Cauchy Biorthogonal Polynomials
Abstract
The paper investigates the properties of certain biorthogonal polynomials appearing in a specific simultaneous Hermite-Pade' approximation scheme. Associated to any totally positive kernel and a pair of positive measures on the positive axis we define biorthogonal polynomials and prove that their zeroes are simple and positive. We then specialize the kernel to the Cauchy kernel 1/{x+y} and show that the ensuing biorthogonal polynomials solve a four-term recurrence relation, have relevant Christoffel-Darboux generalized formulae, and their zeroes are interlaced. In addition, these polynomial solve a combination of Hermite-Pade' approximation problems to a Nikishin system of order 2. The motivation arises from two distant areas; on one side, in the study of the inverse spectral problem for the peakon solution of the Degasperis-Procesi equation; on the other side, from a random matrix model involving two positive definite random Hermitian matrices. Finally, we show how to characterize these polynomials in term of a Riemann-Hilbert problem.
- Publication:
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arXiv e-prints
- Pub Date:
- April 2009
- DOI:
- 10.48550/arXiv.0904.2602
- arXiv:
- arXiv:0904.2602
- Bibcode:
- 2009arXiv0904.2602B
- Keywords:
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- Mathematical Physics
- E-Print:
- 38 pages, partially replaces arXiv:0711.4082