Cubic NLS: Difference between revisions

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== The cubic NLS equation ==
{{equation
| name = Cubic NLS
| equation = <math>iu_t + \Delta u = \pm |u|^2 u</math>
| fields = <math>u: \R \times \R^d \to \mathbb{C}</math>
| data = <math>u(0) \in H^s(\R^d)</math>
| hamiltonian = [[Hamiltonian]]
| linear = [[free Schrodinger equation|Schrodinger]]
| nonlinear = [[semilinear]]
| critical = <math>\dot H^{d/2 - 1}(\R^d)</math>
| criticality = varies
| covariance = [[Galilean]]
| lwp = <math>H^s(\R^d)</math> for <math>s \geq \max(d/2-1, 0)</math>
| gwp = varies
| parent = [[NLS]]
| special = [[Cubic NLS on R|on R]], [[Cubic NLS on T|on T]], [[Cubic NLS on R2|on R^2]], [[Cubic NLS on 2d manifolds|on T^2]], [[Cubic NLS on R3|on R^3]], [[Cubic NLS on R4|on R^4]]
| related = [[Schrodinger maps]], [[mKdV]], [[Zakharov system|Zakharov]]
}}


The '''cubic NLS''' is the equation


<center><math>i u_t + \Delta u = \pm |u|^2 u</math></center>
The '''cubic NLS''' is displayed on the box on the right.  The sign + is ''defocusing'', while the - sign is ''focusing''.  This equation is traditionally studied on Euclidean domains <math>R^d</math>, but other domains are certainly possible.
 
where <math>u(t,x)</math> is complex-valued.  The sign + is ''defocusing'', while the - sign is ''focusing''.  This equation is traditionally studied on Euclidean domains <math>R^d</math>, but other domains are certainly possible.


In one spatial dimension the cubic NLS equation is [[completely integrable]]. but this is not the case in higher dimensions.
In one spatial dimension the cubic NLS equation is [[completely integrable]]. but this is not the case in higher dimensions.


The cubic NLS can be viewed as an oversimplified model of the [[Schrodinger map]] equation.  It also arises as the limit of a number of other
The cubic NLS can be viewed as an oversimplified model of the [[Schrodinger map]] equation.  It also arises as the limit of a number of other
equations, such as the [[mKdV|modified Korteweg-de Vries equation]].
equations, such as the [[mKdV|modified Korteweg-de Vries equation]] and [[Zakharov system]].
 
One can also consider variants of the cubic NLS in which the ([[Hamiltonian]], [[Galilean]]-invariant) nonlinearity <math>\pm |u|^2 u</math> is replaced by a non-Hamiltonian, non-Galilean-invariant cubic polynomial such as <math>u^3</math> or <math>\overline{u}^3</math>.  Typically, for this variant the local theory remains unchanged (or even improves somewhat), but the global theory is lost (especially for large data) due to the lack of conservation laws.


== Scaling analysis ==
== Scaling analysis ==


On Euclidean domains at least, the cubic NLS obeys the scale invariance
On Euclidean domains at least, the cubic NLS obeys the scale invariance
<center><math>u(t,x) \mapsto \frac{1}{\lambda} u(\frac{t}{\lambda^2}, \frac{x}{\lambda}).</math>
 
:<math>u(t,x) \mapsto \frac{1}{\lambda} u(\frac{t}{\lambda^2}, \frac{x}{\lambda}).</math>


Thus the [[critical]] regularity is <math>s_c = \frac{d}{2} - 1</math>.
Thus the [[critical]] regularity is <math>s_c = \frac{d}{2} - 1</math>.
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* [[Cubic NLS on R]] (Mass and energy sub-critical; scattering-critical; completely integrable)
* [[Cubic NLS on R]] (Mass and energy sub-critical; scattering-critical; completely integrable)
* [[Cubic NLS on R|Cubic NLS on the half-line and interval]] (Mass and energy sub-critical)
* [[Cubic NLS on T]] (Mass and energy sub-critical; completely integrable)
* [[Cubic NLS on T]] (Mass and energy sub-critical; completely integrable)
* [[Cubic NLS on R2|Cubic NLS on R^2]] (Mass-critical; energy-subcritical; scattering-subcritical)
* [[Cubic NLS on R2|Cubic NLS on R^2]] (Mass-critical; energy-subcritical; scattering-subcritical)
* [[Cubic NLS on T2|Cubic NLS on R x T]] (Mass-critical; energy-subcritical)
* [[Cubic NLS on 2d manifolds|Cubic NLS on two-dimensional manifolds]] (Mass-critical; energy-subcritical)
* [[Cubic NLS on T2|Cubic NLS on T^2]] (Mass-critical; energy-subcritical)
* [[Cubic NLS on R3|Cubic NLS on R^3]] (Mass-supercritical; energy-subcritical; scattering-subcritical)
* [[Cubic NLS on R3|Cubic NLS on R^3]] (Mass-supercritical; energy-subcritical; scattering-subcritical)
* [[Cubic NLS on T3|Cubic NLS on T^3]] (Mass-supercritical; energy-subcritical)
* [[Cubic NLS on T3|Cubic NLS on three-dimensional manifolds]] (Mass-supercritical; energy-subcritical)
* [[Cubic NLS on R4|Cubic NLS on R^4]] (Mass-supercritical; energy-critical; scattering-subcritical)
* [[Cubic NLS on R4|Cubic NLS on R^4]] (Mass-supercritical; energy-critical; scattering-subcritical)
* [[Cubic NLS on T4|Cubic NLS on T^4]] (Mass-supercritical; energy-critical)
* [[Cubic NLS on T4|Cubic NLS on four-dimensional manifolds]] (Mass-supercritical; energy-critical)
* [[Cubic NLS on S6|Cubic NLS on S^6]] (Mass-supercritical; energy-supercritical)
* [[Cubic NLS on S6|Cubic NLS on six-dimensional manifolds]] (Mass-supercritical; energy-supercritical)


[[Category:Equations]]
[[Category:Equations]]
[[Category:Schrodinger]]
[[Category:Schrodinger]]

Latest revision as of 21:55, 4 March 2007

Cubic NLS
Description
Equation
Fields
Data class
Basic characteristics
Structure Hamiltonian
Nonlinearity semilinear
Linear component Schrodinger
Critical regularity
Criticality varies
Covariance Galilean
Theoretical results
LWP for
GWP varies
Related equations
Parent class NLS
Special cases on R, on T, on R^2, on T^2, on R^3, on R^4
Other related Schrodinger maps, mKdV, Zakharov


The cubic NLS is displayed on the box on the right. The sign + is defocusing, while the - sign is focusing. This equation is traditionally studied on Euclidean domains , but other domains are certainly possible.

In one spatial dimension the cubic NLS equation is completely integrable. but this is not the case in higher dimensions.

The cubic NLS can be viewed as an oversimplified model of the Schrodinger map equation. It also arises as the limit of a number of other equations, such as the modified Korteweg-de Vries equation and Zakharov system.

One can also consider variants of the cubic NLS in which the (Hamiltonian, Galilean-invariant) nonlinearity is replaced by a non-Hamiltonian, non-Galilean-invariant cubic polynomial such as or . Typically, for this variant the local theory remains unchanged (or even improves somewhat), but the global theory is lost (especially for large data) due to the lack of conservation laws.

Scaling analysis

On Euclidean domains at least, the cubic NLS obeys the scale invariance

Thus the critical regularity is .

Specific domains