21,516 research outputs found
Supergroup BF action for supergravity
General relativity can be formulated as a SU(2) BF-theory with constraints,
as has been shown, by Pleba\'nski. The cosmological constant term can be
obtained from the constraint term, following from the consistency of the
equations of motion, as recently shown by Krasnov. We consider an
invariant, supergravity extension of this theory, for which the consistency of
the equations of motion and the constraints contribute as well to the
cosmological constant terms of Townsend's supergravity. The Kalb-Ramond
invariance is shortly discussed.Comment: 14 page
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
Quantum Backflow States from Eigenstates of the Regularized Current Operator
We present an exhaustive class of states with quantum backflow -- the
phenomenon in which a state consisting entirely of positive momenta may have
negative current and the probability flows in the opposite direction to the
momentum. They are characterized by a general function of momenta subject to
very weak conditions. Such a family of states is of interest in the light of a
recent experimental proposal to measure backflow. We find one particularly
simple state which has surprisingly large backflow -- about 41 percent of the
lower bound on flux derived by Bracken and Melloy. We study the eigenstates of
a regularized current operator and we show how some of these states, in a
certain limit, lead to our class of backflow states. This limit also clarifies
the correspondence between the spectrum of the regularized current operator,
which has just two non-zero eigenvalues in our chosen regularization, and the
usual current operator.Comment: 16 pages, 2 figure
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