Hidden Laser Communications Through Matter – An application of meV - scale hidden photons –

Currently, there are a number of light-shining-through-walls experiments searching for hidden photons – light, sub-eV-scale, abelian gauge bosons beyond the standard model which mix kinetically with the standard photon. We show that in the case that one of these experiments finds evidence for hidden photons, laser communications through matter, using methods from free-space optics, can be realized in the very near future, with a channel capacity of more than 1 bit per second, for a distance up to the Earth’s diamater. ∗ e-mail: [email protected] † e-mail: [email protected] ‡ e-mail: [email protected] Many extensions of the standard model predict one or more new abelian gauge bosons (γ) besides the photon (γ). If they are massless or very light, with masses mγ′ in the sub-eV range, their dominant interaction with the standard photon arises from a mixing in the gauge-kinetic terms in the Lagrangian [1], L = − 1 4 F Fμν − 1 4 BBμν − 1 2 χF Bμν + 1 2 m2γ′BμB μ + jμA , (1) where Fμν is the field strength tensor for the ordinary electromagnetic gauge field A , j is its associated current (generated by electrons, etc.), and B is the field strength for the new abelian gauge field B. The parameter χ in Eq. (1) gives the strength of the kinetic mixing between A and B. Within the context of string-inspired extensions of the standard model, it is expected to lie in the range between 10 and 10 (cf. [2–5]), while experimentally or phenomenologically, the current limits, in the micro-eV up to eV range, are displayed in Fig. 1. A prominent role in these current limits are played by laboratory experiments exploiting the lightshining-through-walls (LSW) technique [23–28]. In these experiments, laser light is shone through a vacuum tube and blocked from another vacuum tube that is aligned to the first one. Hidden photons eventually generated in the first vacuum tube by photon – hidden photon oscillations, induced by kinetic mixing, will fly through the beam stopper due to their negligible interaction with matter and reconvert into photons in the second vacuum tube, appearing as light shining through the wall. In this letter, we show that in the case that one of the current experiments finds evidence for hidden photons, laser communications through matter, using methods from free-space optics, can be realized in the very near future, with a channel capacity of more than 1 bit per second, for a distance up to the Earth’s diameter. A similar proposal has been recently discussed in [29] in which the particles used for communication are not hidden photons but axionlike-particles (ALPs). Unfortunately ALPs with the parameters required in [29] are excluded by astrophysical considerations that seem quite difficult to evade (however, see [30]). In contrast, the hidden photons considered in this paper do not suffer from such problems. The proposed communication system is based on the concept of free space optics, exchanging the role of optical light as the transmitter for a beam of hidden photons (cf. Fig. 2). Such a beam can be produced and controlled by a “progenitor” laser beam propagating in vacuum. The probability of vacuum photon → hidden photon oscillations (and viceversa) is given by [12] P (γ → γ) = P (γ → γ) = 4χ sin m2γ′L 4ω ≡ 4χ × a, (2) with ω the laser photon frequency. The oscillation length is given by Losc = 4πω/m 2 γ′. Here we are interested in values in the meV valley (see Fig. 1). For concreteness we will consider the following benchmark points m•γ′ = 2.3× 10 −4 eV ; χ = 2× 10, (3) mNγ′ = 3.0× 10 −3 eV ; χN = 3× 10, (4) which can be probed by laboratory experiments in the near future (cf. Fig. 1). In addition, the first one has interesting phenomenological consequences in cosmology [8], while the second one