Second-Level Concavity of the Riemann $\Xi$ Kernel

Michel Planat, Patrick Solé

Let $\Phi$ be the classical Jacobi-theta kernel in the Fourier representation of the Riemann $\Xi$-function, set $s(t)=\Phi (\sqrt{t})$, and define the first Laguerre expression $f(t)=s'(t)^…