2,081 research outputs found
Meson PVV Interactions are determined by Quark Loops
We show that all abnormal parity three-body meson interactions can be
adequately described by quark loops, evaluated at zero external momentum, with
couplings determined by symmetry. We focus primarily on radiative
meson decays which involve one pseudoscalar. The agreement with experiment for
non-rare decays is surprisingly good and requires very few parameters, namely
the coupling constants and and some mixing angles.
This agreement extends to some three-body decays that are dominated by pion
pairs in a P-wave state.Comment: 21 pages, Revtex, one figur
Momentum and Coordinate Space Three-nucleon Potentials
In this paper we give explicit formulae in momentum and coordinate space for
the three-nucleon potentials due to and meson exchange, derived
from off-mass-shell meson-nucleon scattering amplitudes which are constrained
by the symmetries of QCD and by the experimental data. Those potentials have
already been applied to nuclear matter calculations. Here we display additional
terms which appear to be the most important for nuclear structure. The
potentials are decomposed in a way that separates the contributions of
different physical mechanisms involved in the meson-nucleon amplitudes. The
same type of decomposition is presented for the TM force: the
, the chiral symmetry breaking and the nucleon pair terms are isolated.Comment: LATEX, 33 pages, 3 figures (available as postscript files upon
request
q-Boson approach to multiparticle correlations
An approach is proposed enabling to effectively describe, for relativistic
heavy-ion collisions, the observed deviation from unity of the intercept
\lambda (measured value corresponding to zero relative momentum {\bf p} of two
registered identical pions or kaons) of the two-particle correlation function
C(p,K). The approach uses q-deformed oscillators and the related picture of
ideal gas of q-bosons. In effect, the intercept \lambda is connected with
deformation parameter q. For a fixed value of q, the model predicts specific
dependence of \lambda on pair mean momentum {\bf K} so that, when |{\bf
K}|\gsim 500 - 600 MeV/c for pions or when |{\bf K}|\gsim 700 - 800 MeV/c for
kaons, the intercept \lambda tends to a constant which is less than unity and
determined by q. If q is fixed to be the same for pions and kaons, the
intercepts \lambda_\pi and \lambda_K essentially differ at small mean momenta
{\bf K}, but tend to be equal at {\bf K} large enough (|{\bf K}|\gsim 800MeV/c)
where the effect of resonance decays can be neglected. We argue that it is of
basic interest to check in the experiments on heavy ion collisions: (i) the
exact shape of dependence \lambda = \lambda({\bf K}), and (ii) whether for
|{\bf K}| \gsim 800 MeV/c the resulting \lambda_\pi and \lambda_K indeed
coincide.Comment: 6 pages, revtex, 4 figures, to be published in Mod. Phys. Lett.
Benchmark calculations for polarization observables in 3N scattering
High precision benchmark calculations for phase-shifts and mixing parameters
as well as observables in elastic neutron-deuteron scattering below the
deuteron breakup threshold are presented using a realistic nucleon-nucleon
potential. Two totally different methods, one using a variational principle in
configuration space and the other solving the Faddeev equations in momentum
space are used and compared to each other. The agreement achieved in
phase-shifts and mixing parameters as well as in the polarization observables
is excellent. The extreme sensitivity of the vector analyzing power Ay to small
changes of the phase shifts and mixing parameters is pointed out.Comment: 22 pages, 5 postscript figure
SWIRP (Submm-Wave and Long Wave InfraRed Polarimeter); Development and Characterization of a Sub-Mm Polarimeter for Ice Cloud Investigations
A major source of uncertainty in climate models is the presence, shape and distribution of ice particles in the uppermost layers of the clouds. The effects of this component are poorly constrained, turning ice particles into an almost-free variable in many climate models.NASA-GSFC is developing a new instrument aimed at measuring the size and shape of ice particles. The instrument consists of two sub-mm polarimeters (at 220 and 670 GHz) coupled with a long-wave infrared polarimeter at 10 micron. Each polarimeter has identical V-pol and H-pol channels; the axes of polarization are defined geometrically by the orientation of the waveguide elements, and the purity has been measured in the lab. The instrument is configured as a conical scanner, suitable for deployment as a payload on a small satellite or on a high-altitude sub-orbital platform. From a 400 km orbit, the instrument has a 3dB spatial resolution of 20 (10) km at 220 (670) GHz and a swath of 600 km over 180 degrees of view.The BAPTA (Bearing And Power Transfer Assembly) carries heritage from the SSMIS design, now in its 22nd year of on-orbit operation, but with a much reduced SWaP (Size Weight and Power) footprint, suitable for a small satellite.The main components of the instrument have been fabricated and are undergoing final testing prior to their integration as a single unit. The sub-mm channels have dedicated secondary reflectors which illuminate a shared primary reflector. The receiving units are placed behind the focal point of the optical arrangement, so that all beams equally illuminate the primary reflector and are almost co-located on the ground (within a single 220 GHz footprint). Primary and secondary beam patterns have been measured and verified to match the as-designed expectations. A Zytex (TM) window is deployed to protect the secondary reflectors and the feed horns from debris and other contaminants, and to reduce the heat load from the active (hot) IR calibration unit. The insertion loss of Zytex has been measured and is accounted in the calibration equation of the sub-mm channels.The radiometric performance of the sub-mm receivers has been characterized in the lab and under operational conditions of temperature and pressure.This paper discusses the design constraints on the sub-mm components, details of the scientific goals and their flowdown, and describes the characterization of the polarimeters. Options to optimize the layout and distribution of the masses within the assembly, with the goal of making the instrument even more compact and fully-compatible with cubesat-class satellites will be presented
Impact of boundaries on fully connected random geometric networks
Many complex networks exhibit a percolation transition involving a
macroscopic connected component, with universal features largely independent of
the microscopic model and the macroscopic domain geometry. In contrast, we show
that the transition to full connectivity is strongly influenced by details of
the boundary, but observe an alternative form of universality. Our approach
correctly distinguishes connectivity properties of networks in domains with
equal bulk contributions. It also facilitates system design to promote or avoid
full connectivity for diverse geometries in arbitrary dimension.Comment: 6 pages, 3 figure
Local three-nucleon interaction from chiral effective field theory
The three-nucleon (NNN) interaction derived within the chiral effective field
theory at the next-to-next-to-leading order (N2LO) is regulated with a function
depending on the magnitude of the momentum transfer. The regulated NNN
interaction is then local in the coordinate space, which is advantages for some
many-body techniques. Matrix elements of the local chiral NNN interaction are
evaluated in a three-nucleon basis. Using the ab initio no-core shell model
(NCSM) the NNN matrix elements are employed in 3H and 4He bound-state
calculations.Comment: 17 pages, 9 figure
Does The 3N-Force Have A Hard Core?
The meson-nucleon dynamics that generates the hard core of the RuhrPot
two-nucleon interaction is shown to vanish in the irreducible 3N force. This
result indicates a small 3N force dominated by conventional light
meson-exchange dynamics and holds for an arbitrary meson-theoretic Lagrangian.
The resulting RuhrPot 3N force is defined in the appendix. A completely
different result is expected when the Tamm-Dancoff/Bloch-Horowitz procedure is
used to define the NN and 3N potentials. In that approach, (e.g. full Bonn
potential) both the NN {\it and} 3N potentials contain non-vanishing
contributions from the coherent sum of meson-recoil dynamics and the
possibility of a large hard core requiring explicit calculation cannot be ruled
out.Comment: 16 pages REVTeX + 3 ps fig
Purification and properties of a shortened form of cytochrome P-450 2E1: deletion of the NH2-terminal membrane-insertion signal peptide does not alter the catalytic activities.
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