arXiv subjects

Brandon Murakami

Publications and source records attributed to Brandon Murakami.

9 recordsLinked to original sources

arXiv2014

Searching for Lepton Flavor Violation at a Future High Energy Electron-Positron Collider

We consider theories where lepton flavor is violated, in particular concentrating on the four fermion operator consisting of three electrons and a tau. Strong constraints are available from existing searches for tau -> eee, requiring the scale of the contact interaction to be less than ~(9 TeV)^-2. We reexamine this type of physics, assuming that the particles responsible are heavy (with masses greater than ~TeV) such that a contact interaction description continues to be applicable at the energies for a future e+e- collider. We find that the process e+e- -> e tau can be a very sensitive probe of this kind of physics (even for very conservative assumptions about the detector performance), already improving upon the tau decay bounds to less than ~(11 TeV)^-2 at collider energy sqrt(s) 500 GeV, or reaching beyond ~(35 TeV)^-2 for sqrt(s) = 3 TeV. Even stronger bounds are possible at e-e- colliders in the same energy range.

hep-ph↗

arXiv2013

SuperLFV: An SLHA tool for lepton flavor violating observables in supersymmetric models

We introduce SuperLFV, a numerical tool for calculating low-energy observables that exhibit charged lepton flavor violation (LFV) in the context of the minimal supersymmetric standard model (MSSM). As the Large Hadron Collider and MEG, a dedicated mu -> e gamma experiment, are presently acquiring data, there is need for tools that provide rapid discrimination of models that exhibit LFV. SuperLFV accepts a spectrum file compliant with the SUSY Les Houches Accord (SLHA), containing the MSSM couplings and masses with complex phases at the supersymmetry breaking scale. In this manner, SuperLFV is compatible with but divorced from existing SLHA spectrum calculators that provides the low energy spectrum. Hence, input spectra are not confined to the LFV sources provided by established SLHA spectrum calculators. Input spectra may be generated by personal code or by hand, allowing for arbitrary models not supported by existing spectrum calculators.

hep-ph↗

arXiv2004

Differentiating solutions to the gauge hierarchy problem through rare muon decays

We demonstrate the potential of forthcoming mu -> e gamma and mu-e conversion experiments to implicate or disfavor solutions to the gauge hierarchy problem before the advent of the CERN Large Hadron Collider. Solutions of dynamical electroweak symmetry breaking, little Higgs, supersymmetry, and extra dimensions are considered. Correlations of mu -> e gamma and mu-e conversion branching ratios are analyzed for discriminating patterns. Measurements of these exotic muon decays may have compelling implications for supersymmetric solutions.

hep-ph↗

arXiv2004

See-Saw Induced CMSSM Lepton-Flavour Violation Post-WMAP

The see-saw mechanism of neutrino mass generation, when incorporated in supersymmetric theories with supergravity mediated supersymmetry breaking, results in low-energy lepton-flavour violation arising from the soft supersymmetry breaking slepton masses. The parameter space of supergravity theories with conserved R-parity is severely constrained by the requirement that the LSP provide cold dark matter with a relic density in the range indicated by the recent WMAP measurements, as well as by laboratory constraints. We calculate the $\meg$ branching ratio for the constrained minimal supersymmetric standard model, over the range of parameters consistent with WMAP and laboratory constraints, in families of see-saw model parameterizations which fit the low energy neutrino measurements. We find that over much of the range of see-saw models, for supersymmetry parameters consistent with WMAP and laboratory bounds, the resulting predicted rates for $\meg$ (and other charged lepton flavour violating processes) are within current experimental limits, but that these rates should be detectable with the next generation of lepton-flavour violation experiments.

hep-ph↗

arXiv2003

Abelian D-terms and the superpartner spectrum of anomaly-mediated supersymmetry breaking

We address the tachyonic slepton problem of anomaly mediated supersymmetry breaking using abelian D-terms. We demonstrate that the most general extra U(1) symmetry that does not disrupt gauge coupling unification has a large set of possible charges that solves the problem. It is shown that previous studies in this direction that added both an extra hypercharge D-term and another D-term induced by B-L symmetry (or similar) can be mapped into a single D-term of the general ancillary U(1)_a. The U(1)_a formalism enables identifying the sign of squark mass corrections which leads to an upper bound of the entire superpartner spectrum given knowledge of just one superpartner mass.

hep-ph↗

arXiv2002

The impact of lepton-flavor violating Z' bosons on muon g-2 and other muon observables

A lepton-flavor violating (LFV) Z' boson may mimic some of the phenomena usually attributed to supersymmetric theories. Using a conservative model of LFV Z' bosons, the recent BNL E821 muon g-2 deviation allows for a LFV Z' interpretation with a boson mass up to 4.8 TeV while staying within limits set by muon conversion, mu -> e gamma, and mu -> eee. This model is immediately testable as one to twenty e^+e^- -> mu tau events are predicted for an analysis of the LEP II data. Future muon conversion experiments, MECO and PRIME, are demonstrated to have potential to probe very high boson masses with very small charges, such as a 10 TeV boson with an e-mu charge of 10^-5. Furthermore, the next linear collider is shown to be highly complementary with muon conversion experiments, which are shown to provide the strictest and most relevant bounds on LFV phenomena.

hep-ph↗

arXiv2001

D-term challenges for supersymmetric gauged abelian flavor symmetries

Attention is called to potentially dangerous lepton-flavor violation (LFV) induced by the D-terms of additional U(1) flavor-dependent gauge symmetries in supersymmetric models. In such models, LFV persists despite an arbitrarily high scale for the U(1) breaking and despite arbitrarily small gauge couplings. In light of recent experimental observations of neutrino oscillations, these models are highly motivated experimentally and theoretically. Taking into account also the recent measurement of the muon anomalous magnetic moment, strong bounds are calculated for the magnitude of the D-term-induced LFV. Using current data we find that the slepton mass-mixing parameter (m_{\tilde l_L}^2)_{12}/m_{\tilde l_L}^2 is required to be less than O(10^{-4}) -- a value perhaps already too low compared to expectations. Near future probes will increase sensitivity to 10^{-6}.

hep-ph↗

arXiv2001

Complementarity of muon-conversion and linear collider-based experiments for lepton-flavor violating U(1) gauge bosons

In general, attempts to extend the standard model will include extra gauge structure. We parameterize string and technicolor models for a Z' boson with primitive lepton flavor violating interactions. Calculations for its muon conversion rate (mu N -> e N) on Titanium are made and used to show the potential of forthcoming experiments MECO at Brookhaven National Laboratory and PRIME at the Japan Hadron Facility (to be renamed). For reasonable choices of parameters, such U(1) bosons with masses the order 10 TeV and mu-e Z' charge as low as ~10^-5 are demonstrated to be accessible for MECO and PRIME. Also, a demonstration of the complementarity of parameter space coverage for future colliders and muon conversion experiments is given.

hep-ph↗

arXiv2001

Nucleon scattering with higgsino and wino cold dark matter

Neutralinos that are mostly wino or higgsino are shown to be compatible with the recent DAMA annual modulation signal. The nucleon scattering rates for these dark matter candidates are typically an order of magnitude above the oft-considered bino. Although thermal evolution of higgsino and wino number densities in the early universe implies that they are not viable dark matter candidates, non-thermal sources, such as from gravitino or moduli decay in anomaly mediated supersymmetry breaking, suggest that they can be the dominant source of cold dark matter. Their stealthiness at high energy colliders gives even more impetus to analyze nucleon scattering detection methods. We also present calculations for their predicted scattering rate with Germanium detectors, which have yet to see evidence of WIMP scattering.

hep-ph↗