English

False and partial Eisenstein series related to unimodal sequences

Number Theory 2026-01-28 v1 Combinatorics

Abstract

Motivated by the fact that the classical Jacobi theta function ϑ\vartheta is the exponential generating function of the Eisenstein series, we study the exponential Taylor coefficients (in the elliptic variable) of a related natural partial theta function, as well as a false theta function related to the Dedekind eta function. We prove that the space spanned by these objects is closed under differentiation, analogous to the space of quasimodular forms, and that it contains the quasimodular forms themselves. We further provide their Fourier expansions, establish quasimodular completions, and derive a recursive formula for the Taylor coefficients of the logarithm of the unimodal rank generating function, expressed as partition traces of the false and partial objects.

Keywords

Cite

@article{arxiv.2601.19441,
  title  = {False and partial Eisenstein series related to unimodal sequences},
  author = {Kathrin Bringmann and Badri Vishal Pandey and Jan-Willem van Ittersum},
  journal= {arXiv preprint arXiv:2601.19441},
  year   = {2026}
}

Comments

19 pages, comments welcome