2,182 research outputs found
Narrow Resonances in Effective Field Theory
We discuss the power counting for effective field theories with narrow
resonances near a two-body threshold. Close to threshold, the effective field
theory is perturbative and only one combination of coupling constants is
fine-tuned. In the vicinity of the resonance, a second, ``kinematic''
fine-tuning requires a nonperturbative resummation. We illustrate our results
in the case of nucleon-alpha scattering.Comment: 11 pages, revtex4, 3 ps figure
The Puzzle and the Nuclear Force
The nucleon-deuteron analyzing power in elastic nucleon-deuteron
scattering poses a longstanding puzzle. At energies below
approximately 30 MeV cannot be described by any realistic NN force. The
inclusion of existing three-nucleon forces does not improve the situation.
Because of recent questions about the NN phases, we examine whether
reasonable changes in the NN force can resolve the puzzle. In order to do this
we investigate the effect on the waves produced by changes in different
parts of the potential (viz., the central force, tensor force, etc.), as well
as on the 2-body observables and on . We find that it is not possible with
reasonable changes in the NN potential to increase the 3-body and at the
same time to keep the 2-body observables unchanged. We therefore conclude that
the puzzle is likely to be solved by new three-nucleon forces, such as
those of spin-orbit type, which have not yet been taken into account.Comment: 35 pages in REVTeX, 1 figure in postscript and 3 figures in PiCTe
Diffraction of complex molecules by structures made of light
We demonstrate that structures made of light can be used to coherently
control the motion of complex molecules. In particular, we show diffraction of
the fullerenes C60 and C70 at a thin grating based on a standing light wave. We
prove experimentally that the principles of this effect, well known from atom
optics, can be successfully extended to massive and large molecules which are
internally in a thermodynamic mixed state and which do not exhibit narrow
optical resonances. Our results will be important for the observation of
quantum interference with even larger and more complex objects.Comment: 4 pages, 3 figure
Cross section and analyzing power of pol{p}p -> pn pi+ near threshold
The cross section and analyzing power of the pol{p}p -> pn pi+ reaction near
threshold are estimated in terms of data obtained from the pol{p}p -> d pi+ and
pp -> pp pi0 reactions. A simple final state interaction theory is developed
which depends weakly upon the form of the pion-production operator and includes
some Coulomb corrections. Within the uncertainties of the model and the input
data, the approach reproduces well the measured energy dependence of the total
cross section and the proton analyzing power at a fixed pion c.m. angle of
90deg, from threshold to T_p = 330 MeV. The variation of the differential cross
section with pion angle is also very encouraging.Comment: 20 pages, Latex including 4 eps figure
Striatal dopamine D2 receptor binding of risperidone in schizophrenic patients as assessed by 123I-iodobenzamide SPECT: a comparative study with olanzapine
The aim of this investigation was to compare the degree of striatal dopamine-(D2) receptor blockade by two atypical antipsychotic drugs, risperidone and olanzapine. The percentage of D2 receptor occupancy during treatment was calculated by comparing the results of 123I-iodobenzamide SPECT with those from healthy control subjects. Twenty inpatients suffering from schizophrenia or schizoaffective psychosis according to DSM IV/ICD-10 criteria were treated with clinically recommended doses of risperidone and compared with 13 inpatients treated with up to 20 mg olanzapine. Neuroleptic dose and D2 receptor blockade correlated strongly for both risperidone (Pearson r = –0.86, p = 0.0001) and olanzapine (Pearson r = –0.77, p = 0.002). There was no significant difference between the D2 receptor occupancy of the two substances when given in the clinically recommended dose range (unpaired t-test, t= –0.112, p=0.911)
The NN scattering 3S1-3D1 mixing angle at NNLO
The 3S1-3D1 mixing angle for nucleon-nucleon scattering, epsilon_1, is
calculated to next-to-next-to-leading order in an effective field theory with
perturbative pions. Without pions, the low energy theory fits the observed
epsilon_1 well for momenta less than MeV. Including pions
perturbatively significantly improves the agreement with data for momenta up to
MeV with one less parameter. Furthermore, for these momenta the
accuracy of our calculation is similar to an effective field theory calculation
in which the pion is treated non-perturbatively. This gives phenomenological
support for a perturbative treatment of pions in low energy two-nucleon
processes. We explain why it is necessary to perform spin and isospin traces in
d dimensions when regulating divergences with dimensional regularization in
higher partial wave amplitudes.Comment: 17 pages, journal versio
Charge-Dependence of the Nucleon-Nucleon Interaction
Based upon the Bonn meson-exchange-model for the nucleon-nucleon ()
interaction, we calculate the charge-independence breaking (CIB) of the
interaction due to pion-mass splitting. Besides the one-pion-exchange (OPE), we
take into account the -exchange model and contributions from three and
four irreducible pion exchanges. We calculate the CIB differences in the
effective range parameters as well as phase shift differences for
partial waves up to total angular momentum J=4 and laboratory energies below
300 MeV. We find that the CIB effect from OPE dominates in all partial waves.
However, the CIB effects from the model are noticable up to D-waves and
amount to about 40% of the OPE CIB-contribution in some partial waves, at 300
MeV. The effects from 3 and 4 contributions are negligible except in
and .Comment: 12 pages, RevTex, 14 figure
The cross section minima in elastic Nd scattering: a ``smoking gun'' for three nucleon force effects
Neutron-deuteron elastic scattering cross sections are calculated at
different energies using modern nucleon-nucleon interactions and the
Tucson-Melbourne three-nucleon force adjusted to the triton binding energy.
Predictions based on NN forces only underestimate nucleon-deuteron data in the
minima at higher energies starting around 60 MeV. Adding the three-nucleon
forces fills up those minima and reduces the discrepancies significantly.Comment: 11 pages, 6 figure
Effective Field Theory for Halo Nuclei: Shallow p-Wave States
Halo nuclei are a promising new arena for studies based on effective field
theory (EFT). We develop an EFT for shallow p-wave states and discuss the
application to elastic n-alpha scattering. In contrast to the s-wave case, both
the scattering length and effective range enter at leading order. We also
discuss the prospects of using EFT in the description of other halos, such as
the three-body halo nucleus 6He.Comment: 22 pages, revtex4, 8 ps figures, title changed, references adde
Phase Separation and Coarsening in One-Dimensional Driven Diffusive Systems: Local Dynaimcs Leading to Long-Range Hamiltonians
A driven system of three species of particle diffusing on a ring is studied
in detail. The dynamics is local and conserves the three densities. A simple
argument suggesting that the model should phase separate and break the
translational symmetry is given. We show that for the special case where the
three densities are equal the model obeys detailed balance and the steady-state
distribution is governed by a Hamiltonian with asymmetric long-range
interactions. This provides an explicit demonstration of a simple mechanism for
breaking of ergodicity in one dimension. The steady state of finite-size
systems is studied using a generalized matrix product ansatz. The coarsening
process leading to phase separation is studied numerically and in a mean-field
model. The system exhibits slow dynamics due to trapping in metastable states
whose number is exponentially large in the system size. The typical domain size
is shown to grow logarithmically in time. Generalizations to a larger number of
species are discussed.Comment: Revtex, 29 Pages, 7 figures, uses epsf.sty, submitted to Phys. Rev.
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