Benjamin-Ono equation: Difference between revisions

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<center><math>\partial_t u  + D_x^{1+a} \partial_x u + u\partial_x u = 0.</math></center>
<center><math>\partial_t u  + D_x^{1+a} \partial_x u + u\partial_x u = 0.</math></center>


<span class="GramE">where</span> <span class="SpellE">D_x</span> = <span class="SpellE">sqrt</span>{-Delta} is the positive differentiation operator. When a=1 this is [[KdV]; when a=0 this is the Benjamin-Ono equation (BO) [[Bj1967]], [[On1975]], which models one-dimensional internal waves in deep water. Both of these equations are [[completely integrable]] (see e.g. [[AbFs1983]], [[CoiWic1990]]), though the intermediate cases 0 < a < 1 are not.
where <math>D_x := \sqrt{-\Delta}</math> is the positive differentiation operator. When a=1 this is [[KdV]]; when a=0 this is the Benjamin-Ono equation (BO) [[Bj1967]], [[On1975]], which models one-dimensional internal waves in deep water. Both of these equations are [[completely integrable]] (see e.g. [[AbFs1983]], [[CoiWic1990]]), though the intermediate cases 0 < a < 1 are not.


When a=0, scaling is s = -1/2, and the following results are known:
When a=0, scaling is s = -1/2, and the following results are known:

Revision as of 20:41, 11 August 2006

Benjamin-Ono equation

The generalized Benjamin-Ono equation is the scalar equation

where is the positive differentiation operator. When a=1 this is KdV; when a=0 this is the Benjamin-Ono equation (BO) Bj1967, On1975, which models one-dimensional internal waves in deep water. Both of these equations are completely integrable (see e.g. AbFs1983, CoiWic1990), though the intermediate cases 0 < a < 1 are not.

When a=0, scaling is s = -1/2, and the following results are known:

When 0 < a < 1, scaling is s = -1/2 - a, and the following results are known:

  • LWP in H^s is known for s > 9/8 - 3a/8 KnKoe-p
  • GWP is known when s >= (a+1)/2 when a > 4/5, from the conservation of the Hamiltonian KnPoVe1994b
  • The LWP results are obtained by energy methods; it is known that pure iteration methods cannot work MlSauTz2001
    • However, this can be salvaged by combining the H^s norm || f ||_{H^s} with a weighted Sobolev space, namely || xf ||_{H^{s - 2s_*}}, where s_* = (a+1)/2 is the energy regularity. CoKnSt-p4

One can replace the quadratic non-linearity uu_x by higher powers u^{k-1} u_x, in analogy with KdV and gKdV, giving rise to the gBO-k equations (let us take a=0 for sake of discussion).The scaling exponent is 1/2 - 1/(k-1).

  • For k=3, one has GWP for large data in H^1 [KnKoe-p] and LWP for small data in H^s, s > ½ MlRi-p
    • For small data in H^s, s>1, LWP was obtained in KnPoVe1994b
    • With the addition of a small viscosity term, GWP can also be obtained in H^1 by complete integrability methods in FsLu2000, with asymptotics under the additional assumption that the initial data is in L^1.
    • For s < ½, the solution map is not C^3 [MlRi-p]
  • For k=4, LWP for small data in H^s, s > 5/6 was obtained in KnPoVe1994b.
  • For k>4, LWP for small data in H^s, s >=3/4 was obtained in KnPoVe1994b.
  • For any k >= 3 and s < 1/2 - 1/k the solution map is not uniformly continuous BiLi-p

The KdV-Benjamin Ono (KdV-BO) equation is formed by combining the linear parts of the KdV and Benjamin-Ono equations together.It is globally well-posed in L^2 Li1999, and locally well-posed in H^{-3/4+} KozOgTns2001 (see also HuoGuo-p where H^{-1/8+} is obtained). Similarly one can generalize the non-linearity to be k-linear, generating for instance the modified KdV-BO equation, which is locally well-posed in H^{1/4+} HuoGuo-p. For general gKdV-gBO equations one has local well-posednessin H^3 and above GuoTan1992.One can also add damping terms Hu_x to the equation; this arises as a model for ion-acoustic waves of finite amplitude with linear Landau damping OttSud1982.