29,510 research outputs found
Charge-dependence of the coupling constant and charge-dependence of the NN interaction
The recent determination of the charged coupling constant,
, by the Uppsala Neutron Research Group implies that there may be
considerable charge-splitting of the pion coupling constant. We investigate the
consequences of this for the charge-independence breaking (CIB) of the
scattering length, . We find that depends
sensitively on the difference between and the neutral
coupling constant, . Moreover, if is only about 3%
larger than , then the established theoretical explanation of
(in terms of pion mass splitting) is completely wiped out.Comment: 9 pages, fbs styles, 1 figure; dedicated to Walter Gl\"ockle on the
occasion of his 60th birthda
Nuclear Matter Studies with Density-dependent Meson-Nucleon Coupling Constants
Due to the internal structure of the nucleon, we should expect, in general,
that the effective meson nucleon parameters may change in nuclear medium. We
study such changes by using a chiral confining model of the nucleon. We use
density-dependent masses for all mesons except the pion. Within a
Dirac-Brueckner analysis, based on the relativistic covariant structure of the
NN amplitude, we show that the effect of such a density dependence in the NN
interaction on the saturation properties of nuclear matter, while not large, is
quite significant. Due to the density dependence of the , as
predicted by the chiral confining model, we find, in particular, a looping
behavior of the binding energy at saturation as a function of the saturation
density. A simple model is described, which exhibits looping and which is shown
to be mainly caused by the presence of a peak in the density dependence of the
medium modified coupling constant at low density.
The effect of density dependence of the coupling constants and the meson
masses tends to improve the results for and density of nuclear matter at
saturation. From the present study we see that the relationship between binding
energy and saturation density may not be as universal as found in
nonrelativistic studies and that more model dependence is exhibited once medium
modifications of the basic nuclear interactions are considered.Comment: Acknowledgements have been modified. 34 pages, revtex, uuencoded
gz-compressed tar fil
Near infra-red spectroscopy of V838 Monocerotis
Near IR, multi-epoch, spectroscopic and photometric observations of the
enigmatic, eruptive variable V838 Mon in JHK bands are reported. One of the
unusual features is the detection of several strong neutral TiI lines in
emission in the K band. From the strength of these lines, the mass of the
ejected envelope is estimated to be in the range 10e-7 to 10e-5 M(sun). The
spectra also show the strong presence of the first and second overtones of 12CO
bands seen in the K and H bands. The CO bands show a complex evolution. Deep
water bands at 1.4 and 1.9 micron are also seen later in the object's
evolution. Blackbody fits to the JHK photometric data show that V838 Mon has
evolved to temperatures between 2400 - 2600 K by approximately 130 days after
outburst. The spectra at this stage have the general characteristics of a very
cool M giant.Comment: 7 pages, 5 figures, to appear in Astronomy and Astrophysic
Entanglement generation in spatially separated systems using quantum walk
We present a novel scheme to generate entanglement between two spatially
separated systems. The scheme makes use of spatial entanglement generated by a
single-particle quantum walk which is used to entangle two spatially separated,
not necessarily correlated, systems. This scheme can be used to entangle any
two systems which can interact with the spatial modes entangled during the
quantum walk evolution. A notable feature is that we can control the quantum
walk dynamics and its ability to localize leads to a substantial control and
improvement in the entanglement output.Comment: 9 pages, 5 figure
Volatility and growth: credit constraints and productivity-enhancing investment
We examine how credit constraints affect the cyclical behavior of productivity-enhancing investment and thereby volatility and growth. We first develop a simple growth model where firms engage in two types of investment: a short-term one and a long-term productivity-enhancing one. Because it takes longer to complete, long-term investment has a relatively less procyclical return but also a higher liquidity risk. Under complete financial markets, long-term investment is countercyclical, thus mitigating volatility. But when firms face tight credit constraints, long-term investment turns procyclical, thus amplifying volatility. Tighter credit therefore leads to both higher aggregate volatility and lower mean growth for a given total investment rate. We next confront the model with a panel of countries over the period 1960-2000 and find that a lower degree of financial development predicts a higher sensitivity of both the composition of investment and mean growth to exogenous shocks, as well as a stronger negative effect of volatility on growth
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