6,785 research outputs found
Local Electronic Structure around a Single Impurity in an Anderson Lattice Model for Topological Kondo Insulators
Shortly after the discovery of topological band insulators, the topological
Kondo insulators (TKIs) have also been theoretically predicted. The latter has
ignited revival interest in the properties of Kondo insulators. Currently, the
feasibility of topological nature in SmB has been intensively analyzed by
several complementary probes. Here by starting with a minimal-orbital Anderson
lattice model, we explore the local electronic structure in a Kondo insulator.
We show that the two strong topological regimes sandwiching the weak
topological regime give rise to a single Dirac cone, which is located near the
center or corner of the surface Brillouin zone. We further find that, when a
single impurity is placed on the surface, low-energy resonance states are
induced in the weak scattering limit for the strong TKI regimes and the
resonance level moves monotonically across the hybridization gap with the
strength of impurity scattering potential; while low energy states can only be
induced in the unitary scattering limit for the weak TKI regime, where the
resonance level moves universally toward the center of the hybridization gap.
These impurity induced low-energy quasiparticles will lead to characteristic
signatures in scanning tunneling microscopy/spectroscopy, which has recently
found success in probing into exotic properties in heavy fermion systems.Comment: 8 pages with 4 eps figures embedded, references update
Cherenkov Radiation from Jets in Heavy-ion Collisions
The possibility of Cherenkov-like gluon bremsstrahlung in dense matter is
studied. We point out that the occurrence of Cherenkov radiation in dense
matter is sensitive to the presence of partonic bound states. This is
illustrated by a calculation of the dispersion relation of a massless particle
in a simple model in which it couples to two different massive resonance
states. We further argue that detailed spectroscopy of jet correlations can
directly probe the index of refraction of this matter, which in turn will
provide information about the mass scale of these partonic bound states.Comment: 4 pages, 5 figures, revte
Modified Fragmentation Function from Quark Recombination
Within the framework of the constituent quark model, it is shown that the
single hadron fragmentation function of a parton can be expressed as a
convolution of shower diquark or triquark distribution function and quark
recombination probability, if the interference between amplitudes of quark
recombination with different momenta is neglected. The recombination
probability is determined by the hadron's wavefunction in the constituent quark
model. The shower diquark or triquark distribution functions of a fragmenting
jet are defined in terms of overlapping matrices of constituent quarks and
parton field operators. They are similar in form to dihadron or trihadron
fragmentation functions in terms of parton operator and hadron states.
Extending the formalism to the field theory at finite temperature, we
automatically derive contributions to the effective single hadron fragmentation
function from the recombination of shower and thermal constituent quarks. Such
contributions involve single or diquark distribution functions which in turn
can be related to diquark or triquark distribution functions via sum rules. We
also derive QCD evolution equations for quark distribution functions that in
turn determine the evolution of the effective jet fragmentation functions in a
thermal medium.Comment: 23 pages in RevTex with 8 postscript figure
Quantum partonic transport in QCD matter
We study gradient corrections to the transport equation for energetic light
partons in dense QCD environments. In the diffusion limit, the transport
dynamics is solely controlled by small-angle elastic scatterings, leading to
transverse momentum broadening with respect to the parton's initial direction.
Such a parton propagation is usually considered in the limit of transversely
homogeneous matter. The transport processes admit a classical description and
the transverse spatial dependence of the medium properties emerges only through
the jet quenching parameter. In this work, we show that a gradient expansion of
the all-order evolution equation for the partonic Wigner function leads to an
evolution equation in the Boltzmann-diffusion form only up to the leading order
in transverse gradients. At the second order in gradients, the quantum
corrections associated with non-local interactions give rise to a novel
transport that can be implemented in Monte Carlo simulations. In addition,
using our results, we compute the gradient corrections to the jet quenching
parameter in inhomogeneous matter.Comment: 6 page
Fluctuations of rare particles as a measure of chemical equilibration
We calculate the time evolution of fluctuations for rare particles such as e.g. kaons in 1 AGeV or charmonium in 200 AGeV heavy ion collisions. We find that these fluctuations are a very sensitive probe of the degree of chemical equilibration reached in these collisions. Furthermore, measuring the second factorial moment the size of the initial population can be determined
High Pt hadron-hadron correlations
We propose the formulation of a dihadron fragmentation function in terms of
parton matrix elements. Under the collinear factorization approximation and
facilitated by the cut-vertex technique, the two hadron inclusive cross section
at leading order (LO) in e+ e- annihilation is shown to factorize into a short
distance parton cross section and the long distance dihadron fragmentation
function. We also derive the DGLAP evolution equation of this function at
leading log. The evolution equation for the non-singlet and singlet quark
fragmentation function and the gluon fragmentation function are solved
numerically with the initial condition taken from event generators.
Modifications to the dihadron fragmentation function from higher twist
corrections in DIS off nuclei are computed. Results are presented for cases of
physical interest.Comment: 7 pages, 8 figures, Latex, Proceedings of Hot Quarks 2004, July
18-24, Taos, New Mexic
Early Growth and Development Impairments in Patients with Ganglioside GM3 Synthase Deficiency
Ganglioside GM3 synthase is a key enzyme involved in the biosynthesis of gangliosides. GM3 synthase deficiency (GSD) causes a complete absence of GM3 and all downstream biosynthetic derivatives. The individuals affected by this disorder manifest severe irritability, intractable seizures and profound intellectual disability. However, we have found that most newborns seem symptom-free for a period of time after birth. In order to further understand the onset of the disease, we investigated the early growth and development of patients with this condition through this study. We compared 37 affected individuals with their normal siblings and revealed that all children with GSD had relatively normal intrauterine growth and development, as their weight, length and head circumference were similar to their normal siblings at birth. However, the disease progresses quickly after birth and causes significant constitutional impairments of growth and development by 6 months of age. Neither breastfeeding nor gastrostomy tube placement made significant difference on growth and development as all groups of patients showed the similar pattern. We conclude that GSD causes significant postnatal growth and developmental impairments and the amount of gangliosides in breast milk and general nutritional intervention do not seem to alter these outcomes
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