Multiple gamma function


In mathematics, the multiple gamma function is a generalization of the Euler gamma function and the Barnes G-function. The double gamma function was studied by. At the end of this paper he mentioned the existence of multiple gamma functions generalizing it, and studied these further in.
Double gamma functions are closely related to the q-gamma function, and triple gamma functions are related to the elliptic gamma function.

Definition

For, let
where is the Barnes zeta function.

Properties

Considered as a meromorphic function of, has no zeros. It has poles at for non-negative integers. These poles are simple unless some of them coincide. Up to multiplication by the exponential of a polynomial, is the unique meromorphic function of finite order with these zeros and poles.

Infinite product representation

The multiple gamma function has an infinite product representation that makes it manifest that it is meromorphic, and that also makes the positions of its poles manifest. In the case of the double gamma function, this representation is
where we define the -independent coefficients
where is an -th order residue at.

Reduction to the Barnes G-function

The double gamma function with parameters obeys the relations
It is related to the Barnes G-function by

The double gamma function and conformal field theory

For and, the function
is invariant under, and obeys the relations
For, it has the integral representation
From the function, we define the double Sine function and the Upsilon function by
These functions obey the relations
plus the relations that are obtained by. For they have the integral representations
The functions and appear in correlation functions of two-dimensional conformal field theory, with the parameter being related to the central charge of the underlying Virasoro algebra. In particular, the three-point function of Liouville theory is written in terms of the function.