The 4-string braid group $B_4$ has property RD and exponential mesoscopic rank
The 4-string braid group $B_4$ has property RD and exponential mesoscopic rank
We prove that the braid group B 4 on 4 strings, its central quotient B 4 /〈z〉, and the automorphism group Aut(F 2 ) of the free group F 2 on 2 generators, have the property RD of Haagerup-Jolissaint. We also prove that the braid group B 4 is a …