2,138 research outputs found
Quantum corrections to the effective neutrino mass operator in 5D MSSM
We discuss in detail a five-dimensional Minimal Supersymmetric Standard Model
compactified on extended by the effective Majorana neutrino mass
operator. We study the evolution of neutrino masses and mixings. Masses and
angles, in particular the atmospheric mixing angle , can be
significantly lowered at high energies with respect to their value at low
energy.Comment: 23 pages, 13 figure
Hadronic unquenching effects in the quark propagator
We investigate hadronic unquenching effects in light quarks and mesons.
Within the non-perturbative continuum framework of Schwinger-Dyson and
Bethe-Salpeter equations we quantify the strength of the back reaction of the
pion onto the quark-gluon interaction. To this end we add a Yang-Mills part of
the interaction such that unquenched lattice results for various current quark
masses are reproduced. We find considerable effects in the quark mass function
at low momenta as well as for the chiral condensate. The quark wave function is
less affected. The Gell--Mann-Oakes-Renner relation is valid to good accuracy
up to pion masses of 400-500 MeV. As a byproduct of our investigation we verify
the Coleman theorem, that chiral symmetry cannot be broken spontaneously when
QCD is reduced to 1+1 dimensions.Comment: 27 pages, 15 figures, minor corrections and clarifications; version
to appear in PR
Two regularizations - two different models of Nambu-Jona-Lasinio
Two variants of the Nambu--Jona-Lasinio model -- the model with 4-dimensional
cutoff and the model with dimensionally-analytical regularization -- are
systematically compared. It is shown that they are, in essence, two different
models of light-quark interaction. In the mean-field approximation the
distinction becomes apparent in a behavior of scalar amplitude near the
threshold. For 4-dimensional cutoff the pole term can be extracted, which
corresponds to sigma-meson. For dimensionally-analytical regularization the
singularity of the scalar amplitude is not pole, and this singularity is quite
disappeared at some value of the regularization parameter.
Still more essential distinction of these models exists in the
next-to-leading order of mean-field expansion. The calculations of meson
contributions in the quark chiral condensate and in the dynamical quark mass
demonstrate, that these contributions though their relatively smallness can
destabilize the Nambu--Jona-Lasinio model with 4-dimensional cutoff. On the
contrary, the Nambu--Jona-Lasinio model with dimensionally-analytical
regularization is stabilized with the next-to-leading order, i.e. the value of
the regularization parameter shifts to the stability region, where these
contributions decrease.Comment: 14 pages; Journal version; parameter fixing procedure is modifie
Particle dynamics of a cartoon dune
The spatio-temporal evolution of a downsized model for a desert dune is
observed experimentally in a narrow water flow channel. A particle tracking
method reveals that the migration speed of the model dune is one order of
magnitude smaller than that of individual grains. In particular, the erosion
rate consists of comparable contributions from creeping (low energy) and
saltating (high energy) particles. The saltation flow rate is slightly larger,
whereas the number of saltating particles is one order of magnitude lower than
that of the creeping ones. The velocity field of the saltating particles is
comparable to the velocity field of the driving fluid. It can be observed that
the spatial profile of the shear stress reaches its maximum value upstream of
the crest, while its minimum lies at the downstream foot of the dune. The
particle tracking method reveals that the deposition of entrained particles
occurs primarily in the region between these two extrema of the shear stress.
Moreover, it is demonstrated that the initial triangular heap evolves to a
steady state with constant mass, shape, velocity, and packing fraction after
one turnover time has elapsed. Within that time the mean distance between
particles initially in contact reaches a value of approximately one quarter of
the dune basis length
Chiral restoration effects on the shear viscosity of a pion gas
We investigate the shear viscosity of a pion gas in relativistic kinetic
theory, using the Nambu-Jona-Lasinio model to construct the pion mass and the
pi-pi interaction at finite temperature. Whereas at low temperatures the
scattering properties and, hence, the viscosity are in agreement with
lowest-order chiral perturbation theory, we find strong medium modifications in
the crossover region. Here the system is strongly coupled and the scattering
lengths diverge, similarly as for ultra-cold Fermi gases at a Feshbach
resonance. As a consequence, the ratio eta/s is found to be strongly reduced as
compared to calculations without medium-modified masses and scattering
amplitudes. However, the quantitative results are very sensitive to the details
of the applied approximations.Comment: 15 pages, 12 figures; v2: extended discussions of the dressed sigma
propagator and the low-temperature limit, typos corrected, accepted versio
Spin-orbit fields in asymmetric (001)-oriented GaAs/AlxGa 1-xAs quantum wells
We measure simultaneously the in-plane electron g factor and spin-relaxation rate in a series of undoped inversion-asymmetric (001)-oriented GaAs/AlGaAs quantum wells by spin-quantum beat spectroscopy. In combination the two quantities reveal the absolute values of both the Rashba and the Dresselhaus coefficients and prove that the Rashba coefficient can be negligibly small despite huge conduction-band potential gradients which break the inversion symmetry. The negligible Rashba coefficient is a consequence of the "isomorphism" of conduction- and valence-band potentials in quantum systems where the asymmetry is solely produced by alloy variations. © 2011 American Physical Society
Successful long-term monotherapy with rituximab in a patient with chronic lymphocytic leukemia of the B-cell-lineage: a case report
<p>Abstract</p> <p>Introduction</p> <p>Treatment of chronic lymphocytic leukemia of the B-cell-lineage is strongly based upon clinical staging because of the heterogeneous clinical course of this disease.</p> <p>Case presentation</p> <p>We describe a 62-year-old patient with newly diagnosed chronic lymphocytic leukemia of the B-cell-lineage who did not respond to several chemotherapy regimens including chlorambucil, fludarabine and cyclophosphamide, developing a marked neutropenia and thrombocytopenia with life-threatening infections. Further chemotherapy appeared not feasible because of bone marrow toxicity. The patient was treated with 600 mg/m<sup>2 </sup>rituximab weekly followed by eight courses of biweekly therapy and then by long-term maintenance therapy, achieving almost complete remission of the symptoms and disease control.</p> <p>Conclusion</p> <p>After resistance to standard chemotherapy with chlorambucil and fludarabine, a patient with chronic lymphocytic leukemia of the B-cell-lineage was successfully treated with rituximab.</p
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