Anomalous Z′Z' and Diboson Resonances at the LHC

We propose novel collider searches which can significantly improve the LHC reach to new gauge bosons $Z'$ with mixed anomalies with the electroweak (EW) gauge group. Such a $Z'$ necessarily acquires a Chern-Simons coupling to the EW gauge bosons and these couplings can drive both exotic $Z$ decays into $Z'\gamma$ if the new gauge boson is sufficiently light, as well as $Z'$ decays into EW gauge bosons.While the exotic decay rate of the heavy $Z$ into $Z'\gamma$ is too small to be observed at the LHC, for a light $Z'$, we show the potential of a lepton jet search in association with a photon to probe the rare decay $Z \to Z' \gamma$.Comment: 17 pages, 4 figures. v2: equation corrected, main results in Section 4 unchanged, accepted for publication in JHE

Leptonic Pion Decay And Physics Beyond The Electroweak Standard Model

The ratio of branching ratios in leptonic pion decay $R_{\pi} \equiv (\Gamma(\pi^- \to e \nu_e))/(\Gamma(\pi^- \to \mu \nu_\mu))$ is a powerfully sensitive probe of new interactions beyond the electroweak standard model. This is due to the chirality suppression of the standard model amplitude for the decay, which results in a precise prediction for the ratio, and suppressed amplitudes for new contributions to interfere with. We calculate, including QCD corrections, the contributions to $R_{\pi}$ arising from a broad selection of standard model extensions to which it is sensitive, including: R-parity violating interactions in supersymmetric theories, theories with light (electroweak scale) leptoquark degrees of freedom, non-minimal models of extra doublet Higgs bosons, models in which the quarks and leptons are composite both with and without supersymmetry, and models with strong TeV scale gravitational interactions. Comparing with existing measurements of $R_{\pi}$ we provide limits on each of these classes of models; our calculations also represent state of the art theoretical benchmarks against which the results from the upcoming round of leptonic pion decay experiments may be compared.Comment: 31 pages, 3 figure

Opportunistic Spectrum Sharing using Dumb Basis Patterns: The Line-of-Sight Interference Scenario

We investigate a spectrum-sharing system with non-severely faded mutual interference links, where both the secondary-to-primary and primary-to-secondary channels have a Line-of-Sight (LoS) component. Based on a Rician model for the LoS channels, we show, analytically and numerically, that LoS interference hinders the achievable secondary user capacity. This is caused by the poor dynamic range of the interference channels fluctuations when a dominant LoS component exists. In order to improve the capacity of such system, we propose the usage of an Electronically Steerable Parasitic Array Radiator (ESPAR) antenna at the secondary terminals. An ESPAR antenna requires a single RF chain and has a reconfigurable radiation pattern that is controlled by assigning arbitrary weights to M orthonormal basis radiation patterns. By viewing these orthonormal patterns as multiple virtual dumb antennas, we randomly vary their weights over time creating artificial channel fluctuations that can perfectly eliminate the undesired impact of LoS interference. Because the proposed scheme uses a single RF chain, it is well suited for compact and low cost mobile terminals