#### Alladi Ramakrishnan Hall

#### Applications of moonshine in string compactifications and black holes

#### Justin R. David

##### IISc, Bangalore

*The discovery of Mathieu moonshine in the elliptic genus *

of K3 allows the construction of

twisted elliptic genera to every conjugacy class of the

Mathieu group M23. We show how these twisted elliptic

genera plays play an important role in

both N=2 and N=4 string compactifictions.

In N=2 string compactifications they point to the existence

of a class of Calabi-Yau geometries. In N=4 compactifications

they are inputs to degeneracies of 1/4 BPS states,

which at large values of charges are black holes.

We then study properties of these states at small values

of charges which provide insight to their geometric description

as black holes.

Done