Hariram Krishna | Searcharxiv

arXiv2025

Characterization of Erd\"os matrices by their zero entries

An Erd\"os matrix $E$ is a bistochastic matrix whose sum of squares of entries (Frobenius norm squared) equals its maxtrace (maximum of all the $\sigma$-traces for permutations $\sigma$'s). We characterize all Erd\"os $E$ by the patterns of their zero entries; showing that each such skeleton has at most one $E$. We present an algorithm to find all $n\times n$ Erd\"os matrices, which finds them up to $n\leqslant 5$ quickly and also size $n=6$. We further show some presently known RCDS matrices to be Erd\"os.

math.CO↗

arXiv2022

Bounds for the Bergman kernel and the sup-norm of holomorphic Siegel cusp forms

We prove `polynomial in $k$' bounds on the size of the Bergman kernel for the space of holomorphic Siegel cusp forms of degree $n$ and weight $k$. When $n=1,2$ our bounds agree with the conjectural bounds on the aforementioned size, while the lower bounds match for all $n \ge 1$. For an $L^2$-normalised Siegel cusp form $F$ of degree $2$, our bound for its sup-norm is $O_ε(k^{9/4+ε})$. Further, we show that in any compact set $Ω$ (which does not depend on $k$) contained in the Siegel fundamental domain of $\mathrm{Sp}(2, \mathbb Z)$ on the Siegel upper half space, the sup-norm of $F$ is $O_Ω(k^{3/2 - η})$ for some $η>0$, going beyond the `generic' bound in this setting.

math.NT↗