44,197 research outputs found
Counting Form Factors of Twist-Two Operators
We present a simple method to count the number of hadronic form factors based
on the partial wave formalism and crossing symmetry. In particular, we show
that the number of independent nucleon form factors of spin-n, twist-2
operators (the vector current and energy-momentum tensor being special
examples) is n+1. These generalized form factors define the generalized
(off-forward) parton distributions that have been studied extensively in the
recent literature. In proving this result, we also show how the J^{PC} rules
for onium states arise in the helicity formalism.Comment: 7 pages, LaTeX (revtex
Effect of nickel on the microstructure and mechanical property of die-cast Al–Mg–Si–Mn alloy
The effect of nickel on the microstructure and mechanical properties of a die-cast Al–Mg–Si–Mn alloy has been investigated. The results show that the presence of Ni in the alloy promotes the formation of Ni-rich intermetallics. These occur consistently during solidification in the die-cast Al–Mg–Si–Mn alloy across different levels of Ni content. The Ni-rich intermetallics exhibit dendritic morphology during the primary solidification and lamellar morphology during the eutectic solidification stage. Ni was found to be always associated with iron forming AlFeMnSiNi intermetallics, and no Al3Ni intermetallic was observed when Ni concentrations were up to 2.06 wt% in the alloy. Although with different morphologies, the Ni-rich intermetallics were identified as the same AlFeMnSiNi phase bearing a typical composition of Al[100–140](Fe,Mn)[2–7]SiNi[4–9]. With increasing Ni content, the spacing of the α-Al–Mg2Si eutectic phase was enlarged in the Al–Mg–Si–Mn alloy. The addition of Ni to the alloy resulted in a slight increase in the yield strength, but a significant decrease in the elongation. The ultimate tensile strength (UTS) increased slightly from 300 to 320 MPa when a small amount (e.g. 0.16 wt%) of Ni was added to the alloy, but further increase of the Ni content resulted in a decrease of the UTS.The Engineering and Physical Sciences Research Council (EPSRC), Technology Strategy Board (TSB) and Jaguar Land Rover (JLR) in the United Kingdom
Nucleon-Quarkonium Elastic Scattering and the Gluon Contribution to Nucleon Spin
It is shown that the amplitude for the scattering of a heavy quarkonium
system from a nucleon near threshold is completely determined by the fraction
of angular momentum, as well as linear momentum, carried by gluons in the
nucleon. A form for the quarkonium-nucleon non-relativistic potential is
derived.Comment: 4 pages, no figures. Author's e-mail: [email protected]
Virtual meson cloud of the nucleon and generalized parton distributions
We present the general formalism required to derive generalized parton
distributions within a convolution model where the bare nucleon is dressed by
its virtual meson cloud. In the one-meson approximation the Fock states of the
physical nucleon are expanded in a series involving a bare nucleon and
two-particle, meson-baryon, states. The baryon is assumed here to be either a
nucleon or a described within the constituent quark model in terms of
three valence quarks; correspondingly, the meson, assumed to be a pion, is
described as a quark-antiquark pair. Explicit expressions for the unpolarized
generalized parton distributions are obtained and evaluated in different
kinematics.Comment: 37 pages, 9 figures, minor corrections, and figure 3 replaced;
version to appear in Phys. Rev.
Spin dynamics and magnetic interactions of Mn dopants in the topological insulator BiTe
The magnetic and electronic properties of the magnetically doped topological
insulator BiMnTe were studied using electron spin
resonance (ESR) and measurements of static magnetization and electrical
transport. The investigated high quality single crystals of BiMnTe show a ferromagnetic phase transition for
at K. The Hall measurements reveal a p-type finite
charge-carrier density. Measurements of the temperature dependence of the ESR
signal of Mn dopants for different orientations of the external magnetic field
give evidence that the localized Mn moments interact with the mobile charge
carriers leading to a Ruderman-Kittel-Kasuya-Yosida-type ferromagnetic coupling
between the Mn spins of order 2-3 meV. Furthermore, ESR reveals a
low-dimensional character of magnetic correlations that persist far above the
ferromagnetic ordering temperature
Generalized parton distributions in a meson cloud model
We present a model calculation of the generalized parton distributions where
the nucleon is described by a quark core surrounded by a mesonic cloud. In the
one-meson approximation, we expand the Fock state of the physical nucleon in a
series involving a bare nucleon and two-particle, meson-baryon, states. We
discuss the role of the different Fock-state components of the nucleon by
deriving a convolution formalism for the unpolarized generalized parton
distributions, and showing predictions at different kinematics.Comment: 7 pages, 3 figures; Invited talk at the Fifth International
Conference on Perspectives in Hadronic Physics, Miramare - Trieste (Italy),
22-26 May 200
Trace anomalies and chiral Ward identities
In a simple abelian spinor field theory, the canonical trace identities for
certain axial-vector and axial-scalar operators are reexamined in dimensional
regularization, some disagreements with previous results are found and an
interesting new phenomenon is observed and briefly discussed.Comment: 4 pages, no figure, typos remove
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