12,070 research outputs found
Top quark forward-backward asymmetry from the model
The forward-backward asymmetry in top quark pair production,
measured at the Tevatron, is probably related to the contribution of new
particles. The Tevatron result is more than a deviation from the
standard model prediction and motivates the application of alternative models
introducing new states.
However, as the standard model predictions for the total cross section
and invariant mass distribution for this process are in
good agreement with experiments, any alternative model must reproduce these
predictions. These models can be placed into two categories: One introduces the
s-channel exchange of new vector bosons with chiral couplings to the light
quarks and to the top quark and another relies on the t-channel exchange of
particles with large flavor-violating couplings in the quark sector. In this
work we employ a model which introduces both s- and t-channel nonstandard
contributions for the top quark pair production in proton antiproton
collisions. We use the minimal version of the model (3-3-1 model) that predicts the existence of a new neutral gauge
boson, called . This gauge boson has both flavor-changing couplings
to up and top quarks and chiral coupling to the light quarks and to the top
quark. This very peculiar model coupling can correct the for top quark
pair production for two ranges of mass while leading to cross
section and invariant mass distribution quite similar to the standard model
ones. This result reinforces the role of the 3-3-1 model for any new physics
effect.Comment: 12 pages, 4 figures, 2 table
Multifractal Properties of Aperiodic Ising Model: role of geometric fluctuations
The role of the geometric fluctuations on the multifractal properties of the
local magnetization of aperiodic ferromagnetic Ising models on hierachical
lattices is investigated. The geometric fluctuations are introduced by
generalized Fibonacci sequences. The local magnetization is evaluated via an
exact recurrent procedure encompassing a real space renormalization group
decimation. The symmetries of the local magnetization patterns induced by the
aperiodic couplings is found to be strongly (weakly) different, with respect to
the ones of the corresponding homogeneous systems, when the geometric
fluctuations are relevant (irrelevant) to change the critical properties of the
system. At the criticality, the measure defined by the local magnetization is
found to exhibit a non-trivial F(alpha) spectra being shifted to higher values
of alpha when relevant geometric fluctuations are considered. The critical
exponents are found to be related with some special points of the F(alpha)
function and agree with previous results obtained by the quite distinct
transfer matrix approach.Comment: 10 pages, 7 figures, 3 Tables, 17 reference
Predicting Musical Emotions From Low-level Acoustics and Physiological Measurements: Music and Speech
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