Partition Frequency Moments: Modularity and Congruences

TL;DR

This paper develops a method to analyze frequency moments of partition statistics using modular forms, enabling the detection and proof of Ramanujan-type congruences for partitions and overpartitions.

Contribution

It introduces a pipeline leveraging modularity and divisor sums to certify congruences in partition statistics, including new results for overpartitions.

Findings

Certified Ramanujan-type congruences for partition moments.

Identified zero-class congruences for overpartition moments.

Demonstrated creation of new congruences via Glaisher-character filtering.

Abstract

We study frequency moments of partition statistics arising from Euler products $A(q)=\prod_{r\ge1}(1-q^r)^{-c(r)}$ via a transform that expresses the moment generating functions as $B(q)$ times explicit divisor--sum series determined by $c(r)$. When $A(q)$ is modular (typically an $\eta$--quotient), this yields (quasi)modular forms whose coefficients can be projected to arithmetic progressions and certified modulo primes by a Sturm bound, giving an effective pipeline for detecting and proving Ramanujan--type congruences for frequency moments. For ordinary partitions we recover and certify several congruences for odd moments in nonzero residue classes (e.g.\ $M_3(7n+5)\equiv 0\pmod7$ and $M_3(11n+6)\equiv 0\pmod{11}$). As a second input, we apply the same pipeline to overpartitions and certify a family of zero--class congruences $M_m^{\overline{\ }}(\ell n)\equiv 0\pmod{\ell}$ (including $m=5,7,11,13$), exhibiting a sharp contrast with the ordinary partition case: no nonzero residue--class congruences are observed for overpartition moments in our scan range. We also demonstrate that filtering the statistic via the Glaisher--character dictionary can itself create new Ramanujan--type progressions, e.g.\ a quadratic twist yields the certified congruence $\widehat{M}^{\chi_5}_3(5n+4)\equiv 0\pmod{5}$.