In mathematical harmonic analysis, Harish-Chandra's Ξ function is a special spherical function on a semisimple Lie group, studied by Harish-Chandra (1966, section 16).

Harish-Chandra used it to define Harish-Chandra's Schwartz space.

Wallach (1988, 4.5) gives a detailed description of the properties of Ξ.

${\displaystyle \Xi (g)=\int _{K}a(kg)^{\rho }dk,}$

where

• K is a maximal compact subgroup of a semisimple Lie group with Iwasawa decomposition G=NAK
• g is an element of G
• ρ is a Weyl vector
• a(g) is the element a in the Iwasawa decomposition g=nak

• Harish-Chandra (1966), "Two theorems on semi-simple Lie groups", Annals of Mathematics, Second Series, 83 (1): 74–128, doi:10.2307/1970472, ISSN 0003-486X, JSTOR 1970472, MR 0194556
• Wallach, Nolan R (1988), Real reductive groups. I, Pure and Applied Mathematics, vol. 132, Boston, MA: Academic Press, ISBN 978-0-12-732960-4, MR 0929683