104 research outputs found
Multicanonical reweighting for the QCD topological susceptibility
We introduce a reweighting technique which allows for a continuous sampling
of temperatures in a single simulation and employ it to compute the temperature
dependence of the QCD topological susceptibility at high temperatures. The
method determines the ratio of susceptibility between any two temperatures
within the explored temperature range. We find that the results from the method
agree with our previous determination and that it is competitive with but not
better than existing methods of determining the temperature derivative of the
susceptibility. The method may also be useful in exploring the temperature
dependence of other thermodynamical observables in QCD in a continuous way.Comment: 8 pages in 2-column format, including 5 figures and 2 table
Nucleon axial form factors from two-flavour Lattice QCD
We present preliminary results on the axial form factor and the
induced pseudoscalar form factor of the nucleon. A systematic
analysis of the excited-state contributions to form factors is performed on the
CLS ensemble `N6' with and lattice spacing . The relevant three-point functions were computed with
source-sink separations ranging from to $t_s \sim \
1.4 \ \text{fm}$. We observe that the form factors suffer from non-trivial
excited-state contributions at the source-sink separations available to us. It
is noted that naive plateau fits underestimate the excited-state contributions
and that the method of summed operator insertions correctly accounts for these
effects.Comment: 7 pages, 12 figures; talk presented at Lattice 2014 -- 32nd
International Symposium on Lattice Field Theory, 23-28 June, 2014, Columbia
University New York, N
SU(2) low-energy constants from mixed-action lattice QCD
An analysis of the pion mass and pion decay constant is performed using mixed-action lattice QCD calculations with domain-wall valence quarks on ensembles of rooted, staggered n(f) = 2 + 1 configurations generated by the MILC Collaboration. Calculations were performed at two lattice spacings of b approximate to 0.125 fm and b approximate to 0.09 fm, at two strange quark masses, multiple light quark masses, and a number of lattice volumes. The ratios of light quark to strange quark masses are in the range 0.1 \u3c = m(l)/m(s) \u3c = 0.6, while pion masses are in the range 235 less than or similar to m(pi) less than or similar to 680 MeV. A two-flavor chiral perturbation theory analysis of the lattice QCD calculations constrains the Gasser-Leutwyler coefficients (l) over bar (3) and (l) over bar (4) to be (l) over bar (3) = 4.04(40)((73)(55)) and (l) over bar (4) = 4.30(51)((84)(60)). All systematic effects in the calculations are explored, including those from the finite lattice space-time volume, the finite lattice spacing, and the finite fifth dimension in the domain-wall quark action. A consistency is demonstrated between a chiral perturbation theory analysis at fixed lattice spacing combined with a leading order continuum extrapolation, and the mixed-action chiral perturbation theory analysis which explicitly includes the leading order discretization effects. Chiral corrections to the pion decay constant are found to give f(pi)/f = 1.062(26)((42)(40)) where f is the decay constant in the chiral limit, and when combined with the experimental determination of f(pi) results in a value of f = 122.8(3.0((4.6)(4.8)) MeV. The most recent scale setting by the MILC Collaboration yields a postdiction of f(pi) = 128.2(3.6)((4.4)(6.0))((1.2)(3.3)) MeV at the physical pion mass. A detailed error analysis indicates that precise calculations at lighter pion masses is the single most important systematic to address to improve upon the present work
SU(2) Low-Energy Constants from Mixed-Action Lattice QCD
An analysis of the pion mass and pion decay constant is performed using
mixed-action Lattice QCD calculations with domain-wall valence quarks on
ensembles of rooted, staggered n_f = 2+1 MILC configurations. Calculations were
performed at two lattice spacings of b~0.125 fm and b~0.09 fm, at two strange
quark masses, multiple light quark masses, and a number of lattice volumes. The
ratios of light quark to strange quark masses are in the range 0.1 <= m_l / m_s
<= 0.6, while pion masses are in the range 235 < m_\pi < 680 MeV. A two-flavor
chiral perturbation theory analysis of the Lattice QCD calculations constrains
the Gasser-Leutwyler coefficients bar{l}_3 and bar{l}_4 to be bar{l}_3 =
4.04(40)(+73-55) and bar{l}_4 = 4.30(51)(+84-60). All systematic effects in the
calculations are explored, including those from the finite lattice space-time
volume, the finite lattice spacing, and the finite fifth dimension in the
domain-wall quark action. A consistency is demonstrated between a chiral
perturbation theory analysis at fixed lattice spacing combined with a leading
order continuum extrapolation, and the mixed-action chiral perturbation theory
analysis which explicitly includes the leading order discretization effects.
Chiral corrections to the pion decay constant are found to give f_\pi / f =
1.062(26)(+42-40) where f is the decay constant in the chiral limit. The most
recent scale setting by the MILC Collaboration yields a postdiction of f_\pi =
128.2(3.6)(+4.4-6.0)(+1.2-3.3) MeV at the physical pion mass.Comment: 28 pages, 9 figures; version 2 accepted for publication in PR
Suppression of excited-state effects in lattice determination of nucleon electromagnetic form factors
We study the ability of a variety of fitting techniques to extract the ground
state matrix elements of the vector current from ratios of nucleon three- and
two-point functions that contain contaminations from excited states. Extending
our high-statistics study of nucleon form factors, we are able to demonstrate
that the treatment of excited-state contributions in conjunction with
approaching the physical pion mass has a significant impact on the
-dependence of the form factors.Comment: 7 pages, 5 pdf figures; talk presented at Lattice 2014 -- 32nd
International Symposium on Lattice Field Theory, 23-28 June, 2014, Columbia
University New York, N
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
POSTAL EN TONO CYAN DE MUJER CON MANTILLA JOSEP [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201
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