10,456 research outputs found
Generalized contour deformation method in momentum space: two-body spectral structures and scattering amplitudes
A generalized contour deformation method (GCDM) which combines complex
rotation and translation in momentum space, is discussed. GCDM gives accurate
results for bound, virtual (antibound), resonant and scattering states starting
with a realistic nucleon-nucleon interaction. It provides a basis for full
off-shell -matrix calculations both for real and complex input energies.
Results for both spectral structures and scattering amplitudes compare
perfectly well with exact values for the separable Yamaguchi potential.
Accurate calculation of virtual states in the Malfliet-Tjon and the realistic
CD-Bonn nucleon-nucleon interactions are presented.
GCDM is also a promising method for the computation of in-medium properties
such as the resummation of particle-particle and particle-hole diagrams in
infinite nuclear matter. Implications for in-medium scattering are discussed.Comment: 15 pages, revte
Investigations of the lower and middle atmosphere at the Arecibo Observatory and a description of the new VHF radar project
The atmospheric science research at the Arecibo Observatory is performed by means of (active) radar methods and (passive) optical methods. The active methods utilize the 430 NHz radar, the S-band radar on 2380 MHz, and a recently constructed Very High Frequency (VHF) radar. The passive methods include measurements of the mesopause temperature by observing the rotational emissions from OH-bands. The VHF radar design is discussed
Does inflation targeting matter?
This paper studies the inflation and interest rate performances since the late 1970s for six former highinflation countries that adopted inflation targeting (IT) in the early 1990’s. Using Germany, Switzerland and the US for comparison, we look at various aspects of central bank performance in a pre-IT period (1978-92) and a post-IT period (1993-01). The results of all types of evidence considered uniformly lead to the general conclusion that IT has proven a useful strategy for reducing the level and volatility of inflation. However, IT central banks did not outperform the central banks used as reference cases during the second period. We then present an event study of monetary policy comparing inflation and interest rate developments after the 1978 and the 1998 oil price shocks. Here we find that IT central banks realized significantly larger gains in credibility than the central banks in the reference group. . This result corroborates the conclusion that IT is a useful framework for communicating a monetary policy strategy aiming at low inflation rates. --
Method to determine the optimal parameters of the Arecibo 46.8-MHz antenna system
The spherical reflector at the Arecibo Observatory (AO) offers great advantages for the design of simple and inexpensive high performance steerable antennas at VHF. Light and small feeds have the added benefit that they can be quickly installed in the Arecibo platform. It is important to evaluate the performance of any given feed including the effects of the spherical reflector. The optimization is emphasized of two parameters, namely, the distance below the focal point of the reflector and the beam width of a point feed. For the design of the feed at 46.8 MHz at the AO there were other requirements independent of MST (mesosphere stratosphere troposphere) work. The design of the primary array is discussed along with its performance with the AO spherical reflector
Galilean Lee Model of the Delta Function Potential
The scattering cross section associated with a two dimensional delta function
has recently been the object of considerable study. It is shown here that this
problem can be put into a field theoretical framework by the construction of an
appropriate Galilean covariant theory. The Lee model with a standard Yukawa
interaction is shown to provide such a realization. The usual results for delta
function scattering are then obtained in the case that a stable particle exists
in the scattering channel provided that a certain limit is taken in the
relevant parameter space. In the more general case in which no such limit is
taken finite corrections to the cross section are obtained which (unlike the
pure delta function case) depend on the coupling constant of the model.Comment: 7 pages, latex, no figure
Perturbative Expansion in the Galilean Invariant Spin One-Half Chern-Simons Field Theory
A Galilean Chern-Simons field theory is formulated for the case of two
interacting spin-1/2 fields of distinct masses M and M'. A method for the
construction of states containing N particles of mass M and N' particles of
mass M' is given which is subsequently used to display equivalence to the
spin-1/2 Aharonov-Bohm effect in the N = N' =1 sector of the model. The latter
is then studied in perturbation theory to determine whether there are
divergences in the fourth order (one loop) diagram. It is found that the
contribution of that order is finite (and vanishing) for the case of parallel
spin projections while the antiparallel case displays divergences which are
known to characterize the spin zero case in field theory as well as in quantum
mechanics.Comment: 14 pages LaTeX, including 2 figures using eps
Complex coupled-cluster approach to an ab-initio description of open quantum systems
We develop ab-initio coupled-cluster theory to describe resonant and weakly
bound states along the neutron drip line. We compute the ground states of the
helium chain 3-10He within coupled-cluster theory in singles and doubles (CCSD)
approximation. We employ a spherical Gamow-Hartree-Fock basis generated from
the low-momentum N3LO nucleon-nucleon interaction. This basis treats bound,
resonant, and continuum states on equal footing, and is therefore optimal for
the description of properties of drip line nuclei where continuum features play
an essential role. Within this formalism, we present an ab-initio calculation
of energies and decay widths of unstable nuclei starting from realistic
interactions.Comment: 4 pages, revtex
Medium-mass nuclei from chiral nucleon-nucleon interactions
We compute the binding energies, radii, and densities for selected
medium-mass nuclei within coupled-cluster theory and employ the "bare" chiral
nucleon-nucleon interaction at order N3LO. We find rather well-converged
results in model spaces consisting of 15 oscillator shells, and the doubly
magic nuclei 40Ca, 48Ca, and the exotic 48Ni are underbound by about 1 MeV per
nucleon within the CCSD approximation. The binding-energy difference between
the mirror nuclei 48Ca and 48Ni is close to theoretical mass table evaluations.
Our computation of the one-body density matrices and the corresponding natural
orbitals and occupation numbers provides a first step to a microscopic
foundation of the nuclear shell model.Comment: 5 pages, 5 figure
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