39,705 research outputs found
Electroweak non-resonant corrections to top pair production close to threshold
The production of W+ W- b bbar from e+ e- collisions at energies close to the
t tbar threshold is dominated by the resonant process with a nearly on-shell t
tbar intermediate state. The W b pairs in the final state can also be reached
through the decay of off-shell tops or through background processes containing
no or only single top quarks. This non-resonant production starts to contribute
at NLO to the W+ W- b bbar total cross section in the non-relativistic
power-counting v ~ alpha_s ~ sqrt(alpha_EW). The NLO non-resonant corrections
presented in this talk represent the non-trivial NLO electroweak corrections to
the e+ e- -> W+ W- b bbar cross section in the top anti-top resonance region.
In contrast to the QCD corrections which have been calculated (almost) up to
NNNLO, the parametrically larger NLO electroweak contributions have not been
completely known so far, but are mandatory for the required accuracy at a
future linear collider. We consider the total cross section of the e+ e- -> W+
W- b bbar process and additionally implement cuts on the invariant masses of
the W+ b and W- bbar pairs.Comment: Talk presented at the 35th International Conference of High Energy
Physics - ICHEP2010, July 22-28, 2010, Paris France. 4 pages, 2 figure
Stationary configurations of two extreme black holes obtainable from the Kinnersley-Chitre solution
Stationary axisymmetric systems of two extreme Kerr sources separated by a
massless strut, which arise as subfamilies of the well-known Kinnersley-Chitre
solution, are studied. We present explicit analytical formulas for the
individual masses and angular momenta of the constituents and establish the
range of the parameters for which such systems can be regarded as describing
black holes. The mass-angular momentum relations and the interaction force in
the black-hole configurations are also analyzed. Furthermore, we construct a
charging generalization of the Kinnersley-Chitre metric and, as applications of
the general formulas obtained, discuss two special cases describing a pair of
identical co- and counterrotating extreme Kerr-Newman black holes kept apart by
a conical singularity. From our analysis it follows in particular that the
equality relating the mass, angular momentum per unit mass and
electric charge of a single Kerr-Newman extreme black hole is no longer
verified by the analogous extreme black-hole constituents in binary
configurations.Comment: final version revised according to referee's suggestion
Constraint preserving boundary conditions for the Z4c formulation of general relativity
We discuss high order absorbing constraint preserving boundary conditions for
the Z4c formulation of general relativity coupled to the moving puncture family
of gauges. We are primarily concerned with the constraint preservation and
absorption properties of these conditions. In the frozen coefficient
approximation, with an appropriate first order pseudo-differential reduction,
we show that the constraint subsystem is boundary stable on a four dimensional
compact manifold. We analyze the remainder of the initial boundary value
problem for a spherical reduction of the Z4c formulation with a particular
choice of the puncture gauge. Numerical evidence for the efficacy of the
conditions is presented in spherical symmetry.Comment: 18 pages, 8 figure
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