21,536 research outputs found
Quarkonia in Hamiltonian Light-Front QCD
A constituent parton picture of hadrons with logarithmic confinement
naturally arises in weak coupling light-front QCD. Confinement provides a mass
gap that allows the constituent picture to emerge. The effective renormalized
Hamiltonian is computed to , and used to study charmonium and
bottomonium. Radial and angular excitations can be used to fix the coupling
, the quark mass , and the cutoff . The resultant hyperfine
structure is very close to experiment.Comment: 9 pages, 1 latex figure included in the text. Published version (much
more reader-friendly); corrected error in self-energ
Operator Evolution via the Similarity Renormalization Group I: The Deuteron
Similarity Renormalization Group (SRG) flow equations can be used to
unitarily soften nuclear Hamiltonians by decoupling high-energy intermediate
state contributions to low-energy observables while maintaining the natural
hierarchy of many-body forces. Analogous flow equations can be used to
consistently evolve operators so that observables are unchanged if no
approximations are made. The question in practice is whether the advantages of
a softer Hamiltonian and less correlated wave functions might be offset by
complications in approximating and applying other operators. Here we examine
the properties of SRG-evolved operators, focusing in this paper on applications
to the deuteron but leading toward methods for few-body systems. We find the
advantageous features generally carry over to other operators with additional
simplifications in some cases from factorization of the unitary transformation
operator.Comment: 33 pages, 19 figures. Improved figures 17 and 18. Expanded comments
on OPE in tex
Operator Evolution via the Similarity Renormalization Group I: The Deuteron
Similarity Renormalization Group (SRG) flow equations can be used to
unitarily soften nuclear Hamiltonians by decoupling high-energy intermediate
state contributions to low-energy observables while maintaining the natural
hierarchy of many-body forces. Analogous flow equations can be used to
consistently evolve operators so that observables are unchanged if no
approximations are made. The question in practice is whether the advantages of
a softer Hamiltonian and less correlated wave functions might be offset by
complications in approximating and applying other operators. Here we examine
the properties of SRG-evolved operators, focusing in this paper on applications
to the deuteron but leading toward methods for few-body systems. We find the
advantageous features generally carry over to other operators with additional
simplifications in some cases from factorization of the unitary transformation
operator.Comment: 33 pages, 19 figures. Improved figures 17 and 18. Expanded comments
on OPE in tex
Are low-energy nuclear observables sensitive to high-energy phase shifts?
Conventional nucleon-nucleon potentials with strong short-range repulsion
require contributions from high-momentum wave function components even for
low-energy observables such as the deuteron binding energy. This can lead to
the misconception that reproducing high-energy phase shifts is important for
such observables. Interactions derived via the similarity renormalization group
decouple high-energy and low-energy physics while preserving the phase shifts
from the starting potential. They are used to show that high-momentum
components (and high-energy phase shifts) can be set to zero when using
low-momentum interactions, without losing information relevant for low-energy
observables.Comment: 13 pages, 5 figures; reference and acknowledgment adde
Orbital Properties of Sr3Ru2O7 and Related Ruthenates Probed by 17O-NMR
We report a site-separated O-NMR study of the layered perovskite
ruthenate SrRuO, which exhibits nearly two-dimensional transport
properties and itinerant metamagnetism at low temperatures. The local hole
occupancies and the spin densities in the oxygen orbitals are obtained by
means of tight-binding analyses of electric field gradients and anisotropic
Knight shifts. These quantities are compared with two other layered perovskite
ruthenates: the two-dimensional paramagnet SrRuO and the
three-dimensional ferromagnet SrRuO. The hole occupancies at the oxygen
sites are very large, about one hole per ruthenium atom. This is due to the
strong covalent character of the Ru-O bonding in this compound. The magnitude
of the hole occupancy might be related to the rotation or tilt of the RuO
octahedra. The spin densities at the oxygen sites are also large, 20-40% of the
bulk susceptibilities, but in contrast to the hole occupancies, the spin
densities strongly depend on the dimensionality. This result suggests that the
density-of-states at the oxygen sites plays an essential role for the
understanding of the complex magnetism found in the layered perovskite
ruthenates.Comment: 9 pages, 5 figures, to be published in Phys. Rev.
Note on restoring manifest rotational symmetry in hyperfine and fine structure in light-front QED
We study the part of the renormalized, cutoff QED light-front Hamiltonian
that does not change particle number. The Hamiltonian contains interactions
that must be treated in second-order bound state perturbation theory to obtain
hyperfine structure. We show that a simple unitary transformation leads
directly to the familiar Breit-Fermi spin-spin and tensor interactions, which
can be treated in degenerate first-order bound-state perturbation theory, thus
simplifying analytic light-front QED calculations. To the order in momenta we
need to consider, this transformation is equivalent to a Melosh rotation. We
also study how the similarity transformation affects spin-orbit interactions.Comment: 17 pages, latex fil
Implementing the Lean Sigma Framework in an Indian SME: a case study
Lean and Six Sigma are two widely acknowledged business process improvement strategies available to organisations today for achieving dramatic results in cost, quality and time by focusing on process performance. Lately, Lean and Six Sigma practitioners are integrating the two strategies into a more powerful and effective hybrid, addressing many of the weaknesses and retaining most of the strengths of each strategy. Lean Sigma combines the variability reduction tools and techniques from Six Sigma with the waste and non-value added elimination tools and techniques from Lean Manufacturing, to generate savings to the bottom-line of an organisation. This paper proposes a Lean Sigma framework to reduce the defect occurring in the final product (automobile accessories) manufactured by a die-casting process. The proposed framework integrates Lean tools (current state map, 5S System, and Total Productive Maintenance (TPM)) within Six Sigma DMAIC methodology to enhance the bottom-line results and win customer loyalty. Implementation of the proposed framework shows dramatic improvement in the key metrics (defect per unit (DPU), process capability index, mean and standard deviation of casting density, yield, and overall equipment effectiveness (OEE)) and a substantial financial savings is generated by the organisation
Perturbative Tamm-Dancoff Renormalization
A new two-step renormalization procedure is proposed. In the first step, the
effects of high-energy states are considered in the conventional (Feynman)
perturbation theory. In the second step, the coupling to many-body states is
eliminated by a similarity transformation. The resultant effective Hamiltonian
contains only interactions which do not change particle number. It is subject
to numerical diagonalization. We apply the general procedure to a simple
example for the purpose of illustration.Comment: 20 pages, RevTeX, 10 figure
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