On Handlebody Structures of Rational Balls

Abstract

It is known that for coprime integers $p>q\geq 1$, the lens space $L(p^2,pq-1)$ bounds a rational ball, $B_{p,q}$, arising as the 2-fold branched cover of a (smooth) slice disk in $B^4$ bounding the associated 2-bridge knot. Lekilli and Maydanskiy give handle decompositions for each $B_{p,q}$. Whereas, Yamada gives an alternative definition of rational balls, $A_{m,n}$, bounding $L(p^2,pq-1)$ by their handlebody decompositions alone. We show that these two families coincide - answering a question of Kadokami and Yamada. To that end, we show that each $A_{m,n}$ admits a Stein filling of the "standard" contact structure, $\bar{\xi}_{st}$, on $L(p^2,pq-1)$ investigated by Lisca.