Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

New bounds on millicharged particles from cosmology

Alessandro Melchiorri, Antonello Polosa, Alessandro Strumia

TL;DR

This paper derives cosmological bounds on millicharged particles with sub-eV masses by analyzing distortions in the Cosmic Microwave Background spectrum caused by $\gamma\gamma \to q\bar{q}$ production after recombination. Using FIRAS data, the authors obtain a conservative bound $q \lesssim 10^{-7}e$, with stronger, model-dependent limits that depend on additional light states; these results are incompatible with PVLAS-based interpretations that rely on millicharged production or millicharged-mediated axion-like couplings. They also discuss potential model variants that could, in principle, preserve a blackbody spectrum but find such mechanisms unlikely or highly constrained. The findings strongly constrain low-energy millicharged scenarios and illustrate the power of cosmological observations to test new light particle physics.

Abstract

Particles with millicharge q and sub-eV mass can be produced in photon-photon collisions, distorting the energy spectrum of the Cosmic Microwave Background. We derive the conservative bound q < 10^-7 e (as well as model-dependent bounds two orders of magnitude stronger), incompatible with proposed interpretations of the PVLAS anomaly based on millicharged production or on millicharged-mediated axion-like couplings.

New bounds on millicharged particles from cosmology

TL;DR

This paper derives cosmological bounds on millicharged particles with sub-eV masses by analyzing distortions in the Cosmic Microwave Background spectrum caused by production after recombination. Using FIRAS data, the authors obtain a conservative bound , with stronger, model-dependent limits that depend on additional light states; these results are incompatible with PVLAS-based interpretations that rely on millicharged production or millicharged-mediated axion-like couplings. They also discuss potential model variants that could, in principle, preserve a blackbody spectrum but find such mechanisms unlikely or highly constrained. The findings strongly constrain low-energy millicharged scenarios and illustrate the power of cosmological observations to test new light particle physics.

Abstract

Particles with millicharge q and sub-eV mass can be produced in photon-photon collisions, distorting the energy spectrum of the Cosmic Microwave Background. We derive the conservative bound q < 10^-7 e (as well as model-dependent bounds two orders of magnitude stronger), incompatible with proposed interpretations of the PVLAS anomaly based on millicharged production or on millicharged-mediated axion-like couplings.

Paper Structure

This paper contains 4 sections, 10 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Model-independent cosmological constraints
  3. Conclusions
  4. Acknowledgements

Figures (2)

  • Figure 1: Isocurves of the cosmological abundance $n_q/n_\gamma$ of fermionic (left plot) or scalar (right plot) millicharged particles as function of their mass $m_q$ and charge $q$. The shaded region is excluded by the CMB energy spectrum. The dot-dashed curve is the (robust, but not fully model-independent) constraint estimated in eq. (\ref{['eq:Yd']}), for $q'\sim e$. For comparison, the PVLAS anomaly can be interpreted as production of millicharges with $q\sim \hbox{\rm few}\times10^{-6}e$ and maybe $m_q\sim 0.1\,{\rm eV}$Ringwald.
  • Figure 2: FIRAS data compared to the energy-dependent depletion of the CMB spectrum due to $\gamma\gamma\to q\bar{q}$. We plot $1-r$, with $r$ given in eq. (\ref{['eq:r']}), computed for fermion (scalar) millicharges with $m_q = 0.1\,{\rm eV}$ and $q=10^{-7}e$ ($q=1.7~10^{-7}e$), chosen such that the two cases give roughly equal effects, excluded at about 3 standard deviations.