arXiv subjects
Publications and source records attributed to Stefan Deaconu.
The question of existence of Ulrich bundles on nonsingular projective varieties is posed here in weaker terms: either to find a K-theoretic solution, or to find one in the derived category of the variety. We observe that if any motivic vector bundle is algebraic, there is always a solution in the Grothendieck group. Also, by considering the derived problem, it is noted a formal way of producing Ulrich sheaves on a surface.
We prove, using a theorem of Northcott, that if a number field K with s real embeddings and 2t complex ones has a group of units U such that all elements in U have all its complex conjugates of same absolute value, then one necessarily has t = 1. This fact has an interesting implication in complex hermitian geometry, namely it describes all Oeljeklaus-Toma manifolds carrying locally conformally Kahler structures. It is then shown that the same method also works for the situation concerning the existence of pluriclosed metrics on Oeljeklaus-Toma manifolds.
We show that Oeljeklaus-Toma manifolds $X(K, U)$ where $K$ is a number field of signature $(s, t)$ such that $s\geq 1,$ $t\geq 2$ and $s\geq 2t$ admit no lck metric. Combined with the earlier results by K. Oeljeklaus - M. Toma and A. Dubickas this completely solves the problem of existence of LCK metrics on Oeljeklaus-Toma manifolds.