1,556 research outputs found
Extrinsic Diophantine approximation on manifolds and fractals
Fix , and let be either a
real-analytic manifold or the limit set of an iterated function system (for
example, could be the Cantor set or the von Koch snowflake). An
Diophantine approximation to a point is a rational point
close to which lies of . These
approximations correspond to a question asked by K. Mahler ('84) regarding the
Cantor set. Our main result is an extrinsic analogue of Dirichlet's theorem.
Specifically, we prove that if does not contain a line segment, then for
every , there exists such that
infinitely many vectors satisfy
. As this formula agrees with
Dirichlet's theorem in up to a multiplicative constant, one
concludes that the set of rational approximants to points in which lie
outside of is large. Furthermore, we deduce extrinsic analogues of the
Jarn\'ik--Schmidt and Khinchin theorems from known results
Unconventional height functions in simultaneous Diophantine approximation
Simultaneous Diophantine approximation is concerned with the approximation of
a point by points , with a
view towards jointly minimizing the quantities and
. Here is the so-called "standard height" of the
rational point . In this paper the authors ask: What changes if we
replace the standard height function by a different one? As it turns out, this
change leads to dramatic differences from the classical theory and requires the
development of new methods. We discuss three examples of nonstandard height
functions, computing their exponents of irrationality as well as giving more
precise results. A list of open questions is also given
Diophantine approximation in Banach spaces
In this paper, we extend the theory of simultaneous Diophantine approximation
to infinite dimensions. Moreover, we discuss Dirichlet-type theorems in a very
general framework and define what it means for such a theorem to be optimal. We
show that optimality is implied by but does not imply the existence of badly
approximable points
A variational principle in the parametric geometry of numbers, with applications to metric Diophantine approximation
We establish a new connection between metric Diophantine approximation and
the parametric geometry of numbers by proving a variational principle
facilitating the computation of the Hausdorff and packing dimensions of many
sets of interest in Diophantine approximation. In particular, we show that the
Hausdorff and packing dimensions of the set of singular matrices
are both equal to , thus proving a conjecture of
Kadyrov, Kleinbock, Lindenstrauss, and Margulis (preprint 2014) as well as
answering a question of Bugeaud, Cheung, and Chevallier (preprint 2016). We
introduce the notion of a , which generalizes the notion of a
(Roy, 2015) to the setting of matrix approximation. Our main theorem
takes the following form: for any class of templates closed under
finite perturbations, the Hausdorff and packing dimensions of the set of
matrices whose successive minima functions are members of (up to
finite perturbation) can be written as the suprema over of certain
natural functions on the space of templates. Besides implying KKLM's
conjecture, this theorem has many other applications including computing the
Hausdorff and packing dimensions of the set of points witnessing a conjecture
of Starkov (2000), and of the set of points witnessing a conjecture of Schmidt
(1983).Comment: Announcemen
A variational principle in the parametric geometry of numbers
We extend the parametric geometry of numbers (initiated by Schmidt and
Summerer, and deepened by Roy) to Diophantine approximation for systems of
linear forms in variables, and establish a new connection to the metric
theory via a variational principle that computes fractal dimensions of a
variety of sets of number-theoretic interest. The proof relies on two novel
ingredients: a variant of Schmidt's game capable of computing the Hausdorff and
packing dimensions of any set, and the notion of templates, which generalize
Roy's rigid systems. In particular, we compute the Hausdorff and packing
dimensions of the set of singular systems of linear forms and show they are
equal, resolving a conjecture of Kadyrov, Kleinbock, Lindenstrauss and
Margulis, as well as a question of Bugeaud, Cheung and Chevallier. As a
corollary of Dani's correspondence principle, the divergent trajectories of a
one-parameter diagonal action on the space of unimodular lattices with exactly
two Lyapunov exponents with opposite signs has equal Hausdorff and packing
dimensions. Other applications include quantitative strengthenings of theorems
due to Cheung and Moshchevitin, which originally resolved conjectures due to
Starkov and Schmidt respectively; as well as dimension formulas with respect to
the uniform exponent of irrationality for simultaneous and dual approximation
in two dimensions, completing partial results due to Baker, Bugeaud, Cheung,
Chevallier, Dodson, Laurent and Rynne
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