A new exponent of simultaneous rational approximation
Volume 192 / 2020
Abstract
We introduce a new exponent of simultaneous rational approximation for pairs of real numbers \xi ,\eta , in complement to the classical exponents \lambda (\xi ,\eta ) of best approximation, and \widehat{\lambda} (\xi ,\eta ) of uniform approximation. It generalizes Fischler’s exponent \beta _0(\xi ) in the sense that \widehat{\lambda}_{\min} (\xi ,\xi ^2) = 1/\beta _0(\xi ) whenever \lambda (\xi ,\xi ^2) = 1. Using parametric geometry of numbers, we provide a complete description of the set of values taken by (\lambda ,\widehat{\lambda}_{\min} ) at pairs (\xi ,\eta ) with 1,\xi ,\eta linearly independent over \mathbb Q .