Inequality on $t_\nu (K)$ defined by Livingston and Naik and its applications

Abstract:

Let $D_+(K,t)$ denote the positive $t$-twisted double of $K$. For a fixed integer-valued additive concordance invariant $\nu$ that bounds the smooth four genus of a knot and determines the smooth four genus of positive torus knots, Livingston and Naik defined $t_\nu (K)$ to be the greatest integer $t$ such that $\nu (D_+(K,t)) = 1$. Let $K_1$ and $K_2$ be any knots; then we prove the following inequality: $t_\nu (K_1) + t_\nu (K_2) \leq t_\nu (K_1 \# K_2) \leq min(t_\nu (K_1) - t_\nu (-K_2), t_\nu (K_2) - t_\nu (-K_1)).$ As an application we show that $t_\tau (K) \neq t_s(K)$ for infinitely many knots and that their difference can be arbitrarily large, where $t_\tau (K)$ (respectively $t_s(K)$) is $t_\nu (K)$ when $\nu$ is an Ozváth-Szabó invariant $\tau$ (respectively when $\nu$ is a normalized Rasmussen $s$ invariant).