  Motivated by recent findings, we discuss the existence of a direct and robust
mechanism providing discontinuous absorbing transitions in short range systems
with single species, with no extra symmetries or conservation laws. We consider
variants of the contact process, in which at least two adjacent particles
(instead of one, as commonly assumed) are required to create a new species.
Many interaction rules are analyzed, including distinct cluster annihilations
and a modified version of the original pair contact process (PCP). Through
detailed time dependent numerical simulations we find that for our modified
models, the phase transitions are of first-order, hence contrasting with their
corresponding usual formulations in the literature, which are of second-order.
By calculating the order-parameter distributions, the obtained bimodal shapes
as well as the finite scale analysis reinforce coexisting phases, so a
discontinuous transition. These findings strongly suggest that above particle
creation requirements constitute a minimum and fundamental mechanism
determining the phase coexistence in short-range contact processes.
