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arXiv 2204.01299math.APmath-phmath.MP
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关于具有阶梯状初始数据的反聚焦mKdV方程的大时间渐进行为

On the large-time asymptotics of the defocusing mKdV equation with step-like initial data

School of Mathematical Sciences, Fudan University(复旦大学数学科学学院)

Taiyang Xu, Yidan Zhang

AI总结:

研究反聚焦mKdV方程在阶梯状初始数据下的大时间渐进行为,通过反散射变换和非线性最陡下降法,得到稀疏波解在三个不同区域的渐近行为。

摘要:

我们研究了反聚焦修正的Korteweg-de Vries(mKdV)方程的Cauchy问题,初始数据在x→-∞时趋近于非零常数cl,在x→+∞时趋近于非零常数cr。假设cl>cr>0,解表现出稀疏波结构。我们首先为满足这些阶梯状边界条件的解发展了反散射变换。利用相关的散射数据,我们证明了Cauchy问题存在唯一的全局解,并通过Riemann-Hilbert(RH)问题来表征。通过将此RH问题应用于非线性最陡下降法,我们严格得到了稀疏波解在三个不同的时空区域中的大时间渐进行为,每个区域由不同的主导行为特征化。它们是:(I)左侧区域,其中解趋近于左侧背景常数,模一个小振荡修正;(II)中心区域,其中解表现出缓慢变化的轮廓,过渡于两个常数之间;(III)右侧区域,其中解趋向于右侧背景常数,直至一个代数小修正。严格推导了主导项、次主导项以及误差界。

英文摘要:

We study the Cauchy problem for the defocusing modified Korteweg-de Vries (mKdV) equation with step-like initial data approaching nonzero constants $c_l$ and $c_r$ as $x \to -\infty$ and $x\to+\infty$, respectively. Assuming $c_l>c_r>0$, the solution exhibits a rarefaction wave structure. We first develop the inverse scattering transform for the solution satisfying these step-like boundary conditions. Using the associated scattering data, we prove that there exists a unique global solution of the Cauchy problem and characterize it in terms of a Riemann-Hilbert (RH) problem. By applying the nonlinear steepest descent method to this RH problem, we rigorously obtain large-time asymptotics of rarefaction wave solution in three distinct space-time regions, each characterized by a different leading order behavior. They are: (I) a left-field region where the solution approaches the left background constant, modulo a small oscillatory correction, (II) a central region where the solution exhibits a slowly varying profile that transitions between the two constants, and (III) a right-field region where the solution tends to the right background constant, up to an algebraically small correction. Rigorous derivations of the leading terms, sub-leading terms as well as the error bounds are presented.

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