Concurrency in timed automata

We introduce Concurrent Timed Automata <f>(CTAs)</f> where automata running in parallel are synchronized. We consider the subclasses of <f>CTAs</f> obtained by admitting, or not, diagonal clock constraints and constant updates, and by letting, or not, sequential automata to update the same clocks. We prove that such subclasses recognize the same languages but differ w.r.t. the succinctness of the models. Moreover, we distinguish between subclasses that are polynomially closed w.r.t. finite union and finite intersection, and subclasses that do not have such properties. [Copyright &y& Elsevier]