1,161 research outputs found
Light Gluino Constituents of Hadrons and a Global Analysis of Hadron Scattering Data
Light strongly interacting supersymmetric particles may be treated as
partonic constituents of nucleons in high energy scattering processes. We
construct parton distribution functions for protons in which a light gluino is
included along with standard model quark, antiquark, and gluon constituents. A
global analysis is performed of a large set of data from deep-inelastic lepton
scattering, massive lepton pair and vector boson production, and hadron jet
production at large values of transverse momentum. Constraints are obtained on
the allowed range of gluino mass as a function of the value of the strong
coupling strength alpha_s(M_Z) determined at the scale of the Z boson mass. We
find that gluino masses as small as 10 GeV are admissible provided that
alpha_s(M_Z) \ge 0.12. Current hadron scattering data are insensitive to the
presence of gluinos heavier than ~ 100 - 150 GeV.Comment: 31 pages, 12 figures, RevTe
Lifetime of quasiparticles in hot QED plasmas
The calculation of the lifetime of quasiparticles in a QED plasma at high
temperature remains plagued with infrared divergences, even after one has taken
into account the screening corrections. The physical processes responsible for
these divergences are the collisions involving the exchange of very soft,
unscreened, magnetic photons, whose contribution is enhanced by the thermal
Bose-Einstein occupation factor. The self energy diagrams which diverge in
perturbation theory contain no internal fermion loops, but an arbitrary number
of internal magnetostatic photon lines. By generalizing the Bloch-Nordsieck
model at finite temperature, we can resum all the singular contributions of
such diagrams, and obtain the correct long time behaviour of the retarded
fermion propagator in the hot QED plasma: , where is the plasma frequency and
.Comment: 13 pages, LaTe
Single-top-squark production via R-parity-violating supersymmetric couplings in hadron collisions
Single-top-squark production via q q' -> \bar{\tilde{t_1}} probes
R-parity-violating extensions of the minimal supersymmetric standard model
though the \lambda''_{3ij} couplings. For masses in the range 180-325 GeV, and
\lambda''_{3ij} > 0.02-0.06, we show that discovery of the top squark is
possible with 2 fb^{-1} of integrated luminosity at run II of the Fermilab
Tevatron. The bound on \lambda''_{3ij}$ can be reduced by up to an order of
magnitude with existing data from run I, and by two orders of magnitude at run
II if the top squark is not found.Comment: To appear in Phys. Rev. Lett., minor changes, 4 pages, RevTeX, 5 eps
fig
Dilepton-tagged jets in relativistic nucleus-nucleus collisions: A case study
We study the A+B -> l+ l- + jet +X process in nucleus-nucleus collisions at
relativistic energies. The dilepton as well as the jet will pass through the
matter produced in such collisions. The recoiling dilepton will carry
information about the kinematical features of the jet, and will thus prove to
be a very effective tool in isolating in-medium effects such as energy-loss and
fragmentation function modifications. We estimate the contributions due to
correlated charm and bottom decay and we identify a window where they are small
as compared to pairs from the NLO Drell-Yan process.Comment: 7 pages, 9 figures Two figures modified, references adde
Galaxy Zoo: Are Bars Responsible for the Feeding of Active Galactic Nuclei at 0.2 < z < 1.0?
We present a new study investigating whether active galactic nuclei (AGN)
beyond the local universe are preferentially fed via large-scale bars. Our
investigation combines data from Chandra and Galaxy Zoo: Hubble (GZH) in the
AEGIS, COSMOS, and GOODS-S surveys to create samples of face-on, disc galaxies
at 0.2 < z < 1.0. We use a novel method to robustly compare a sample of 120 AGN
host galaxies, defined to have 10^42 erg/s < L_X < 10^44 erg/s, with inactive
control galaxies matched in stellar mass, rest-frame colour, size, Sersic
index, and redshift. Using the GZH bar classifications of each sample, we
demonstrate that AGN hosts show no statistically significant enhancement in bar
fraction or average bar likelihood compared to closely-matched inactive
galaxies. In detail, we find that the AGN bar fraction cannot be enhanced above
the control bar fraction by more than a factor of two, at 99.7% confidence. We
similarly find no significant difference in the AGN fraction among barred and
non-barred galaxies. Thus we find no compelling evidence that large-scale bars
directly fuel AGN at 0.2<z<1.0. This result, coupled with previous results at
z=0, implies that moderate-luminosity AGN have not been preferentially fed by
large-scale bars since z=1. Furthermore, given the low bar fractions at z>1,
our findings suggest that large-scale bars have likely never directly been a
dominant fueling mechanism for supermassive black hole growth.Comment: 13 pages, 5 figures, 2 tables, accepted by MNRA
Two dimensional Dirac fermions in the presence of long-range correlated disorder
We consider 2D Dirac fermions in the presence of three types of disorder:
random scalar potential, random gauge potential and random mass with long-range
correlations decaying as a power law. Using various methods such as the
self-consistent Born approximation (SCBA), renormalization group (RG), the
matrix Green function formalism and bosonisation we calculate the density of
states and study the full counting statistics of fermionic transport at lower
energy. The SCBA and RG show that the random correlated scalar potentials
generate an algebraically small energy scale below which the density of states
saturates to a constant value. For correlated random gauge potential, RG and
bosonisation calculations provide consistent behavior of the density of states
which diverges at zero energy in an integrable way. In the case of correlated
random mass disorder the RG flow has a nontrivial infrared stable fixed point
leading to a universal power-law behavior of the density of states and also to
universal transport properties. In contrast to uncorrelated case the correlated
scalar potential and random mass disorders give rise to deviation from the
pseudodiffusive transport already to lowest order in disorder strength.Comment: 17 pages, 8 figures, revtex
Lifetimes of quasiparticles and collective excitations in hot QED plasmas
The perturbative calculation of the lifetime of fermion excitations in a QED
plasma at high temperature is plagued with infrared divergences which are not
eliminated by the screening corrections. The physical processes responsible for
these divergences are the collisions involving the exchange of longwavelength,
quasistatic, magnetic photons, which are not screened by plasma effects. The
leading divergences can be resummed in a non-perturbative treatement based on a
generalization of the Bloch-Nordsieck model at finite temperature. The
resulting expression of the fermion propagator is free of infrared problems,
and exhibits a {\it non-exponential} damping at large times: , where is the plasma
frequency and .Comment: LaTex file, 57 pages, 11 eps figures include
Direct probes of R-parity-violating supersymmetric couplings via single-top-squark production
We study the s-channel production of a single top squark in hadron collisions
through an R-parity-violating mechanism, examining in detail the case in which
the squark decays through an R-parity-conserving process into a bottom quark, a
lepton, and missing energy. We show that the top squark can be discovered if
its mass is less than 400 GeV, or that the current bound on the size of the
R-parity-violating couplings can be reduced by up to one order of magnitude
with existing data and by two orders of magnitude at the forthcoming run II of
the Fermilab Tevatron.Comment: To appear in Phys. Rev. D; 32 pgs., 17 ps figs., uses RevTeX; 1 new
fig., slight textual clarification
Inclusive Prompt Photon Production in Hadronic Final States of Annihilation
We provide complete analytic expressions for the inclusive prompt photon
production cross section in hadronic final states of annihilation
reactions through one-loop order in quantum chromodynamics perturbation theory.
Computed explicitly are direct photon production through first order in the
electromagnetic strength and the quark-to-photon and
gluon-to-photon fragmentation contributions through first order in the strong
coupling . The full angular dependence of the cross sections is
displayed, separated into transverse and
longitudinal components, where
specifies the direction of the photon with respect to the collision
axis. We discuss extraction of fragmentation functions from data.Comment: 40 pages, RevTex, 30 figures in postscript available in a separate
fil
A model for malaria treatment evaluation in the presence of multiple species
Plasmodium (P.) falciparum and P. vivax are the two most common causes of
malaria. While the majority of deaths and severe morbidity are due to P.
falciparum, P. vivax poses a greater challenge to eliminating malaria outside
of Africa due to its ability to form latent liver stage parasites
(hypnozoites), which can cause relapsing episodes within an individual patient.
In areas where P. falciparum and P. vivax are co-endemic, individuals can carry
parasites of both species simultaneously. These mixed infections complicate
dynamics in several ways; treatment of mixed infections will simultaneously
affect both species, P. falciparum can mask the detection of P. vivax, and it
has been hypothesised that clearing P. falciparum may trigger a relapse of
dormant P. vivax. When mixed infections are treated for only blood-stage
parasites, patients are at risk of relapse infections due to P. vivax
hypnozoites.
We present a stochastic mathematical model that captures interactions between
P. falciparum and P. vivax, and incorporates both standard schizontocidal
treatment (which targets blood-stage parasites) and radical treatment (which
additionally targets liver-stage parasites). We apply this model to assess the
implications of different treatment coverage of radical cure for mixed and P.
vivax infections and a so-called "unified radical cure" treatment strategy for
P. falciparum, P. vivax and mixed infections. We find that a unified radical
cure strategy, with G6PD screening, leads to a substantially lower incidence of
malaria cases and deaths overall. We perform a one-way sensitivity analysis to
highlight important model parameters
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