  Noisy and ac forcing can cooperatively lead to the emergence of sine-Gordon
breathers robust to dissipation. This phenomenon is studied, for both Neumann
and periodic boundary conditions (NBC and PBC, respectively), at different
values of the main system parameters, such as the noise intensity and the ac
frequency-amplitude pair. In all the considered cases, nonmonotonicities of the
probability of generating only breathers versus the noise strength are
observed, implying that optimal noise ranges for the breather formation process
exist. Within the latter scenarios, the statistics of the breathers' number,
position, and amplitude are analyzed. The number of breathers is found to grow,
on average, with the noise amplitude. The breathers' spatial distribution is
sharply peaked at the system's edges for NBC, whereas it is essentially uniform
for PBC. The average breather amplitude is dictated by the ac
frequency-amplitude pair. Finally, a size analysis shows that the minimum
system length for the generation mechanism is given by the typical breather
half-width (width) in NBC (PBC).
