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Updated Bounds on Milli-Charged Particles

Sacha Davidson, Steen Hannestad, Georg Raffelt

TL;DR

The paper updates experimental and observational bounds on milli-charged particles with charge $\epsilon e$ and mass $m_{\epsilon}$, spanning laboratory, cosmological, and astrophysical constraints and distinguishing models with and without a paraphoton. It computes Big-Bang Nucleosynthesis bounds by embedding milli-charged species into the early-universe Boltzmann dynamics and derives strong, mass-dependent limits, while stellar cooling arguments (globular clusters and white dwarfs) and Supernova 1987A provide complementary, often tighter constraints at low masses. Milli-charged neutrinos are discussed in the context of hypercharge redefinitions and anomaly cancellation, yielding extremely stringent bounds ($\epsilon<10^{-21}$) in certain realizations, though flavor-dependent charges could be viable in other scenarios. Overall, the strongest low-mass bounds push $\epsilon$ down to about $2\times10^{-14}$ for $m_{\epsilon} \lesssim 5\ \mathrm{keV}$, while a MeV–TeV window remains open for non-neutrino milli-charged fermions; the results are summarized in an updated figure and applicable to models with or without a paraphoton.

Abstract

We update the bounds on fermions with electric charge $εe$ and mass $m_ε$. For $m_ε\lsim m_e$ we find $10^{-15}\lsimε<1$ is excluded by laboratory experiments, astrophysics and cosmology. For larger masses, the limits are less restrictive and depend on $m_ε$. For milli-charged neutrinos, the limits are stronger, especially if the different flavors mix as suggested by current experimental evidence.

Updated Bounds on Milli-Charged Particles

TL;DR

The paper updates experimental and observational bounds on milli-charged particles with charge and mass , spanning laboratory, cosmological, and astrophysical constraints and distinguishing models with and without a paraphoton. It computes Big-Bang Nucleosynthesis bounds by embedding milli-charged species into the early-universe Boltzmann dynamics and derives strong, mass-dependent limits, while stellar cooling arguments (globular clusters and white dwarfs) and Supernova 1987A provide complementary, often tighter constraints at low masses. Milli-charged neutrinos are discussed in the context of hypercharge redefinitions and anomaly cancellation, yielding extremely stringent bounds () in certain realizations, though flavor-dependent charges could be viable in other scenarios. Overall, the strongest low-mass bounds push down to about for , while a MeV–TeV window remains open for non-neutrino milli-charged fermions; the results are summarized in an updated figure and applicable to models with or without a paraphoton.

Abstract

We update the bounds on fermions with electric charge and mass . For we find is excluded by laboratory experiments, astrophysics and cosmology. For larger masses, the limits are less restrictive and depend on . For milli-charged neutrinos, the limits are stronger, especially if the different flavors mix as suggested by current experimental evidence.

Paper Structure

This paper contains 12 sections, 35 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Laboratory Bounds
  3. Big-Bang Nucleosynthesis
  4. Dominant Processes
  5. Solving the Boltzmann Equation
  6. BBN Limits
  7. Stellar Evolution
  8. Globular Clusters
  9. White Dwarfs
  10. Supernova 1987A
  11. Milli-Charged Neutrinos
  12. Conclusion

Figures (1)

  • Figure 1: Regions of mass-charge space ruled out for milli-charged particles. The solid and dashed lines apply to the model with a paraphoton; solid and dotted lines apply in the absence of a paraphoton. The bounds arise from the following constraints: AC---accelerator experiments; Op---the Tokyo search for the invisible decay of ortho-positronium japan; SLAC---the SLAC milli-charged particle search SLAC; L---the Lamb shift; BBN---nucleosynthesis; $\Omega$ ---$\Omega < 1$; RG---plasmon decay in red giants; WD---plasmon decay in white dwarfs; DM---dark matter searches; SN---Supernova 1987A.