137,078 research outputs found
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
Towards a Connection Between Nuclear Structure and QCD
As we search for an ever deeper understanding of the structure of hadronic
matter one of the most fundamental questions is whether or not one can make a
connection to the underlying theory of the strong interaction, QCD. We build on
recent advances in the chiral extrapolation problem linking lattice QCD at
relatively large ``light quark'' masses to the physical world to estimate the
scalar polarizability of the nucleon. The latter plays a key role in modern
relativistic mean-field descriptions of nuclei and nuclear matter (such as QMC)
and, in particular, leads to a very natural saturation mechanism. We
demonstrate that the value of the scalar polarizability extracted from the
lattice data is consistent with that needed for a successful description of
nuclei within the framework of QMC. In a very real sense this is the first hint
of a direct connection between QCD and the properties of finite nuclei.Comment: Lecture presented at: 18th Nishinomiya-Yukawa Memorial Symposium On
Strangeness In Nuclear Matter : 4-5 Dec 2003, Nishinomiya, Japa
And the winner is: galaxy mass
The environment is known to affect the formation and evolution of galaxies
considerably best visible through the well-known morphology-density
relationship. We study the effect of environment on the evolution of early-type
galaxies for a sample of 3,360 galaxies morphologically selected by visual
inspection from the SDSS in the redshift range 0.05<z<0.06, and analyse
luminosity-weighted age, metallicity, and alpha/Fe ratio as function of
environment and galaxy mass. We find that on average 10 per cent of early-type
galaxies are rejuvenated through minor recent star formation. This fraction
increases with both decreasing galaxy mass and decreasing environmental
density. However, the bulk of the population obeys a well-defined scaling of
age, metallicity, and alpha/Fe ratio with galaxy mass that is independent of
environment. Our results contribute to the growing evidence in the recent
literature that galaxy mass is the major driver of galaxy formation. Even the
morphology-density relationship may actually be mass-driven, as the consequence
of an environment dependent characteristic galaxy mass coupled with the fact
that late-type galaxy morphologies are more prevalent in low-mass galaxies.Comment: 5 pages, proceedings of JENAM 2010, Symposium 2: "Environment and the
formation of galaxies: 30 years later
Wide-angle perfect absorber/thermal emitter in the THz regime
We show that a perfect absorber/thermal emitter exhibiting an absorption peak
of 99.9% can be achieved in metallic nanostructures that can be easily
fabricated. The very high absorption is maintained for large angles with a
minimal shift in the center frequency and can be tuned throughout the visible
and near-infrared regime by scaling the nanostructure dimensions. The stability
of the spectral features at high temperatures is tested by simulations using a
range of material parameters.Comment: Submitted to Phys. Rev. Let
A simple toy model for effective restoration of chiral symmetry in excited hadrons
A simple solvable toy model exhibiting effective restoration of chiral
symmetry in excited hadrons is constructed. A salient feature is that while
physics of the low-lying states is crucially determined by the spontaneous
breaking of chiral symmetry, in the high-lying states the effects of chiral
symmetry breaking represent only a small correction. Asymptotically the states
approach the regime where their properties are determined by the underlying
unbroken chiral symmetry.Comment: This is the published version of this paper. Note that the title has
changed from earlier versions as has the abstract. The emphasis is slightly
different from previous versions but the essential physical content is the
sam
A Classification and Analysis of Higgs-flavor Models
A classification is given of Higgs-flavor models. In these models, there are
several Higgs doublets in an irreducible multiplet R_{Phi} of a non-abelian
symmetry G_{Phi}, under which the quarks and leptons do not transform (thus
giving minimal flavor-changing for the fermions). It is found that different
G_{Phi} and R_{Phi} lead to very distinctive spectra of the extra Higgs
doublets, including different numbers of "sequential Higgs" and of "inert
Higgs" that could play the role of dark matter, different mass relations, and
different patterns of SU(2)_L-breaking splittings within the Higgs doublets.Comment: 35 page
Energy-level pinning and the 0.7 spin state in one dimension: GaAs quantum wires studied using finite-bias spectroscopy
We study the effects of electron-electron interactions on the energy levels
of GaAs quantum wires (QWs) using finite-bias spectroscopy. We probe the energy
spectrum at zero magnetic field, and at crossings of opposite-spin-levels in
high in-plane magnetic field B. Our results constitute direct evidence that
spin-up (higher energy) levels pin to the chemical potential as they populate.
We also show that spin-up and spin-down levels abruptly rearrange at the
crossing in a manner resembling the magnetic phase transitions predicted to
occur at crossings of Landau levels. This rearranging and pinning of subbands
provides a phenomenological explanation for the 0.7 structure, a
one-dimensional (1D) nanomagnetic state, and its high-B variants.Comment: 6 pages, 4 figure
Baryon resonances and hadronic interactions in a finite volume
In a finite volume, resonances and multi-hadron states are identified by
discrete energy levels. When comparing the results of lattice QCD calculations
to scattering experiments, it is important to have a way of associating the
energy spectrum of the finite-volume lattice with the asymptotic behaviour of
the S-matrix. A new technique for comparing energy eigenvalues with scattering
phase shifts is introduced, which involves the construction of an exactly
solvable matrix Hamiltonian model. The model framework is applied to the case
of decay, but is easily generalized to include
multi-channel scattering. Extracting resonance parameters involves matching the
energy spectrum of the model to that of a lattice QCD calculation. The
resulting fit parameters are then used to generate phase shifts. Using a sample
set of pseudodata, it is found that the extraction of the resonance position is
stable with respect to volume for a variety of regularization schemes, and
compares favorably with the well-known Luescher method. The model-dependence of
the result is briefly investigated.Comment: 7 pages, 3 figures. Talk presented at the 30th International
Symposium on Lattice Field Theory (Lattice 2012), June 24-29, 2012, Cairns,
Australi
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