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Questions about modular forms and related areas

19 votes
Accepted

Are umbral moonshine and umbral calculus connected?

We used the word "umbral" because umbral moonshine involves mock modular forms whose lack of modularity is characterized by another function known as the shadow of the mock modular form. Umbra is the …
Jeff Harvey's user avatar
  • 5,546
2 votes

What is the relationship between the Leech lattice and Dedekind eta function?

Steve Carnahan in his answer to this question Where do the product expansions of modular forms come from? gives a conceptual explanation of the product form for $\Delta$, but it has nothing to do with …
Jeff Harvey's user avatar
  • 5,546
4 votes
Accepted

Index one weak Jacobi forms and weakly holomorphic modular forms?

Section 4.2 of this paper https://arxiv.org/pdf/1208.4074.pdf by Dabholkar, Murthy and Zagier may be what you want. The theta coefficients of weak Jacobi forms of weight k and index m are 2m component …
Jeff Harvey's user avatar
  • 5,546
8 votes
2 answers
805 views

Reference request for Hecke operators for principal congruence subgroup of modular group

I am looking for references that discuss Hecke operators $T_n$ acting on modular forms for the principal congruence subgroup $\Gamma(N)$ of the modular group $SL(2,Z)$ and am happy to restrict to the …
Jeff Harvey's user avatar
  • 5,546
6 votes
0 answers
430 views

More on Moonshine for the Thompson group and weakly holomorphic weight one half modular forms

This question is a follow-up to Monstrous Moonshine for Thompson group $Th$? and is based on various comments to that question, in particular S. Carnahan's mention of the connection to known Moonshin …
Jeff Harvey's user avatar
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11 votes
Accepted

Monstrous moonshine for $M_{24}$ and K3?

I can answer your first question. In arXiv:1208.4074 by Dabholkar, Murthy and Zagier you can find a formula that implies $H^{(2)}(\tau)= \frac{48 F_2^{(2)}(\tau)- 2 E_2(\tau)}{\eta(\tau)^3}$ where $E_ …
Jeff Harvey's user avatar
  • 5,546
12 votes
Accepted

Computing Thompson series for the monster group

From MathSciNet: MR1037906 (90m:11065) Reviewed McKay, John(3-CONC); Strauss, Hubertus(3-CONC) The q-series of monstrous moonshine and the decomposition of the head characters. Comm. Algebra 18 (19 …
Jeff Harvey's user avatar
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8 votes
Accepted

Mock Theta Functions

In addition to Zagier's excellent Bourbaki seminar I would also recommend some notes by Ken Ono that include both a summary of the history of mock theta functions and mock modular forms and a survey o …
Jeff Harvey's user avatar
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6 votes
2 answers
1k views

What is the modern understanding of the order of a mock theta function?

Ramanujan introduced mock theta functions and described them by an "order" which he did not define. As a result of the work of Zwegers and others we now have a better understanding of mock theta funct …
Jeff Harvey's user avatar
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