On stable rationality of some conic bundles and moduli spaces of Prym curves

We prove that a very general hypersurface of bidegree (2, n) in P^2 x P^2 for n bigger than or equal to 2 is not stably rational, using Voisin's method of integral Chow-theoretic decompositions of the diagonal and their preservation under mild degenerations. At the same time, we also analyse possible ways to degenerate Prym curves, and the way how various loci inside the moduli space of stable Prym curves are nested. No deformation theory of stacks or sheaves of Azumaya algebras like in recent work of Hasset-Kresch-Tschinkel is used, rather we employ a more elementary and explicit approach via Koszul complexes, which is enough to treat this special case.Comment: 23 pages; Macaulay 2 code used for verification of parts of the paper available at http://www.math.uni-hamburg.de/home/bothmer/m2.html and at the end of the TeX file; v2: in section 4, we now included a proof of the main theorem that works for all n (unconditional on the parity) that was communicated to us by Zhi Jiang, Zhiyu Tian, and Letao Zhang. Several other minor expository improvement

Formulas for the number of (n−2)-gaps of binary objects in arbitrary dimension

AbstractIn this paper we define the notion of a gap in an arbitrary digital binary object S in a digital space of arbitrary dimension. Then we obtain an explicit formula for the number of gaps in S of maximal dimension, derive combinatorial relations for digital curves, and discuss possible applications to image analysis of digital surfaces (in particular planes) and curves

Entanglement Classification from a Topological Perspective

Classification of entanglement is an important problem in Quantum Resource Theory. In this paper we discuss an embedding of this problem in the context of Topological Quantum Field Theories (TQFT). This approach allows classifying entanglement patterns in terms of topological equivalence classes. In the bipartite case a classification equivalent to the one by Stochastic Local Operations and Classical Communication (SLOCC) is constructed by restricting to a simple class of connectivity diagrams. Such diagrams characterize quantum states of TQFT up to braiding and tangling of the ``connectome.'' In the multipartite case the same restricted topological classification only captures a part of the SLOCC classes, in particular, it does not see the W entanglement of three qubits. Nonlocal braiding of connections may solve the problem, but no finite classification is attempted in this case. Despite incompleteness, the connectome classification has a straightforward generalization to any number and dimension of parties and has a very intuitive interpretation, which might be useful for understanding specific properties of entanglement and for design of new quantum resources.Comment: 18 pages, 1 figure, version accepted to PRD. Significantly updated text following comments of referee(s). Extra references adde