9,416 research outputs found
A note on BRST quantization of SU(2) Yang-Mills mechanics
The quantization of SU(2) Yang-Mills theory reduced to 0+1 space-time
dimensions is performed in the BRST framework. We show that in the unitary
gauge the BRST procedure has difficulties which can be solved by
introduction of additional singlet ghost variables. In the Lorenz gauge
one has additional unphysical degrees of freedom, but the BRST
quantization is free of the problems in the unitary gauge.Comment: 17 page
Experimental studies of QCD using flavour tagged jets with DELPHI
Identified and events from DELPHI are
used to measure the ratio of the mean charged particle multiplicity
distribution between gluon and quark jets. The dependence of this ratio with
the jet energy is established using about three million Z decays. Results
from all other detectors are discussed and compared. A nice agreement is found
among all them. The ratio between the normalized total three-jet cross sections
of and events is also
determined. The preliminary value obtained indicates that quarks are
experimentaly seen to radiate less than light quarks due to their higher mass.
The suggested experimental error is 300 MeV for the mass
determination at the M scale.Comment: Latex, 5 pages, 3 figures,to appear in the Proceedings of the High
Energy Physics International Euroconference on Quantum Chromodynamics (QCD
'96), Montpellier, France, 4-12th July 1996. Ed. S. Narison, Nucl Phys. B
(Proc. Suppl.
Extracting the top-quark running mass using +1-jet events produced at the Large Hadron Collider
We present the calculation of the next-to-leading order QCD corrections for
top-quark pair production in association with an additional jet at hadron
colliders, using the modified minimal subtraction scheme to renormalize the
top-quark mass. The results are compared to measurements at the Large Hadron
Collider run I. In particular, we determine the top-quark running mass from a
fit of the theoretical results presented here to the LHC data
Electronic structure of few-electron concentric double quantum rings
The ground state structure of few-electron concentric double quantum rings is
investigated within the local spin density approximation. Signatures of
inter-ring coupling in the addition energy spectrum are identified and
discussed. We show that the electronic configurations in these structures can
be greatly modulated by the inter-ring distance: At short and long distances
the low-lying electron states localize in the inner and outer rings,
respectively, and the energy structure is essentially that of an isolated
single quantum ring. However, at intermediate distances the electron states
localized in the inner and the outer ring become quasi-degenerate and a rather
entangled, strongly-correlated system is formed.Comment: 16 pages (preprint format), 6 figure
Higher dimensional VSI spacetimes
We present the explicit metric forms for higher dimensional vanishing scalar
invariant (VSI) Lorentzian spacetimes. We note that all of the VSI spacetimes
belong to the higher dimensional Kundt class. We determine all of the VSI
spacetimes which admit a covariantly constant null vector, and we note that in
general in higher dimensions these spacetimes are of Ricci type III and Weyl
type III. The Ricci type N subclass is related to the chiral null models and
includes the relativistic gyratons and the higher dimensional pp-wave
spacetimes. The spacetimes under investigation are of particular interest since
they are solutions of supergravity or superstring theory.Comment: 14 pages, changes in second paragraph of the discussio
Experimental determination of the b quark mass in DELPHI
The running mass of the b quark as defined in the MS-bar renormalization
scheme, m_b, was measured at the M_Z scale using 2.8 million hadronic Z^0
decays collected by the DELPHI experiment at LEP. The result is m_b(M_Z) = 2.67
+- 0.25 (stat.) +- 0.34 (frag.) +- 0.27(theo.) GeV/c^2 which differs from that
obtained at the Upsilon scale, by m_b(M_\Upsilon/2)-m_b(M_Z) = 1.49 +- 0.52
GeV/c^2. This measurement, performed far from the production
threshold, provides the first experimental observation of the running of the
quark masses.Comment: Talk given at the QCD 97 conference held in Montpellier, July 1997.
Also available here http://hep.ph.liv.ac.uk/~martis
InAs/InP single quantum wire formation and emission at 1.5 microns
Isolated InAs/InP self-assembled quantum wires have been grown using in situ
accumulated stress measurements to adjust the optimal InAs thickness. Atomic
force microscopy imaging shows highly asymmetric nanostructures with average
length exceeding more than ten times their width. High resolution optical
investigation of as-grown samples reveals strong photoluminescence from
individual quantum wires at 1.5 microns. Additional sharp features are related
to monolayer fluctuations of the two dimensional InAs layer present during the
early stages of the quantum wire self-assembling process.Comment: 4 pages and 3 figures submitted to Applied Physics Letter
Charged particle production in the fragmentation of quark and gluon jets
Recent results on the total production and angular distribution of charged particles originated from the fragmentation of quark and gluon jets are presented. Experimental studies of the multiplicity as a function of the quark and gluon jet energy, the inter-jet particle flow and the individual fragmentation fucntions are reviewed and compared to expectations from QCD
Exciton Gas Compression and Metallic Condensation in a Single Semiconductor Quantum Wire
We study the metal-insulator transition in individual self-assembled quantum
wires and report optical evidences of metallic liquid condensation at low
temperatures. Firstly, we observe that the temperature and power dependence of
the single nanowire photoluminescence follow the evolution expected for an
electron-hole liquid in one dimension. Secondly, we find novel spectral
features that suggest that in this situation the expanding liquid condensate
compresses the exciton gas in real space. Finally, we estimate the critical
density and critical temperature of the phase transition diagram at
cm and K, respectively.Comment: 4 pages, 5 figure
Clonal hematopoiesis in cardiovascular disease and therapeutic implications.
Clonal hematopoiesis arises from somatic mutations that provide a fitness advantage to hematopoietic stem cells and the outgrowth of clones of blood cells. Clonal hematopoiesis commonly involves mutations in genes that are involved in epigenetic modifications, signaling and DNA damage repair. Clonal hematopoiesis has emerged as a major independent risk factor in atherosclerotic cardiovascular disease, thrombosis and heart failure. Studies in mouse models of clonal hematopoiesis have shown an increase in atherosclerosis, thrombosis and heart failure, involving increased myeloid cell inflammatory responses and inflammasome activation. Although increased inflammatory responses have emerged as a common underlying principle, some recent studies indicate mutation-specific effects. The discovery of the association of clonal hematopoiesis with cardiovascular disease and the recent demonstration of benefit of anti-inflammatory treatments in human cardiovascular disease converge to suggest that anti-inflammatory treatments should be directed to individuals with clonal hematopoiesis. Such treatments could target specific inflammasomes, common downstream mediators such as IL-1β and IL-6, or mutations linked to clonal hematopoiesis.A.T. and J.J.F. are supported by a grant from the Leducq Foundation (TNE-18CVD04). A.T. is supported by NIH
grant 155431. We thank M. A. Zuriaga for assistance with figure design.S
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