Volumes for twist link cone-manifolds

Recently, the explicit volume formulae for hyperbolic cone-manifolds, whose underlying space is the 3-sphere and the singular set is the knot $4_1$ and the links $5^2_1$ and $6^2_2$, have been obtained by the second named author and his collaborators. In this paper we explicitly find the hyperbolic volume for cone-manifolds with the link $6^2_3$ as singular set. Trigonometric identities (Tangent, Sine and Cosine Rules) between complex lengths of singular components and cone angles are obtained for an infinite family of two-bridge links containing $5^2_1$ and $6^2_3$.Comment: 23 pages, 1 figure. Revised version with minor changes. Accepted for publication in the Boletin de la Sociedad Matematica Mexicana, special issue in honor of Francisco "FICO" Gonzales Acun

Dijkgraaf-Witten invariants of surfaces and projective representations of groups

We compute the Dijkgraaf-Witten invariants of surfaces in terms of projective representations of groups. As an application we prove that the complex Dijkgraaf-Witten invariants of surfaces of positive genus are positive integers.Comment: second version: a mistake corrected in the non-orientable case and a few improvements adde