8,881 research outputs found
t-channel production of heavy charged leptons
We study the pair production of heavy charged exotic leptons at e+ e-
colliders in the SU(2)_L x SU(2)_I x U(1)_Y model. This gauge group is a
subgroup of the grand unification group E6; SU(2)_I commutes with the electric
charge operator, and the three corresponding gauge bosons are electrically
neutral. In addition to the standard photon and Z boson contributions, we also
include the contributions from extra neutral gauge bosons. A t-channel
contribution due to W_I-boson exchange, which is unsuppressed by mixing angles,
is quite important. We calculate the left-right and forward-backward
asymmetries, and discuss how to differentiate different models.Comment: Increased discussion of experimental signatures. Version accepted by
PR
Searching For Anomalous Couplings
The capability of current and future measurements at low and high energy
colliders to probe for the existence of anomalous, CP conserving,
dipole moment-type couplings is examined. At present, constraints
on the universality of the tau charged and neutral current interactions as well
as the shape of the energy spectrum provide the strongest
bounds on such anomalous couplings. The presence of these dipole moments are
shown to influence, e.g., the extraction of from
decays and can lead to apparent violations of CVC expectations.Comment: 24 pages, 9 figure
On Cavity Approximations for Graphical Models
We reformulate the Cavity Approximation (CA), a class of algorithms recently
introduced for improving the Bethe approximation estimates of marginals in
graphical models. In our new formulation, which allows for the treatment of
multivalued variables, a further generalization to factor graphs with arbitrary
order of interaction factors is explicitly carried out, and a message passing
algorithm that implements the first order correction to the Bethe approximation
is described. Furthermore we investigate an implementation of the CA for
pairwise interactions. In all cases considered we could confirm that CA[k] with
increasing provides a sequence of approximations of markedly increasing
precision. Furthermore in some cases we could also confirm the general
expectation that the approximation of order , whose computational complexity
is has an error that scales as with the size of the
system. We discuss the relation between this approach and some recent
developments in the field.Comment: Extension to factor graphs and comments on related work adde
Outcome of pregnancy in the era of highly active antiretroviral: a 10-year experience in Southern Ireland
Introduction: Since the introduction of HAART the desire to become a mother in women with HIV has become a viable option due to the drastic reduction in vertical transmission. The aim of this study was to look at the epidemiology, clinical characteristics, and safety of antiretroviral drugs and rate of vertical transmission in our cohort in the Munster region, Ireland. Methods: We retrospectively reviewed all pregnant women with HIV who attended the ID clinic from January 2002 to April 2012. Patients’ demographics, pertinent laboratory data, and pharmacy records were reviewed and statistically analysed. Results: 105 HIV-positive women, with a total of 165 pregnancies, were seen from January 2002 to April 2012 at Cork University Hospital: 46 patients were previously known to be HIV-infected at their first pregnancy and 59 were diagnosed during antenatal screening (median of 32 week gestation at diagnosis). The median age at the time of pregnancy was 32 and the HIV transmission was 90% sexual: 39 women were from Europe/Asia and 66 were African; only two women were HCV co-infected and one was HBV co-infected. Of the patients diagnosed with HIV prior to pregnancy, 13 were on treatment, all of whom had no detectable virus at the start and during pregnancy. The median CD4+ at the start of pregnancy was 490 cells/µl. The median weeks of gestation at the start of HAART was 28 before 2006 and 20 after 2006, in accordance with National Guidelines. The HAART regime used was in line with current Guidelines. 18 pregnancies ended in miscarriage before week 12 gestation and 2 pregnancies resulted in intrauterine death at 28 weeks. 145 pregnancies progressed to delivery at full term but 10 infants were born before the 37th week, with one baby born at 23 weeks: 63 had SVD and 82 underwent C-section, of whom 12 emergency C-section due to prolonged membrane rupture. Most of the C-sections were planned due to obstetric reasons. 2 infants were born HIV+: in one case the mother was a late presenter at 38 of gestation; and in other the mother had poor compliance with viral load detectable at the time of labour. The overall number of pregnancies per year has been stable over the ten years (average of 14 pregnancies per year). Conclusion: The use of cART with high level of adherence and a close clinical management during pregnancy has shown to dramatically reduce the vertical transmission of HIV in our cohort
Survival probability in diffractive Higgs production in high density QCD
In this paper, the contribution of hard processes described by the BFKL
pomeron exchange, is taken into account by calculating the first enhanced
diagram. The survival probability is estimated, using the ratio of the first
enhanced diagram and the single pomeron amplitude, taking into account all
essential pomeron loop diagrams in the toy model of Mueller. The triple pomeron
vertex is calculated explicitly in the momentum representation. This
calculation is used for estimating the survival probability, It turns out that
the survival probability is small, at . Hard pomeron re-scattering
processes contribute substantially to the survival probability.Comment: 28 pages, 7 figure
A very fast inference algorithm for finite-dimensional spin glasses: Belief Propagation on the dual lattice
Starting from a Cluster Variational Method, and inspired by the correctness
of the paramagnetic Ansatz (at high temperatures in general, and at any
temperature in the 2D Edwards-Anderson model) we propose a novel message
passing algorithm --- the Dual algorithm --- to estimate the marginal
probabilities of spin glasses on finite dimensional lattices. We show that in a
wide range of temperatures our algorithm compares very well with Monte Carlo
simulations, with the Double Loop algorithm and with exact calculation of the
ground state of 2D systems with bimodal and Gaussian interactions. Moreover it
is usually 100 times faster than other provably convergent methods, as the
Double Loop algorithm.Comment: 23 pages, 12 figures. v2: improved introductio
Pair of Heavy-Exotic-Quarks at LHC
We study the production and signatures of heavy exotic quarks pairs at LHC in
the framework of the vector singlet model (VSM), vector doublet model (VDM) and
fermion-mirror-fermion (FMF) model. The pair production cross sections for the
electroweak and strong sector are computed.Comment: 7 pages, 6 figures. accept at Int. Jour. of Mod. Phy
The Production of Associated With Photons or Jets as a Probe of New Gauge Boson Couplings
We examine the production of a new gauge boson in association with
photons or jets at future hadron supercolliders as a probe of its couplings to
fermions. Associated jet production is found to be rather insensitive to these
couplings and suffers from large uncertainties as well as substantial
backgrounds. On the other hand, the ratio of rates for associated photon
production to that of conventional production has a rather clean signature
(once appropriate cuts are made), and is found to be quite sensitive to the
choice of extended electroweak model, while being simultaneously insensitive to
structure function uncertainties and QCD corrections. Rates at both the SSC and
LHC are significant for masses in the 1 TeV range.Comment: 14pp, 6 figs(not included), LaTex, ANL-HEP-PR-92-5
Fast nucleon emission as a probe of the isospin momentum dependence
In this article we investigate the structure of the non-local part of the
symmetry term, that leads to a splitting of the effective masses of protons and
neutrons in asymmetric matter. Based on microscopic transport simulations we
suggest some rather sensitive observables in collisions of neutron-rich
(unstable) ions at intermediate () energies. In particular we focus the
attention on pre-equilibrium nucleon emissions. We discuss interesting
correlations between the N/Z content of the fast emitted particles and their
rapidity or transverse momentum, that show a nice dependence on the
prescription used for the effective mass splitting.Comment: 5 pages, 6 figures, revtex
- …