7,773 research outputs found
Measuring the Higgs Branching Fraction into two Photons at Future Linear \ee Colliders
We examine the prospects for measuring the \gaga branching fraction of a
Standard Model-like Higgs boson with a mass of 120 GeV at the future TESLA
linear \ee collider, assuming an integrated luminosity of 1 ab and
center-of-mass energies of 350 GeV and 500 GeV. The Higgs boson is produced in
association with a fermion pair via the Higgsstrahlung process \ee ,
with \qq or \nn, or the WW fusion reaction . A relative uncertainty on BF(\hgg) of~16% can be achieved in
unpolarized \ee collisions at =~500 GeV, while for =~350
GeV the expected precision is slightly poorer. With appropriate initial state
polarizations BF(\hgg)/BF(\hgg) can be improved to 10%. If this
measurement is combined with the expected error for the total Higgs width, a
precision of 10% on the \gaga Higgs boson partial width appears feasible.Comment: 14 pages, 5 figure
Hidden Grassmann structure in the XXZ model V: sine-Gordon model
We study one-point functions of the sine-Gordon model on a cylinder. Our
approach is based on a fermionic description of the space of descendent fields,
developed in our previous works for conformal field theory and the sine-Gordon
model on the plane. In the present paper we make an essential addition by
giving a connection between various primary fields in terms of yet another kind
of fermions. The one-point functions of primary fields and descendants are
expressed in terms of a single function defined via the data from the
thermodynamic Bethe Ansatz equations.Comment: 36 pages. Some corrections are done in latest version, especially in
the subsection 10.
Brain natriuretic peptide and NT-proBNP levels reflect pulmonary artery systolic pressure in trekkers at high altitude.
Our objective was to evaluate the utility of the natriuretic peptides BNP (brain natriuretic peptide) and NT-proBNP as markers of pulmonary artery systolic pressure (PASP) in trekkers ascending to high altitude (HA). 20 participants had BNP and NT-proBNP assayed and simultaneous echocardiographic assessment of PASP performed during a trek to 5150 m. PASP increased significantly (p=0.006) with ascent from 24+/-4 to 39+/-11 mm Hg at 5150 m. At 5150 m those with a PASP>/=40 mm Hg (n=8) (versus those with PASP/=400 pg/ml) rise in NT-proBNP at 5150 m (n=4) PASP was significantly higher: 45.9+/-7.5 vs. 32.2+/-6.2 mm Hg (p=0.015). BNP and NT-proBNP may reflect elevated PASP, a central feature of high altitude pulmonary oedema, at HA
Thermodynamics and short-range correlations of the XXZ chain close to its triple point
The XXZ quantum spin chain has a triple point in its ground state
- phase diagram. This first order critical point is located at the
joint end point of the two second order phase transition lines marking the
transition from the gapless phase to the fully polarized phase and to the
N\'eel ordered phase, respectively. We explore the magnetization and the
short-range correlation functions in its vicinity using the exact solution of
the model. In the critical regime above the triple point we observe a strong
variation of all physical quantities on a low energy scale of order
induced by the transversal quantum fluctuations. We interpret this phenomenon
starting from a strong-coupling perturbation theory about the highly degenerate
ground state of the Ising chain at the triple point. From the perturbation
theory we identify the relevant scaling of the magnetic field and of the
temperature. Applying the scaling to the exact solutions we obtain explicit
formulae for the magnetization and short-range correlation functions at low
temperatures.Comment: 18 pages, 7 figures, v2: figures rearranged, v3: a typo correcte
Neutrophil gelatinase-associated lipocalin: its response to hypoxia and association with acute mountain sickness.
Acute Mountain Sickness (AMS) is a common clinical challenge at high altitude (HA). A point-of-care biochemical marker for AMS could have widespread utility. Neutrophil gelatinase-associated lipocalin (NGAL) rises in response to renal injury, inflammation and oxidative stress. We investigated whether NGAL rises with HA and if this rise was related to AMS, hypoxia or exercise. NGAL was assayed in a cohort (n = 22) undertaking 6 hours exercise at near sea-level (SL); a cohort (n = 14) during 3 hours of normobaric hypoxia (FiO2 11.6%) and on two trekking expeditions (n = 52) to over 5000 m. NGAL did not change with exercise at SL or following normobaric hypoxia. During the trekking expeditions NGAL levels (ng/ml, mean ± sd, range) rose significantly (P < 0.001) from 68 ± 14 (60-102) at 1300 m to 183 ± 107 (65-519); 143 ± 66 (60-315) and 150 ± 71 (60-357) at 3400 m, 4270 m and 5150 m respectively. At 5150 m there was a significant difference in NGAL between those with severe AMS (n = 7), mild AMS (n = 16) or no AMS (n = 23): 201 ± 34 versus 171 ± 19 versus 124 ± 12 respectively (P = 0.009 for severe versus no AMS; P = 0.026 for mild versus no AMS). In summary, NGAL rises in response to prolonged hypobaric hypoxia and demonstrates a relationship to the presence and severity of AMS
Short-distance thermal correlations in the XXZ chain
Recent studies have revealed much of the mathematical structure of the static
correlation functions of the XXZ chain. Here we use the results of those
studies in order to work out explicit examples of short-distance correlation
functions in the infinite chain. We compute two-point functions ranging over 2,
3 and 4 lattice sites as functions of the temperature and the magnetic field
for various anisotropies in the massless regime . It turns
out that the new formulae are numerically efficient and allow us to obtain the
correlations functions over the full parameter range with arbitrary precision.Comment: 25 pages, 5 colored figure
Time-reversal symmetry breaking Abelian chiral spin liquid in Mott phases of three-component fermions on the triangular lattice
We provide numerical evidence in favor of spontaneous chiral symmetry
breaking and the concomitant appearance of an Abelian chiral spin liquid for
three-component fermions on the triangular lattice described by an SU(3)
symmetric Hubbard model with hopping amplitude () and on-site
interaction . This chiral phase is stabilized in the Mott phase with one
particle per site in the presence of a uniform -flux per plaquette, and in
the Mott phase with two particles per site without any flux. Our approach
relies on effective spin models derived in the strong-coupling limit in powers
of for general SU and arbitrary uniform charge flux per plaquette,
which are subsequently studied using exact diagonalizations and variational
Monte Carlo simulations for , as well as exact diagonalizations of the
SU() Hubbard model on small clusters. Up to third order in , and for
the time-reversal symmetric cases (flux or ), the low-energy
description is given by the - model with Heisenberg coupling and real
ring exchange . The phase diagram in the full - parameter range
contains, apart from three already known, magnetically long-range ordered
phases, two previously unreported phases: i) a lattice nematic phase breaking
the lattice rotation symmetry and ii) a spontaneous time-reversal and parity
symmetry breaking Abelian chiral spin liquid. For the Hubbard model, an
investigation that includes higher-order itinerancy effects supports the
presence of a phase transition inside the insulating region, occurring at
[] between the
three-sublattice magnetically ordered phase at small and this Abelian
chiral spin liquid.Comment: 21 pages, 23 figure
Traces on the Sklyanin algebra and correlation functions of the eight-vertex model
We propose a conjectural formula for correlation functions of the Z-invariant
(inhomogeneous) eight-vertex model. We refer to this conjecture as Ansatz. It
states that correlation functions are linear combinations of products of three
transcendental functions, with theta functions and derivatives as coefficients.
The transcendental functions are essentially logarithmic derivatives of the
partition function per site. The coefficients are given in terms of a linear
functional on the Sklyanin algebra, which interpolates the usual trace on
finite dimensional representations. We establish the existence of the
functional and discuss the connection to the geometry of the classical limit.
We also conjecture that the Ansatz satisfies the reduced qKZ equation. As a
non-trivial example of the Ansatz, we present a new formula for the
next-nearest neighbor correlation functions.Comment: 35 pages, 2 figures, final versio
A Q-operator for the twisted XXX model
Taking the isotropic limit in a recent representation theoretic construction
of Baxter's Q-operators for the XXZ model with quasi-periodic boundary
conditions we obtain new results for the XXX model. We show that quasi-periodic
boundary conditions are needed to ensure convergence of the Q-operator
construction and derive a quantum Wronskian relation which implies two
different sets of Bethe ansatz equations, one above the other below the
"equator" of total spin zero. We discuss the limit to periodic boundary
conditions at the end and explain how this construction might be useful in the
context of correlation functions on the infinite lattice. We also identify a
special subclass of solutions to the quantum Wronskian for chains up to a
length of 10 sites and possibly higher.Comment: 19 page
Smartphone-Enabled Heart Rate Variability and Acute Mountain Sickness
INTRODUCTION: The autonomic system and sympathetic activation appears integral in the pathogenesis of acute mountain sickness (AMS) at high altitude (HA), yet a link between heart rate variability (HRV) and AMS has not been convincingly shown. In this study we investigated the utility of the smartphone-derived HRV score to predict and diagnose AMS at HA. METHODS: Twenty-one healthy adults were investigated at baseline at 1400 m and over 10 days during a trek to 5140 m. HRV was recorded using the ithlete HRV device. RESULTS: Acute mountain sickness occurred in 11 subjects (52.4%) at >2650 m. HRV inversely correlated with AMS Scores (r = -0.26; 95% CI, -0.38 to -0.13: P 5 had a sensitivity of 83% and specificity of 60% to identify severe AMS (likelihood ratio 1.9). Baseline HRV at 1400 m was not predictive of either AMS at higher altitudes. CONCLUSIONS: The ithlete HRV score can be used to help in the identification of severe AMS; however, a baseline score is not predictive of future AMS development at HA
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