73 research outputs found
Isospin-0 s-wave scattering length from twisted mass lattice QCD
We present results for the isospin-0 s-wave scattering length
calculated with Osterwalder-Seiler valence quarks on Wilson twisted mass gauge
configurations. We use three ensembles with unitary (valence) pion
mass at its physical value (250MeV), at 240MeV (320MeV) and
at 330MeV (400MeV), respectively. By using the stochastic Laplacian
Heaviside quark smearing method, all quark propagation diagrams contributing to
the isospin-0 correlation function are computed with sufficient
precision. The chiral extrapolation is performed to obtain the scattering
length at the physical pion mass. Our result agrees reasonably well with various experimental measurements and
theoretical predictions. Since we only use one lattice spacing, certain
systematics uncertainties, especially those arising from unitary breaking, are
not controlled in our result.Comment: 21 pages, 5 figures, 6 table
Isovector electromagnetic form factors of the nucleon from lattice QCD and the proton radius puzzle
We present results for the isovector electromagnetic form factors of the
nucleon computed on the CLS ensembles with flavors of
-improved Wilson fermions and an -improved
vector current. The analysis includes ensembles with four lattice spacings and
pion masses ranging from 130 MeV up to 350 MeV and mainly targets the low-
region. In order to remove any bias from unsuppressed excited-state
contributions, we investigate several source-sink separations between 1.0 fm
and 1.5 fm and apply the summation method as well as explicit two-state fits.
The chiral interpolation is performed by applying covariant chiral perturbation
theory including vector mesons directly to our form factor data, thus avoiding
an auxiliary parametrization of the dependence. At the physical point, we
obtain for the nucleon
isovector magnetic moment, in good agreement with the experimental value and
for the corresponding square-radius, again in good agreement with the value
inferred from the -scattering determination [Bernauer et~al., Phys. Rev.
Lett., 105, 242001 (2010)] of the proton radius. Our estimate for the isovector
electric charge radius, , however, is in
slight tension with the larger value inferred from the aforementioned
-scattering data, while being in agreement with the value derived from the
2018 CODATA average for the proton charge radius
The Electric Dipole Form Factor of the Nucleon in Chiral Perturbation Theory to Sub-leading Order
The electric dipole form factor (EDFF) of the nucleon stemming from the QCD
theta term and from the quark color-electric dipole moments is calculated in
chiral perturbation theory to sub-leading order. This is the lowest order in
which the isoscalar EDFF receives a calculable, non-analytic contribution from
the pion cloud. In the case of the theta term, the expected lower bound on the
deuteron electric dipole moment is |d_d| > 1.4 10^(-4) \theta e fm. The
momentum dependence of the isovector EDFF is proportional to a non-derivative
time-reversal-violating pion-nucleon coupling, and the scale for momentum
variation ---appearing, in particular, in the radius of the form factor--- is
the pion mass.Comment: 14 pages, 3 figure
Intermediate window observable for the hadronic vacuum polarization contribution to the muon from O improved Wilson quarks
Following the publication of the new measurement of the anomalous magnetic moment of the muon, the discrepancy between experiment and the theory prediction from the g−2 theory initiative has increased to 4.2σ. Recent lattice QCD calculations predict values for the hadronic vacuum polarization contribution that are larger than the data-driven estimates, bringing the Standard Model prediction closer to the experimental measurement. Euclidean time windows in the time-momentum representation of the hadronic vacuum polarization contribution to the muon g−2 can help clarify the discrepancy between the phenomenological and lattice predictions.
We present our calculation of the intermediate distance window contribution using Nf=2+1 flavors of O(a) improved Wilson quarks. We employ ensembles at six lattice spacings below 0.1fm and pion masses down to the physical value. We present a detailed study of the continuum limit, using two discretizations of the vector current and two independent sets of improvement coefficients. Our result at the physical point displays a tension of 3.9σ with a recent evaluation of the intermediate window based on the data-driven method
The Nucleon Electric Dipole Form Factor From Dimension-Six Time-Reversal Violation
We calculate the electric dipole form factor of the nucleon that arises as a
low-energy manifestation of time-reversal violation in quark-gluon interactions
of effective dimension 6: the quark electric and chromoelectric dipole moments,
and the gluon chromoelectric dipole moment. We use the framework of two-flavor
chiral perturbation theory to one loop
Pion transition form factor from twisted-mass lattice QCD and the hadronic light-by-light π 0 -pole contribution to the muon g − 2
Pseudoscalar-pole contributions to the muon at the physical point
Pseudoscalar-pole diagrams are an important component of estimates of the
hadronic light-by-light (HLbL) contribution to the muon g−2. We report on our computation of the transition form factors P→γ∗γ∗ for the neutral pseudoscalar mesons P=π0
and η . The calculation is performed using twisted-mass lattice QCD with physical quark masses. On the lattice, we have access to a broad range of (space-like) photon four-momenta and therefore produce form factor data complementary to the experimentally accessible single-virtual direction, which directly leads to an estimate of the pion- and η
-pole components of the muon g−2 . For the pion, our result for the g−2 contribution in the continuum is comparable with previous lattice and data-driven determinations, with combined relative uncertainties below 10% . For the η meson, we report on a preliminary determination from a single lattice spacing
Differentiation of binding sites on reconstituted hepatic scavenger receptors using oxidized low-density lipoprotein
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