Ribbon distance bounds from Bar-Natan Homology and $\alpha$-Homology

Abstract

We prove a lower bound on the ribbon distance via Bar-Natan Homology. This lower bound agrees with Alishahi's lower bound on the unknotting number via Bar-Natan Homology, which furthers a pattern first observed by Sarkar: Sarkar's lower bound on the ribbon distance via Lee Homology agreed with Alishahi and Dowlin's lower bound on the unknotting number via Lee Homology. We also prove a lower bound on the ribbon distance via $\alpha$-homology, a variant of Khovanov homology defined recently by Khovanov and Robert.