511 research outputs found
Fake projective planes, automorphic forms, exceptional collections
On the projective plane there is a unique cubic root of the canonical bundle
and this root is acyclic. On fake projective planes such root exists and is
unique if there are no 3-torsion divisors (and usually exists, but not unique,
otherwise). Earlier we conjectured that any such cubic root must be acyclic. In
the present note we give two short proofs of this statement and show acyclicity
of some other line bundles on the fake projective planes with at least
automorphisms. Similarly to our earlier work we employ simple representation
theory for non-abelian finite groups. The novelty stems from the idea that if
some line bundle is non-linearizable with respect to a finite abelian group,
then it should be linearized by a finite, \emph{non-abelian}, Heisenberg group.
For the second proof, we also demonstrate vanishing of odd Betti numbers for a
class of abelian covers, and use a linearization of an auxiliary line bundle as
well.Comment: 13 pages; completely reorganized, title changed, references expande
The motivic nearby fiber and degeneration of stable rationality
We prove that stable rationality specializes in regular families whose fibers are integral and have at most ordinary double points as singularities. Our proof is based on motivic specialization techniques and the criterion of Larsen and Lunts for stable rationality in the Grothendieck ring of varieties
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