8,720 research outputs found
Summary on tau Leptonic Branching Ratios and Universality
The large samples of tau decays available from CLEO and the four LEP
experiment have resulted in new, precise measurements of the leptonic branching
ratios of the . The experimental techniques to obtain these results are
reviewed with special emphasis on the DELPHI measurement. World averages are
found to be Be = (17.81 +/- 0.06) % and Bmu = (17.36 +/- 0.06) %. These results
are consistent with universality in the charged current couplings to a
precision of about 0.25 %. The branching ratio measurements can also be used to
constrain the "low energy parameter" eta. It is shown that the sensitivity to
eta depends on details of the momentum acceptance for muon identification in
the different experiments. Assuming universality in the couplings, the estimate
eta = 0.012 +/- 0.024 is obtained.Comment: 10 pages, LaTeX, including 9 figures, uses epsf and espcrc2. Invited
talk at the Fifth Intl. Workshop on Tau Lepton Physics, 14-17 September 1998,
Santander (Spain
Non-classical computing: feasible versus infeasible
Physics sets certain limits on what is and is not computable. These limits are very far from having been reached by current technologies. Whilst proposals for hypercomputation are almost certainly infeasible, there are a number of non classical approaches that do hold considerable promise. There are a range of possible architectures that could be implemented on silicon that are distinctly different from the von Neumann model. Beyond this, quantum simulators, which are the quantum equivalent of analogue computers, may be constructable in the near future
New physics in transitions after LHC run 1
We present results of global fits of all relevant experimental data on rare
decays. We observe significant tensions between the Standard Model
predictions and the data. After critically reviewing the possible sources of
theoretical uncertainties, we find that within the Standard Model, the tensions
could be explained if there are unaccounted hadronic effects much larger than
our estimates. Assuming hadronic uncertainties are estimated in a sufficiently
conservative way, we discuss the implications of the experimental results on
new physics, both model independently as well as in the context of the minimal
supersymmetric standard model and models with flavour-changing bosons. We
discuss in detail the violation of lepton flavour universality as hinted by the
current data and make predictions for additional lepton flavour universality
tests that can be performed in the future. We find that the ratio of the
forward-backward asymmetries in and
at low dilepton invariant mass is a particularly sensitive probe of lepton
flavour universality and allows to distinguish between different new physics
scenarios that give the best description of the current data.Comment: 49 pages, 12 figures. v4: matches version published in EPJ
- âŚ