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Roberto G. Ferretti

Publications and source records attributed to Roberto G. Ferretti.

5 recordsLinked to original sources
arXiv2010

A further improvement of the quantitative Subspace Theorem

In 2002, Evertse and Schlickewei obtained a quantitative version of the so-called Absolute Parametric Subspace Theorem. This result deals with a parametrized class of twisted heights. One of the consequences of this result is a quantitative version of the Absolute Subspace Theorem, giving an explicit upper bound for the number of subspaces containing the solutions of the Diophantine inequality under consideration. In the present paper, we further improve Evertse's and Schlickewei's quantitative version of the Absolute Parametric Subspace Theorem, and deduce an improved quantitative version of the Absolute Subspace Theorem. We combine ideas from the proof of Evertse and Schlickewei (which is basically a substantial refinement of Schmidt's proof of his Subspace Theorem from 1972, with ideas from Faltings' and Wuestholz' proof of the Subspace Theorem.

math.NT↗
arXiv2004

A generalization of the Subspace Theorem with polynomials of higher degree

Recently, Corvaja and Zannier obtained an extension of the Subspace Theorem with arbitrary homogeneous polynomials of arbitrary degreee instead of linear forms. Their result states that the set of solutions in P^n(K) (K number field) of the inequality being considered is not Zariski dense. In our paper we prove by a different method a generalization of their result, in which the solutions are taken from an arbitrary projective variety X instead of P^n. Further, we give a quantitative version which states in a precise form that the solutions with large height lie ina finite number of proper subvarieties of X, with explicit upper bounds for the number and for the degrees of these subvarieties.

math.NT↗
arXiv1998

Mumford's Degree of Contact and Diophantine Approximations

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 $X$ of a projective space $P^n$, does there exists a system of diophantine approximations on $P^n$ whose solutions are Zariski dense in $P^n$, but lie in finitely many proper subvarieties of $X$? One can gain insight into this problem using a theorem of G. Faltings and G. Wüstholz. 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 $X$. This invariant measures the semistability of the Chow (or Hilbert) point of $X$ under the action of an appropriate reductive algebraic group. Whence, the lower bound in the Faltings-Wüstholz theorem may be translated into a GIT language. This means that in order to show that a system of diophantine approximations on $X$ is not under the control of Schmidt Subspace Theorem, we must check the Chow-unstability of $X^s$, for some large $s>0$.

math.AG↗