Asymptotics of sharp constants of Markov-Bernstein inequalities in integral norm with Jacobi weight

Abstract

The classical A. Markov inequality establishes a relation between the maximum modulus or the $L^{\infty}\left([-1,1]\right)$ norm of a polynomial $Q_{n}$ and of its derivative: $\|Q'_{n}\|\leqslant M_{n} n^{2}\|Q_{n}\|$, where the constant $M_{n}=1$ is sharp. The limiting behavior of the sharp constants $M_{n}$ for this inequality, considered in the space $L^{2}\left([-1,1], w^{(α,β)}\right)$ with respect to the classical Jacobi weight $w^{(α,β)}(x):=(1-x)^α(x+1)^β$, is studied. We prove that, under the condition $|α- β| < 4 $, the limit is $\lim_{n \to \infty} M_{n} = 1/(2 j_ν)$ where $j_ν$ is the smallest zero of the Bessel function $J_ν(x)$ and $2 ν= \mbox{min}(α, β) - 1$.