arXiv subjects
Publications and source records attributed to John K. Elwood.
The observed quark hierarchies suggest a simple family symmetry. Generalized to leptons through grand-unified quantum numbers, it produces a neutrino mixing matrix with order-one ν_μ - ν_τ mixing, and order-λ^3 ν_e - ν_μ and ν_e - ν_τ mixings. The intrafamily hierarchy and observed neutrino mass differences together require this symmetry to be anomalous, suggesting through the Green-Schwarz mechanism a string or M-theory origin for the symmetry.
The H1 and ZEUS collaborations have recently reported a significant excess of events at high $Q^2$ in positron-proton collisions. While there exists insufficient data to conclusively determine the origin of this excess, one possibility is that it is due to a new leptoquark at mass scale around 200 GeV. We examine the type of leptoquark states that exist in superstring derived standard-like models, and show that, while these models may contain the standard leptoquark states which exist in Grand Unified Theories, they also generically contain new and exotic leptoquark states with fractional lepton number, $\pm1/2$. In contrast to the traditional GUT-type leptoquark states, the couplings of the exotic leptoquarks to the Standard Model states are generated after the breaking of $U(1)_{B-L}$. This important feature of the exotic leptoquark states may result in local discrete symmetries which forbid some of the undesired leptoquark couplings. We examine these couplings in several models and study the phenomenological implications. The flavor symmetries of the superstring models are found to naturally suppress leptoquark flavor changing processes.
We investigate the role of the transverse spin dependence in Drell Yan lepton pair production to NLO in QCD at parton level. In our analysis we deal with the large $p_T$ distributions. We give very compact expressions for the virtual $O(α_s^2)$ corrections to the cross section and show that the singularities factorize. The study is performed in the $\bar{MS}$ scheme in Dimensional Regularization, and with the t'Hooft-Veltman prescription for $γ_5$. A discussion of the structure of the real emissions is included, and detailed methods for the study of these contributions are formulated.
We present a model for the observed hierarchies among the Yukawa couplings of the standard model in the context of an effective low energy theory with an anomalous U(1) symmetry. This symmetry, a generic feature of superstring compactification, is a remnant of the Green-Schwarz anomaly cancellation mechanism. The gauge group is that of the standard model, augmented by X, the anomalous U(1), and two family-dependent phase symmetries $Y^{(1)}$ and $Y^{(2)}$. The correct hierarchies are reproduced only when $sin^2θ_w=3/8$ at the cut-off. To cancel anomalies, right-handed neutrinos and other standard model singlets must be introduced. Independently of the charges of the right-handed neutrinos, this model produces the same neutrino mixing matrix and an inverted hierarchy of neutrino masses. The heaviest is the electron neutrino with a mass $\sim 1$ meV, and mixing of the order of $λ_c^3$ with each of the other two neutrinos.
The production of the excited charmed baryon doublet $Λ_c^*$ via fragmentation is studied. An analysis of the subsequent hadronic decays of the doublet within the framework of heavy hadron chiral perturbation theory produces expressions for both the angular distribution of the decay products and the polarization of the final state heavy baryon in terms of various nonperturbative fragmentation parameters. Future experimental investigation of this system will determine these parameters. In addition, recent experimental results are shown to fix one of the parameters in the heavy hadron chiral Lagrangian.
Using chiral perturbation theory we calculate the imaginary parts of the $K_L \rightarrow π^+ π^- e^+ e^-$ form factors that arise from $ππ\rightarrow π^+ π^-$ and $ππ\rightarrow π^+ π^- γ^*$ rescattering. We discuss their influence on CP violating variables in $K_L \rightarrow π^+ π^- e^+ e^-$.
We calculate all of the form factors for the one-photon, $K_L \rightarrow π^+ π^- γ^* \rightarrow π^+ π^- e^+e^-$ contribution to the $K_L \rightarrow π^+ π^- e^+e^-$ decay amplitude at leading order in chiral perturbation theory. These form factors depend on one unknown constant that is a linear combination of coefficients of local ${\cal O}(p^4)$ operators in the chiral lagrangian for weak radiative kaon decay. We determine the differential rate for $\K$ and also the magnitude of two CP violating observables.