A simple proof of higher order Turán inequalities for Boros-Moll sequences

Abstract

Recently, the higher order Turán inequalities for the Boros-Moll sequences $\{d_{\ell }(m){\}}_{\ell =0}^m$ were obtained by Guo. In this paper, we show a different approach to this result. Our proof is based on a criterion derived by Hou and Li, which need only checking four simple inequalities related to sufficiently sharp bounds for $d_{\ell }(m{)}^2/(d_{\ell -1}(m)d_{\ell +1}(m))$. In order to do so, we adopt the upper bound given by Chen and Gu in studying the reverse ultra log-concavity of Boros-Moll polynomials, and establish a desired lower bound for $d_{\ell }(m{)}^2/(d_{\ell -1}(m)d_{\ell +1}(m))$ which also implies the log-concavity of $\{\ell !d_{\ell }(m){\}}_{\ell =0}^m$ for $m\ge 2$. We also show a sharper lower bound for $d_{\ell }(m{)}^2/(d_{\ell -1}(m)d_{\ell +1}(m))$ which may be available for some deep results on inequalities of Boros-Moll sequences.

12 pages