Instability of colliding metastable strings
  The breaking of $U(1)_R$ symmetry plays a crucial role in modeling the
breaking of supersymmetry (SUSY). In the models that possess both SUSY
preserving and SUSY breaking vacua, tube-like cosmic strings called R-tubes,
whose surfaces are constituted by domain walls interpolating a false and a true
vacuum with some winding numbers, can exist. Their (in)stability can strongly
constrain SUSY breaking models theirselves. In the present study, we
investigate the dynamical (in)stability of two colliding metastable tube-like
strings by field-theoretic simulations. From them, we find that the strings
become unstable, depending on the relative collision angle and speed of two
strings, and the false vacuum is eventually filled out by the true vacuum owing
to rapid expansion of the strings or unstable bubbles created as remnants of
the collision.
