Norm-inflation results for the BBM equation

Considered here is the periodic initial-value probem for the regularized long-wave (BBM) equation $$u_t+u_x+u{u}_x-u_{xxt}=0.$$ Adding to previous work in the literature, it is shown here that for any $s<0$, there is smooth initial data that is small in the $L_2$-based Sobolev spaces $H^s$, but the solution emanating from it becomes arbitrarily large in arbitrarily small time. This so called {\it norm inflation} result has as a consequence the previously determined conclusion that this problem is ill-posed in these negative-norm spaces.