半线性可逆偏微分方程的拟不变修正Sobolev范数
Quasi invariant modified Sobolev norms for semi linear reversible PDEs
摘要：
本文考虑一类无限维可逆微分系统。假设线性频率上的非共振条件，我们构造了这类系统的几乎不变的伪范数，它们接近于Sobolev类范数。这使我们能够证明，如果索伯列夫范数的索引$s$的初始数据$z_0$是足够小的（顺序$ε$），然后索伯列夫范数的解决方案是有界的$2ε$在很长的时间（顺序$ε^{-r}$与$r$任意）。结果表明，该定理适用于包括d维环面上的非线性薛定谔方程在内的一大类可逆半线性偏微分方程。我们也将我们的方法应用到一个系统的耦合NLS方程是可逆的，但不是哈密顿。我们还注意到，对于同一类可逆系统，我们可以证明伯克霍夫范式定理，该定理反过来又意味着索伯列夫范数的相同界限。然而，我们证明拟不变伪范数存在性的技巧要简单直接得多。
英文摘要：
We consider a general class of infinite dimensional reversible differential systems. Assuming a non resonance condition on the linear frequencies, we construct for such systems almost invariant pseudo norms that are closed to Sobolev-like norms. This allows us to prove that if the Sobolev norm of index $s$ of the initial data $z_0$ is sufficiently small (of order $ε$) then the Sobolev norm of the solution is bounded by $2ε$ during very long time (of order $ε^{-r}$ with $r$ arbitrary). It turns out that this theorem applies to a large class of reversible semi linear PDEs including the non linear Schrödinger equation on the d-dimensional torus. We also apply our method to a system of coupled NLS equations which is reversible but not Hamiltonian. We also notice that for the same class of reversible systems we can prove a Birkhoff normal form theorem that in turn implies the same bounds on the Sobolev norms. Nevertheless the technics that we use to prove the existence of quasi invariant pseudo norms is much more simple and direct.
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