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arXiv · 2110.06768

Double coset operators and eta-quotients

Hai-Gang Zhou·Xiao-Jie Zhu
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Abstract

We study a type of generalized double coset operators which may change the characters of modular forms. For any pair of characters $v_1$ and $v_2$, we describe explicitly those operators mapping modular forms of character $v_1$ to those of $v_2$. We give three applications, concerned with eta-quotients. For the first application, we give many pairs of eta-quotients of small weights and levels, such that there are operators maps one eta-quotient to another. We also find out these operators. For the second application, we apply the operators to eta-powers whose exponents are positive integers not greater than $24$. This results in recursive formulas of the coefficients of these functions, generalizing Newman's theorem. For the third application, we describe a criterion and an algorithm of whether and how an eta-power of arbitrary integral exponent can be expressed as a linear combination of certain eta-quotients.

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Hai-Gang Zhou, Xiao-Jie Zhu. 2021-10-13. Double coset operators and eta-quotients. https://doi.org/10.1016/j.jnt.2023.02.017

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