3,699 research outputs found
Top quark mass definition and top quark pair production near threshold at the NLC
We suggest an infrared-insensitive quark mass, defined by subtracting the
soft part of the quark self energy from the pole mass. We demonstrate the deep
relation of this definition with the static quark-antiquark potential. At
leading order in 1/m this mass coincides with the PS mass which is defined in a
completely different manner. Going beyond static limit, the small normalization
point introduces recoil corrections which are calculated here as well. Using
this mass concept and other concepts for the quark mass we calculate the cross
section of e+ e- -> t t-bar near threshold at NNLO accuracy adopting three
alternative approaches, namely (1) fixing the pole mass, (2) fixing the PS
mass, and (3) fixing the new mass which we call the PS-bar mass. We demonstrate
that perturbative predictions for the cross section become much more stable if
we use the PS or the PS-bar mass for the calculations. A careful analysis
suggests that the top quark mass can be extracted from a threshold scan at NLC
with an accuracy of about 100-200 MeV.Comment: published version, 21 pages in LaTeX including 11 PostScript figure
The Threshold t-tbar Cross Section at NNLL Order
The total cross section for top quark pair production close to threshold in
e+e- annihilation is investigated. Details are given about the calculation at
next-to-next-to-leading logarithmic order. The summation of logarithms leads to
a convergent expansion for the normalization of the cross section, and small
residual dependence on the subtraction parameter nu. A detailed analysis of the
residual nu dependence is carried out. A conservative estimate for the
remaining uncertainty in the normalization of the total cross section from QCD
effects is . This makes precise extractions of the strong
coupling and top width feasible, and further studies of electroweak effects
mandatory.Comment: 33 pages, 11 figs, a program to produce the cross section will be
available soo
The alternatively spliced fibronectin CS1 isoform regulates IL-17A levels and mechanical allodynia after peripheral nerve injury.
BackgroundMechanical pain hypersensitivity associated with physical trauma to peripheral nerve depends on T-helper (Th) cells expressing the algesic cytokine, interleukin (IL)-17A. Fibronectin (FN) isoform alternatively spliced within the IIICS region encoding the 25-residue-long connecting segment 1 (CS1) regulates T cell recruitment to the sites of inflammation. Herein, we analyzed the role of CS1-containing FN (FN-CS1) in IL-17A expression and pain after peripheral nerve damage.MethodsMass spectrometry, immunoblotting, and FN-CS1-specific immunofluorescence analyses were employed to examine FN expression after chronic constriction injury (CCI) in rat sciatic nerves. The acute intra-sciatic nerve injection of the synthetic CS1 peptide (a competitive inhibitor of the FN-CS1/α4 integrin binding) was used to elucidate the functional significance of FN-CS1 in mechanical and thermal pain hypersensitivity and IL-17A expression (by quantitative Taqman RT-PCR) after CCI. The CS1 peptide effects were analyzed in cultured primary Schwann cells, the major source of FN-CS1 in CCI nerves.ResultsFollowing CCI, FN expression in sciatic nerve increased with the dominant FN-CS1 deposition in endothelial cells, Schwann cells, and macrophages. Acute CS1 therapy attenuated mechanical allodynia (pain from innocuous stimulation) but not thermal hyperalgesia and reduced the levels of IL-17A expression in the injured nerve. CS1 peptide inhibited the LPS- or starvation-stimulated activation of the stress ERK/MAPK pathway in cultured Schwann cells.ConclusionsAfter physical trauma to the peripheral nerve, FN-CS1 contributes to mechanical pain hypersensitivity by increasing the number of IL-17A-expressing (presumably, Th17) cells. CS1 peptide therapy can be developed for pharmacological control of neuropathic pain
Top Quark Pair Production close to Threshold: Top Mass, Width and Momentum Distribution
The complete NNLO QCD corrections to the total cross section in the kinematic region close to the top-antitop
threshold are calculated by solving the corresponding Schroedinger equations
exactly in momentum space in a consistent momentum cutoff regularization
scheme. The corrections coming from the same NNLO QCD effects to the top quark
three-momentum distribution are determined. We discuss
the origin of the large NNLO corrections to the peak position and the
normalization of the total cross section observed in previous works and propose
a new top mass definition, the 1S mass M_1S, which stabilizes the peak in the
total cross section. If the influence of beamstrahlung and initial state
radiation on the mass determination is small, a theoretical uncertainty on the
1S top mass measurement of 200 MeV from the total cross section at the linear
collider seems possible. We discuss how well the 1S mass can be related to the
mass. We propose a consistent way to implement the top quark width
at NNLO by including electroweak effects into the NRQCD matching coefficients,
which then can become complex.Comment: 53 pages, latex; minor changes, a number of typos correcte
Running of the heavy quark production current and 1/k potential in QCD
The 1/k contribution to the heavy quark potential is first generated at one
loop order in QCD. We compute the two loop anomalous dimension for this
potential, and find that the renormalization group running is significant. The
next-to-leading-log coefficient for the heavy quark production current near
threshold is determined. The velocity renormalization group result includes the
alpha_s^3 ln^2(alpha_s) ``non-renormalization group logarithms'' of Kniehl and
Penin.Comment: 30 pages, journal versio
Leptonic constants of heavy quarkonia in potential approach of NRQCD
We consider a general scheme for calculating the leptonic constant of heavy
quarkonium QQ-bar in the framework of nonrelativistic quantum chromodynamics,
NRQCD, operating as the effective theory of nonrelativistic heavy quarks. We
explore the approach of static potential in QCD, which takes into account both
the evolution of effective charge in the three-loop approximation and the
linearly raising potential term, which provides the quark confinement. The
leptonic constants of bb-bar and cc-bar systems are evaluated by making use of
two-loop anomalous dimension for the current of nonrelativistic quarks, where
the factor for the normalization of matrix element is introduced in order to
preserve the renormalization group invariance of estimates.Comment: 18 pages, 6 eps-figures, discussion and references added, vNRQCD
analysis considere
A Late Eocene- Oligocene through-flowing river between the Upper Yangtze and South China Sea
We test the hypothesis of a major Paleogene river draining the SE Tibetan Plateau and the central modern Yangtze Basin that then flowed South to the South China Sea. We test this model using U Pb dated detrital zircon grains preserved in Paleogene sedimentary rocks in northern Vietnam and SW China. We applied a series of statistical tests to compare the U-Pb age spectra of the rocks in order to highlight differences and similarities between them and with potential source bedrocks. Monte Carlo mixing models imply that erosion was dominantly derived from the Indochina and Songpan-Garzê Blocks and to a lesser extent the Yangtze Craton. Some of the zircon populations indicate local erosion and sedimentation, but others show close similarity both within northern Vietnam, as well as more widely in the Eocene Jianchuan, Paleocene-Oligocene Simao and Oligocene-Miocene Yuanjiang basins of China. The presence of younger (<200 Ma) zircons from the Qamdo Block of Tibet are less easily explicable in terms of recycling by erosion of older sedimentary rocks and imply a regional drainage linking SE Tibet and the South China Sea in the Late Eocene-Oligocene. Detrital zircons from offshore in the South China Sea showed initial local erosion, but with a connection to a river stretching to SE Tibet in the Late Oligocene. A change from regional to local sources in the Early Miocene in the Yuanjiang Basin indicates the timing of disruption of the old drainage driven by regional plateau uplift
The QCD heavy-quark potential to order v^2: one loop matching conditions
The one-loop QCD heavy quark potential is computed to order v^2 in the color
singlet and octet channels. Several errors in the previous literature are
corrected. To be consistent with the velocity power counting, the full
dependence on |p' + p|/|p' - p| is kept. The matching conditions for the NRQCD
one-loop potential are computed by comparing the QCD calculation with that in
the effective theory. The graphs in the effective theory are also compared to
terms from the hard, soft, potential, and ultrasoft regimes in the threshold
expansion. The issue of off-shell versus on-shell matching and gauge dependence
is discussed in detail for the 1/(m k) term in the potential. Matching on-shell
gives a 1/(m k) potential that is gauge independent and does not vanish for
QED.Comment: 28 pages, References added and minor changes to section III, results
unchange
Re-orientation Transition in Molecular Thin Films: Potts Model with Dipolar Interaction
We study the low-temperature behavior and the phase transition of a thin film
by Monte Carlo simulation. The thin film has a simple cubic lattice structure
where each site is occupied by a Potts parameter which indicates the molecular
orientation of the site. We take only three molecular orientations in this
paper which correspond to the 3-state Potts model. The Hamiltonian of the
system includes: (i) the exchange interaction between nearest-neighbor
sites and (ii) the long-range dipolar interaction of amplitude
truncated at a cutoff distance (iii) a single-ion perpendicular
anisotropy of amplitude . We allow between surface spins, and
otherwise. We show that the ground state depends on the the ratio
and . For a single layer, for a given , there is a critical value
below (above) which the ground-state (GS) configuration of molecular axes
is perpendicular (parallel) to the film surface. When the temperature is
increased, a re-orientation transition occurs near : the low- in-plane
ordering undergoes a transition to the perpendicular ordering at a finite ,
below the transition to the paramagnetic phase. The same phenomenon is observed
in the case of a film with a thickness. We show that the surface phase
transition can occur below or above the bulk transition depending on the ratio
. Surface and bulk order parameters as well as other physical quantities
are shown and discussed.Comment: 7 pages, 11 figures, submitted for publicatio
Heavy-quarkonium creation and annihilation with O(alpha_s^3 ln(alpha_s)) accuracy
We calculate the O(alpha_s^3 ln(alpha_s)) contributions to the
heavy-quarkonium production and annihilation rates. Our result sheds new light
on the structure of the high-order perturbative corrections and opens a new
perspective for a high-precision theoretical analysis. We also determine the
three-loop anomalous dimensions of the nonrelativistic vector and pseudoscalar
currents.Comment: 10 pages (Latex). Eq. (6) corrected, conclusions unchange
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