180 research outputs found
Spontaneous symmetry breaking of (1+1)-dimensional theory in light-front field theory (III)
We investigate (1+1)-dimensional field theory in the symmetric and
broken phases using discrete light-front quantization. We calculate the
perturbative solution of the zero-mode constraint equation for both the
symmetric and broken phases and show that standard renormalization of the
theory yields finite results. We study the perturbative zero-mode contribution
to two diagrams and show that the light-front formulation gives the same result
as the equal-time formulation. In the broken phase of the theory, we obtain the
nonperturbative solutions of the constraint equation and confirm our previous
speculation that the critical coupling is logarithmically divergent. We discuss
the renormalization of this divergence but are not able to find a satisfactory
nonperturbative technique. Finally we investigate properties that are
insensitive to this divergence, calculate the critical exponent of the theory,
and find agreement with mean field theory as expected.Comment: 21 pages; OHSTPY-HEP-TH-94-014 and DOE/ER/01545-6
Dynamical Chiral Symmetry Breaking on the Light Front.II. The Nambu--Jona-Lasinio Model
An investigation of dynamical chiral symmetry breaking on the light front is
made in the Nambu--Jona-Lasinio model with one flavor and N colors. Analysis of
the model suffers from extraordinary complexity due to the existence of a
"fermionic constraint," i.e., a constraint equation for the bad spinor
component. However, to solve this constraint is of special importance. In
classical theory, we can exactly solve it and then explicitly check the
property of ``light-front chiral transformation.'' In quantum theory, we
introduce a bilocal formulation to solve the fermionic constraint by the 1/N
expansion. Systematic 1/N expansion of the fermion bilocal operator is realized
by the boson expansion method. The leading (bilocal) fermionic constraint
becomes a gap equation for a chiral condensate and thus if we choose a
nontrivial solution of the gap equation, we are in the broken phase. As a
result of the nonzero chiral condensate, we find unusual chiral transformation
of fields and nonvanishing of the light-front chiral charge. A leading order
eigenvalue equation for a single bosonic state is equivalent to a leading order
fermion-antifermion bound-state equation. We analytically solve it for scalar
and pseudoscalar mesons and obtain their light-cone wavefunctions and masses.
All of the results are entirely consistent with those of our previous analysis
on the chiral Yukawa model.Comment: 23 pages, REVTEX, the version to be published in Phys.Rev.D; Some
clarifications in discussion of the LC wavefunctions adde
Optical Absorption Characteristics of Silicon Nanowires for Photovoltaic Applications
Solar cells have generated a lot of interest as a potential source of clean
renewable energy for the future. However a big bottleneck in wide scale
deployment of these energy sources remain the low efficiency of these
conversion devices. Recently the use of nanostructures and the strategy of
quantum confinement have been as a general approach towards better charge
carrier generation and capture. In this article we have presented calculations
on the optical characteristics of nanowires made out of Silicon. Our
calculations show these nanowires form excellent optoelectronic materials and
may yield efficient photovoltaic devices
Calcitonin concentrations in patients with chronic kidney disease and medullary thyroid carcinoma or c-cell hyperplasia
It is currently not known which level of pentagastrin-stimulated calcitonin serum concentration indicates medullary thyroid carcinoma in patients with chronic kidney disease (CKD). We examined CKD stage 3–5 patients who had total thyroidectomy because of a pentagastrin-stimulated calcitonin concentration greater than 100pg/ml, and tested the diagnostic performance of basal and pentagastrin-stimulated calcitonin levels for differentiating medullary thyroid carcinoma and C-cell hyperplasia in this patient population. A total of 180 CKD patients presented with an elevated calcitonin level and had a pentagastrin stimulation test. Forty patients showed a maximum pentagastrin-stimulated calcitonin concentration greater than 100pg/ml, and 22 patients had a total thyroidectomy. Seven of these 22 patients presented with a medullary thyroid carcinoma, all other patients showed C-cell hyperplasia. Patients with medullary thyroid carcinoma showed higher unstimulated (212pg/ml (36–577) vs 42pg/ml (17–150); P<0.001) and higher maximum pentagastrin-stimulated calcitonin concentrations (862pg/ml (431–2423) vs 141pg/ml (102–471); P<0.001) as compared to patients with C-cell hyperplasia. The sensitivity (100%) and specificity (93%) estimates suggested that a maximum pentagastrin-stimulated calcitonin concentration greater than 400pg/ml indicates the presence of medullary thyroid carcinoma in patients with CKD. Receiver-operating characteristic (ROC) analysis revealed an area under the ROC plot of 0.99 for maximum pentagastrin-stimulated calcitonin concentrations. A maximum pentagastrin-stimulated calcitonin concentration greater than 400pg/ml appears to be a clinically meaningful threshold for thyroidectomy
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