592 research outputs found
The Jacobi Polynomials QCD analysis for the polarized structure function
We present the results of our QCD analysis for polarized quark distribution
and structure function . We use very recently experimental data
to parameterize our model. New parameterizations are derived for the quark and
gluon distributions for the kinematic range , GeV^2. The analysis is based on the Jacobi polynomials
expansion of the polarized structure functions. Our calculations for polarized
parton distribution functions based on the Jacobi polynomials method are in
good agreement with the other theoretical models. The values of
and are determined.Comment: 23 pages, 8 figures and 4 table
Heart of Darkness: The Significance of the Zeptobarn Scale for Neutralino Direct Detection
The direct detection of dark matter through its elastic scattering off
nucleons is among the most promising methods for establishing the particle
identity of dark matter. The current bound on the spin-independent scattering
cross section is sigma^SI < 10 zb for dark matter masses m_chi ~ 100 GeV, with
improved sensitivities expected soon. We examine the implications of this
progress for neutralino dark matter. We work in a supersymmetric framework
well-suited to dark matter studies that is simple and transparent, with models
defined in terms of four weak-scale parameters. We first show that robust
constraints on electric dipole moments motivate large sfermion masses mtilde >
1 TeV, effectively decoupling squarks and sleptons from neutralino dark matter
phenomenology. In this case, we find characteristic cross sections in the
narrow range 1 zb 70 GeV. As sfermion masses are
lowered to near their experimental limit mtilde ~ 400 GeV, the upper and lower
limits of this range are extended, but only by factors of around two, and the
lower limit is not significantly altered by relaxing many particle physics
assumptions, varying the strange quark content of the nucleon, including the
effects of galactic small-scale structure, or assuming other components of dark
matter. Experiments are therefore rapidly entering the heart of dark
matter-favored supersymmetry parameter space. If no signal is seen,
supersymmetric models must contain some level of fine-tuning, and we identify
and analyze several possibilities. Barring large cancellations, however, in a
large and generic class of models, if thermal relic neutralinos are a
significant component of dark matter, experiments will discover them as they
probe down to the zeptobarn scale.Comment: 35 pages, 11 figures; v2: references added, figures extended to 2 TeV
neutralino masses, XENON100 results included, published versio
Electromagnetic proton form factors in large QCD
The electromagnetic form factors of the proton are obtained using a
particular realization of QCD in the large limit (),
which sums up the infinite number of zero-width resonances to yield an Euler's
Beta function (Dual-). The form factors and
, as well as agree very well with reanalyzed space-like
data in the whole range of momentum transfer. In addition, the predicted ratio
is in good agreement with recent polarization transfer
measurements at Jefferson Lab.Comment: 10 page
The neutrino signal at HALO: learning about the primary supernova neutrino fluxes and neutrino properties
Core-collapse supernova neutrinos undergo a variety of phenomena when they
travel from the high neutrino density region and large matter densities to the
Earth. We perform analytical calculations of the supernova neutrino fluxes
including collective effects due to the neutrino-neutrino interactions, the
Mikheev-Smirnov-Wolfenstein (MSW) effect due to the neutrino interactions with
the background matter and decoherence of the wave packets as they propagate in
space. We predict the numbers of one- and two-neutron charged and
neutral-current electron-neutrino scattering on lead events. We show that, due
to the energy thresholds, the ratios of one- to two-neutron events are
sensitive to the pinching parameters of neutrino fluxes at the neutrinosphere,
almost independently of the presently unknown neutrino properties. Besides,
such events have an interesting sensitivity to the spectral split features that
depend upon the presence/absence of energy equipartition among neutrino
flavors. Our calculations show that a lead-based observatory like the Helium
And Lead Observatory (HALO) has the potential to pin down important
characteristics of the neutrino fluxes at the neutrinosphere, and provide us
with information on the neutrino transport in the supernova core.Comment: 30 pages, 12 figures, 6 tables, minor correction
Signatures of photon and axion-like particle mixing in the gamma-ray burst jet
Photons couple to Axion-Like Particles (ALPs) or more generally to any pseudo
Nambu-Goldstone boson in the presence of an external electromagnetic field.
Mixing between photons and ALPs in the strong magnetic field of a Gamma-Ray
Burst (GRB) jet during the prompt emission phase can leave observable imprints
on the gamma-ray polarization and spectrum. Mixing in the intergalactic medium
is not expected to modify these signatures for ALP mass > 10^(-14) eV and/or
for < nG magnetic field. We show that the depletion of photons due to
conversion to ALPs changes the linear degree of polarization from the values
predicted by the synchrotron model of gamma ray emission. We also show that
when the magnetic field orientation in the propagation region is perpendicular
to the field orientation in the production region, the observed synchrotron
spectrum becomes steeper than the theoretical prediction and as detected in a
sizable fraction of GRB sample. Detection of the correlated polarization and
spectral signatures from these steep-spectrum GRBs by gamma-ray polarimeters
can be a very powerful probe to discover ALPs. Measurement of gamma-ray
polarization from GRBs in general, with high statistics, can also be useful to
search for ALPs.Comment: 17 pages, 3 figures. Accepted for publication in JCAP with minor
change
Spin Structure of the Pion in a Light-Cone Representation
The spin structure of the pion is discussed by transforming the wave function
for the pion in the naive quark model into a light-cone representation. It is
shown that there are higher helicity () states in
the full light-cone wave function for the pion besides the ordinary helicity
() component wave functions as a consequence from
the Melosh rotation relating spin states in light-front dynamics and those in
instant-form dynamics. Some low energy properties of the pion, such as the
electromagnetic form factor, the charged mean square radius, and the weak decay
constant, could be interrelated in this representation with reasonable
parameters.Comment: 15 Latex pages, 2 figures upon reques
Neutrino oscillations in magnetically driven supernova explosions
We investigate neutrino oscillations from core-collapse supernovae that
produce magnetohydrodynamic (MHD) explosions. By calculating numerically the
flavor conversion of neutrinos in the highly non-spherical envelope, we study
how the explosion anisotropy has impacts on the emergent neutrino spectra
through the Mikheyev-Smirnov-Wolfenstein effect. In the case of the inverted
mass hierarchy with a relatively large theta_(13), we show that survival
probabilities of electron type neutrinos and antineutrinos seen from the
rotational axis of the MHD supernovae (i.e., polar direction), can be
significantly different from those along the equatorial direction. The event
numbers of electron type antineutrinos observed from the polar direction are
predicted to show steepest decrease, reflecting the passage of the
magneto-driven shock to the so-called high-resonance regions. Furthermore we
point out that such a shock effect, depending on the original neutrino spectra,
appears also for the low-resonance regions, which leads to a noticeable
decrease in the electron type neutrino signals. This reflects a unique nature
of the magnetic explosion featuring a very early shock-arrival to the resonance
regions, which is in sharp contrast to the neutrino-driven delayed supernova
models. Our results suggest that the two features in the electron type
antineutrinos and neutrinos signals, if visible to the Super-Kamiokande for a
Galactic supernova, could mark an observational signature of the magnetically
driven explosions, presumably linked to the formation of magnetars and/or
long-duration gamma-ray bursts.Comment: 25 pages, 21 figures, JCAP in pres
Linear square-mass trajectories of radially and orbitally excited hadrons in holographic QCD
We consider a new approach towards constructing approximate holographic duals
of QCD from experimental hadron properties. This framework allows us to derive
a gravity dual which reproduces the empirically found linear square-mass
trajectories of universal slope for radially and orbitally excited hadrons.
Conformal symmetry breaking in the bulk is exclusively due to infrared
deformations of the anti-de Sitter metric and governed by one free mass scale
proportional to Lambda_QCD. The resulting background geometry exhibits dual
signatures of confinement and provides the first examples of holographically
generated linear trajectories in the baryon sector. The predictions for the
light hadron spectrum include new relations between trajectory slopes and
ground state masses and are in good overall agreement with experiment.Comment: 33 pages, 5 figures, updated to the extended version published in
JHEP, vector meson bulk potential and metric corrected, comments and
references added, phenomenology and conclusions unchange
Natural T cell–mediated protection against seasonal and pandemic Influenza: results of the Flu Watch cohort study
Rationale: A high proportion of influenza infections are asymptomatic. Animal and human challenge studies and observational studies suggest T cells protect against disease among those infected, but the impact of T-cell immunity at the population level is unknown.
Objectives: To investigate whether naturally preexisting T-cell responses targeting highly conserved internal influenza proteins could provide cross-protective immunity against pandemic and seasonal influenza.
Methods: We quantified influenza A(H3N2) virus–specific T cells in a population cohort during seasonal and pandemic periods between 2006 and 2010. Follow-up included paired serology, symptom reporting, and polymerase chain reaction (PCR) investigation of symptomatic cases.
Measurements and Main Results: A total of 1,414 unvaccinated individuals had baseline T-cell measurements (1,703 participant observation sets). T-cell responses to A(H3N2) virus nucleoprotein (NP) dominated and strongly cross-reacted with A(H1N1)pdm09 NP (P < 0.001) in participants lacking antibody to A(H1N1)pdm09. Comparison of paired preseason and post-season sera (1,431 sets) showed 205 (14%) had evidence of infection based on fourfold influenza antibody titer rises. The presence of NP-specific T cells before exposure to virus correlated with less symptomatic, PCR-positive influenza A (overall adjusted odds ratio, 0.27; 95% confidence interval, 0.11–0.68; P = 0.005, during pandemic [P = 0.047] and seasonal [P = 0.049] periods). Protection was independent of baseline antibodies. Influenza-specific T-cell responses were detected in 43%, indicating a substantial population impact.
Conclusions: Naturally occurring cross-protective T-cell immunity protects against symptomatic PCR-confirmed disease in those with evidence of infection and helps to explain why many infections do not cause symptoms. Vaccines stimulating T cells may provide important cross-protective immunity
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