English

A characterization of ordinary modular eigenforms with CM

Number Theory 2025-10-28 v2

Abstract

For a rational prime p3p \geq 3 we show that a pp-ordinary modular eigenform ff of weight k2k\geq 2, with pp-adic Galois representation ρf\rho_f, mod pm{p^m} reductions ρf,m\rho_{f,m}, and with complex multiplication (CM), is characterized by the existence of pp-ordinary CM companion forms hmh_m modulo pmp^m for all integers m1m \geq 1 in the sense that ρf,mρhm,mχk1\rho_{f,m}\sim \rho_{h_m,m}\otimes\chi^{k-1}, where χ\chi is the pp-adic cyclotomic character.

Keywords

Cite

@article{arxiv.1206.0177,
  title  = {A characterization of ordinary modular eigenforms with CM},
  author = {Rajender Adibhatla and Panagiotis Tsaknias},
  journal= {arXiv preprint arXiv:1206.0177},
  year   = {2025}
}

Comments

9 pages. Elementary proof of the main theorem added in Section 5

R2 v1 2026-06-21T21:13:01.500Z