Harish-Chandra's Schwartz space

The definition of the Schwartz space uses Harish-Chandra's Ξ function and his σ function. The σ function is defined by

${\displaystyle \sigma (x)=\|X\|}$

for x=k exp X with k in K and X in p for a Cartan decomposition G = K exp p of the Lie group G, where ||X|| is a K-invariant Euclidean norm on p, usually chosen to be the Killing form. (Harish-Chandra 1966, section 7).

The Schwartz space on G consists roughly of the functions all of whose derivatives are rapidly decreasing compared to Ξ. More precisely, if G is connected then the Schwartz space consists of all smooth functions f on G such that

${\displaystyle {\frac {(1+\sigma )^{r}|Df|}{\Xi }}}$

is bounded, where D is a product of left-invariant and right-invariant differential operators on G (Harish-Chandra 1966, section 9).

• Harish-Chandra (1966), "Discrete series for semisimple Lie groups. II. Explicit determination of the characters", Acta Mathematica, 116: 1–111, doi:10.1007/BF02392813, ISSN 0001-5962, MR 0219666, S2CID 125806386
• 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