MODULAR GROUP IMAGES ARISING FROM DRINFELD DOUBLES OF DIHEDRAL GROUPS

We show that the image of the representation of the modular group $\SL(2, \Z)$ arising from the representation category $\Rep(D(G))$ of the Drinfeld double $D(G)$ is isomorphic to the group $\PSL(2, \Zn) \times S_3$, when $G$ is either the dihedral group of order $2n$ or the dihedral group of order $4n$ for some odd integer $n \geq 3$. $~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~$

___

  • B. Bakalov and A. Kirillov, Jr., Lectures on Tensor Categories and Modular Functors, University Lecture Series, 21, Amer. Math. Soc., 2001.
  • H. Behr and J. Mennicke, A presentation of the groups PSL(2; p), Canadian J. Math., 20 (1968), 1432-1438.
  • J. L. Cardy, Operator content of two-dimensional conformally invariant theories, Nuclear Phys. B, 270(2) (1986), 186-204.
  • A. Coste and T. Gannon, Congruence subgroups and rational conformal field theory, preprint, arXiv:math/9909080 [math.QA], (1999).
  • A. Coste, T. Gannon and P. Ruelle, Finite group modular data, Nucl. Phys. B, 581(3) (2000), 679-717.
  • R. C. Gunning, Lectures on Modular Forms, Notes by Armand Brumer, Annals of Mathematics Studies, 48, Princeton University Press, Princeton, N.J., 1962.
  • D. L. McQuillan, Classification of normal congruence subgroups of the modular group, Amer. J. Math., 87(2) (1965), 285-296.
  • S.-H. Ng and P. Schauenburg, Congruence subgroups and generalized Frobenius-Schur indicators, Comm. Math. Phys., 300(1) (2010), 1-46.
  • Y. Sommerhauser and Y. Zhu, Hopf Algebras and Congruence Subgroups, Mem. Amer. Math. Soc., 219(1028), 2012.