4,035 research outputs found
Entropy for Quark States
We discuss the quantum state structure using the standard model for three
colored quarks in the fundamental representations of making up the
singlet ground state of the hadrons. This allows us to calculate a finite von
Neumann entropy from the quantum reduced density matrix, which we explicitly
evaluate for the quarks in a model for the meson and baryon states. Finally we
look into the general effects and implications of entanglement in the
color space.Comment: 9 pages, 0 figure
Light bottom squark and gluino confront electroweak precision measurements
We address the compatibility of a light sbottom (mass 2\sim 5.5 \gev) and a
light gluino (mass 12\sim 16 \gev) with electroweak precision measurements.
Such light particles have been suggested to explain the observed excess in the
quark production cross section at the Tevatron. The electroweak observables
may be affected by the sbottom and gluino through the SUSY-QCD corrections to
the vertex. We examine, in addition to the SUSY-QCD corrections, the
electroweak corrections to the gauge boson propagators from the stop which are
allowed to be light from the SU(2) symmetry. We find that this scenario is
strongly disfavored from electroweak precision measurements unless the heavier
sbottom mass eigenstate is lighter than 180\gev and the left-right mixing in
the stop sector is sufficiently large. This implies that one of the stops
should be lighter than about 98\gev.Comment: 4 pages, revtex, 2 figures. Reference added, version to appear in
Phys.Rev.Let
Experimental limits on New Physics from charm decay
Recent measurements in the charm sector are reviewed, concentrating on
results which are sensitive to New Physics effects. The scope of the
presentation includes D0-D0bar mixing searches, a CPT / Lorentz invariance
study, and a range of searches for rare and forbidden decays. Results from the
BaBar, Belle, CDF, CLEO, and FOCUS collaborations are presented, including an
important first observation.Comment: 14 pages, 5 tables, 17 figures. Invited talk presented at the 21st
International Symposium On Lepton And Photon Interactions At High Energies
(LP03) 11-16 August 2003, Batavia, Illinois. To appear in the proceedings of
the symposiu
Calculation of HELAS amplitudes for QCD processes using graphics processing unit (GPU)
We use a graphics processing unit (GPU) for fast calculations of helicity
amplitudes of quark and gluon scattering processes in massless QCD. New HEGET
({\bf H}ELAS {\bf E}valuation with {\bf G}PU {\bf E}nhanced {\bf T}echnology)
codes for gluon self-interactions are introduced, and a C++ program to convert
the MadGraph generated FORTRAN codes into HEGET codes in CUDA (a C-platform for
general purpose computing on GPU) is created. Because of the proliferation of
the number of Feynman diagrams and the number of independent color amplitudes,
the maximum number of final state jets we can evaluate on a GPU is limited to 4
for pure gluon processes (), or 5 for processes with one or more
quark lines such as and . Compared with the usual
CPU-based programs, we obtain 60-100 times better performance on the GPU,
except for 5-jet production processes and the processes for which
the GPU gain over the CPU is about 20
Search for rare leptonic B decays at the Tevatron
Results of a search for the Flavor-Changing Neutral Current decay using collision data at TeV
collected at Fermilab Tevatron collider by the CDF and D{\O}detectors are
presented. CDF reports upper limits on and
at the 95% C.L. using 171 pb. The D{\O}Collaboration used 240 pb
to set an even more stringent limit on the branching ratio for of at the 95% C.L.Comment: 5 pages, 2 figures, submitted to DPF 2004 conference proceedings, UC
Riverside, C
Energy diffusion in frustrated quantum spin chains exhibiting Gaussian orthogonal ensemble level statistics
Frustrated quantum spin chains with the next-nearest-neighbor (NNN)
couplings are typically deterministic many-body systems exhibiting Gaussian
orthogonal ensemble (GOE) spectral statistics. We investigate energy diffusion
for these spin chains in the presence of a periodically oscillating magnetic
field. Diffusion coefficients are found to obey the power law with respect to
both the field strength and driving frequency with its power varying depending
on the linear response and non-perturbative regimes. The widths of the linear
response and the non-perturbative regimes depend on the strength of
frustrations. We have also elucidated a mechanism for oscillation of energy
diffusion in the case of weakened frustrations.Comment: 6 pages, 6 figure
Consequences of a Possible Di-Gamma Resonace at TRISTAN
If high mass di-gamma events observed at LEP are due to the production of a
di-gamma resonance via its leptonic coupling, its consequences can be observed
at TRISTAN. We find that a predicted decay branching rate is too small to
account for the observed events if the resonance spin is zero, due to a strong
cancellation in the decay amplitudes. Such a cancellation is absent if the
resonance has a spin two. We study the consequences of a tensor production in
the processes , and at TRISTAN
energies. Complete helicity amplitudes with tensor boson exchange contributions
are given, and the signal can clearly be identified from various distributions.
TRISTAN experiments are also sensitive to the virtual tensor boson exchange
effects, which reduce to the contact interaction terms in the high mass limit.Comment: 23 pages in revtex, 7 figures (not included) available upon request,
KEK-TH-35
Weak boson fusion production of supersymmetric particles at the LHC
We present a complete calculation of weak boson fusion production of
colorless supersymmetric particles at the LHC, using the new matrix element
generator SUSY-MadGraph. The cross sections are small, generally at the
attobarn level, with a few notable exceptions which might provide additional
supersymmetric parameter measurements. We discuss in detail how to consistently
define supersymmetric weak couplings to preserve unitarity of weak gauge boson
scattering amplitudes to fermions, and derive sum rules for weak supersymmetric
couplings.Comment: 24 p., 3 fig., 9 tab., published in PRD; numbers in Table IV
corrected to those with kinematic cuts cite
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