In this short note, we answer a question of Martin and Sanders [Integr. Equ. Oper. Theory, 85 (2) (2016), 191-220] by showing the existence disjoint frequently hypercyclic operators which fail to be weakly mixing and, therefore, satisfy Disjoint Hypercyclicity Criterion. We also show that given an operator $T$ such $T \oplus T$ is hypercyclic, set $S$ $T, S$ are but Criterion SOT dense in algeb...
