Explicit estimates for the logarithmic derivative and the reciprocal of the Riemann zeta-function

Abstract: In this article, we improve on two explicit bounds of order $\log t$ for $\sigma$ close to $1$: $|\zeta'(\sigma +it)/\zeta(\sigma +it)|$ and $|1/\zeta(\sigma +it)|$. Our method provides marked improvements in the constants, especially with regards to the latter. These savings come from replacing a lemma of Borel and Carath\'{e}dory, with a Jensen-type one of Heath-Brown's. Using an argument involving the trigonometric polynomial, we additionally provide a slight asymptotic improvement: $1/\zeta(\sigma +it) \ll (\log t)^{11/12}$.