218 research outputs found
Q^2-Evolution of Nucleon's Chiral-Odd Twist-3 Structure Function: h_L(x,Q^2)
We investigate the -evolution of the chiral-odd spin-dependent parton
distribution relevant for the polarized Drell-Yan processes.
The results are obtained in the leading logarithmic order in the framework of
the renormalization group and the standard QCD perturbation theory. We
calculate the anomalous dimension matrix for the twist-3 operators for
in the one-loop order. The operator mixing among the relevant twist-3 operators
including the operators proportional to the QCD equations of motion is treated
properly in a consistent scheme. Implications for future experiments are also
discussed.Comment: HUPD-9419, Latex file, 21 pages, 7 figures available on reques
Dark Energy and the quietness of the Local Hubble Flow
The linearity and quietness of the Local () Hubble Flow (LHF) in
view of the very clumpy local universe is a long standing puzzle in standard
and in open CDM cosmogony. The question addressed in this paper is whether the
antigravity component of the recently discovered dark energy can cool the
velocity flow enough to provide a solution to this puzzle. We calculate the
growth of matter fluctuations in a flat universe containing a fraction
of dark energy obeying the time independent equation of state
. We find that dark energy can indeed cool the LHF. However the
dark energy parameter values required to make the predicted velocity dispersion
consistent with the observed value have been ruled out
by other observational tests constraining the dark energy parameters and
. Therefore despite the claims of recent qualitative studies dark
energy with time independent equation of state can not by itself explain the
quietness and linearity of the Local Hubble Flow.Comment: 4 pages, 3 figures, accepted in Phys. Rev. D. Minor corrections, one
figure adde
Cosmic Microwave Background Anisotropy with Cosine-Type Quintessence
We study the Cosmic Microwave Background (CMB) anisotropies produced by
cosine-type quintessence models. In our analysis, effects of the adiabatic and
isocurvature fluctuations are both taken into account. For purely adiabatic
fluctuations with scale invariant spectrum, we obtain a stringent constraint on
the model parameters using the CMB data from COBE, BOOMERanG and MAXIMA.
Furthermore, it is shown that isocurvature fluctuations have significant
effects on the CMB angular power spectrum at low multipoles in some parameter
space, which may be detectable in future satellite experiments. Such a signal
may be used to test the cosine-type quintessence models.Comment: 21 pages, 9 figure
New hadrons as ultra-high energy cosmic rays
Ultra-high energy cosmic ray (UHECR) protons produced by uniformly
distributed astrophysical sources contradict the energy spectrum measured by
both the AGASA and HiRes experiments, assuming the small scale clustering of
UHECR observed by AGASA is caused by point-like sources. In that case, the
small number of sources leads to a sharp exponential cutoff at the energy
E<10^{20} eV in the UHECR spectrum. New hadrons with mass 1.5-3 GeV can solve
this cutoff problem. For the first time we discuss the production of such
hadrons in proton collisions with infrared/optical photons in astrophysical
sources. This production mechanism, in contrast to proton-proton collisions,
requires the acceleration of protons only to energies E<10^{21} eV. The diffuse
gamma-ray and neutrino fluxes in this model obey all existing experimental
limits. We predict large UHE neutrino fluxes well above the sensitivity of the
next generation of high-energy neutrino experiments. As an example we study
hadrons containing a light bottom squark. These models can be tested by
accelerator experiments, UHECR observatories and neutrino telescopes.Comment: 17 pages, revtex style; v2: shortened, as to appear in PR
When Will Adolescents Tell Someone About Dating Violence Victimization?
This study examined factors that influence help-seeking among a diverse sample of
adolescents who experienced dating violence. A sample of 57 high school students in
an urban community reported on the prevalence and characteristics of dating violence
in their relationships. Someone observing a dating violence incident and a survivor’s
attaching an emotional meaning to the event significantly influenced adolescents to talk
to someone. When dating violence occurred in isolation, survivors were more likely to
receive no support from others in the aftermath of the incident. Differences between
boys’ and girls’ help-seeking and implications for dating violence intervention and prevention
programming are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90887/1/Black-Tolman-Callahan-Saunders- Weisz- 2008-When will adolescents tell someone about dating violence VAW.pd
Early-universe constraints on a Primordial Scaling Field
In the past years 'quintessence' models have been considered which can
produce the accelerated expansion in the universe suggested by recent
astronomical observations. One of the key differences between quintessence and
a cosmological constant is that the energy density in quintessence,
, could be a significant fraction of the overall energy even in
the early universe, while the cosmological constant will be dynamically
relevant only at late times. We use standard Big Bang Nucleosynthesis and the
observed abundances of primordial nuclides to put constraints on
at temperatures near . We point out that current experimental data
does not support the presence of such a field, providing the strong constraint
at C.L. and strengthening previous
results. We also consider the effect a scaling field has on CMB anisotropies
using the recent data from Boomerang and DASI, providing the CMB constraint
at during the radiation dominated epoch.Comment: 5 pages, 4 figures. The revised version includes the new Boomerang
and DASI dat
Longitudinal quark polarization in transversely polarized nucleons.
Accounting for transverse momenta of the quarks, a longitudinal quark spin asymmetry exists in a transversely polarized nucleon target. The relevant leading quark distribution g_{1T}(x,k_T^2) can be measured in the semi-inclusive deep-inelastic scattering. The average k_T^2 weighted distribution function g^{(1)}_{1T} can be obtained directly from the inclusive measurement of g_2
On the Degeneracy Inherent in Observational Determination of the Dark Energy Equation of State
Using a specific model for the expansion rate of the Universe as a function
of scale factor, it is demonstrated that the equation of state of the dark
energy cannot be determined uniquely from observations at redshifts
unless the fraction of the mass density of the Universe
in nonrelativistic particles, , somehow can be found independently. A
phenomenological model is employed to discuss the utility of additional
constraints from the formation of large scale structure and the positions of
CMB peaks in breaking the degeneracy among models for the dark energy.Comment: 12 pages, 3 figures. Several references adde
- …