256 research outputs found
Two-Loop Four-Gluon Amplitudes in N=4 Super-Yang-Mills
Using cutting techniques we obtain the two-loop N=4 super-Yang-Mills helicity
amplitudes for four-gluon scattering in terms of scalar integral functions. The
N=4 amplitudes are considerably simpler than corresponding QCD amplitudes and
therefore provide a testing ground for exploring two-loop amplitudes. The
amplitudes are constructed directly in terms of gauge invariant quantities and
therefore remain relatively compact throughout the calculation. We also present
a conjecture for the leading color four-gluon amplitudes to all orders in the
perturbative expansion.Comment: Latex, 13 pages, 9 figures, minor changes to signs in eq.(14
Domain wall solutions with Abelian gauge fields
We study kink (domain wall) solutions in a model consisting of two complex
scalar fields coupled to two independent Abelian gauge fields in a Lagrangian
that has gauge plus discrete symmetry. We find
consistent solutions such that while the U(1) symmetries of the fields are
preserved while in their respective vacua, they are broken on the domain wall.
The gauge field solutions show that the domain wall is sandwiched between
domains with constant magnetic fields.Comment: 11 pages, 6 figures, JHEP for style, but to appear in PLB. Added
discussion about the boundary conditions and the physical picture based on
superconductivity. Reference adde
Baseline local hemodynamics as predictor of lumen remodeling at 1-year follow-up in stented superficial femoral arteries
In-stent restenosis (ISR) is the major drawback of superficial femoral artery (SFA) stenting. Abnormal hemodynamics after stent implantation seems to promote the development of ISR. Accordingly, this study aims to investigate the impact of local hemodynamics on lumen remodeling in human stented SFA lesions. Ten SFA models were reconstructed at 1-week and 1-year follow-up from computed tomography images. Patient-specific computational fluid dynamics simulations were performed to relate the local hemodynamics at 1-week, expressed in terms of time-averaged wall shear stress (TAWSS), oscillatory shear index and relative residence time, with the lumen remodeling at 1-year, quantified as the change of lumen area between 1-week and 1-year. The TAWSS was negatively associated with the lumen area change (ρ = − 0.75, p = 0.013). The surface area exposed to low TAWSS was positively correlated with the lumen area change (ρ = 0.69, p = 0.026). No significant correlations were present between the other hemodynamic descriptors and lumen area change. The low TAWSS was the best predictive marker of lumen remodeling (positive predictive value of 44.8%). Moreover, stent length and overlapping were predictor of ISR at follow-up. Despite the limited number of analyzed lesions, the overall findings suggest an association between abnormal patterns of WSS after stenting and lumen remodeling
Defining the Force between Separated Sources on a Light Front
The Newtonian character of gauge theories on a light front requires that the
longitudinal momentum P^+, which plays the role of Newtonian mass, be
conserved. This requirement conflicts with the standard definition of the force
between two sources in terms of the minimal energy of quantum gauge fields in
the presence of a quark and anti-quark pinned to points separated by a distance
R. We propose that, on a light front, the force be defined by minimizing the
energy of gauge fields in the presence of a quark and an anti-quark pinned to
lines (1-branes) oriented in the longitudinal direction singled out by the
light front and separated by a transverse distance R. Such sources will have a
limited 1+1 dimensional dynamics. We study this proposal for weak coupling
gauge theories by showing how it leads to the Coulomb force law. For QCD we
also show how asymptotic freedom emerges by evaluating the S-matrix through one
loop for the scattering of a particle in the N_c representation of color
SU(N_c) on a 1-brane by a particle in the \bar N_c representation of color on a
parallel 1-brane separated from the first by a distance R<<1/Lambda_{QCD}.
Potential applications to the problem of confinement on a light front are
discussed.Comment: LaTeX, 15 pages, 12 figures; minor typos corrected; numerical
correction in equation 3.
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