Birational invariants and A^1-connectedness
Abstract
We study some aspects of the relationship between A^1-homotopy theory and birational geometry. We study the so-called A^1-singular chain complex and zeroth A^1-homology sheaf of smooth algebraic varieties over a field k. We exhibit some ways in which these objects are similar to their counterparts in classical topology and similar to their motivic counterparts (the (Voevodsky) motive and zeroth Suslin homology sheaf). We show that if k is infinite the zeroth A^1-homology sheaf is a birational invariant of smooth proper varieties, and we explain how these sheaves control various cohomological invariants, e.g., unramified \'etale cohomology. In particular, we deduce a number of vanishing results for cohomology of A^1-connected varieties. Finally, we give a partial converse to these vanishing statements by giving a characterization of A^1-connectedness by means of vanishing of unramified invariants.
Keywords
Cite
@article{arxiv.1001.4574,
title = {Birational invariants and A^1-connectedness},
author = {Aravind Asok},
journal= {arXiv preprint arXiv:1001.4574},
year = {2015}
}
Comments
24 pages; To appear Crelle's journal. Part II of ArXiV v2 (regarding the Luroth problem) is being reworked and will be uploaded separately; the old version is still available at http://www-bcf.usc.edu/~asok