12 research outputs found
On Nucleon Electromagnetic Form Factors: A Pre'cis
Electron scattering at large Q^2 probes a nucleon's quark core. This core's
contribution to electromagnetic form factors may be calculated using Poincare'
covariant Faddeev amplitudes combined with a nucleon-photon vertex that
automatically fulfills a Ward-Takahashi identity for on-shell nucleons. The
calculated behaviour of G_E^p(Q^2)/G_M^p(Q^2) on 2<Q^2(GeV^2)<6 agrees with
that inferred from polarisation transfer data, and exhibits a zero at
Q^2\approx 6.5 GeV^2. There is some evidence that F_2(Q^2)/F_1(Q^2) \propto
[\ln(Q^2/\Lambda^2)]^2/Q^2 for Q^2>6 GeV^2.Comment: Contribution to the proceedings of "Baryons 04," the 10th
International Conference on the Structure of Baryons, 25-29/Oct./04, Ecole
Polytechnique, Palaiseau; 5 pages, 3 figure
Schwinger functions and light-quark bound states, and sigma terms
We explore the viability of using solely spacelike information about a
Schwinger function to extract properties of bound states. In a concrete example
it is not possible to determine properties of states with masses \gsim 1.2 GeV.
Modern Dyson-Schwinger equation methods supply a well-constrained tool that
provide access to hadron masses and \sigma-terms. We report values of the
latter for a range of hadrons. Of interest is analysis relating to a u,d scalar
meson, which is compatible with a picture of the lightest 0^{++} as a bound
state of a dressed-quark and -antiquark supplemented by a material pion cloud.
A constituent-quark \sigma-term is defined, which affords a means for assessing
the flavour-dependence of dynamical chiral symmetry breaking.Comment: To appear in the proceedings of Workshop on Light-Cone QCD and
Nonperturbative Hadron Physics 2005 (LC 2005), Cairns, Queensland, Australia,
7-15 Jul 200
Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background
The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generically polarized gravitational waves. We find no evidence for a background of any polarization, and place the first direct bounds on the contributions of vector and scalar polarizations to the stochastic background. Under log-uniform priors for the energy in each polarization, we limit the energy densities of tensor, vector, and scalar modes at 95% credibility to Ω0T<5.58×10-8, Ω0V<6.35×10-8, and Ω0S<1.08×10-7 at a reference frequency f0=25 Hz. © 2018 American Physical Society
Polaron effective mass
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