143 research outputs found
Hard pion bremsstrahlung in the Coulomb region
Hard high-energy pion-nucleus bremsstrahlung, ,
is studied in the Coulomb region, i.e. the small-angle region where the nuclear
scattering is dominated by the Coulomb interaction. Special attention is
focussed on the possibility of measuring the pion polarizability in such
reactions. We study the sensitivity to the structure of the underlying the
pion-Compton amplitude through a model with , , and a_1
exchanges. It is found that the effective energy in the virtual pion-Compton
scattering is often so large that the threshold approximation does not apply.Comment: 18 pages, 5 figure
N=4 central charge superspace at work for supergravity coupled to an arbitrary number of abelian vector multiplets
We present the description in central charge superspace of N=4 supergravity
with antisymmetric tensor coupled to an arbitrary number of abelian vector
multiplets. All the gauge vectors of the coupled system are treated on the same
footing as gauge fields corresponding to translations along additional bosonic
coordinates. It is the geometry of the antisymmetric tensor which singles out
which combinations of these vectors belong to the supergravity multiplet and
which are the additional coupled ones. Moreover, basic properties of
Chapline-Manton coupling mechanism, as well as the SO(6,n)/SO(6)*SO(n) sigma
model of the Yang-Mills scalars are found as arising from superspace geometry.Comment: 18 page
Production of Polarized Vector Mesons off Nuclei
Using the light-cone QCD dipole formalism we investigate manifestations of
color transparency (CT) and coherence length (CL) effects in electroproduction
of longitudinally (L) and transversally (T) polarized vector mesons. Motivated
by forthcoming data from the HERMES experiment we predict both the A and Q^2
dependence of the L/T- ratios, for rho^0 mesons produced coherently and
incoherently off nuclei. For an incoherent reaction the CT and CL effects add
up and result in a monotonic A dependence of the L/T-ratio at different values
of Q^2. On the contrary, for a coherent process the contraction of the CL with
Q^2 causes an effect opposite to that of CT and we expect quite a nontrivial A
dependence, especially at Q^2 >> m_V^2.Comment: Revtex 24 pages and 14 figure
Chiral Anomaly and
Measurement of the process has revealed a possible conflict
with what should be a solid prediction generated by the chiral anomaly. We show
that inclusion of appropirate energy-momentum dependence in the matrix element
reduces the discrepancy.Comment: 8 page standard Latex fil
Magnetooptical Study of Zeeman Effect in Mn modulation-doped InAs/InGaAs/InAlAs Quantum Well Structures
We report on a magneto-photoluminescence (PL) study of Mn modulation-doped
InAs/InGaAs/InAlAs quantum wells. Two PL lines corresponding to the radiative
recombination of photoelectrons with free and bound-on-Mn holes have been
observed. In the presence of a magnetic field applied in the Faraday geometry
both lines split into two circularly polarized components. While temperature
and magnetic field dependences of the splitting are well described by the
Brillouin function, providing an evidence for exchange interaction with spin
polarized manganese ions, the value of the splitting exceeds the expected value
of the giant Zeeman splitting by two orders of magnitude for a given Mn
density. Possible reasons of this striking observation are discussed
Radiative Tau Decays with One Pseudoscalar Meson
We have calculated the decay . We present
the photon energy spectrum, the meson-photon invariant mass spectrum and the
integrated rate as a function of a photon energy cut or an invariant mass cut.
Both the internal bremsstrahlung and the structure dependent radiation have
been taken into account. To this aim we have parametrized the form factors
and , which determine the structure dependent radiation. Observables
especially suited for the measurement of the structure dependent form factors
are found and implications on the width of the discussed.Comment: p.20, TTP93-1, LaTe
Cyclic peroxides and related initiating systems for radical polymerization of methyl methacrylate
Cyclic peroxides as initiators for the radical polymerization of methyl methacrylate were proposed. The initial rates, initiation rates, and effective activation energies of polymerization initiated by cyclic peroxides and cyclic peroxide-1-pyridyl-2-ferrocene systems were determined. The radical yields to the volume upon the thermal decomposition of cyclic peroxides and their catalytic decomposition in the presence of 1-pyridyl-2-ferrocene were determined. In combination with 1-pyridyl-2-ferrocene cyclic peroxides form efficient initiating systems favoring an increase in the polymerization rate, a decrease in the molecular weights, and an increase in syndiotacticity of the synthesized poly(methyl methacrylate). © 2013 Springer Science+Business Media New York
Weak Decays in the light--front Quark Model
We study the form factors of heavy--to--heavy and heavy--to--light weak
decays using the light--front relativistic quark model. For the
heavy--to--heavy B \ra D^{(\ast)} semileptonic decays we calculate the
corresponding Isgur--Wise function for the whole kinematic region. For the
heavy--to--light B\ra P and B\ra V semileptonic decays we calculate the
form factors at ; in particular, we have derived the dependence of the
form factors on the --quark mass in the m_b \ra \infty limit. This
dependence can not be produced by extrapolating the scaling behavior of the
form factors at using the single--pole assumption. This shows that
the dependence of the form factors in regions far away from the
zero--recoil could be much more complicated than that predicted by the
single--pole assumption.Comment: 24 pages, Latex, Postscript figure included at the en
Exchange current contributions in null-plane quantum models of elastic electron deuteron scattering
We investigate exchange current contributions to elastic electron-deuteron
scattering using exactly Poincar\'e invariant quantum mechanics with a
null-plane kinematic symmetry. Our model exchange current is motivated by
one-pion-exchange physics. Exact current conservation and current covariance
are satisfied by using this current to compute a linearly independent set of
current matrix elements. The remaining current matrix elements are generated
from the independent matrix elements using the covariance and current
conservation constraints. The presence of the exchange current increases the
sensitivity to the choice of independent current matrix elements. Two choices
of independent matrix elements that have distinct motivations lead to a good
description of all of the elastic scattering observables for momentum transfers
below 8 (GeV).Comment: 49 Pages, 24 figure
- …