# Feynam Loop Diagrams

Edit and compile if you like:

\documentclass[tikz,svgnames]{standalone}

\usetikzlibrary{patterns}

\begin{document}
\begin{tikzpicture}[
very thick,
q0/.style={->,DarkBlue,semithick,yshift=5pt,shorten >=5pt,shorten <=5pt},
cross/.style={
path picture={
\draw[black,thick]
(path picture bounding box.south east) -- (path picture bounding box.north west)
(path picture bounding box.south west) -- (path picture bounding box.north east);
}
}
]

% Loop
\node[above] (1) at (0,\radius) {$m_1^2$, $\gamma_1^2$};
\node[below] (2) at (0,-\radius) {$m_2^2$, $\gamma_2^2$};
\draw[q0] (140:0.75*\radius) arc (140:40:0.75*\radius) node[midway,below] {$q_0$};

% External lines
\filldraw
(-2*\radius,0) -- (-\radius,0) circle (2pt) node[below left] {$g$}
(\radius,0) circle (2pt) node[below right] {$g$} -- (2*\radius,0);
\draw[q0] (-2*\radius,0) -- (-\radius,0) node[midway,above] {$q_0$};
\draw[q0] (\radius,0) -- (2*\radius,0) node[midway,above] {$q_0$};

\node[xshift=4cm,scale=1.5] at (0,0) {$+$};

\begin{scope}[xshift=8cm]
% Loop
\node[above=3pt] (1) at (0,\radius) {$m_1^2$, $\gamma_1^2$};
\node[below] (2) at (0,-\radius) {$m_2^2$, $\gamma_2^2$};
\draw[q0,yshift=-10pt] (220:0.75*\radius) arc (220:320:0.75*\radius) node[midway,above] {$q_0$};

% External lines
\filldraw
(-2*\radius,0) -- (-\radius,0) circle (2pt) node[below left] {$g$}
(\radius,0) circle (2pt) node[below right] {$g$} -- (2*\radius,0);
\draw[q0] (-2*\radius,0) -- (-\radius,0) node[midway,above] {$q_0$};
\draw[q0] (\radius,0) -- (2*\radius,0) node[midway,above] {$q_0$};
\end{scope}

\end{tikzpicture}
\end{document}