Inequivalent Quantizations of Gauge Theories

It is known that the quantization of a system defined on a topologically non-trivial configuration space is ambiguous in that many inequivalent quantum systems are possible. This is the case for multiply connected spaces as well as for coset spaces. Recently, a new framework for these inequivalent quantizations approach has been proposed by McMullan and Tsutsui, which is based on a generalized Dirac approach. We employ this framework for the quantization of the Yang-Mills theory in the simplest fashion. The resulting inequivalent quantum sectors are labelled by quantized non-dynamical topological charges.Comment: 24 pages, LaTeX, to be publ. in Int.J.Mod.Phys.

Search for Hidden photons with Sumico

We searched for solar hidden photons in the visible photon energy range using a hidden photon detector add-on attached to Sumico. It consists of a parabolic mirror of dia. 0.5m and f=1m installed in a vacuum chamber, and a low noise photomultiplier tube at the focal point. No evidence for the existence of hidden photons was found in the latest measurement giving a new limit on the photon-hidden photon mixing parameter in the hidden photon mass range 0.001-1eV.Comment: 6 pages. Contributed to the 9th Patras Workshop on Axions, WIMPs and WISPs, Mainz, June 24-28, 201

The Effective Particle-Hole Interaction and the Optical Response of Simple Metal Clusters

Following Sham and Rice [L. J. Sham, T. M. Rice, Phys. Rev. 144 (1966) 708] the correlated motion of particle-hole pairs is studied, starting from the general two-particle Greens function. In this way we derive a matrix equation for eigenvalues and wave functions, respectively, of the general type of collective excitation of a N-particle system. The interplay between excitons and plasmons is fully described by this new set of equations. As a by-product we obtain - at least a-posteriori - a justification for the use of the TDLDA for simple-metal clusters.Comment: RevTeX, 15 pages, 5 figures in uufiles format, 1 figure avaible from [email protected]

IR Sensor Based on Low Bandgap Organic Photodiode With Up-Converting Phosphor

We report an infrared (IR) sensor which is fabricated by integrating a PCPDTBT:PCBM organic photodiode (OPD) with an up-converting (UC) phosphor. The UC phosphor extends the response range by absorbing incoming light with a wavelength of 986 nm and re-emitting at 804 nm, which is a wavelength that can be absorbed by the active layer, resulting in a generation of a photocurrent. In order to ensure low reverse bias leakage current, PEDOT:PSS was not used as a hole transporting layer, which reduced reverse leakage current by two orders of magnitude compared with conventional hole transporting layers. An IR-emitting laser diode (with emission at 986 nm) is used as a light source to illuminate the sensor. The results demonstrate the proof of principle of sensing using polymer-based OPDs in the near-IR, with wider applications possible in areas, such as telecommunications or sensors if different UC phosphors are applied

Determination of the local structure of Sr2−x_{2-x}Mx_xIrO4_4 (M = K, La) as a function of doping and temperature

The local structure of correlated spin-orbit insulator Sr$_{2-x}$M$_x$IrO$_4$ (M = K, La) has been investigated by Ir L$_3$-edge extended x-ray absorption fine structure measurements. The measurements were performed as a function of temperature for different dopings induced by substitution of Sr with La or K. It is found that Ir-O bonds have strong covalency and they hardly show any change across the N\'eel temperature. In the studied doping range, neither Ir-O bonds nor their dynamics, measured by their mean square relative displacements, show any appreciable change upon carrier doping, indicating possibility of a nanoscale phase separation in the doped system. On the other hand, there is a large increase of the static disorder in Ir-Sr correlation, larger for K doping than La doping. Similarities and differences with respect to the local lattice displacements in cuprates are briefly discussed.Comment: Main text: 6 pages, 4 figures, Supplemental information: 2 pages, 2 figure