Illuminating the Hidden Sector of String Theory by Shining Light through a Magnetic Field

Abstract

Many models of physics beyond the Standard Model predict minicharged particles to which current and near future low-energy experiments are highly sensitive. Such minicharges arise generically from kinetic-mixing in theories containing at least two U(1) gauge factors. Here, we point out that the required multiple U(1) factors, the size of kinetic-mixing, and suitable matter representations to allow for a detection in the near future occur naturally in the context of string theory embeddings of the Standard Model. A detection of minicharged particles in a low energy experiment would likely be a signal of an underlying string theory and may provide a means of testing it.

Figures (4)

• Figure 1: (a) One-loop diagram which contributes to kinetic-mixing in field theory, and (b) its equivalent in open string theory (from Ref. Abel:2004rp).
• Figure 2: Kinetic-mixing in open string models with SUSY breaking on "hidden" branes. The visible sector consists of a phenomenologically well determined supersymmetric configuration of D3-branes at a fixed point in the 6 dimensional compact manifold, possibly with D7-branes passing through to cancel local tadpoles. Global absence of tadpoles is assumed to require additional branes and/or anti-branes in the bulk. Closed string interactions are mediated from hidden to visible sector by cylinder diagrams, and are equivalent to Fig. \ref{['fig:string']}.
• Figure 3: Possible values for the kinetic-mixing parameter $\chi$, as a function of the string scale, in the bottom-up approach discussed in the text. Values in the shaded region above the black (lower) and blue (upper) lines are predicted in models with D3- and D4-branes, respectively, for $R/r\geq 1$. The red (vertical) line gives the largest string scale allowed by phenomenology in these models. The area above the green solid (horizontal) line is excluded by current experiments searching for minicharged particles while the green dashed line gives an idea of the expected sensitivity in the near future.
• Figure 4: Two-loop induced fermion masses in the hidden sector are directly related to the supersymmetry breaking. The dashed lines and gauge bosons are all stretched between visible and hidden branes, while the internal propagator is a fermion mass propagator of order 1 TeV.