85,235 research outputs found
Chiral extrapolations for nucleon magnetic moments
Lattice QCD simulations have made significant progress in the calculation of
nucleon electromagnetic form factors in the chiral regime in recent years. With
simulation results achieving pion masses of order ~180 MeV, there is an
apparent challenge as to how the physical regime is approached. By using
contemporary methods in chiral effective field theory, both the quark-mass and
finite-volume dependence of the isovector nucleon magnetic moment are carefully
examined. The extrapolation to the physical point yields a result that is
compatible with experiment, albeit with a combined statistical and systematic
uncertainty of 10%. The extrapolation shows a strong finite-volume dependence;
lattice sizes of L > 5 fm must be used to simulate results within 2% of the
infinite-volume result for the magnetic moment at the physical pion mass.Comment: 7 pages, 12 figures, 1 tabl
Power Counting Regime of Chiral Effective Field Theory and Beyond
Chiral effective field theory complements numerical simulations of quantum
chromodynamics (QCD) on a space-time lattice. It provides a model-independent
formalism for connecting lattice simulation results at finite volume and a
variety of quark masses to the physical world. The asymptotic nature of the
chiral expansion places the focus on the first few terms of the expansion.
Thus, knowledge of the power-counting regime (PCR) of chiral effective field
theory, where higher-order terms of the expansion may be regarded as
negligible, is as important as knowledge of the expansion itself. Through the
consideration of a variety of renormalization schemes and associated
parameters, techniques to identify the PCR where results are independent of the
renormalization scheme are established. The nucleon mass is considered as a
benchmark for illustrating this general approach. Because the PCR is small, the
numerical simulation results are also examined to search for the possible
presence of an intrinsic scale which may be used in a nonperturbative manner to
describe lattice simulation results outside of the PCR. Positive results that
improve on the current optimistic application of chiral perturbation theory
beyond the PCR are reported.Comment: 18 pages, 55 figure
Are you a researcher as well as a medical illustrator?
When we list the areas of practice for medical illustrators we always include research, but how involved in research are we? The aim of this activity is to encourage your professional development not just as a medical illustrator but your involvement with research whether that is undertaking your own research, undertaking evidence based practice (1) , working as part of a research team, advising researchers on the value of medical illustration or supporting a student undertaking a research project for their degree or post-graduate qualification
Leading Quenching Effects in the Proton Magnetic Moment
We present the first investigation of the extrapolation of quenched nucleon
magnetic moments in quenched chiral effective field theory. We utilize
established techniques in finite-range regularisation and compare with standard
dimensional regularisation methods. Finite-volume corrections to the relevant
loop integrals are also addressed. Finally, the contributions of dynamical sea
quarks to the proton moment are estimated using a recently discovered
phenomenological link between quenched and physical QCD.Comment: 9 pages, 11 figs; v2: revised finite volume discussio
Chiral effective field theory beyond the power-counting regime
Novel techniques are presented, which identify the chiral power-counting
regime (PCR), and realize the existence of an intrinsic energy scale embedded
in lattice QCD results that extend outside the PCR. The nucleon mass is
considered as a benchmark for illustrating this new approach. Using
finite-range regularization, an optimal regularization scale can be extracted
from lattice simulation results by analyzing the renormalization of the low
energy coefficients. The optimal scale allows a description of lattice
simulation results that extend beyond the PCR by quantifying and thus handling
any scheme-dependence. Preliminary results for the nucleon magnetic moment are
also examined, and a consistent optimal regularization scale is obtained. This
indicates the existence of an intrinsic scale corresponding to the finite size
of the source of the pion cloud.Comment: 6 pages, 4 figures, conferenc
Empirical studies of upper atmospheric species
The first month of spin-scan ozone imaging (SOI) data (October 1981) was processed and compared with total ozone mapping spectrometer and ground based data. Short term variations in the ozone field have been revealed using animated sequences of SOI data. High correlations were observed between SOI ozone and upper tropospheric meteorological data. The relationship between ozone and temperature in the stratosphere was investigated by examining Nimbus 4 backscattered ultraviolet ozone and selective chopper radiometer temperature measurements as well as solar Nimbus 7 solar backscattered ultraviolet ozone and stratospheric and mesospheric sounder temperature measurements. Results from these ozone temperature studies were compared with calculations from theoretical 2-D models. All of the lims infrared monitor of the stratosphere data was processed at 10 pressure levels and correlations between various species have been performed. The Venus Atmospheric Drag model was modified taking into account recent investigations on the Venus thermosphere and the resulting model was considered for incorporation into the Venus International Reference Atmosphere
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