Microwave Background Constraints on Mixing of Photons with Hidden Photons

TL;DR

This work revisits cosmological bounds on photon-hidden photon mixing by exploiting the high-precision FIRAS CMB spectrum and including medium-induced, resonant $\gamma\leftrightarrow\gamma_s$ conversions in the expanding universe. By modeling the cosmological photon effective mass $m_\gamma$ through the primordial plasma and applying an adiabaticity-aware treatment of resonances, the authors derive FIRAS-based constraints on the mixing angle $\chi_0$ that are strongest for hidden-photon masses in the range $10^{-14}$–$10^{-7}$ eV. The resulting bounds, roughly $\chi_0 \lesssim 10^{-7}-10^{-5}$ in this mass window, close a previously unconstrained region of parameter space and complement existing laboratory and astrophysical limits. The study also highlights the sensitivity of the bounds to the ionization history and plasma modeling, suggesting future refinements could further tighten or extend the constraints, and notes potential cosmological or astrophysical implications for specific mass ranges.

Abstract

Various extensions of the Standard Model predict the existence of hidden photons kinetically mixing with the ordinary photon. This mixing leads to oscillations between photons and hidden photons, analogous to the observed oscillations between different neutrino flavors. In this context, we derive new bounds on the photon-hidden photon mixing parameters using the high precision cosmic microwave background spectral data collected by the Far Infrared Absolute Spectrophotometer instrument on board of the Cosmic Background Explorer. Requiring the distortions of the CMB induced by the photon-hidden photon mixing to be smaller than experimental upper limits, this leads to a bound on the mixing angle < 10^{-7}-10^{-5} for hidden photon masses between 10^{-14} eV and 10^{-7} eV. This low-mass and low-mixing region of the hidden photon parameter space was previously unconstrained.

Figures (3)

• Figure 1: Left panel: The ionization fraction of hydrogen. For redshifts above $z=11$ the line is taken from the data of Seager:1999bc. The re-ionization period between $z=6$ and $z=11$ is modeled. Right panel: Effective photon mass as function of redshift. The thin line uses $X_e=1$, the blue, magenta, green and red lines are for $\omega/T=1,3,4,10$, respectively. The two sharp dips bound the region where $m_\gamma$ becomes imaginary.
• Figure 2: Bounds from distortions of the CMB blackbody due to $\gamma\to\gamma_s$ photon depletion: 95% C.L. (solid) and 99% C.L. (dashed).
• Figure 3: Bounds from resonant $\gamma\to\gamma_s$ depletion of the CMB blackbody as constrained by FIRAS data in this work (gray region) and in Jaeckel:2008fi (black region). The gray diagonal line separates the region where the resonance happens at small damping (left, this work) or at strong damping (right, cf. Jaeckel:2008fi). Plotted for comparison are bounds from tests of the Coulomb $1/r^2$ law Bartlett:1988yyWilliams:1971ms, magnetic fields of Jupiter and earth Goldhaber:1971mr, photon-regeneration-experiments Afanasev:2008fvAhlers:2007qfAhlers:2007rdCameron:1993mrChou:2007zzcFouche:2008jk, arguments of the lifetime of the Sun and the CAST search of solar axions Redondo:2008aaAndriamonje:2007ew. The solid black line indicates the best possible bound Eq. (\ref{['eq:chi']}) that can be obtained from astrophysical or cosmological sources whose photon flux is known to be unmodified by photon-HP mixing to order unity.