Quantization and non-holomorphic modular forms (Q1578780)

Although the derivative of a modular form is not a modular form in general, certain combinations of derivatives of modular forms produce modular forms. Indeed, the polynomials in the derivatives of modular forms for a discrete subgroup \(\Gamma\) of \(\text{SL}(2,\mathbb R)\) that are again modular forms were studied by \textit{R. J. Rankin} [J. Indian Math. Soc., New Ser. 20, 103--116 (1956; Zbl 0072.08601)], and as a special case of such polynomials \textit{H. Cohen} [Math. Ann. 217, 271--285 (1975; Zbl 0311.10030)] investigated certain bilinear operators on the graded ring of modular forms, which may be considered as noncommutative products of modular forms. Such products are known as the Rankin-Cohen brackets, and they can be extended to the case of Hilbert or Siegel modular forms. They are also closely linked to various objects including pseudodifferential operators, Jacobi-like forms, and transvectants. One of the main goals of this monograph is to generalize the Rankin-Cohen brackets of modular forms to the case of non-holomorphic automorphic forms. In fact, the author envisions the non-holomorphic analogue of Rankin-Cohen brackets as a machine for producing Maass cusp forms. In the process of constructing the bilinear products, which generalize the Rankin-Cohen brackets, the author uses various techniques from pseudodifferential analysis, partial differential equations, and harmonic analysis such as the Radon transform, the Rankin-Selberg unfolding method, Weyl symbols, and Poisson brackets. In addition he discusses connections of such bilinear products with quantization theory.