Probing Hidden Sector Photons through the Higgs Window

TL;DR

This work investigates hidden-sector photons that mix with the SM photon and acquire mass via a hidden-Higgs, emphasizing how the mass-generation mechanism—specifically the Higgs mechanism with a Higgs Portal—alters experimental and cosmological bounds. By analyzing gauge kinetic mixing, external magnetic-field effects, and Higgs-Portal interactions, the authors show that at high momentum transfer the hidden-Higgs behaves like a minicharged particle, leading to markedly stronger bounds on the mixing parameter $\chi$ for light $m_{\gamma'}$. They also demonstrate that strong magnetic fields can restore the hidden U(1) symmetry inside the field, reshaping light-shining-through-walls constraints, and that Higgs-Portal mixing introduces observable couplings to $\gamma'$, $Z$, and the SM Higgs, producing independent fifth-force constraints on the portal parameters. Overall, the study reveals a rich phenomenology in the Higgs-generated hidden-photon sector, offering sharper laboratory and astrophysical probes and a clear path to distinguish Higgs- versus Stückelberg-origin masses.

Abstract

We investigate the possibility that a (light) hidden sector extra photon receives its mass via spontaneous symmetry breaking of a hidden sector Higgs boson, the so-called hidden-Higgs. The hidden-photon can mix with the ordinary photon via a gauge kinetic mixing term. The hidden-Higgs can couple to the Standard Model Higgs via a renormalizable quartic term - sometimes called the Higgs Portal. We discuss the implications of this light hidden-Higgs in the context of laser polarization and light-shining-through-the-wall experiments as well as cosmological, astrophysical, and non-Newtonian force measurements. For hidden-photons receiving their mass from a hidden-Higgs we find in the small mass regime significantly stronger bounds than the bounds on massive hidden sector photons alone.

Figures (7)

• Figure 1: Current bounds on hidden-sector photons from analyzing the magnetic fields of Jupiter and Earth Goldhaber:1971mr, Coulomb law tests Williams:1971msBartlett:1988yy (gold), electroweak precision data Feldman:2007wj (lightgray), searches of solar hidden-photons with the CAST experiment (purple) Popov:1991Popov:1999Andriamonje:2007ewRedondo:2008aa and light-shining-through-walls (LSW) experiments Cameron:1993mrRobilliard:2007bqChou:2007zzAhlers:2007rdAhlers:2007qf (grey) as well as CMB measurements of the effective number of neutrinos and the blackbody nature of the spectrum (black) Mangano:2006urIchikawa:2006vmKomatsu:2008hkJaeckel:2008fi. Improvements of the solar bounds can be achieved using the SuperKamiokande detector or upgrading the CAST experiment Gninenko:2008pz. The region $m_{\gamma^{\prime}}\lesssim {\rm few}\,\,{\rm meV}$ could be tested by an experiment using microwave cavities Jaeckel:2007chPenny or experiments searching for magnetic fields leaking through a superconducting shielding Jaeckel:2008sz.
• Figure 2: Contributions to the coupling of the photon to the current generated by a hidden-sector particle $h$ in a situation where the hidden-photon is massive. The first is the direct contribution via the charge $Q_{\rm EM, mixing}\, e$ that arises from the shift \ref{['shift']} of the hidden-photon field. The second is due to the $A^{\mu}-X^{\mu}$ oscillations caused by the non-diagonal mass term \ref{['massterm']}. Note that the second diagram is only present if the hidden-photon has non-vanishing mass $m^{2}_{\gamma^{\prime}}\neq 0$.
• Figure 3: Upper limits on the kinetic mixing parameter as a function of the hidden-photon mass from the non-observation of light-shining-through-the-wall in the experiments BFRT, BMV and GammeV. Left Panel: Hidden photon mass arising via the Stückelberg mechanism. See Ref. Ahlers:2007qf for details. Right Panel: Hidden photon mass arising via the Higgs mechanism. For strong magnetic fields $|q_\theta eB|\gg \mu_\theta^2$ the hidden $\mathrm{U}(1)$ is unbroken and LSW bounds from scalar MCP loops (cf. Ahlers:2007rd) apply. In this region, $m^2_{\gamma'} = (q_Xg_X\mu_\theta)^2/\lambda_\theta$ corresponds to the mass the hidden-photon would have in vacuum. Inside the magnetic field the hidden-photon mass is zero. For $|q_\theta eB|\ll \mu_\theta^2$ we have LSW bounds from photon-hidden-photon oscillations arising from the mass term (grey area). We use the benchmark point $q_X= 1/2$, $g_X=e$, $\kappa=0$, and $\lambda_\theta=1$..
• Figure 4: Diagrams contributing to photon--hidden-Higgs oscillations in an external magenetic field.
• Figure 5: Bounds on the Higgs--hidden-Higgs mixing $\sin\alpha$ from fifth force experiments as a function of the hidden-Higgs mass $m_{h}$ (left panel). Using a Higgs mass of $m_{H}=120\,{\rm GeV}$ we can translate these constraints into bounds on the scaled Higgs Portal term $\kappa^2/(4\lambda_\phi\lambda_\theta)$ as a function of the hidden-Higgs mass (right panel). For the latter we get interesting constraints in the $\mu{\rm eV}$ to $0.1$ eV range. Note, that the hidden-Higgs mass is related to the hidden-photon mass by Eq. (\ref{['mg']}) and symmetry breaking of the hidden $\text{U}(1)_X$ requires $\kappa^2/(4\lambda_\phi\lambda_\theta)<1$.