Lesson 04: LaTeX Basics¶

HEP papers are written in LaTeX, specifically using the RevTeX 4-2 document class for APS journals. This lesson covers the conventions that apply throughout: document setup, figures, equations, cross-references, and citations. The goal is not to teach LaTeX from scratch, but to establish the specific patterns used in this subfield so you do not have to rediscover them from journal guidelines or by copying someone else's preamble.

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Where to write: Overleaf¶

The standard collaborative tool in HEP is Overleaf. Overleaf is a browser-based LaTeX editor that compiles in the cloud, tracks history, and lets multiple authors edit simultaneously, removing the need to install a local LaTeX distribution or manage a shared repository for the source files.

When starting a new paper, create a new project on Overleaf and share it with your collaborators. This is how most papers in this subfield are written in practice.

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Document class and essential packages¶

\documentclass[aps,prd,twocolumn,superscriptaddress,bibnotes,longbibliography,
               preprintnumbers,floatfix,10pt]{revtex4-2}

\usepackage{graphicx}
\usepackage{xcolor}
\usepackage{amsmath,amsfonts,amsthm,amssymb}
\usepackage[colorlinks]{hyperref}
\usepackage{mathtools}
\usepackage{bm}
\usepackage{multirow}

Set all hyperlinks to violet. This is the standard in these papers:

\hypersetup{
    pdfnewwindow=true,
    colorlinks=true,
    linkcolor=violet,
    citecolor=violet,
    filecolor=violet,
    urlcolor=violet
}

Set the figure path once in the preamble:

\graphicspath{{./figures/}}

All \newcommand definitions go at the top of the preamble, before \begin{document}. Remove any \Scomm{} or \AGcomm{} author-note macros from any submitted draft.

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Figures¶

Single-column figure¶

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{figure}[t]
\centering
\includegraphics[width=\columnwidth]{figures/filename.pdf}
\caption{Caption text here. \textit{Key takeaway in italics.}}
\label{fig:descriptive_name}
\end{figure}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Two-column-wide figure¶

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{figure*}[t]
\centering
\includegraphics[width=\textwidth]{figures/filename.pdf}
\caption{...}
\label{fig:descriptive_name}
\end{figure*}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Rules:

• \centering always appears before \includegraphics. Never use {\centering ...} or \begin{center}.
• \label{} always immediately follows \caption{} on the next line.
• Width is \columnwidth (single-column) or \textwidth (two-column). Never [width=...] without specifying the fraction.
• The final takeaway sentence of a caption is wrapped in \textit{...}.
• Multi-panel captions label panels with \textbf{Left panel:}, \textbf{Right panel:}, etc.
• Placement: the first figure in the paper uses [b]; all others use [t]. Never [h] or [H].
• Figure filenames are lowercase_with_underscores.pdf, no uppercase, no spaces.

Caption structure¶

Each caption has a three-sentence structure:

1. What it shows (result-first): "Energy deposited in S4714 as a fraction of stellar luminosity, as a function of DM mass."
2. What data or model was used: "Solid (dotted) lines show the full Gould formalism (naive estimate). Experimental constraints from [refs] are included."
3. Key takeaway (optional): "The spiked profile yields the largest predicted deposition, reaching O(L★) well below current sensitivity." Wrap in \textit{...}.

Captions must be self-contained. A reader should understand what the figure shows without reading the main text. Do not repeat verbatim what the surrounding paragraph says.

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Equations¶

Single equation¶

%
\begin{equation}
    \sigma_j(E_\nu) = \frac{G_F^2}{\pi}(E_\nu - \omega_j)^2 B_j(GT).
    \label{eq:descriptive_name}
\end{equation}
%

Aligned equations¶

%
\begin{eqnarray}
    \mathcal{R}^\mathrm{CC} & \propto & \phi_{\nu_e} \label{eq:CC} \\
    \mathcal{R}^\mathrm{ES} & \propto & \phi_{\nu_e} + \tfrac{1}{6}(\phi_{\nu_\mu} + \phi_{\nu_\tau}), \label{eq:ES}
\end{eqnarray}
%

Rules:

• A bare % comment line appears immediately above and below every equation block.
• Four-space indentation inside equation environments.
• Equations end with punctuation (. or ,) matching the surrounding sentence.
• Equation labels: eq:descriptive_name, lowercase, underscores only.

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Math notation¶

Upright text in subscripts: always \mathrm{} for multi-letter labels:

✅ Write this	❌ Not this
\mathcal{R}^\mathrm{CC}	\mathcal{R}^{CC}
\phi_\mathrm{tot}	\phi_{tot}
\frac{\mathrm{d}\Phi}{\mathrm{d}E}	\frac{d\Phi}{dE}

Approximate equalities:

Symbol	When to use
$\sim$	Order-of-magnitude equalities: "σ ~ 10⁻³³ cm²"
$\simeq$	Approximate numerical equality in equations (within 10–20%)
$\approx$	Reserved for numerical approximations. Do not use for rough estimates

Calligraphic letters: \mathcal{R} for rates, \mathcal{N} for counts.

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Cross-references in text¶

This is one of the most common sources of inconsistency in drafts. Follow these patterns exactly:

Object	Correct format	LaTeX
Figure	Figure~\ref{fig:name}	Always "Figure", never "Fig."
Equation	Eq.~(\ref{eq:name})	"Eq." with tilde and explicit parentheses
Section	Section~\ref{sec:name}	Spelled out
Appendix	Appendix~\ref{app:name}	Spelled out

Do not use \eqref{}. Use Eq.~(\ref{}) explicitly. Do not use \autoref{} or \Cref{}.

The non-breaking tilde ~ between the word and \ref{} is required in every case.

✅ Write this	❌ Not this
Figure~\ref{fig:dm_density}	Fig.~\ref{fig:dm_density}
Eq.~(\ref{eq:gould})	\eqref{eq:gould}
Section~\ref{sec:results}	Sec.~\ref{sec:results}

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Label naming conventions¶

Use these prefixes consistently:

Type	Prefix	Example
Section	sec:	\label{sec:results}
Appendix	app:	\label{app:systematics}
Figure	fig:	\label{fig:dm_density}
Equation	eq:	\label{eq:gould}
Table	tab:	\label{tab:stellar_params}

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Citations¶

Citation style:

✅ Write this	❌ Not this
"...as shown in Ref. [42]"	"...as has been shown [42]" (too passive)
"...from Refs. [42, 43]"	"...previously [42, 43, 44, 45, 46]" (too many at once)

Maximum 3–4 references per claim. For large literature clusters, use a review reference.

Citation ordering: When citing multiple references simultaneously, order them chronologically by publication or submission year (oldest first). Within the same year, sort alphabetically by first author surname.

% Correct: oldest → newest
\cite{Author1995abc, Author2003xyz, Author2017def, Author2022ghi}

Do not cite in the abstract.

Spell out experiment names on first use: "the Xenon One Ton experiment (XENON1T) [ref]", then use "XENON1T" throughout.

BibTeX keys: Use INSPIRE-style keys (Author:YYYYabc). Include arXiv IDs for preprints.

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Text formatting details¶

• En-dash for ranges: 3--10 not 3-10.
• Non-breaking space before units: 100~kton-year, 1.5~km, $\sim$3~MeV.
• Percent: 10\% with no space before \%.
• Acknowledgements: \section*{Acknowledgements}, asterisk (unnumbered), British spelling.

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Section separators in source files¶

Major sections (Introduction, Results, Conclusions, Appendices) are separated by double comment-line blocks:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\section{Section Title}

Figure environments are wrapped in shorter single-line comment blocks:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{figure}[t]
...
\end{figure}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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Appendix block¶

\appendix
\counterwithin{figure}{section}
\vspace{0.75cm}
\centerline{\Large {\bf Appendices}}
\vspace{0.75cm}

Here, we provide additional details...

\section{Appendix Title}
\label{app:name}

\counterwithin{figure}{section} must appear immediately after \appendix to produce "Figure A1", "Figure B1" labels. Each appendix is a full \section{}, not a \subsection{}.

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Bibliography¶

\clearpage
\bibliography{bibliography}

\clearpage before \bibliography flushes all pending floats. The longbibliography class option is already set. Do not override it.

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Further reading¶

• RevTeX 4-2 documentation: the official documentation for the document class used throughout this track. The full author's guide covers every option and package interaction not addressed here.
• Physical Review D author guidelines: the journal-level specifications that underlie the conventions in this lesson. Worth bookmarking before submission.
• The Not So Short Introduction to LaTeX (Oetiker et al.): the standard first reference for learning LaTeX properly. If the conventions in this lesson feel unfamiliar, work through the relevant sections here before applying them.

What to read next¶

Lesson 05 is the revision checklist, a systematic pass through everything covered in this track, designed to be run on a full draft before submission.