156 research outputs found
Confinement and scaling in deep inelastic scattering
We show that parton confinement in the final state generates large
corrections to Bjorken scaling, thus leaving less room for the logarithmic
corrections. In particular, the -scaling violations at large are
entirely described in terms of power corrections. For treatment of these
non-perturbative effects, we derive a new expansion in powers of for
the structure function that is free of infra-red singularities and which
reduces corrections to the leading term. The leading term represents scattering
from an off-mass-shell parton, which keeps the same virtual mass in the final
state. It is found that this quasi-free term is a function of a new variable
, which coincides with the Bjorken variable for . The
two variables are very different, however, at finite . In particular, the
variable depends on the invariant mass of the spectator particles.
Analysis of the data at large shows excellent scaling in the variable , and determines the value of the diquark mass to be close to zero. -scaling allows us to extract the structure function near the elastic
threshold. It is found to behave as . Predictions for the
structure functions based on -scaling are made.Comment: Discussion of target mass corrections is added. Accepted for
publication in Phys. Rev.
Experimental feasibility of measuring the gravitational redshift of light using dispersion in optical fibers
This paper describes a new class of experiments that use dispersion in
optical fibers to convert the gravitational frequency shift of light into a
measurable phase shift or time delay. Two conceptual models are explored. In
the first model, long counter-propagating pulses are used in a vertical fiber
optic Sagnac interferometer. The second model uses optical solitons in
vertically separated fiber optic storage rings. We discuss the feasibility of
using such an instrument to make a high precision measurement of the
gravitational frequency shift of light.Comment: 11 pages, 12 figure
Accelerated Cosmological Models in First-Order Non-Linear Gravity
The evidence of the acceleration of universe at present time has lead to
investigate modified theories of gravity and alternative theories of gravity,
which are able to explain acceleration from a theoretical viewpoint without the
need of introducing dark energy. In this paper we study alternative
gravitational theories defined by Lagrangians which depend on general functions
of the Ricci scalar invariant in minimal interaction with matter, in view of
their possible cosmological applications. Structural equations for the
spacetimes described by such theories are solved and the corresponding field
equations are investigated in the Palatini formalism, which prevents
instability problems. Particular examples of these theories are also shown to
provide, under suitable hypotheses, a coherent theoretical explanation of
earlier results concerning the present acceleration of the universe and
cosmological inflation. We suggest moreover a new possible Lagrangian,
depending on the inverse of sinh(R), which gives an explanation to the present
acceleration of the universe.Comment: 23 pages, Revtex4 fil
Nonlinear Effects in the Amplitude of Cosmological Density Fluctuations
The amplitude of cosmological density fluctuations, sigma_8, has been studied
and estimated by analysing many cosmological observations. The values of the
estimates vary considerably between the various probes. However, different
estimators probe the value of sigma_8 in different cosmological scales and do
not take into account the nonlinear evolution of the parameter at late times.
We show that estimates of the amplitude of cosmological density fluctuations
derived from cosmic flows are systematically higher than those inferred at
early epochs from the CMB because of nonlinear evolution at later times. We
discuss the past and future evolution of linear and nonlinear perturbations,
derive corrections to the value of sigma_8 and compare amplitudes after
accounting for these differences.Comment: 9 pages, 4 figures, 1 table. Accepted for publication in JCA
Large lepton asymmetry from Q-balls
We propose a scenario which can explain large lepton asymmetry and small
baryon asymmetry simultaneously. Large lepton asymmetry is generated through
Affleck-Dine (AD) mechanism and almost all the produced lepton numbers are
absorbed into Q-balls (L-balls). If the lifetime of the L-balls is longer than
the onset of electroweak phase transition but shorter than the epoch of big
bang nucleosynthesis (BBN), the large lepton asymmetry in the L-balls is
protected from sphaleron effects. On the other hand, small (negative) lepton
numbers are evaporated from the L-balls due to thermal effects, which are
converted into the observed small baryon asymmetry by virtue of sphaleron
effects. Large and positive lepton asymmetry of electron type is often
requested from BBN. In our scenario, choosing an appropriate flat direction in
the minimal supersymmetric standard model (MSSM), we can produce positive
lepton asymmetry of electron type but totally negative lepton asymmetry.Comment: 10 pages, 3 figures, ReVTeX
Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV
A search for pair-production of supersymmetric particles under the assumption
that R-parity is violated via a dominant LQDbar coupling has been performed
using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV.
The observed candidate events in the data are in agreement with the Standard
Model expectation. This result is translated into lower limits on the masses of
charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for
m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81
GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the
95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure
Adenovirus-mediated correction of the genetic defect in hepatocytes from patients with familial hypercholesterolemia
Familial hypercholesterolemia (FH) is an inherited deficiency of LDL receptors that has been an important model for liver-directed gene therapy. We are developing approaches for treating FH that are based on direct delivery of recombinant LDL receptor genes to liver in vivo. As a first step towards this goal, replication-defective recombinant adenoviruses were constructed which contained either the lacZ gene or the human LDL receptor cDNA expressed from a ÎČ-actin promoter. Primary cultures of hepatocytes were established from two patients with homozygous FH and one nonFH patient, and subsequently exposed to recombinant adenoviruses at MOIs ranging from 0.1 to 5. Essentially all of the cells expressed high levels of the transgene without demonstrable expression of an early or late adenoviral gene product; the level of recombinant-derived LDL receptor protein in transduced FH hepatocytes exceeded the endogenous levels by at least 20-fold. These studies support the utility of recombinant adenoviruses for efficient transduction of recombinant LDL receptor genes into human FH hepatocytes without expression of viral proteins.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45545/1/11188_2005_Article_BF01233250.pd
The integrated Sachs-Wolfe Effect -- Large Scale Structure Correlation
We discuss the correlation between late-time integrated Sachs-Wolfe (ISW)
effect in the cosmic microwave background (CMB) temperature anisotropies and
the large scale structure of the local universe. This correlation has been
proposed and studied in the literature as a probe of the dark energy and its
physical properties. We consider a variety of large scale structure tracers
suitable for a detection of the ISW effect via a cross-correlation. In addition
to luminous sources, we suggest the use of tracers such as dark matter halos or
galaxy clusters. A suitable catalog of mass selected halos for this purpose can
be constructed with upcoming wide-field lensing and Sunyaev-Zel'dovich (SZ)
effect surveys. With multifrequency data, the presence of the ISW-large scale
structure correlation can also be investigated through a cross-correlation of
the frequency cleaned SZ and CMB maps. While convergence maps constructed from
lensing surveys of the large scale structure via galaxy ellipticities are less
correlated with the ISW effect, lensing potentials that deflect CMB photons are
strongly correlated and allow, probably, the best mechanism to study the
ISW-large scale structure correlation with CMB data alone.Comment: 10 Pages, PRD submitte
Hypoxic Pulmonary Vasoconstriction in Humans:Tale or Myth
Hypoxic Pulmonary vasoconstriction (HPV) describes the physiological adaptive process of lungs to preserves systemic oxygenation. It has clinical implications in the development of pulmonary hypertension which impacts on outcomes of patients undergoing cardiothoracic surgery. This review examines both acute and chronic hypoxic vasoconstriction focusing on the distinct clinical implications and highlights the role of calcium and mitochondria in acute versus the role of reactive oxygen species and Rho GTPases in chronic HPV. Furthermore it identifies gaps of knowledge and need for further research in humans to clearly define this phenomenon and the underlying mechanism
- âŠ