  The Lorentzian type IIB matrix model is a promising candidate for a
non-perturbative formulation of superstring theory. However, it was recently
found that a Euclidean space-time appears in the conventional large-$N$ limit.
In this work, we study the model with a Lorentz invariant mass term which can
be considered as an IR regulator. By performing complex Langevin simulations to
overcome the sign problem, we observe the emergence of expanding space-time
with Lorentzian signature.
