# News & Events

## Open Seminar

Date/Time:
Monday, April 25, 2016 - 15:35 to 16:00
Venue:
SMS, Seminar Room
Speaker:
Abhash Kumar Jha
Affiliation:
NISER, Bhubaneswar
Title:
THE ADJOINT OF SOME LINEAR MAPS COSTRUCTED USING RANKIN-COHEN BRACKETS AND SPECIAL VALUES OF CERTAIN DIRICHLET SERIES

AbstractModular forms are important objects in number theory and it has a wide range of applications in all other branches of Mathematics as well as in Physics. A modular for has Fourier expansion and the Fourier coefficients determine the modular form. Dirichlet series (e.g.,Riemann Zeta function) are important objects in number theory, used to study the distribution and properties of primes. Certain special values of Dirichlet series appears as Fourier coefficients of modular form. Kohnen [1991] constructed certain cusp forms whose Fourier coefficients involve special values of certain Dirichlet series of Rankin type by computing the adjoint map w.r.t. the Petersson scalar product of the product map by a fixed cusp form. Using differential operators one can define certain bilinear operators called the Rankin-Cohen brackets which is generalization of product. Recently the work of Kohnen has been generalized by Herrero [2015], where the author computed the adjoint of the map constructed using Rankin-Cohen brackets instead of product by a fixed cusp form. Fourier coefficients of the image of a cusp form under the adjoint map involves special values of certain Dirichlet series of Rankin-Selberg type similar to the one which appeared in the product case with certain twisting arising from binomial coefficients appearing in the Rankin-Cohen bracket. The work of Kohnen has been generalised to other automorphic forms (e.g., Jacobi forms, Siegel modular forms, Hilbert modular forms etc.,). Rankin-Cohen brackets for Jacobi forms and Siegel modular forms of genus two were studied by Choie explicitly using certain differential operators. Therefore it is natural to ask, how one can extend the work of Herrero to the case of Jacobi forms and Siegel modular forms of genus 2. A part of the thesis discuss about these generalizations. We shall also discuss the similar generaliza- tion for the case of half integral weight modular forms developed by Shimura [1973] and as a consequence, we get non-vanishing of certain Rankin- Selberg type Dirichlet series associated with modular forms. We shall also see how our method can be used to give a different proof of Rankin’s method in case of certain automorphic forms.

NB: This is a Thesis Colloquium/Open Seminar, School of Mathematical Sciences, NISER-Bhubaneswar.