Special functions associated with automorphisms of the space of solutions to special double confluent Heun equation
arXiv:2102.12377
Abstract
The family of quads of interrelated functions holomorphic on the universal cover of the complex plane without zero (for brevity, pqrs-functions), revealing a number of remarkable properties, is introduced. In particular, under certain conditions the transformations of the argument of pqrs-functions represented by lifts of the replacements , and are equivalent to linear transformations with known coefficients. Pqrs-functions arise in a natural way in constructing of certain linear operators acting as automorphisms on the space of solutions to the special double confluent Heun equation (sDCHE). Earlier such symmetries were known to exist only in the case of integer value of one of the constant parameters when the predecessors of pqrs-functions appear as polynomials. In the present work, leaning on the generalized notion of pqrs-functions, discrete symmetries of the space of solutions to sDCHE are extended to the general case, apart from some natural exceptions.
Revised version: An additional assertion is added to Theorem 3 + one more reference is added + some minor text modifications