arXiv subjects
Publications and source records attributed to Christopher Kolda.
Recent progress in the gauge-mediated supersymmetry breaking is reviewed, with emphasis on the theoretical problems which gauge-mediated models so successfully solve, as well as those problems which are endemic to the models themselves and still beguile theorists today.
We demonstrate that in the presence of mixing between different scalar leptoquark multiplets it is possible to simultaneously account for the HERA high-$Q^2$ neutral current anomaly, and produce a charged current anomaly of comparable magnitude. The reduced branching ratio to electrons and jets of the lightest leptoquark state results in a significant weakening of the CDF/D0 limits on scalar leptoquarks; masses consistent with the HERA neutral current excess are comfortably within the allowed range. We show that the possibilities for such a successful mixed leptoquark scenario are quite limited, and we investigate some aspects of their phenomenology.
A recent proposal seeks to explain the anomaly in the HERA high-Q^2 neutral current e^+p data by modifying the parton distribution functions at moderate-to-high-x and large Q^2. We investigate the consequences of this proposal for the HERA high-Q^2 data itself, in the neutral current e^-p channel and especially in the charged current e^\pm p channels. We find that there are striking signatures in the charged current which already serve to rule out many possibilities, including the (symmetric) intrinsic charm hypothesis. For those not ruled out, interesting signals are predicted in e^-p scattering.
The most general Lagrangian for a model with two U(1) gauge symmetries contains a renormalizable operator which mixes their gauge kinetic terms. Such kinetic mixing can be generated at arbitrarily high scales but will not be suppressed by large masses. In models whose supersymmetry (SUSY)-breaking hidden sectors contain U(1) gauge factors, we show that such terms will generically arise and communicate SUSY-breaking to the visible sector through mixing with hypercharge. In the context of the usual supergravity- or gauge-mediated communication scenarios with D-terms of order the fundamental scale of SUSY-breaking, this effect can destabilize the gauge hierarchy. Even in models for which kinetic mixing is suppressed or the D-terms are arranged to be small, this effect is a potentially large correction to the soft scalar masses and therefore introduces a new measurable low-energy parameter. We calculate the size of kinetic mixing both in field theory and in string theory, and argue that appreciable kinetic mixing is a generic feature of string models. We conclude that the possibility of kinetic mixing effects cannot be ignored in model-building and in phenomenological studies of the low-energy SUSY spectra.
Taking the reported high-Q^2 anomaly at HERA as a signal of new physics, we show that several independent considerations point towards s-channel leptoquark production as the most attractive interpretation. We argue that even this option is highly constrained by flavor-changing processes: the couplings must be accurately diagonal in the quark and lepton mass eigenstate basis and should preserve individual quark and lepton family numbers. We propose a dynamical mechanism that might produce this pattern; it has distinctive experimental consequences.
We consider the low-energy signatures of, and high-energy motivations for, scenarios of semi-perturbative gauge coupling unification. Such scenarios can leave striking imprints on the low-energy sparticle spectrum, including novel gaugino mass ratios (including $M_2/M_1\approx1$), substantial compression of the intra-generational squark-to-slepton mass ratios, and an overall lifting of scalar masses relative to the gauginos. We also demonstrate that the unification scale can be raised to $M_X \approx 4\times10^{17}$ GeV while still in the perturbative regime -- close to the 1-loop heterotic string scale. We employ a 3-loop calculation of the running of the gauge couplings as a test of the perturbativity of the high-scale theory.