Discrete Torsion in Perturbative Heterotic String Theory

In this paper we analyze discrete torsion in perturbative heterotic string theory. In previous work we have given a purely mathematical explanation of discrete torsion as the choice of orbifold group action on a B field, in the case that d H = 0; in this paper, we perform the analogous calculations in heterotic strings where d H is nonzero.Comment: 15 pages, LaTeX; v2: typos fixe

On the global moduli of Calabi-Yau threefolds

In this note we initiate a program to obtain global descriptions of Calabi-Yau moduli spaces, to calculate their Picard group, and to identify within that group the Hodge line bundle, and the closely-related Bagger-Witten line bundle. We do this here for several Calabi-Yau's obtained in [DW09] as crepant resolutions of the orbifold quotient of the product of three elliptic curves. In particular we verify in these cases a recent claim of [GHKSST16] by noting that a power of the Hodge line bundle is trivial -- even though in most of these cases the Picard group is infinite.Comment: 28 pages, LaTeX, 3 figures; v2: thorough revision, error corrected, added autho