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Constraints on millicharged particles from Planck

A. D. Dolgov, S. L. Dubovsky, G. I. Rubtsov, I. I. Tkachev

TL;DR

This paper tests whether millicharged particles can appreciably contribute to the cosmic contents by leveraging Planck CMB data. By extending the standard \LambdaCDM framework with the millicharged abundance $\Omega_{mcp} h^2$ and solving the linearized plasma equations via CAMB, then exploring parameter space with COSMOMC, the authors derive a stringent upper limit $\Omega_{mcp} h^2 < 0.001$ (95% CL). They show that millicharged matter suppresses high-$l$ power, biasing the inferred scalar spectral index $n_s$ upward, which under some neutrino assumptions can relax the tension with Harrison-Zeldovich-inspired inflation models. The results imply that while Planck data significantly constrain millicharged abundance, such particles could still play a role in phenomena like galactic magnetic seed fields and influence the viability of certain inflationary scenarios.

Abstract

We revisit cosmic microwave background (CMB) constraints on the abundance of millicharged particles based on the Planck data. The stringent limit Omega_{mcp}h^2 < 0.001 (95% CL) may be set using the CMB data alone if millicharged particles participate in the acoustic oscillations of baryon-photon plasma at the recombination epoch. The latter condition is valid for a wide region of charges and masses of the particles. Adding the millicharged component to LCDM shifts prefered scalar spectral index of primordial perturbations to somewhat larger values as compared to minimal model, even approaching Harrison-Zeldovich spectrum under some assumptions.

Constraints on millicharged particles from Planck

TL;DR

This paper tests whether millicharged particles can appreciably contribute to the cosmic contents by leveraging Planck CMB data. By extending the standard \LambdaCDM framework with the millicharged abundance and solving the linearized plasma equations via CAMB, then exploring parameter space with COSMOMC, the authors derive a stringent upper limit (95% CL). They show that millicharged matter suppresses high- power, biasing the inferred scalar spectral index upward, which under some neutrino assumptions can relax the tension with Harrison-Zeldovich-inspired inflation models. The results imply that while Planck data significantly constrain millicharged abundance, such particles could still play a role in phenomena like galactic magnetic seed fields and influence the viability of certain inflationary scenarios.

Abstract

We revisit cosmic microwave background (CMB) constraints on the abundance of millicharged particles based on the Planck data. The stringent limit Omega_{mcp}h^2 < 0.001 (95% CL) may be set using the CMB data alone if millicharged particles participate in the acoustic oscillations of baryon-photon plasma at the recombination epoch. The latter condition is valid for a wide region of charges and masses of the particles. Adding the millicharged component to LCDM shifts prefered scalar spectral index of primordial perturbations to somewhat larger values as compared to minimal model, even approaching Harrison-Zeldovich spectrum under some assumptions.

Paper Structure

This paper contains 4 sections, 4 equations, 3 figures.

Table of Contents

  1. Introduction
  2. CMB constraints on millicharged matter abundance
  3. Millicharged matter and constraints on Inflation
  4. Conclusions

Figures (3)

  • Figure 1: The marginalized likelihood in the $\Omega_{mcp} h^2$ - $\Omega_b h^2$ plane. The countours constrain 68%, 95% and 99% regions. Left panel corresponds to 3 effectively massless neutrino species, see text for exact values of these parameters. In the right panel the constraints on the number and mass of neutrinos are relaxed.
  • Figure 2: The marginalized likelihood in the 2D planes: $\Omega_{mcp} h^2$ versus $m_\nu$, and $n_\nu$. The countours constrain 68%, 95% and 99% regions.
  • Figure 3: Same as in Fig. \ref{['mcp_likeli']} but in the $\Omega_{mcp} h^2$ - $n_s$ plane.