Higher Siegel theta lifts on Lorentzian lattices and harmonic Maass forms

We investigate so-called "higher" Siegel theta lifts on Lorentzian lattices in the spirit of Bruinier-Ehlen-Yang and Bruinier-Schwagenscheidt. We give an series representation of the lift in terms of Gauss hypergeometric functions, and evaluate the lift as the constant term of a Fourier series involving the Rankin-Cohen bracket of harmonic Maass forms and theta functions. We also note how one could obtain the Fourier expansion. We discuss one explicit example, and show how one could obtain infinite families of relationships between Hurwitz class numbers and divisor power sums.