4,789 research outputs found
Implications of R-parity violating supersymmetry for atomic and hadronic EDMs
We calculate the electric dipole moments (EDM) of the neutral Hg(199) atom,
deuteron, nucleons and neutral hyperons Lambda, Sigma(0) and Xi(0) in the
framework of a generic SUSY model without R-parity conservation (RPV SUSY) on
the basis of the SU(3) version of chiral perturbation theory (ChPT). We
consider CP-violation in the hadronic sector induced by the chromoelectric
quark dipole moments and CP-violating 4-quark effective interactions. From the
null experimental results on the neutron and Hg(199) atom EDMs we derive limits
on the imaginary parts of certain products Im(lambda' lambda'*) of the
trilinear RPV-couplings and demonstrate that they are more stringent than those
existing in the literature. Using these limits we give predictions for the EDMs
of neutral hyperons.
We also estimate the prospects of future storage ring experiments on the
deuteron EDM and show that the expected improvement of the above limits in
these experiments may reach several orders of magnitude.Comment: 11 pages, 1 figure, accepted for publication in Phys. Rev.
Axial form factor of the nucleon in the perturbative chiral quark model
We apply the perturbative chiral quark model (PCQM) at one loop to analyze
the axial form factor of the nucleon. This chiral quark model is based on an
effective Lagrangian, where baryons are described by relativistic valence
quarks and a perturbative cloud of Goldstone bosons as dictated by chiral
symmetry. We apply the formalism to obtain analytical expressions for the axial
form factor of the nucleon, which is given in terms of fundamental parameters
of low-energy pion-nucleon physics (weak pion decay constant, strong
pion-nucleon form factor) and of only one model parameter (radius of the
nucleonic three-quark core).Comment: 23 pages, 5 figures, accepted for publication in J. Phys.
D* K molecular structure of the Ds1(2460) meson
We discuss a possible interpretation of the Ds1(2460) meson as a hadronic
molecule - a bound state of D* and K mesons. Using a phenomenological
Lagrangian approach we determine the strong Ds1 to Ds* pi0 and radiative Ds1 to
Ds gamma decays. In order of magnitude our results for the partial strong and
radiative decay widths are consistent with previous calculations.Comment: 11 pages, 3 figure
Colloids dragged through a polymer solution: experiment, theory and simulation
We present micro-rheological measurments of the drag force on colloids pulled
through a solution of lambda-DNA (used here as a monodisperse model polymer)
with an optical tweezer. The experiments show a violation of the
Stokes-Einstein relation based on the independently measured viscosity of the
DNA solution: the drag force is larger than expected. We attribute this to the
accumulation of DNA infront of the colloid and the reduced DNA density behind
the colloid. This hypothesis is corroborated by a simple drift-diffusion model
for the DNA molecules, which reproduces the experimental data surprisingly
well, as well as by corresponding Brownian dynamics simulations.Comment: 9 pages, 13 figures, 3 table
Strong decays of radially excited mesons in a chiral approach
We study radial excitations of pseudoscalar and vector (q bar q) mesons
within a chiral approach. We derive a general form for a chiral Lagrangian
describing processes involving excited pseudoscalar and vector mesons. The
parameters of the chiral Lagrangian are fitted using data and previous
calculations in the framework of the 3P0 model. Finite-width effects are
examined and predictions for mesons previously not discussed are given.
Available experimental data is analyzed whenever possible. Possible hints for
exotic mesons and open interpretation-issues are discussed.Comment: 16 page
Relativistic structure of one-meson and one-gluon exchange forces and the lower excitation spectrum of the Nucleon and the Delta
The lower excitation spectrum of the nucleon and is calculated in a
relativistic chiral quark model. Corrections to the baryon mass spectrum from
the second order self-energy and exchange diagrams induced by pion and gluon
fields are estimated in the field -theoretical framework. Convergent results
for the self-energy terms are obtained when including the intermediate quark
and antiquark states with a total momentum up to . Relativistic
one-meson and color-magnetic one-gluon exchange forces are shown to generate
spin 0, 1, 2, etc. operators, which couple the lower and the upper components
of the two interacting valence quarks and yield reasonable matrix elements for
the lower excitation spectrum of the Nucleon and Delta. The only contribution
to the ground state nucleon and comes from the spin 1 operators, which
correspond to the exchanged pion or gluon in the l=1 orbit, thus indicating,
that the both pion exchange and color-magnetic gluon exchange forces can
contribute to the spin of baryons. Is is shown also that the contribution of
the color-electric component of the gluon fields to the baryon spectrum is
enormously large (more than 500 MeV with a value ) and one needs
to restrict to very small values of the strong coupling constant or to exclude
completely the gluon-loop corrections to the baryon spectrum. With this
restriction, the calculated spectrum reproduces the main properties of the
data, however needs further contribution from the two-pion exchange and
instanton induced exchange (for the nucleon sector) forces in consistence with
the realistic NN-interaction models.Comment: 15 pages, 4 figures, 7 table
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