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Exceptional points for associated Legendre functions of the second kind

Mathematical Physics 2023-01-31 v1 General Relativity and Quantum Cosmology High Energy Physics - Theory math.MP Quantum Physics

Abstract

We consider the complex ν\nu plane structure of the associated Legendre function of the second kind Qν1/2K(coshρ)Q^{-1/2-K}_{\nu}(\cosh\rho). We find that for any noninteger value for KK Qν1/2K(coshρ)Q^{-1/2-K}_{\nu}(\cosh\rho) has an infinite number of poles in the complex ν\nu plane, but for any negative integer KK there are no poles at all. For K=0K=0 or any positive integer KK there is only a finite number of poles, with there only being one single pole (at ν=0\nu=0) when K=0K=0. This pattern is characteristic of the exceptional points that appear in a wide variety of physical contexts. However, unusually for theories with exceptional points, Qν1/2K(coshρ)Q^{-1/2-K}_{\nu}(\cosh\rho) has an infinite number of them. Other than in the PTPT-symmetry Jordan-block case, exceptional points usually occur at complex values of parameters. While not being Jordan-block exceptional points themselves, the exceptional points associated with the Qν1/2K(coshρ)Q^{-1/2-K}_{\nu}(\cosh\rho) nonetheless occur at real values of KK.

Cite

@article{arxiv.2301.04092,
  title  = {Exceptional points for associated Legendre functions of the second kind},
  author = {Tianye Liu and Daniel A. Norman and Philip D. Mannheim},
  journal= {arXiv preprint arXiv:2301.04092},
  year   = {2023}
}

Comments

6 pages

R2 v1 2026-06-28T08:08:43.420Z