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Register a new userThe effect of a positive bound state on the KdV solution. A case study
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Authors
Alexei Rybkin
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We consider a slowly decaying oscillatory potential such that the corresponding 1D Schrodinger operator has a positive eigenvalue embedded into the absolutely continuous spectrum. This potential does not fall into a known class of initial data for which the Cauchy problem for the Korteweg-de Vries (KdV) equation can be solved by the inverse scattering transform. We nevertheless show that the KdV equation with our potential does admit a closed form classical solution in terms of Hankel operators. Comparing with rapidly decaying initial data our solution gains a new term responsible for the positive eigenvalue. To some extend this term resembles a positon (singular) solution but remains bounded. Our approach is based upon certain limiting arguments and techniques of Hankel operators.
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The tt* equation that we will study here is classed as case 4a by Guest et al. in their series of papers Isomomodromy aspects of the tt* equations of Cecotti and Vafa. In their comprehensive works, Guest et al. give a lot of beautiful formulas on and finally achieve a complete picture of asymptotic data, Stokes data and holomorphic data. But, some of their formulas are complicated, lacking of intuitional explanation or other relevant results that could directly support them. In this paper, we will first verify numerically their formulas among the asymptotic data and Stokes data. Then, we will enlarge the solution class assumed by Guest et al. from the Stoke data side. Based on the numerical results, we put forward a conjecture on the enlarged class of solutions. At last, some trial to enlarge the solution class from the asymptotic data are done. It is the truncation structure of the tt* equation that enables us to do those numerical studies with a satisfactory high precision.
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