Cubic DNLS on R

Cubic DNLS on $R$

Suppose the non-linearity has the form f = i (u u u)_x. Then:

• Scaling is $s_{c}=0$.
• LWP for $s=1/2$ Tk-p.
  • This is sharp in the uniform sense BiLi-p (see also Tk-p for failure of analytic well-posedness below 1/2).
  • For $s>1$ this was proven in HaOz1994.
• GWP for $s>1/2$ and small $L^{2}$ norm CoKeStTkTa2002b. The $s=1/2$ case remains open.
  • for $s>2/3$ and small $L^{2}$ norm this was proven in CoKeStTkTa2001b.
  • For $s>32/33$ with small $L^{2}$ norm this was proven in Tk-p.
  • For $s>1$ and small norm this was proven in HaOz1994. One can also handle certain pure power additional terms Oz1996.
  • The small $L^{2}$ norm condition is required in order to gauge transform the problem; see HaOz1992, Oz1996.
• Solutions do not scatter to free Schrodinger solutions. In the focussing case this can be easily seen from the existence of solitons. But even in the defocussing case wave operators do not exist, and must be replaced by modified wave operators (constructed in HaOz1994 for small data).

This equation has the same scaling as the quintic NLS, and there is a certain gauge invariance which unifies the two (together with an additional nonlinear term u u_x u).

For non-linearities of the form $f=a(u{\overline {u}})_{x}u+b(u{\overline {u}})_{x}u_{x}$ one can obtain GWP for small data KyTs1994 for arbitrary complex constants $a,b$. See also Ts1994.