Hidden Photons in Extra Dimensions

Additional U(1) gauge symmetries and corresponding vector bosons, called hidden photons, interacting with the regular photon via kinetic mixing are well motivated in extensions of the Standard Model. Such extensions often exhibit extra spatial dimensions. In this note we investigate the effects of hidden photons living in extra dimensions. In four dimensions such a hidden photon is only detectable if it has a mass or if there exists additional matter charged under it. We note that in extra dimensions suitable masses for hidden photons are automatically present in form of the Kaluza-Klein tower.Comment: 5 pages, 4 figures; Proceedings of the 9th Patras Workshop on Axions, WIMPs and WISPs, Mainz, June 24-28, 201

Hidden photons with Kaluza-Klein towers

One of the simplest extensions of the Standard Model (SM) is an extra U(1) gauge group under which SM matter does not carry any charge. The associated boson -- the hidden photon -- then interacts via kinetic mixing with the ordinary photon. Such hidden photons arise naturally in UV extensions such as string theory, often accompanied by the presence of extra spatial dimensions. In this note we investigate a toy scenario where the hidden photon extends into these extra dimensions. Interaction via kinetic mixing is observable only if the hidden photon is massive. In four dimensions this mass needs to be generated via a Higgs or Stueckelberg mechanism. However, in a situation with compactified extra dimensions there automatically exist massive Kaluza-Klein modes which make the interaction observable. We present phenomenological constraints for our toy model. This example demonstrates that the additional particles arising in a more complete theory can have significant effects on the phenomenology.Comment: 20 pages, 3 figure

Inter-cluster filaments in a Λ\LambdaCDM Universe

The large--scale structure (LSS) in the Universe comprises a complicated filamentary network of matter. We study this network using a high--resolution simulation of structure formation of a $\Lambda$ Cold Dark Matter cosmology. We investigate the distribution of matter between neighbouring large haloes whose masses are comparable to massive clusters of galaxies. We identify a total of 228 filaments between neighbouring clusters. Roughly half of the filaments are either warped or lie off the cluster--cluster axis. We find that straight filaments on the average are shorter than warped ones. More massive clusters are connected to more filaments than less massive ones on average. This finding indicates that the most massive clusters form at the intersections of the filamentary backbone of LSS. For straight filaments, we compute mass profiles. Radial profiles show a fairly well--defined radius, $r_s$, beyond which the profiles follow an $r^{-2}$ power law fairly closely. For the majority of filaments, $r_s$ lies between 1.5 $h^{-1}$ Mpc and 2.0 $h^{-1}$ Mpc. The enclosed overdensity inside $r_s$ varies between a few times up to 25 times mean density, independent of the length of the filaments. Along the filaments' axes, material is not distributed uniformly. Towards the clusters, the density rises, indicating the presence of the cluster infall regions. In addition, we also find some sheet--like connections between clusters. In roughly a fifth of all cluster--cluster connections where we could not identify a filament or sheet, projection effects lead to filamentary structures in the projected mass distribution. (abridged)Comment: 10 pages, 18 figures; submitted to MNRAS; updated: final version, accepted for publicatio

Fluorescence of laser created electron-hole plasma in graphene

We present an experimental observation of non-linear up- and down-converted optical luminescence of graphene and thin graphite subject to picosecond infrared laser pulses. We show that the excitation yields to a high density electron-hole plasma in graphene. It is further shown that the excited charge carries can efficiently exchange energy due to scattering in momentum space. The recombination of the resulting non-equilibrium electron-hole pairs yields to the observed white light luminescence. Due to the scattering mechanism the power dependence of the luminescence is quadratic until it saturates for higher laser power. Studying the luminescence intensity as a function of layer thickness gives further insight into its nature and provides a new tool for substrate independent thickness determination of multilayer flakes

Understanding plastic deformation in thermal glasses from single-soft-spot dynamics

By considering the low-frequency vibrational modes of amorphous solids, Manning and Liu [Phys. Rev. Lett. 107, 108302 (2011)] showed that a population of "soft spots" can be identified that are intimately related to plasticity at zero temperature under quasistatic shear. In this work we track individual soft spots with time in a two-dimensional sheared thermal Lennard Jones glass at temperatures ranging from deep in the glassy regime to above the glass transition temperature. We show that the lifetimes of individual soft spots are correlated with the timescale for structural relaxation. We additionally calculate the number of rearrangements required to destroy soft spots, and show that most soft spots can survive many rearrangements. Finally, we show that soft spots are robust predictors of rearrangements at temperatures well into the super-cooled regime. Altogether, these results pave the way for mesoscopic theories of plasticity of amorphous solids based on dynamical behavior of individual soft spots.Comment: 9 pages, 6 figure