21,225 research outputs found
Dynamically generated baryon resonances
Identifying a zero-range exchange of vector mesons as the driving force for
the s-wave scattering of pseudo-scalar mesons off the baryon ground states, a
rich spectrum of molecules is formed. We argue that chiral symmetry and
large- considerations determine that part of the interaction which
generates the spectrum. We suggest the existence of strongly bound
crypto-exotic baryons, which contain a charm-anti-charm pair. Such states are
narrow since they can decay only via OZI-violating processes. A narrow nucleon
resonance is found at mass 3.52 GeV. It is a coupled-channel bound state of the
system, which decays dominantly into the
channel. Furthermore two isospin singlet hyperon states at mass
3.23 GeV and 3.58 GeV are observed as a consequence of coupled-channel
interactions of the and states. Most striking is the small width of about 1
MeV of the lower state. The upper state may be significantly broader due to a
strong coupling to the state. The spectrum of crypto-exotic
charm-zero states is completed with an isospin triplet state at 3.93 GeV and an
isospin doublet state at 3.80 GeV. The dominant decay modes involve again the
meson.Comment: Talk presented at N*2005, 10 pages, 1 figur
A stratospheric aerosol model with perturbations induced by the space shuttle particulate effluents
A one dimensional steady state stratospheric aerosol model is developed that considers the subsequent perturbations caused by including the expected space shuttle particulate effluents. Two approaches to the basic modeling effort were made: in one, enough simplifying assumptions were introduced so that a more or less exact solution to the descriptive equations could be obtained; in the other approach very few simplifications were made and a computer technique was used to solve the equations. The most complex form of the model contains the effects of sedimentation, diffusion, particle growth and coagulation. Results of the perturbation calculations show that there will probably be an immeasurably small increase in the stratospheric aerosol concentration for particles larger than about 0.15 micrometer radius
The first WIMPy halos
Dark matter direct and indirect detection signals depend crucially on the
dark matter distribution. While the formation of large scale structure is
independent of the nature of the cold dark matter (CDM), the fate of
inhomogeneities on sub-galactic scales, and hence the present day CDM
distribution on these scales, depends on the micro-physics of the CDM
particles. We study the density contrast of Weakly Interacting Massive
Particles (WIMPs) on sub-galactic scales. We calculate the damping of the
primordial power spectrum due to collisional damping and free-streaming of
WIMPy CDM and show that free-streaming leads to a CDM power spectrum with a
sharp cut-off at about . We also calculate the transfer
function for the growth of the inhomogeneities in the linear regime, taking
into account the suppression in the growth of the CDM density contrast after
matter-radiation equality due to baryons and show that our analytic results are
in good agreement with numerical calculations. Combining the transfer function
with the damping of the primordial fluctuations we produce a WMAP normalized
primordial CDM power spectrum, which can serve as an input for high resolution
CDM simulations. We find that the smallest inhomogeneities typically have
co-moving radius of about 1 pc and enter the non-linear regime at a redshift of
. We study the effect of scale dependence of the primordial power
spectrum on these numbers and also use the spherical collapse model to make
simple estimates of the properties of the first generation of WIMP halos to
form. We find that the very first WIMPy halos may have a significant impact on
indirect dark matter searches.Comment: 33 pages, 9 figures. Version to appear in JCAP, includes
clarification of the differences with respect to Loeb and Zaldarriaga
astro-ph/0504112 calculation (bottom line is that the mass cut-off scales
differ by a factor of order a few
Stratosphere aerosol and cloud measurements at McMurdo Station Antarctica during the spring of 1987
Measurements of stratospheric aerosols with balloonborne optical particle counters on 6 occasions at McMurdo Station (78 deg S) in the spring of 1986 indicated subsidence of the stratospheric sulfate layer during the time that the ozone hole was forming (Hofmann et al., 1988). Since dynamic models of ozone depletion involving upwelling in the spring polar vortex would suggest the opposite, we repeated the measurements with an increased frequency (about one sounding per week) in 1987. During 3 of the aerosol soundings in 1986, temperatures in the 15 to 20 km range were low enough (less than 80 C) for HNO3 to co-condense with water according to several theories of polar stratospheric cloud formation. However, particles were not observed with the characteristic size suggested by theory (approx. 0.5 microns). For this reason, it was proposed that polar stratospheric clouds may predominantly consist of large (approx. 5 to 50 microns) ice crystals at very low (approx. 10 sup 4- 10 sup 3 cm cubed) concentrations (Rosen et al., 1988). The particle counter employed would be relatively insensitive to these low concentrations. With the increased frequency of soundings in 1987, and adding additional size discrimination in the 1 to 2 micron region, this hypothesis could be verified if suitably low temperatures were encountered
Optimized phase switching using a single atom nonlinearity
We show that a nonlinear phase shift of pi can be obtained by using a single
two level atom in a one sided cavity with negligible losses. This result
implies that the use of a one sided cavity can significantly improve the pi/18
phase shift previously observed by Turchette et al. [Phys. Rev. Lett. 75, 4710
(1995)].Comment: 6 pages, 3 figures, added comments on derivation and assumption
Theoretical and experimental research on parameter tracking systems Final report, 15 Jul. 1964 - Aug. 1965
Parameter tracking systems based on equation error approach for mathematical model of unknown plan
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