Mechanisms of unstable blowup in a quadratic nonlinear Schr\"odinger equation

In the work Cho et al. [Jpn. J. Ind. Appl. Math. 33 (2016): 145-166] the authors conjecture that the quadratic nonlinear Schr\"odinger equation (NLS) i uₜ = uₓₓ + u² for x ∈ T is globally well-posed for real initial data. While this may be true in a generic sense, we present evidence that this conjecture is false. Moreover we conjecture that the set of real initial data which blows up under the NLS dynamics is the stable manifold of the zero equilibrium for the nonlinear heat equation uₜ = uₓₓ + u².