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Properties of associated Legendre conical functions

Mathematical Physics 2025-08-05 v1 General Relativity and Quantum Cosmology math.MP

Abstract

We present some new properties of associated Legendre conical functions of the first and second kind, P1/2+iτ1/2K(χ)P^{-1/2-K}_{-1/2+i \tau}(\chi) and Q1/2+iτ1/2K(χ)Q^{-1/2-K}_{-1/2+i \tau}(\chi). In particular we show that with the τ\tau-independent RnK(χ)=(2π)3/2tanhKχsinh1/2χ[Γ(1+K)]102πdω(1cosω/coshχ)Keinω\mathcal{R}^{K}_{n}(\chi)=(2\pi)^{-3/2}\tanh^{-K}\chi\sinh^{-1/2}\chi[\Gamma(1+K)]^{-1}\int_{0}^{2\pi} d\omega \left (1-\cos \omega/\cosh\chi\right)^{K}e^{in\omega} for any general KK, we can set P1/2+iτ1/2K(χ)=2nRnK(χ)sin[(τin)χ)]/(τin)P^{-1/2-K}_{-1/2+i \tau}(\chi)=2\sum_{n}\mathcal{R}^{K}_{n}(\chi)\sin[(\tau-in)\chi)]/(\tau-in), where nn ranges from -\ell to \ell in unit steps when KK is a non-negative integer \ell, and from -\infty to \infty in unit steps otherwise. Also we can set Q1/2+iτ1/2K(χ)=πnRnKK(χ)eiχ(τi(nK))/(τi(nK))Q^{-1/2-K}_{-1/2+i \tau}(\chi)=-\pi\sum_n\mathcal{R}^K_{n-K}(\chi)e^{-i \chi(\tau-i(n-K))}/(\tau-i(n-K)), where nn ranges from 00 to 22\ell in unit steps when KK is a non-negative integer \ell, and from 00 to \infty in unit steps otherwise. With these forms isolating the entire τ\tau dependence, and especially its associated pole structure, we can use these forms to determine closed form expressions for integrals over τ\tau of associated Legendre conical functions and their products. The Q1/2+iτ1/2K(χ)Q^{-1/2-K}_{-1/2+i \tau}(\chi) have an integral representation containing the integral χdωeiωτ(coshωcoshχ)K\int_{\chi}^{\infty}d\omega e^{i\omega\tau}(\cosh\omega-\cosh\chi)^{K}, an integral that only converges at ω=\omega=\infty if Re[K]<Im[τ]{\rm Re}[K]<{\rm Im}[\tau]. We show how to use the divergence of this integral outside of this range in order to characterize the complex τ\tau plane pole structure of Q1/2+iτ1/2K(χ)Q^{-1/2-K}_{-1/2+i \tau}(\chi). We present a new treatment of the Borwein integral and the Nyquist-Shannon sampling theorem.

Keywords

Cite

@article{arxiv.2508.01804,
  title  = {Properties of associated Legendre conical functions},
  author = {Daniel A. Norman and Philip D. Mannheim and Tianye Liu},
  journal= {arXiv preprint arXiv:2508.01804},
  year   = {2025}
}

Comments

22 pages

R2 v1 2026-07-01T04:31:56.544Z