\section{Conventions} This section discusses the conventions we use for various physics quantities in the code. \subsection{Units} In EvtGen, $c=1$, such that mass, energy and momentum are all measured in units of GeV. Similarly, time and space have units of mm. \subsection{Four-vectors} There are two types of four-vectors used in EvtGen, {\tt EvtVector4R} and {\tt EvtVector4C}, which are real and complex respectively. A four-vector is represented by $p^{\mu}=(E,\vec{p})$. When a four-vector is used its components are always corresponding to raised indices. A contraction of two vectors $p$ and $k$ ({\tt p*k}) automatically lowers the indices on $k$ according to the metric $g={\rm diag}(1,-1,-1,-1)$ so that {\tt p*p} is the mass squared of a particle with four-momentum $p$. \subsection{Tensors} We currently only support complex second rank tensors. As in the case of vectors, tensors are always reperesented with all indices raised. The convention for the totaly antisymmetric tensor, $\epsilon_{\alpha\beta\mu\nu}$, is $\epsilon_{0123}=+1$. \subsection{Dirac spinors} \label{sect:diracspinor} Dirac spinors are represented as a 4 component spinor in the Dirac-Pauli representation, with initial state fermions or final state anti-fermions. \subsection{Gamma matrices} Dirac gamma matrices are also represented in the Dirac-Pauli representation, which has \begin{eqnarray} \gamma^0=\left[\begin{array}{rrrr} 1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & -1 & 0 \\ 0 & 0 & 0 & -1 \\ \end{array}\right],& & \gamma^1=\left[\begin{array}{rrrr} 0 & 0 & 0 & 1 \\ 0 & 0 & 1 & 0 \\ 0 & -1 & 0 & 0 \\ -1 & 0 & 0 & 0 \\ \end{array}\right],\\ \gamma^2=\left[\begin{array}{rrrr} 0 & 0 & 0 & -i \\ 0 & 0 & i & 0 \\ 0 & i & 0 & 0 \\ -i & 0 & 0 & 0 \\ \end{array}\right],& & \gamma^3=\left[\begin{array}{rrrr} 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & -1 \\ -1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ \end{array}\right]. \end{eqnarray} This gives \begin{equation} \gamma^5=i\gamma^0\gamma^1\gamma^2\gamma^3 ={i\over4!}\epsilon_{\lambda\mu\nu\pi} \gamma^{\lambda}\gamma^{\mu}\gamma^{\nu}\gamma^{\pi} =\left[\begin{array}{rrrr} 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & 1 \\ 1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ \end{array}\right]. \end{equation}