Pullback of parabolic bundles and covers of P1∖{0,1,∞}{\mathbb P}^1\setminus\{0,1,\infty\}

We work over an algebraically closed ground field of characteristic zero. A $G$-cover of ${\mathbb P}^1$ ramified at three points allows one to assign to each finite dimensional representation $V$ of $G$ a vector bundle $\oplus \mathscr{O}(s_i)$ on ${\mathbb P}^1$ with parabolic structure at the ramification points. This produces a tensor functor from representation of $G$ to vector bundles with parabolic structure that characterises the original cover. This work attempts to describe this tensor functor in terms of group theoretic data. More precisely, we construct a pullback functor on vector bundles with parabolic structure and describe the parabolic pullback of the previously described tensor functor.Comment: 25 page

Pushforwards of Tilting Sheaves

We investigate the behaviour of tilting sheaves under pushforward by a finite Galois morphism. We determine conditions under which such a pushforward of a tilting sheaf is a tilting sheaf. We then produce some examples of Severi Brauer flag varieties and arithmetic toric varieties in which our method produces a tilting sheaf, adding to the list of positive results in the literature. We also produce some counterexamples to show that such a pushfoward need not be a tilting sheaf.Comment: 21 page

The Period-Index Problem of the Canonical Gerbe of Symplectic and Orthogonal Bundles

We consider regularly stable parabolic symplectic and orthogonal bundles over an irreducible smooth projective curve over an algebraically closed field of characteristic zero. The morphism from the moduli stack of such bundles to its coarse moduli space is a $\mu_2$-gerbe. We study the period and index of this gerbe, and solve the corresponding period-index problem.Comment: 19 pages. Complete rewrite of the previous version, including expanded results on the moduli of parabolic G-bundles. To appear in the Journal of Algebra. Comments welcom