11,191 research outputs found
Diquarks and Exotic Spectroscopy
We propose that the recently discovered \Theta baryon is a bound state of
four quarks and an antiquark, containing two highly correlated ud-pairs. If so,
the \Theta baryon has positive parity, and it lies in an near-ideally mixed
SU(3)_{f} \mathbf{\bar{10}}_{f} oplus \mathbf{8}_{f}. The Roper resonance and
the P_{11}(1710) fit naturally into this classification. We predict an isospin
3/2 multiplet of \Xi's (S=-2) with J^{\Pi}=\half^{+} around 1750 MeV. A search
for manifestly exotic \Xi^{+} and \Xi^{--} in this mass range could provide a
sharp test of our proposal. We predict that charm and bottom analogues of the
\Theta baryon are stable against strong decays.Comment: 5 pages, 2 figures, revtex 4, minor corrections and revisions for
journal publicatio
Casimir forces beyond the proximity approximation
The proximity force approximation (PFA) relates the interaction between
closely spaced, smoothly curved objects to the force between parallel plates.
Precision experiments on Casimir forces necessitate, and spur research on,
corrections to the PFA. We use a derivative expansion for gently curved
surfaces to derive the leading curvature modifications to the PFA. Our methods
apply to any homogeneous and isotropic materials; here we present results for
Dirichlet and Neumann boundary conditions and for perfect conductors. A Pad\'e
extrapolation constrained by a multipole expansion at large distance and our
improved expansion at short distances, provides an accurate expression for the
sphere-plate Casimir force at all separations.Comment: 4 pages, 1 figur
The Drell-Yan process and Deep Inelastic Scattering from the lattice
We report on measurements of the h_1 structure function, relevant to
calculating cross-sections for the Drell-Yan process. This is a quantity which
can not be measured in Deep Inelastic Scattering, it gives additional
information on the spin carried by the valence quarks, as well as insights on
how relativistic the quarks are.Comment: 3 pages, Latex, 3 figures, espcrc2.sty included, Talk presented at
LATTICE96(phenomenology
On the relation between nuclear and nucleon Structure Functions and their moments
Calculations of nuclear Structure Functions (SF) F_k^A(x,Q^2) routinely
exploit a generalized convolution, involving the SF for nucleons F_k^N and the
linking SF f^{PN,A} of a fictitious nucleus, composed of point-particles, with
the latter usually expressed in terms of hadronic degrees of freedom. For
finite Q^2 the approach seemed to be lacking a solid justification and the same
is the case for recently proposed, effective nuclear parton distribution
functions (pdf), which exactly reproduce the above-mentioned hadronically
computed F_k^A. Many years ago Jaffe and West proved the above convolution in
the Plane Wave Impulse Approximation (PWIA) for the nuclear components in the
convolution. In the present note we extend the above proof to include classes
of nuclear Final State Interactions (FSI). One and the same function appears to
relate parton distribution functions (pdf) in nuclei and nucleons, and SF for
nuclear targets and for nucleons. That relation is the previously conjectured
one,with an entirely different interpretation of f^{PN,A}. We conclude with an
extensive analysis of moments of nuclear SF based on the generalized
convolution. Characteristics of those moments are shown to be quite similar to
the same for a nucleon. We conclude that the above evidences asymptotic freedom
of a nucleon in a medium and not of a composite nucleus.Comment: 18 pages, 9 figure
Spheroidal and elliptical galaxy radial velocity dispersion determined from Cosmological General Relativity
Radial velocity dispersion in spheroidal and elliptical galaxies, as a
function of radial distance from the center of the galaxy, has been derived
from Cosmological Special Relativity. For velocity dispersions in the outer
regions of spherical galaxies, the dynamical mass calculated for a galaxy using
Carmelian theory may be 10 to 100 times less than that calculated from standard
Newtonian physics. This means there is no need to include halo dark matter. The
velocity dispersion is found to be approximately constant across the galaxy
after falling from an initial high value at the center.Comment: 10 pages, 3 figure
Inhibition of Friend erythroleukaemia-cell tumours in vivo by a synthetic analogue of prostaglandin E2.
The effect of 16,16-dimethyl-PGE2-methyl ester (di-M-PGE2), a long-acting synthetic analogue of prostaglandin E2, on the replication of Friend erythroleukaemia cells (FLC) in vivo has been studied. Pre-treatment in vitro of both undifferentiated and differentiated FLC with di-M-PGE2 (1 microgram/ml) did not alter rates of tumour appearance or growth, but increased the median survival of DBA/2J mice. Systemic administration of di-M-PGE2 (10 microgram/mouse/day) was not toxic to the mice, but significantly inhibited tumour growth and increased median survival in mice injected s.c. with undifferentiated FLC. These effects of di-M-PGE2 were much more pronounced in mice receiving differentiated (DMSO-treated) FLC. In this latter group, the appearance of tumour was also significantly delayed by di-M-PGE2. The different effects of di-M-PGE2 treatment on tumours derived from undifferentiated and differentiated cells suggest that the analogue is acting directly on tumour-cell replication rather than on factors related to the host response
Streaming velocities as a dynamical estimator of Omega
It is well known that estimating the pairwise velocity of galaxies, v_{12},
from the redshift space galaxy correlation function is difficult because this
method is highly sensitive to the assumed model of the pairwise velocity
dispersion. Here we propose an alternative method to estimate v_{12} directly
from peculiar velocity samples, which contain redshift-independent distances as
well as galaxy redshifts. In contrast to other dynamical measures which
determine beta = sigma_8 x Omega^{0.6}, our method can provide an estimate of
(sigma_8)^2 x Omega^{0.6} for a range of sigma_8 (here Omega is the
cosmological mass density parameter while sigma_8 is the standard normalization
parameter for the spectrum of matter density fluctuations). We demonstrate how
to measure this quantity from realistic catalogues.Comment: 8 pages of text, 4 figures Subject headings: Cosmology: theory -
observation - peculiar velocities: large scale flows Last name of one of the
authors was misspelled. It is now corrected. Otherwise the manuscript is
identical to its original versio
Tortuous ways to the extraction of neutron observables from inclusive lepton scattering
We analyze new JLAB data for inclusive electron scattering on various
targets. Computed and measured total inclusive cross sections in the range
show on a logarithmic scale reasonable agreement
for all targets. However, closer inspection of the Quasi-Elastic components
bares serious discrepancies. EMC ratios which may contain less systematic
errors fare the same. The above observations for the new data do not enable the
extraction of the magnetic form factor (FF) and the Structure Function
(SFs) of the neutron, although the application of exactly the same
analysis to older data had been successful. We add to the above analysis older
CLAS collaboration on . Removing some scattered points, it appears
possible to obtain the above mentioned neutron information. We compare our
results with others from alternative sources. Particular attention is paid to
the A=3 iso-doublet. Present data exist only for He, but the available
input and charge symmetry also enable computations for H. Their average is
the computed iso-scalar part and is compared with the empirical modification of
He towards a fictitious A=3 iso-singlet.Comment: 27 pages, 30 figure
Measuring Omega with Galaxy Streaming Velocities
The mean pairwise velocity of galaxies has traditionally been estimated from
the redshift space galaxy correlation function. This method is notorious for
being highly sensitive to the assumed model of the pairwise velocity
dispersion. Here we propose an alternative method to estimate the streaming
velocity directly from peculiar velocity samples, which contain
redshift-independent distances as well as galaxy redshifts. This method can
provide an estimate of for a range of where
is the cosmological density parameter, while is the
standard normalization for the power spectrum of density fluctuations. We
demonstrate how to measure this quantity from realistic catalogues and identify
the main sources of bias and errorsComment: Proceedings of New Worlds in Astroparticle Physics, 6 pages, 2
figure
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