English

Mumford's Degree of Contact and Diophantine Approximations

Algebraic Geometry 2007-05-23 v1 Number Theory

Abstract

The Schmidt Subspace Theorem affirms that the solutions of some particular system of diophantine approximations in projective spaces accumulates on a finite number of proper linear subspaces. Given a subvariety XX of a projective space PnP^n, does there exists a system of diophantine approximations on PnP^n whose solutions are Zariski dense in PnP^n, but lie in finitely many proper subvarieties of XX? One can gain insight into this problem using a theorem of G. Faltings and G. W\"ustholz. Their construction requires the hypothesis that the sum of some expected values has to be large. This sum turns out to be proportional to a degree of contact of a weighted flag of sections over the variety XX. This invariant measures the semistability of the Chow (or Hilbert) point of XX under the action of an appropriate reductive algebraic group. Whence, the lower bound in the Faltings-W\"ustholz theorem may be translated into a GIT language. This means that in order to show that a system of diophantine approximations on XX is not under the control of Schmidt Subspace Theorem, we must check the Chow-unstability of XsX^s, for some large s>0s>0.

Keywords

Cite

@article{arxiv.math/9804011,
  title  = {Mumford's Degree of Contact and Diophantine Approximations},
  author = {Roberto G. Ferretti},
  journal= {arXiv preprint arXiv:math/9804011},
  year   = {2007}
}

Comments

12 pages, LaTex2e