
The problem of counting quantum degeneracies of certain black holes in string theory has led to interesting new connections with topics in number theory including Siegel modular forms, mock modular forms, and generalized Borcherds superalgebras.
Links:
[1] http://www.mpim-bonn.mpg.de/de/taxonomy/term/39
[2] http://www.mpim-bonn.mpg.de/de/node/3444
[3] http://www.mpim-bonn.mpg.de/de/node/178