Late time CMB anisotropies constrain mini-charged particles

TL;DR

The paper investigates how mini-charged particles (MCPs), possibly with hidden photons, modify photon propagation in transverse magnetic fields and how this affects late-time CMB anisotropies via the SZ effect. It develops a quantitative framework using a Holdom-type Lagrangian with kinetic mixing $\chi$ and an effective visible charge $\epsilon=(e_h/e)\tan\chi$, yielding a photon survival probability $P_{\gamma\to\gamma}$ that depends on domain-averaged parameters and the adiabatic parameter $\lambda$, with masses $m_\pm^2$ and $\,\mu^2=-2\omega^2 e_h^2 \Delta N_i$. By modeling cluster magnetic fields as multiple domains and comparing to Coma cluster SZ data across frequencies, the authors derive bounds in the $(m_\epsilon,\epsilon)$ plane, finding the strongest constraints without hidden photons (e.g., $\epsilon<4\times10^{-10}$ for $\lambda\gg1$ and $\mu^2\ll\omega_P^2$) and dimmer bounds when hidden photons are present (scaling with $e_h$). They further discuss hyperweak hidden couplings in LARGE volume string scenarios, showing that the SZ bounds probe relevant ranges of $\epsilon$ for $e_h$ values expected in these models, and outline a future ISW-based test that could improve constraints with knowledge of magnetic fields in superclusters. Overall, the work provides a novel, astrophysical constraint on MCP parameter space in low-density environments and highlights potential synergy with laboratory searches and string-inspired scenarios.

Abstract

Observations of the temperature anisotropies induced as light from the CMB passes through large scale structures in the late universe are a sensitive probe of the interactions of photons in such environments. In extensions of the Standard Model which give rise to mini-charged particles, photons propagating through transverse magnetic fields can be lost to pair production of such particles. Such a decrement in the photon flux would occur as photons from the CMB traverse the magnetic fields of galaxy clusters. Therefore late time CMB anisotropies can be used to constrain the properties of mini-charged particles. We outline how this test is constructed, and present new constraints on mini-charged particles from observations of the Sunyaev-Zel'dovich effect in the Coma cluster.

Figures (3)

• Figure 1: The absolute value of the real (solid) and imaginary (dashed) parts of the MCP-induced mass $\mu^2$ are shown for photon polarization parallel (black) and perpendicular (red) to the magnetic field direction. The MCP particle is a Dirac spinor with mass $m_\epsilon$ and electric charge $\epsilon$. The scalar case is very similar. They only depend on the adiabatic parameter $\lambda$. The imaginary part of $\mu^2$ is always negative while the real part is negative for $\lambda \lesssim 20$ and becomes positive for larger values.
• Figure 2: The constraints of the SZ effect on MCPs. The solid black line shows the upper bound in the mini-charge, MCP mass phase space on models which contain MCPs but no hidden photons (we consider a Dirac fermion, but scalars are very similar). The gray region shows the excluded region for models which include hidden photons. The different plots show different values of the hidden sector gauge coupling, given in units of the electric charge.
• Figure 3: Bounds on mini-charged particles for very weak hidden sector gauge couplings. They apply also to models with only mini-charged particles. The solid black line shows the upper bound on the mini-charge obtained in this paper from the SZ effect. The green area is a prediction in LARGE volume scenarios in string theory with a hyperweak U(1) and a string scale $M_{s}\lesssim10^{11}\,{\rm GeV}$. For comparison, we have also included bounds arising from accelerators Davidson:1993sjDavidson:2000hf, Lamb shift Gluck:2007ia, positronium decays Badertscher:2006fm, tests of Coulomb's Law Jaeckel:2009dh, accelerator cavities Gies:2006hv, laser polarization experiments Ahlers:2007qf, the CMB Melchiorri:2007sq and supernova dimming Ahlers:2009kh. All these bounds arise from physics occurring in low density/temperature regions.