The low energy frontier: probes with photons

TL;DR

The paper analyzes sub-eV hidden photons arising from an extra U(1) gauge sector with kinetic mixing to the SM photon. It discusses the phenomenology of massive hidden photons, including photon-hidden photon oscillations, plasma effects, and experimental and cosmological constraints, as well as the possibility of a massless hidden photon altering gauge coupling unification through hypercharge renormalization. It highlights a meV-scale region in the mass-mixing plane ('meV valley') accessible to ALPS laboratory searches and CAST solar observations, with cosmological implications via a resonant early-universe conversion producing a hidden CMB. The results show that hidden photons can be probed across terrestrial, solar, and cosmological arenas and can either mask or aid unification depending on chi and the mass.

Abstract

I discuss different aspects of the phenomenology of hypothetical sub eV mass particles arising in the context of extensions of the standard model. I focus on a simple extension based on an additional U(1) gauge symmetry and its corresponding gauge boson, called ``hidden photon''. Kinetic mixing with the standard photon leads to photon-hidden photon oscillations that are searched for in laboratory experiments like ALPS at DESY. Hidden photons produced in the interior of the Sun could be also detected in axion helioscopes like CAST at CERN and could play an interesting role in late cosmology, where the presence of additional feebly interacting relativistic particles seems to be favored. All these effects disappear as the hidden photon mass decreases, allowing phenomenologically large kinetic mixings. However, in this case such a hidden photon will even play a role in gauge coupling unification.

Figures (2)

• Figure 1: The "meV Valley" in the mass-mixing plane of a hidden photon is bounded at low masses by searches from deviations of the Coulomb law and from seaches of solar hidden photons with the CAST helioscope at higher masses. Light-shinning-through-walls (LSW) experiments have explored the peaceful realm around $m_{\gamma^\prime}\sim$ meV and an upgraded ALPS setup will penetrate even deeper in the near future. In the early universe a part of the CMB can resonantly oscillate into hidden photons contributing, as neutrinos do, to the radiation density at decoupling. Values higher than $N_\nu^\mathrm{eff}>5$ can be excluded, but a value slightly higher than 3, $N_\nu^\mathrm{eff}\simeq 3.8$ is still preferred (Red line). The precise determination of the CMB spectrum by FIRAS constraints the distortions that the creation of this hidden CMB would imprint on it. An experiment exploiting microwave cavities could be sensitive to most of the region of cosmological interest. See the text for references.
• Figure 2: One-loop running of the SM gauge couplings with an exotic renormalization of the hypercharge coupling $g_1$ due to kinetic mixing with an additional massless U(1) gauge boson. LEFT: standard model, RIGHT: with supersymmetry. Note that $\alpha_{1,2,3}= g_{1,2,3}^2/(4\pi)$ and $g_1$ has been normalized with the usual SU(5) factor $\sqrt{5/3}$.