412 research outputs found
Lepton distribution as a probe of new physics in production and decay of the t quark and its polarization
We investigate the possibilities of studying new physics in various processes
of t-quark production using kinematical distributions of the secondary lepton
coming from decay of t quarks. We show that the angular distributions of the
secondary lepton are insensitive to the anomalous tbW vertex and hence are pure
probes of new physics in a generic process of t-quark production. The energy
distribution of the lepton is distinctly affected by anomalous tbW couplings
and can be used to analyze them independent of the production process of t
quarks. The effects of t polarization on the distributions of the decay lepton
are demonstrated for top-pair production process at a gamma-gamma collider
mediated by a heavy Higgs boson.Comment: 15 pages, 7 figures, uses axodraw.sty (included), references added.
v3 to appear in Journal of High Energy Physics. Incorporates minor changes in
the discussion on radiative corrections which do not affect the results. Typo
in reference correcte
Systematic study of autocorrelation time in pure SU(3) lattice gauge theory
Results of our autocorrelation measurement performed on Fujitsu AP1000 are
reported. We analyze (i) typical autocorrelation time, (ii) optimal mixing
ratio between overrelaxation and pseudo-heatbath and (iii) critical behavior of
autocorrelation time around cross-over region with high statistic in wide range
of for pure SU(3) lattice gauge theory on , and
lattices. For the mixing ratio K, small value (3-7) looks optimal in the
confined region, and reduces the integrated autocorrelation time by a factor
2-4 compared to the pseudo-heatbath. On the other hand in the deconfined phase,
correlation times are short, and overrelaxation does not seem to matter For a
fixed value of K(=9 in this paper), the dynamical exponent of overrelaxation is
consistent with 2 Autocorrelation measurement of the topological charge on
lattice at = 6.0 is also briefly mentioned.Comment: 3 pages of A4 format including 7-figure
Electroweak corrections to Higgs production through ZZ fusion at the linear collider
We present the full order alpha electroweak radiative corrections to e+e- ->
e+e-H. The computation is performed with the help of GRACE-loop. The extraction
of the full QED corrections is performed, these are quite large at threshold.
The genuine weak corrections, for the linear collider energies, when expressed
in the G_mu scheme are of order -2 to -4 for Higgs masses preferred by the
latest precision data. We also extract the m_t^2 type corrections and make a
comparison with the weak corrections for the process e+e- ->nu nu H.Comment: 16 pages and 6 figure
Full one-loop electroweak radiative corrections to single Higgs production in e+ e-
We present the full electroweak radiative corrections to
single Higgs production in \epemt. This takes into account the full one-loop
corrections as well as the effects of hard photon radiation. We include both
the fusion and Higgs-strahlung processes. The computation is performed with the
help of {\tt GRACE-loop} where we have implemented a generalised non-linear
gauge fixing condition. The latter includes 5 gauge parameters that can be used
for checks on our results. Besides the UV, IR finiteness and gauge parameter
independence checks it proves also powerful to test our implementation of the
5-point function. We find that for a 500GeV machine and a light Higgs of mass
150GeV, the total correction is small when the results are
expressed in terms of . The total correction decreases
slightly for higher energies. For moderate centre of mass energies the total
decreases as the Higgs mass increases, reaching -10% for
GeV and GeV. In order to quantify the genuine weak
corrections we have subtracted the universal virtual and bremsstrahlung
correction from the full . We find, for GeV, a
weak correction slowly decreasing from -2% to -4% as the energy increases from
GeV to TeV after expressing the tree-level results in
terms of Comment: 16 pages, 3 figures. Only correction is a reference to a web-pag
Autocorrelation in Updating Pure SU(3) Lattice Gauge Theory by the use of Overrelaxed Algorithms
We measure the sweep-to-sweep autocorrelations of blocked loops below and
above the deconfinement transition for SU(3) on a lattice using
20000-140000 Monte-Carlo updating sweeps. A divergence of the autocorrelation
time toward the critical is seen at high blocking levels. The peak is
near = 6.33 where we observe 440 210 for the autocorrelation time
of Wilson loop on blocked lattice. The mixing of 7 Brown-Woch
overrelaxation steps followed by one pseudo-heat-bath step appears optimal to
reduce the autocorrelation time below the critical . Above the critical
, however, no clear difference between these two algorithms can be seen
and the system decorrelates rather fast.Comment: 4 pages of A4 format including 6-figure
Particle Collisions on Stringy Black Hole Background
The collision of two particles in the background of a Sen black hole is
studied. With the equations of motion of the particles, the center-of-mass
energy is investigated when the collision takes place at the horizon of a Sen
black hole. For an extremal Sen black hole, we find that the center-of-mass
energy will be arbitrarily high with two conditions: (1) spin and (2)
one of the colliding particles has the critical angular momentum
. For a nonextremal Sen black hole, we show that, in order to
obtain an unlimited center-of-mass energy, one of the colliding particles
should have the critical angular momentum ( is
the radius of the outer horizon for a nonextremal black hole). However, a
particle with the angular momentum could not approach the
black hole from outside of the horizon through free fall, which implies that
the collision with arbitrarily high center-of-mass energy could not take place.
Thus, there is an upper bound of the center-of-mass energy for the nonextremal
black hole. We also obtain the maximal center-of-mass energy for a
near-extremal black hole and the result implies that the Planck-scale energy is
hard to be approached. Furthermore, we also consider the back-reaction effects.
The result shows that, neglecting the gravitational radiation, it has a weak
effect on the center-of-mass energy. However, we argue that the maximum allowed
center-of-mass energy will be greatly reduced to below the Planck-scale when
the gravitational radiation is included.Comment: 17 pages, 4 figures, published versio
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