Interactions checklist

[rjanish]

We have most of these done, but a list might be hand since we ought to review them together anyway. We need to compute (or understand why we can ignore) stopping powers for the following initial particles and processes. For the dominant process at a given energy for a given initial particle, we need to understand where it deposits the energy and how that energy subsequently evolves to thermalization. (Note: I'm staring by listing everything, even stuff we are confident is irrelevant, just to be thorough).

Hadrons

• [charged only] Coulomb scattering off electrons
• [charged only] Coulomb scattering off ions
• [charged only] inverse Compton scattering off WD photons (ignore - suppressed by hadron mass)
• inelastic nuclear collisions (spallation)
• elastic hadronic ion collisions
• Scattering into phonon modes (considering binding energy of Coulomb lattice)
• Cherenkov radiation
• bremsstrahlung (ignore - suppressed by hadron mass)

Electron

• Coulomb scattering off electrons
• Coulomb scattering off ions
• inverse Compton scattering off WD photons
• Scattering into phonon modes (considering binding energy of Coulomb lattice)
• Cherenkov radiation
  • note: SK says he wouldn't trust the usual formulae at our densities.
• bremsstrahlung
• direct e+e- pair production
• electronuclear

Photon

• Compton scattering off of electrons
• Bremsstrahlung (free-free) absorption
• Compton scattering off ions (ignore - this probably becomes photonuclear at high-energies, though?)
• e+e- pair production
• photonuclear

Neutrinos

• ultra-high energy neutrino-nuclear inelastic scattering (can induce hadronic shower via hadron or charged lepton production)

Other complications to consider:

• How do nuclear interactions scale to high energies?
  • ingle-particle cross-sections will generically grow i.e. photonuclear k^0.08 dependence, neutrino scalings. Easy explanation why (SR - could be t-channel scattering)?
  • There can be a LPM-like enhancement of nuclear interactions at high density or high-energy (low-momentum transfer). It is similar to the brem LPM effect, but this time it is a coherent multi-target interaction. why? fyi this is described in the PDG as "coherent photonuclear interactions".
  • LPM suppression is less strong for higher order EM radiative processes because these tend to kinematically involve larger momentum transfers. If the LPM suppression of the first-order process is of order $\alpha$, then the higher-order process may eventually become more dominant. This manifests in the case of direct pair production which overtakes brem at some obscenely high energy for this reason, but dpp is a particularly "easy" higher-order process to compute (SK gives the results in one of his papers). Otherwise, if this is the case at some energy, it may be wise (SK agreed) at first attempt to just ignore all EM processes completely.
• Depositing energy into plasma oscillations?
• Effects of a magnetic field (!!!)
  • shortening of L transverse to field lines
  • synchrotron radiation for charged particles
  • how would this change above interactions by changing the states of the target WD constituents?

[vijayoct27]

Thanks RJ, this is a useful checklist. let's add/edit this as we discuss one by one.

[vijayoct27]

made some minor updates to what RJ first put. no major changes.

[rjanish]

update: check free-free absorption of photons

[vijayoct27]

boom