected components. 
Per Alexandersson
math-ph math.MP