3,793 research outputs found
Effects of Higgs sector CP violation in top-quark pair production at the LHC
A striking manifestation of CP violation in the electroweak symmetry breaking
sector would be the existence of neutral Higgs boson(s) with undefined CP
parity. We analyse signatures of such a boson, with a mass of about 300 GeV or
larger, produced in high energy proton-proton collisions at LHC energies in its
top-quark antitop-quark decay channel. The large irreducible
background is taken into account. We propose, both for the dilepton and the
lepton + jets decay channels of , several correlations and asymmetries
with which (Higgs sector) CP violation can be traced. We show that for
judiciously chosen cuts on the invariant mass these CP observables
yield, for an LHC integrated luminosity of 100 , statistically
significant signals for a range of Higgs boson masses and Yukawa couplings.Comment: 36 pages, 25 Postscript figure
Magnetic helicity in stellar dynamos: new numerical experiments
The theory of large scale dynamos is reviewed with particular emphasis on the
magnetic helicity constraint in the presence of closed and open boundaries. In
the presence of closed or periodic boundaries, helical dynamos respond to the
helicity constraint by developing small scale separation in the kinematic
regime, and by showing long time scales in the nonlinear regime where the scale
separation has grown to the maximum possible value. A resistively limited
evolution towards saturation is also found at intermediate scales before the
largest scale of the system is reached. Larger aspect ratios can give rise to
different structures of the mean field which are obtained at early times, but
the final saturation field strength is still decreasing with decreasing
resistivity. In the presence of shear, cyclic magnetic fields are found whose
period is increasing with decreasing resistivity, but the saturation energy of
the mean field is in strong super-equipartition with the turbulent energy. It
is shown that artificially induced losses of small scale field of opposite sign
of magnetic helicity as the large scale field can, at least in principle,
accelerate the production of large scale (poloidal) field. Based on mean field
models with an outer potential field boundary condition in spherical geometry,
we verify that the sign of the magnetic helicity flux from the large scale
field agrees with the sign of alpha. For solar parameters, typical magnetic
helicity fluxes lie around 10^{47} Mx^2 per cycle.Comment: 23 pages, 27 figures, Astron. Nach
Hydromagnetic turbulence in computer simulations
In ordinary turbulence research it has been a long standing tradition to
solve the equations in spectral space giving the best possible accuracy. This
is indeed a natural choice for incompressible problems with periodic
boundaries, but it is no longer optimal in many astrophysical circumstances. It
is argued that lower order spatial derivatives schemes are unacceptable in view
of their low overall accuracy, even when mass, momentum, and energy are
conserved to machine accuracy. High order finite difference schemes are
therefore found to be quite efficient and physically appropriate. They are also
easily and efficiently implemented on massively parallel computers. High order
schemes also yield sufficient overall accuracy. Our code uses centered finite
differences which make the adaptation to other problems simple. Since the code
is not written in conservative form, conservation of mass, energy and momentum
can be used to monitor to quality of the solution. A third order Runge-Kutta
scheme with 2N-storage is used for calculating the time advance.Comment: 6 pages, 4 figures (Proceedings of CCP2001 in Aachen
Spin properties of top quark pairs produced at hadron colliders
We discuss the spin properties of top quark pairs produced at hadron
colliders at next-to-leading order in the coupling constant alpha_s of the
strong interaction. Specifically we present, for some decay channels, results
for differential angular distributions that are sensitive to t tbar spin
correlations.Comment: Invited talk given by A. Brandenburg at the Cracow epiphany
conference on heavy flavours, 3 - 6 January 2003, Cracow, Polan
Investigation of Top quark spin correlations at hadron collider
We report on our results about hadronic production at NLO QCD
including spin effects, especially on spin correlations.Comment: talk given at the 32nd International Conference on High Energy
Physics (ICHEP'04), Beijing, China, 16-22 Aug. 200
Letter from W. A. Brandenburg to Friend and Alumnus
Letter to Friend and Alumnus, regarding the Twenty-First Anniversary, from President W. A. Brandenbur
Christmas Letter to Alumnus of K.S.T.C. from Brandenburg (undated)
Christmas Letter (undated) on the subject of the meaning of Christmas, includes poem Abou Ben Adhe
Christmas Letter to Alumnus of K.S.T.C. from Brandenburg, 1938
Christmas Letter, December 13, 1938, on the subject of peace and the meaning of Christma
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