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