.. Copyright Celeritas contributors: see top-level COPYRIGHT file for details
.. SPDX-License-Identifier: CC-BY-4.0

Summary
=======

The implemented physics models are meant to match the defaults constructed in
``G4EmStandardPhysics``.  Known differences are:

* Particles other than electrons, positrons, and gammas are not currently
  supported.
* As with the AdePT project, Celeritas currently extends the range of Urban MSC
  to higher energies rather than implementing the Wentzel-VI and discrete
  Coulomb scattering.
* Celeritas imports tracking cutoffs and other parameters from
  ``G4EmParameters``, but some custom model cutoffs are not accessible to
  Celeritas.

The following table summarizes the EM processes and models in Celeritas.

.. only:: html

   .. table:: Electromagnetic physics processes and models available in Celeritas.

      +----------------+---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      | Particle       | Processes           |  Models                     | Celeritas Implementation                            | Applicability            |
      +================+=====================+=============================+=====================================================+==========================+
      | :math:`e^-`    | Ionization          |  Møller                     | :cpp:class:`celeritas::MollerBhabhaInteractor`      |       0--100 TeV         |
      |                +---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      |                | Bremsstrahlung      |  Seltzer--Berger            | :cpp:class:`celeritas::SeltzerBergerInteractor`     |       0--1 GeV           |
      |                |                     +-----------------------------+-----------------------------------------------------+--------------------------+
      |                |                     |  Relativistic               | :cpp:class:`celeritas::RelativisticBremInteractor`  |   1 GeV -- 100 TeV       |
      |                +---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      |                | Coulomb scattering  |  Urban                      | :cpp:class:`celeritas::UrbanMscScatter`             |   100 eV -- 100 TeV      |
      |                |                     +-----------------------------+-----------------------------------------------------+--------------------------+
      |                |                     |  Coulomb                    | :cpp:class:`celeritas::CoulombScatteringInteractor` |       0--100 TeV         |
      +----------------+---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      | :math:`e^+`    | Ionization          |  Bhabha                     | :cpp:class:`celeritas::MollerBhabhaInteractor`      |       0--100 TeV         |
      |                +---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      |                | Bremsstrahlung      |  Seltzer-Berger             | :cpp:class:`celeritas::SeltzerBergerInteractor`     |       0--1 GeV           |
      |                |                     +-----------------------------+-----------------------------------------------------+--------------------------+
      |                |                     |  Relativistic               | :cpp:class:`celeritas::RelativisticBremInteractor`  |   1 GeV -- 100 TeV       |
      |                +---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      |                | Coulomb scattering  |  Urban                      | :cpp:class:`celeritas::UrbanMscScatter`             |   100 eV -- 100 TeV      |
      |                |                     +-----------------------------+-----------------------------------------------------+--------------------------+
      |                |                     |  Coulomb                    | :cpp:class:`celeritas::CoulombScatteringInteractor` |       0--100 TeV         |
      |                +---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      |                | Annihilation        | :math:`e^+,e^- \to 2\gamma` | :cpp:class:`celeritas::EPlusGGInteractor`           |       0--100 TeV         |
      +----------------+---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      | :math:`\gamma` | Photoelectric       |  Livermore                  | :cpp:class:`celeritas::LivermorePEInteractor`       |       0--100 TeV         |
      |                +---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      |                | Compton scattering  |  Klein--Nishina             | :cpp:class:`celeritas::KleinNishinaInteractor`      |       0--100 TeV         |
      |                +---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      |                | Pair production     |  Bethe--Heitler             | :cpp:class:`celeritas::BetheHeitlerInteractor`      |       0--100 TeV         |
      |                +---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      |                | Rayleigh scattering |  Livermore                  | :cpp:class:`celeritas::RayleighInteractor`          |       0--100 TeV         |
      +----------------+---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      | :math:`\mu^-`  | Ionization          |  ICRU73QO                   | :cpp:class:`celeritas::MuHadIonizationInteractor`   |       0--200 keV         |
      |                +                     +-----------------------------+-----------------------------------------------------+--------------------------+
      |                |                     |  Bethe--Bloch               | :cpp:class:`celeritas::MuHadIonizationInteractor`   |   200 keV--1 GeV         |
      |                +                     +-----------------------------+-----------------------------------------------------+--------------------------+
      |                |                     |  Mu Bethe--Bloch            | :cpp:class:`celeritas::MuHadIonizationInteractor`   |   200 keV--100 TeV       |
      |                +---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      |                | Bremsstrahlung      |  Mu bremsstrahlung          | :cpp:class:`celeritas::MuBremsstrahlungInteractor`  |       0--100 TeV         |
      |                +---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      |                | Pair production     |  Mu pair production         | :cpp:class:`celeritas::MuPairProductionInteractor`  |   0.85 GeV--100 TeV      |
      +----------------+---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      | :math:`\mu^+`  | Ionization          |  Bragg                      | :cpp:class:`celeritas::MuHadIonizationInteractor`   |       0--200 keV         |
      |                +                     +-----------------------------+-----------------------------------------------------+--------------------------+
      |                |                     |  Bethe--Bloch               | :cpp:class:`celeritas::MuHadIonizationInteractor`   |   200 keV--1 GeV         |
      |                +                     +-----------------------------+-----------------------------------------------------+--------------------------+
      |                |                     |  Mu Bethe--Bloch            | :cpp:class:`celeritas::MuHadIonizationInteractor`   |   200 keV--100 TeV       |
      |                +---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      |                | Bremsstrahlung      |  Mu bremsstrahlung          | :cpp:class:`celeritas::MuBremsstrahlungInteractor`  |       0--100 TeV         |
      |                +---------------------+-----------------------------+-----------------------------------------------------+--------------------------+
      |                | Pair production     |  Mu pair production         | :cpp:class:`celeritas::MuPairProductionInteractor`  |   0.85 GeV--100 TeV      |
      +----------------+---------------------+-----------------------------+-----------------------------------------------------+--------------------------+

.. only:: latex

   .. raw:: latex

      \begin{table}[h]
        \caption{Electromagnetic physics processes and models available in Celeritas.}
        \begin{threeparttable}
        \begin{tabular}{llllr}
          \toprule
          Particle         & Processes                  & Models      & Celeritas Implementation                           & Applicability \\
          \midrule
          \multirow{4}{*}{$e^-$}    & Ionization                          & Møller               & \texttt{\scriptsize celeritas::MollerBhabhaInteractor}      & 0--100 TeV \\
                                    \cline{2-5}
                                    & \multirow{2}{*}{Bremsstrahlung}     & Seltzer--Berger      & \texttt{\scriptsize celeritas::SeltzerBergerInteractor}     & 0--1 GeV \\
                                                                          \cline{3-5}
                                    &                                     & Relativistic         & \texttt{\scriptsize celeritas::RelativisticBremInteractor}  & 1 GeV -- 100 TeV \\
                                    \cline{2-5}
                                    & \multirow{2}{*}{Coulomb scattering} & Urban                & \texttt{\scriptsize celeritas::UrbanMscScatter}             & 100 eV -- 100 TeV \\
                                                                          \cline{3-5}
                                    &                                     & Coulomb              & \texttt{\scriptsize celeritas::CoulombScatteringInteractor} & 0--100 TeV \\
                                    \cline{2-5}
          \hline
          \multirow{5}{*}{$e^+$}    & Ionization                          & Bhabha               & \texttt{\scriptsize celeritas::MollerBhabhaInteractor}      & 0--100 TeV \\
                                    \cline{2-5}
                                    & \multirow{2}{*}{Bremsstrahlung}     & Seltzer--Berger      & \texttt{\scriptsize celeritas::SeltzerBergerInteractor}     & 0--1 GeV \\
                                                                          \cline{3-5}
                                    &                                     & Relativistic         & \texttt{\scriptsize celeritas::RelativisticBremInteractor}  & 1 GeV -- 100 TeV \\
                                    \cline{2-5}
                                    & \multirow{2}{*}{Coulomb scattering} & Urban                & \texttt{\scriptsize celeritas::UrbanMscScatter}             & 100 eV -- 100 TeV \\
                                                                          \cline{3-5}
                                    &                                     & Coulomb              & \texttt{\scriptsize celeritas::CoulombScatteringInteractor} & 0--100 TeV \\
                                    \cline{2-5}
                                    & Annihilation                        & $e^+,e^-\to 2\gamma$ & \texttt{\scriptsize celeritas::EPlusGGInteractor}           & 0--100 TeV \\
          \hline
          \multirow{4}{*}{$\gamma$} & Photoelectric                       & Livermore            & \texttt{\scriptsize celeritas::LivermorePEInteractor}       & 0--100 TeV \\
                                    \cline{2-5}
                                    & Compton scattering                  & Klein--Nishina       & \texttt{\scriptsize celeritas::KleinNishinaInteractor}      & 0--100 TeV \\
                                    \cline{2-5}
                                    & Pair production                     & Bethe--Heitler       & \texttt{\scriptsize celeritas::BetheHeitlerInteractor}      & 0--100 TeV \\
                                    \cline{2-5}
                                    & Rayleigh scattering                 & Livermore            & \texttt{\scriptsize celeritas::RayleighInteractor}          & 0--100 TeV \\
          \hline
          \multirow{3}{*}{$\mu^-$}  & \multirow{2}{*}{Ionization}         & ICRU73QO             & \texttt{\scriptsize celeritas::MuHadIonizationInteractor}   & 0--200 keV \\
                                                                          \cline{3-5}
                                    &                                     & Bethe--Bloch         & \texttt{\scriptsize celeritas::MuHadIonizationInteractor}   & 200 keV -- 1 GeV \\
                                                                          \cline{3-5}
                                    &                                     & Mu Bethe--Bloch      & \texttt{\scriptsize celeritas::MuHadIonizationInteractor}   & 200 keV -- 100 TeV \\
                                    \cline{2-5}
                                    & Bremsstrahlung                      & Mu bremsstrahlung    & \texttt{\scriptsize celeritas::MuBremsstrahlungInteractor}  & 0--100 TeV \\
                                    \cline{2-5}
                                    & Pair production                     & Mu pair production   & \texttt{\scriptsize celeritas::MuPairProductionInteractor}  & 0.85 GeV--100 TeV \\
          \hline
          \multirow{3}{*}{$\mu^+$}  & \multirow{2}{*}{Ionization}         & Bragg                & \texttt{\scriptsize celeritas::MuHadIonizationInteractor}   & 0--200 keV \\
                                                                          \cline{3-5}
                                    &                                     & Bethe--Bloch         & \texttt{\scriptsize celeritas::MuHadIonizationInteractor}   & 200 keV -- 1 GeV \\
                                                                          \cline{3-5}
                                    &                                     & Mu Bethe--Bloch      & \texttt{\scriptsize celeritas::MuHadIonizationInteractor}   & 200 keV -- 100 TeV \\
                                    \cline{2-5}
                                    & Bremsstrahlung                      & Mu bremsstrahlung    & \texttt{\scriptsize celeritas::MuBremsstrahlungInteractor}  & 0--100 TeV \\
                                    \cline{2-5}
                                    & Pair production                     & Mu pair production   & \texttt{\scriptsize celeritas::MuPairProductionInteractor}  & 0.85 GeV--100 TeV \\
          \bottomrule
        \end{tabular}
        \end{threeparttable}
      \end{table}