# Scattering for NLW/NLKG

The *Strauss exponent*

plays a key role in the GWP and scattering theory. We have ; ; note that is always between the and critical powers, and is always between the and critical powers.

Another key power is

which lies between the critical power and .

**Caveats**: the cases may be somewhat different from what is stated here (partly because some of the powers here are not well-defined). Also, in many of the NLW results one needs some additional decay at spatial infinity (e.g. finiteness of the conformal energy), except in the special -critical case. This is because (unlike NLS and NLKG) there is no a priori bound on the norm (even with conservation of energy).

Scattering for small data for arbitrary NLW:

- Known for Sr1981.
- For one has blow-up Si1984.
- When this is extended to , but scattering fails for Hi-p3
- When this is extended to , but scattering fails for Hi-p3
- An alternate argument based on conformal compactification but giving slightly different results are in BcKkZz1999

Scattering for large data for defocusing NLW:

- Known for BaSa1998, BaGd1997 (GWP was established earlier in GiVl1987).
- Known for , BaeSgZz1990
- When this is extended to Hi-p3
- When this is extended to Hi-p3
- For one expects scattering when , but this is not known.

Scattering for small smooth compactly supported data for arbitrary NLW:

- GWP and scattering when GeLbSo1997
- For this is in Jo1979

- Blow-up for arbitrary nonzero data when Si1984 (see also Rm1987, JiZz2003
- At the critical power there is blowup for non-negative non-trivial data YoZgq-p2

Scattering for small data for arbitrary NLKG:

- Decay estimates are known when MsSrWa1980, Br1984, Sr1981, Pe1985.
- Known when Na1999c, Na1999d, Na2001. Indeed, one has existence of wave operators and asymptotic completeness in these cases.

Scattering for large data for defocussing NLKG:

- In this case one has an a priori bound and one does not need decay at spatial infinity.
- Scattering is known for Na1999c, Na1999d, Na2001

Scattering for small smooth compactly supported data for arbitrary NLKG:

- GWP and scattering for when LbSo1996
- When this can be obtained by energy estimates and decay estimates.
- In principle this extends to higher dimensions but there is a difficulty with lack of smoothness in the nonlinearity.

- Blowup in the non-Hamiltonian case when KeTa1999. The endpoint remains open but one probably also has blow-up here.
- Failure of scattering for was shown in Gs1973.

An interesting (and apparently under-explored) problem is what happens to these global existence and scattering results when there is an obstacle. For NLW-5 on one has global regularity for convex obstacles SmhSo1995, and for smooth non-linearities there is the general quasilinear theory. If one adds a suitable damping term near the obstacle then one can recover some global existence results Nk2001.

On the Schwarzschild manifold some scattering and decay results for NLW and NLWKG can be found in BchNic1993, Nic1996, BluSf2003