Zariski surface
In algebraic geometry, a branch of mathematics, a Zariski surface is a surface over a field of characteristic p > 0 such there is a dominant inseparable map of degree p from the projective plane to the surface. In particular, all Zariski surfaces are unirational. They were named by Piotr Blass after his Harvard mentor Oscar Zariski who used them in 1958 to give examples of unirational surfaces in characteristic p > 0 that are not rational. (In characteristic 0 by contrast, Castelnuovo's theorem implies that all unirational surfaces are rational.)
Zariski surfaces are birational to surfaces in affine 3-space A3 defined by irreducible polynomials of the form
- zp = f(x, y).
Properties of Zariski surfaces
Piotr Blass and Jeff Lang have computed the Picard group of the generic Zariski surface using some ideas of Pierre Deligne and Alexander Grothendieck during 1980-1993.
The following problem posed by Oscar Zariski in 1971 is still open: let p ≥ 5, let S be a Zariski surface with vanishing geometric genus. Is S necessarily a rational surface? For p = 2 and for p = 3 the answer to the above problem is negative as shown in 1977 by Piotr Blass in his University of Michigan Ph.D. thesis and by William E. Lang in his Harvard Ph.D. thesis in 1978.
Any Zariski surface with vanishing bigenus is rational and that all Zariski surfaces are simply connected. Zariski surfaces form a rich family including surfaces of general type, K3 surfaces, Enriques surfaces, quasi elliptic surfaces and also rational surfaces. In every characteristic the family of birationally distinct Zariski surfaces is infinite.
Zariski threefolds and manifolds of higher dimension have been similarly defined and a broad theory is slowly emerging as of 2006 in preprint form. There is only a very rudimentary theory of moduli of Zariski surfaces to be further developed as of 2006.
The Japanese school of geometers, following work of the Russian school of geometers, recently showed that every supersingular K3 surface in characteristic two is a Zariski surface. Michael Artin had previously invented a subtle numerical invariant called the Artin invariant that gives an important stratification of the moduli space of such supersingular K3 surfaces in characteristic two. The Albanese variety of a Zariski surface is always trivial.However as was shown by David Mumford school of geometry the Picard scheme need not be reduced again we refer to William E.Lang Harvard 1978 Ph.D. thesis. In 1980 Spencer Bloch and Piotr Blass proved that a Zariski surface which is irrational does not admit a finite purely inseparable degree p map onto the projective plane.Iacopo Barsotti remarked that this illustrates a very strong form of simple connectivity of the projective plane.
Torsten Ekedahl from Sweden computed the crystalline cohomology of Zariski surfaces in some cases. Ofer Gaber and Ray Hoobler studied with Piotr Blass the Brauer group of Zariski surfaces This work is considered inconclusive as of today 2006.
Oscar Zariski and Piotr Blass revived the theory of adjoint surfaces created by the Italian geometers to compute numerical invariants of Zariski surfaces. This has been continued by Joseph Lipmann and also more recently by the computer algebra group in Linz Austria mainly by Joseph Schicho. Currently attempts are being made to use Zariski surfaces for coding ,encryption and also for mathematical physics applications. As of 2006 these efforts are inconclusive.
Computer algebra has been used extensively to compute Picard groups of Zariski surfaces. After seminal work of Jacobson,Cartier,Samuel and Jeffey Lang in his Purdue Ph.D. thesis 1980 the computer program was created by David Joyce in Pascal. Students of Jeffrey Lang at the University of Kansas have simplified this program and expressed it using Wolfram Mathematica language and system.
Zariski surfaces clearly provide a vast laboratory for testing both the simplest and the most esoteric parts of modern algebraic geometry. This theory is very far from being complete.
See also
References
- A list of of Piotr Blass's books and papers on Zariski surfaces
- Zariski Surfaces And Differential Equations in Characteristic p > 0 by Piotr Blass, Jeffrey Lang ISBN 0-8247-7637-2
- Blass, Piotr; Lang, Jeffrey Surfaces de Zariski factorielles. (Factorial Zariski surfaces). C. R. Acad. Sci. Paris Sér. I Math. 306 (1988), no. 15, 671--674.
- Zariski, Oscar On Castelnuovo's criterion of rationality pa=P2=0 of an algebraic surface. Illinois J. Math. 2 1958 303--315.