28,765 research outputs found
Parton Distributions in Impact Parameter Space
Fourier transform of the generalized parton distributions (GPDs) at zero
skewness with respect to the transverse momentum transfer gives the
distribution of partons in the impact parameter space. We investigate the GPDs
as well as the impact parameter dependent parton distributions (ipdpdfs) by
expressing them in terms of overlaps of light front wave functions (LFWFs) and
present a comparative study using three different model LFWFs.Comment: 13 pages, 6 figure
Centroids of Gamow-Teller transitions at finite temperature in fp-shell neutron-rich nuclei
The temperature dependence of the energy centroids and strength distributions
for Gamow-Teller (GT) excitations in several fp-shell nuclei is studied.
The quasiparticle random phase approximations (QRPA) is extended to describe GT
states at finite temperature. A shift to lower energies of the GT strength
is found, as compared to values obtained at zero temperature.Comment: 12 pages, contains 3 tables. E-mail: [email protected],
[email protected]
Charm Meson Mixing: An Experimental Review
We review current experimental results on charm mixing and CP violation. We
survey experimental techniques, including time-dependent, time-independent, and
quantum-correlated measurements. We review techniques that use a slow pion tag
from D*+ --> pi+ D0 + c.c. decays and those that do not, and cover two-body and
multi-body D0 decay modes. We provide a summary of D-mixing results to date and
comment on future experimental prospects at the LHC and other new or planned
facilities.Comment: 53 pages, 29 figures, 8 table
The late time radio emission from SN 1993J at meter wavelengths
We present the investigations of SN 1993J using low frequency observations
with the Giant Meterwave Radio Telescope. We analyze the light curves of SN
1993J at 1420, 610, 325 and 243 MHz during years since explosion.The
supernova has become optically thin early on in the 1420 MHz and 610 MHz bands
while it has only recently entered the optically thin phase in the 325 MHz
band. The radio light curve in the 235 MHz band is more or less flat. This
indicates that the supernova is undergoing a transition from an optically thick
to optically thin limit in this frequency band. In addition, we analyze the SN
radio spectra at five epochs on day 3000, 3200, 3266, 3460 and 3730 since
explosion. Day 3200 spectrum shows a synchrotron cooling break. SN 1993J is the
only young supernova for which the magnetic field and the size of the radio
emitting region are determined through unrelated methods. Thus the mechanism
that controls the evolution of the radio spectra can be identified. We suggest
that at all epochs, the synchrotron self absorption mechanism is primarily
responsible for the turn-over in the spectra. Light curve models based on free
free absorption in homogeneous or inhomogeneous media at high frequencies
overpredict the flux densities at low frequencies. The discrepancy is
increasingly larger at lower and lower frequencies. We suggest that an extra
opacity, sensitively dependent on frequency, is likely to account for the
difference at lower frequencies. The evolution of the magnetic field
(determined from synchrotron self absorption turn-over) is roughly consistent
with . Radio spectral index in the optically thin part
evolves from at few tens of days to in about
10 years.Comment: 37 pages, 9 figures in LaTex; scheduled for ApJ 10 September 2004,
v612 issue; send comments to: [email protected]
Three-dimensional measurements of fatigue crack closure
Fatigue crack growth and retardation experiments conducted in polycarbonate test specimen are described. The transparent test material allows optical interferometry measurements of the fatigue crack opening (and closing) profiles. Crack surface displacements are obtained through the specimen thickness and three dimensional aspects of fatigue crack closure are discussed
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