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Estimating the critical determinants of a class of three-dimensional star bodies

Werner Georg Nowak (2017)

Communications in Mathematics

In the problem of (simultaneous) Diophantine approximation in  3 (in the spirit of Hurwitz’s theorem), lower bounds for the critical determinant of the special three-dimensional body K 2 : ( y 2 + z 2 ) ( x 2 + y 2 + z 2 ) 1 play an important role; see [1], [6]. This article deals with estimates from below for the critical determinant Δ ( K c ) of more general star bodies K c : ( y 2 + z 2 ) c / 2 ( x 2 + y 2 + z 2 ) 1 , where c is any positive constant. These are obtained by inscribing into K c either a double cone, or an ellipsoid, or a double paraboloid, depending on the size of c .

On the critical determinants of certain star bodies

Werner Georg Nowak (2017)

Communications in Mathematics

In a classic paper, W.G. Spohn established the to-date sharpest estimates from below for the simultaneous Diophantine approximation constants for three and more real numbers. As a by-result of his method which used Blichfeldt’s Theorem and the calculus of variations, he derived a bound for the critical determinant of the star body | x 1 | ( | x 1 | 3 + | x 2 | 3 + | x 3 | 3 ) 1 . In this little note, after a brief exposition of the basics of the geometry of numbers and its significance for Diophantine approximation, this latter result is improved...

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