23,075 research outputs found
Top quark spin correlations at hadron colliders: Predictions at next-to-leading order QCD
The collider experiments at the Tevatron and the LHC will allow for detailed
investigations of the properties of the top quark. This requires precise
predictions of the hadronic production of pairs and of their
subsequent decays. In this Letter we present for the reactions the first calculation of the dilepton
angular distribution at next-to-leading order (NLO) in the QCD coupling,
keeping the full dependence on the spins of the intermediate state.
The angular distribution reflects the degree of correlation of the and
spins which we determine for different choices of and
spin bases. In the case of the Tevatron, the QCD corrections are sizeable, and
the distribution is quite sensitive to the parton content of the proton.Comment: 9 pages, 2 figure
Top Quark Pair Production and Decay including Spin Effects at Hadron Colliders: Predictions at NLO QCD
Top quark-antiquark () pairs will be produced copiously at the
Tevatron collider and in huge numbers at the LHC. This will make possible
detailed investigations of the properties and interactions of this quark
flavor. The analysis and interpretation of future data requires precise
predictions of the hadronic production of pairs and of their
subsequent decays. In this talk the reactions are considered and results are presented of our calculation
of the dilepton angular distribution at next-to-leading order QCD, keeping the
full dependence on the spins of the intermediate state. The angular
distribution is determined for different choices of reference axes that can be
identified with the and spin axes. While the QCD corrections to
the leading-order distribution turn out to be small in the case of the LHC, we
find them to be sizeable in the case of the Tevatron and find, moreover, the
angular distribution to be sensitive to the parton content of the proton.Comment: Talk given at 3rd Circum-Pan-Pacific Symposium on "High Energy Spin
Physics", Beijing, China, 8-13, 200
Multifractal detrended fluctuation analysis in examining scaling properties of the spatial patterns of soil water storage
Knowledge about the scaling properties of soil water storage is crucial in transferring locally measured fluctuations to larger scales and vice-versa. Studies based on remotely sensed data have shown that the variability in surface soil water has clear scaling properties (i.e., statistically self similar) over a wider range of spatial scales. However, the scaling property of soil water storage to a certain depth at a field scale is not well understood. The major challenges in scaling analysis for soil water are the presence of localized trends and nonstationarities in the spatial series. The objective of this study was to characterize scaling properties of soil water storage variability through multifractal detrended fluctuation analysis (MFDFA). A field experiment was conducted in a sub-humid climate at Alvena, Saskatchewan, Canada. A north-south transect of 624-m long was established on a rolling landscape. Soil water storage was monitored weekly between 2002 and 2005 at 104 locations along the transect. The spatial scaling property of the surface 0 to 40 cm depth was characterized using the MFDFA technique for six of the soil water content series (all gravimetrically determined) representing soil water storage after snowmelt, rainfall, and evapotranspiration. For the studied transect, scaling properties of soil water storage are different between drier periods and wet periods. It also appears that local controls such as site topography and texture (that dominantly control the pattern during wet states) results in multiscaling property. The nonlocal controls such as evapotranspiration results in the reduction of the degree of multiscaling and improvement in the simple scaling. Therefore, the scaling property of soil water storage is a function of both soil moisture status and the spatial extent considered
Study the Heavy Molecular States in Quark Model with Meson Exchange Interaction
Some charmonium-like resonances such as X(3872) can be interpreted as
possible molecular states. Within the quark model, we study
the structure of such molecular states and the similar
molecular states by taking into account of the light meson exchange (,
, , and ) between two light quarks from different
mesons
Extended calculations of energy levels, radiative properties, , hyperfine interaction constants, and Land\'e -factors for nitrogen-like \mbox{Ge XXVI}
Employing two state-of-the-art methods, multiconfiguration
Dirac--Hartree--Fock and second-order many-body perturbation theory, highly
accurate calculations are performed for the lowest 272 fine-structure levels
arising from the , , , ~(), (), and ()
configurations in nitrogen-like Ge XXVI. Complete and consistent atomic data,
including excitation energies, lifetimes, wavelengths, hyperfine structures,
Land\'e -factors, and E1, E2, M1, M2 line strengths, oscillator
strengths, and transition rates among these 272 levels are provided.
Comparisons are made between the present two data sets, as well as with other
available experimental and theoretical values. The present data are accurate
enough for identification and deblending of emission lines involving the
levels, and are also useful for modeling and diagnosing fusion plasmas
Correlation Induced Insulator to Metal Transitions
We study a spinless two-band model at half-filling in the limit of infinite
dimensions. The ground state of this model in the non-interacting limit is a
band-insulator. We identify transitions to a metal and to a charge-Mott
insulator, using a combination of analytical, Quantum Monte Carlo, and zero
temperature recursion methods. The metallic phase is a non-Fermi liquid state
with algebraic local correlation functions with universal exponents over a
range of parameters.Comment: 12 pages, REVTE
Non-Fermi Liquids in the Extended Hubbard Model
I summarize recent work on non-Fermi liquids within certain generalized
Anderson impurity model as well as in the large dimensionality () limit of
the two-band extended Hubbard model. The competition between local charge and
spin fluctuations leads either to a Fermi liquid with renormalized
quasiparticle excitations, or to non-Fermi liquids with spin-charge separation.
These results provide new insights into the phenomenological similarities and
differences between different correlated metals. While presenting these
results, I outline a general strategy of local approach to non-Fermi liquids in
correlated electron systems.Comment: 30 pages, REVTEX, 14 figures included. To appear in ``Non Fermi
Liquid Physics'', J. Phys: Cond. Matt. (1997
Extended Calculations of Spectroscopic Data: Energy Levels, Lifetimes and Transition rates for O-like ions from Cr XVII to Zn XXIII
Employing two state-of-the-art methods, multiconfiguration
Dirac--Hartree--Fock and second-order many-body perturbation theory, the
excitation energies and lifetimes for the lowest 200 states of the ,
, , , , , , , and configurations, and multipole (electric
dipole (E1), magnetic dipole (M1), and electric quadrupole (E2)) transition
rates, line strengths, and oscillator strengths among these states are
calculated for each O-like ion from Cr XVII to Zn XXIII. Our two data sets are
compared with the NIST and CHIANTI compiled values, and previous calculations.
The data are accurate enough for identification and deblending of new emission
lines from the sun and other astrophysical sources. The amount of data of high
accuracy is significantly increased for the states of several O-like
ions of astrophysics interest, where experimental data are very scarce
Dynamics of Neural Networks with Continuous Attractors
We investigate the dynamics of continuous attractor neural networks (CANNs).
Due to the translational invariance of their neuronal interactions, CANNs can
hold a continuous family of stationary states. We systematically explore how
their neutral stability facilitates the tracking performance of a CANN, which
is believed to have wide applications in brain functions. We develop a
perturbative approach that utilizes the dominant movement of the network
stationary states in the state space. We quantify the distortions of the bump
shape during tracking, and study their effects on the tracking performance.
Results are obtained on the maximum speed for a moving stimulus to be
trackable, and the reaction time to catch up an abrupt change in stimulus.Comment: 6 pages, 7 figures with 4 caption
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