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B. Three Basic Formulae

One needs only three basic formulae in order to derive the main results reported in this paper: one is the extension of the Gaussian integral to a $D$-component vector variable, and the other two are representations for the Dirac delta-function.


Generalized Gaussian Integral:

\begin{displaymath}
\int d{\bf X}
\exp\left(-{1\over 2}  X^i  A_{ij}  X^j + B...
...{\bf B}
\cdot
{\bf A}^{-1}
\cdot
\vec{\bf B}/2
  \right)
\end{displaymath} (59)

where

\begin{displaymath}
{\bf A} = \left(  A _{ij}  \right)
\quad {\rm and} \quad
\vec{\bf B} = \left(  B _{i}   \right)
\end{displaymath} (60)


Dirac-delta representations


a) Functional Fourier Transform:

\begin{displaymath}
\delta[\vec{\bf X}(\lambda)]=({\rm {}const.})\times
\int [{\...
...  \vec{\bf P} (\lambda) \cdot
\vec{\bf X} (\lambda)  \right)
\end{displaymath} (61)

b) Gaussian Representation:

\begin{displaymath}
\delta^D(x)\equiv \lim_{\epsilon\rightarrow 0}
\left(  {1\over\pi\epsilon}  \right)^{D/2}
\exp\left(-x^2/\epsilon \right)
\end{displaymath} (62)



Stefano Ansoldi