Rational Hadamard products via Quantum Diagonal Operators
  We use the remark that, through Bargmann-Fock representation, diagonal operators of the Heisenberg-Weyl algebra are scalars for the Hadamard product to give some properties (like the stability of periodic fonctions) of the Hadamard product by a rational fraction. In particular, we provide through this way explicit formulas for the multiplication table of the Hadamard product in the algebra of rational functions in $\C[[z]]$. 
G\'erard Henry Edmond Duchamp (LIPN), Silvia Goodenough (LIPN), Karol   A. Penson (LPTMC)