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math.NT2026
Petersson-rigid lattices of signature (2,1) and their harmonic weak Maass forms
Eungang Cho
An even lattice of signature is Petersson-rigid if the orthogonal group of its discriminant form acts absolutely irreducibly on the space of cusp forms of weight $\frac…
math.NT2026
Petersson-Rigid Lattices in a Census of 100 Rank-Three Root Bases
Eungang Cho
The first paper worked out one family of four lattices in full -- and . This paper generalizes it. We enumerate the 44 symmetrizable rank-three hyperbolic…
math.NT2026
Forced Shadows of an Obstructed Hyperbolic Kac-Moody Denominator
Eungang Cho
The four orders of the quaternion algebra B6 carry four reflective wall data on lattices of signature (3,2); three integrate to Borcherds denominators and one is obstructed. The fa…