Shining Light on Polarizable Dark Particles

TL;DR

The work examines self-conjugate polarizable dark particles that couple to photons through polarizability, proposing a virtual-light-by-light probe as a discovery channel independent of particle stability.A CP-even EFT framework is developed, organizing dimension-6 and dimension-8 polarizability operators for spins 0, 1/2, 1, and two microscopic origins—mediated and intrinsic polarizability—with the latter exemplified by a neutral bosonic open string.Four-photon amplitudes are computed for spin-0 polarizability, including helicity amplitudes and EFT-consistency checks, and the relation to local four-photon operators is established via matching.Forecasts for exclusive diphoton production with forward proton tagging at the LHC show sensitivity to TeV-scale masses and operator cutoffs at 13 TeV with 300 fb$^{-1}$, potentially enhanced with multiple polarizable states.The study highlights complementarity with collider missing-energy searches and considers implications for dark matter scenarios, including conditions under which indirect detection bounds may be evaded.

Abstract

We investigate the possibilities of searching for a self-conjugate polarizable particle in the self-interactions of light. We first observe that polarizability can arise either from the exchange of mediator states or as a consequence of the inner structure of the particle. To exemplify this second possibility we calculate the polarizability of a neutral bosonic open string, and find it is described only by dimension-8 operators. Focussing on the spin-0 case, we calculate the light-by-light scattering amplitudes induced by the dimension-6 and 8 polarizability operators. Performing a simulation of exclusive diphoton production with proton tagging at the LHC, we find that the imprint of the polarizable dark particle can be potentially detected at 5$σ$ significance for mass and cutoff reaching values above the TeV scale, for $\sqrt{s}=$13~TeV and 300 fb$^{-1}$ of integrated luminosity. If the polarizable dark particle is stable, it can be a dark matter candidate, in which case we argue this exclusive diphoton search may complement the existing LHC searches for polarizable dark matter.

Figures (3)

• Figure 1: Four-photon interaction induced by a virtual polarizable dark particle.
• Figure 2: Sensitivity of the exclusive diphoton channel to a spin-0 dark particle with dimension-8 polarizability with coefficient $c^0_{8a,8b}(\Lambda)=10$, represented in the mass-cutoff plane, and assuming $\sqrt{s}=13$ TeV, $L=300$ fb$^{-1}$. The dashed lines correspond to the $5~\sigma$ sensitivity in presence of $N=5$ copies of the dark particle. The two dotted lines corresponds to the $5~\sigma$ sensitivities for the spin-0 state of the neutral string assuming $q=1$ and $q=2$, and taking $\Lambda=l_s^{-1}$, .
• Figure 3: Same as Fig. \ref{['fig:sens']}, for dimension-6 polarizability $\mathcal{O}^0_{6a}$ (left) and dimension-8 polarizability $\hat{\mathcal{O}}^0_{6a}$ (right) with coefficients $c^0_{6a}(\Lambda)=10$, $\hat{c}^0_{6a}(\Lambda)=10$.