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# Forum Mathematicum

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Volume 29, Issue 1 (Jan 2017)

# Products of vector valued Eisenstein series

Martin Westerholt-Raum
• Corresponding author
• Institutionen för Matematiska vetenskaper, Chalmers tekniska högskolan och Göteborgs universitet, SE-412 96 Göteborg, Sweden
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Published Online: 2016-05-12 | DOI: https://doi.org/10.1515/forum-2014-0198

## Abstract

We prove that products of at most two vector valued Eisenstein series that originate in level 1 span all spaces of cusp forms for congruence subgroups. This can be viewed as an analogue in the level aspect to a result that goes back to Rankin, and Kohnen and Zagier, which focuses on the weight aspect. The main feature of the proof are vector valued Hecke operators. We recover several classical constructions from them, including classical Hecke operators, Atkin–Lehner involutions, and oldforms. As a corollary to our main theorem, we obtain a vanishing condition for modular forms reminiscent of period relations deduced by Kohnen and Zagier in the context their previously mentioned result.

MSC 2010: 11F11; 11F67

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Revised: 2016-01-07

Published Online: 2016-05-12

Published in Print: 2017-01-01

The author thanks the Max Planck Institute for Mathematics for their hospitality. The paper was partially written, while he was supported by the ETH Zurich Postdoctoral Fellowship Program and by the Marie Curie Actions for People COFUND Program.

Citation Information: Forum Mathematicum, ISSN (Online) 1435-5337, ISSN (Print) 0933-7741,

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