Abstract
This work has been motivated by recent papers that quantify the density of values of generic quadratic forms and other polynomials at integer points, in particular ones that use Rogers’ second moment estimates. In this paper, we establish such results in a very general framework. Given any subhomogeneous function (a notion to be defined) \(f: \mathbb {R}^n \rightarrow \mathbb {R}\), we derive a necessary and sufficient condition on the approximating function \(\psi \) for guaranteeing that a generic element \(f\circ g\) in the G-orbit of f is \(\psi \)-approximable; that is, \(|f\circ g(\mathbf {v})| \le \psi (\Vert \mathbf {v}\Vert )\) for infinitely many \(\mathbf {v}\in \mathbb {Z}^n.\) We also deduce a sufficient condition in the case of uniform approximation. Here G can be any closed subgroup of \(\mathrm {ASL}_n(\mathbb {R})\) satisfying certain axioms that allow for the use of Rogers-type estimates.
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Acknowledgements
The first-named author is immensely grateful to Gregory Margulis for a multitude of conversations on the subject of the Oppenheim Conjecture and related topics. Thanks are also due to Jayadev Athreya, Anish Ghosh, Alex Gorodnik, Jiyoung Han, Dubi Kelmer, Dave Morris, and Amos Nevo for stimulating discussions, and to the anonymous referee for several useful suggestions.
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Communicated by Adrian Constantin.
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D. K. has been supported by NSF Grants DMS-1600814 and DMS-1900560.
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Kleinbock, D., Skenderi, M. Khintchine-type theorems for values of subhomogeneous functions at integer points. Monatsh Math 194, 523–554 (2021). https://doi.org/10.1007/s00605-020-01498-1
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DOI: https://doi.org/10.1007/s00605-020-01498-1
Keywords
- Oppenheim conjecture
- Metric Diophantine approximation
- Geometry of numbers
- Counting lattice points
- \(\psi \)-Approximability