2,943 research outputs found
The Decay Amplitude from Lattice QCD
We report on the first realistic \emph{ab initio} calculation of a hadronic
weak decay, that of the amplitude for a kaon to decay into two \pi-mesons
with isospin 2. We find Re in good agreement with the
experimental result and for the hitherto unknown imaginary part we find
{Im}. Moreover combining our result for
Im\, with experimental values of Re\,, Re\, and
, we obtain the following value for the unknown ratio
Im\,/Re\, within the Standard Model:
.
One consequence of these results is that the contribution from Im\, to the
direct CP violation parameter (the so-called Electroweak
Penguin, EWP, contribution) is Re. We
explain why this calculation of represents a major milestone for lattice
QCD and discuss the exciting prospects for a full quantitative understanding of
CP-violation in kaon decays.Comment: 5 pages, 1 figur
A mixed Finite Element formulation for incompressibility using linear displacement and pressure interpolations
In this work shall be presented a stabilized finite element method to deal with incompressibility
in solid mechanics. A mixed formulation involving pressure and displacement fields
is used and a continuous linear interpolation is considered for both fields. To overcome
the Ladyzhenskaya-Babuska-Brezzi condition, a stabilization technique based on the orthogonal
sub-grid scale method is introduced. The main advantage of the method is the
possibility of using linear triangular finite elements, which are easy to generate for real
industrial applications. Results are compared with several improved formulations, as the
enhanced assumed strain method (EAS) and the Q1P0-formulation, in nearly incompressible
problems and in the context of linear elasticity and J2-plasticity
Standard-model prediction for direct CP violation in decay
We report the first lattice QCD calculation of the complex kaon decay
amplitude with physical kinematics, using a lattice
volume and a single lattice spacing , with GeV. We find
Re GeV and Im GeV, where the first error is statistical
and the second systematic. The first value is in approximate agreement with the
experimental result: Re GeV while the second
can be used to compute the direct CP violating ratio
Re, which is
below the experimental value . The real
part of is CP conserving and serves as a test of our method while the
result for Re provides a new test of the
standard-model theory of CP violation, one which can be made more accurate with
increasing computer capability.Comment: 9 pages, 3 figures. Updated to match published versio
The kaon semileptonic form factor in Nf=2+1 domain wall lattice QCD with physical light quark masses
We present the first calculation of the kaon semileptonic form factor with
sea and valence quark masses tuned to their physical values in the continuum
limit of 2+1 flavour domain wall lattice QCD. We analyse a comprehensive set of
simulations at the phenomenologically convenient point of zero momentum
transfer in large physical volumes and for two different values of the lattice
spacing. Our prediction for the form factor is f+(0)=0.9685(34)(14) where the
first error is statistical and the second error systematic. This result can be
combined with experimental measurements of K->pi decays for a determination of
the CKM-matrix element for which we predict |Vus|=0.2233(5)(9) where the first
error is from experiment and the second error from the lattice computation.Comment: 21 pages, 7 figures, 6 table
Curvas de dessorção e calor latente de vaporização para as sementes de milho pipoca (Zea mays).
O objetivo deste trabalho foi determinar as curvas de umidade de equilibrio higroscopico e o calor latente de vaporizacao para as sementes de milho pipoca (Zea mays). O teor de umidade inicial das sementes era 23% b.u. As sementes foram submetidas e dessorcao, sob diversas condicoes de temperatura (20, 30, 40 e 50oC) e umidade relativa do ar (30, 40, 50, 60, 70, 80 e 90%) com tres repeticoes, ate atingirem a umidade de equilibrio. A temperatura e a umidade relativa do ar foram controladas por meio de uma unidade condicionadora de ar "Aminco-Air". Os seguintes modelos matematicos foram ajustados aos dados experimentais. Henderson, Henderson modificado, Chang-Pfost, Copace e Sigma-Copace; as constantes dessas equacoes foram por regressao, enquanto o calor latente de vaporizacao foi calculado utilizando-se a equacao de Henderson modificada, estimando-se uma equacao empirica para calcular o calor latente de vaporizacao para o milho pipoca, em funcao da temperatura e do teor de umidade do grao. De acordo com os resultados obtidos concluiu-se que as equacoes de Copace e Sigma-Copace foram as que melhor se ajustaram aos dados experimentais, em todas as faixas estudadas de temperatura e umidade relativa do ar, podendo ser utilizadas para se calcular a umidade de equilibrio das sementes de milho pipoca. A equacao empirica determinada para calcular o calor latente de vaporizacao da agua dos graos do milho pipoca mostrou-se adequada
Continuum Limit of from 2+1 Flavor Domain Wall QCD
We determine the neutral kaon mixing matrix element in the continuum
limit with 2+1 flavors of domain wall fermions, using the Iwasaki gauge action
at two different lattice spacings. These lattice fermions have near exact
chiral symmetry and therefore avoid artificial lattice operator mixing.
We introduce a significant improvement to the conventional NPR method in
which the bare matrix elements are renormalized non-perturbatively in the
RI-MOM scheme and are then converted into the MSbar scheme using continuum
perturbation theory. In addition to RI-MOM, we introduce and implement four
non-exceptional intermediate momentum schemes that suppress infrared
non-perturbative uncertainties in the renormalization procedure. We compute the
conversion factors relating the matrix elements in this family of RI-SMOM
schemes and MSbar at one-loop order. Comparison of the results obtained using
these different intermediate schemes allows for a more reliable estimate of the
unknown higher-order contributions and hence for a correspondingly more robust
estimate of the systematic error. We also apply a recently proposed approach in
which twisted boundary conditions are used to control the Symanzik expansion
for off-shell vertex functions leading to a better control of the
renormalization in the continuum limit.
We control chiral extrapolation errors by considering both the NLO SU(2)
chiral effective theory, and an analytic mass expansion. We obtain
B_K^{\msbar}(3 GeV) = 0.529(5)_{stat}(15)_\chi(2)_{FV}(11)_{NPR}. This
corresponds to . Adding
all sources of error in quadrature we obtain , with an overall combined error of 3.6%.Comment: 65 page
The Kaon B-parameter from Quenched Domain-Wall QCD
We present numerical results for the kaon B-parameter, B_K, determined in the
quenched approximation of lattice QCD. Our simulations are performed using
domain-wall fermions and the renormalization group improved, DBW2 gauge action
which combine to give quarks with good chiral symmetry at finite lattice
spacing. Operators are renormalized non-perturbatively using the RI/MOM scheme.
We study scaling by performing the simulation on two different lattices with
a^{-1} = 1.982(30) and 2.914(54) GeV. We combine this quenched scaling study
with an earlier calculation of B_K using two flavors of dynamical, domain-wall
quarks at a single lattice spacing to obtain
B_K(MS,NDR,mu=2GeV)=0.563(21)(39)(30), were the first error is statistical, the
second systematic (without quenching errors) and the third estimates the error
due to quenching.Comment: 77 pages, 44 figures, to be published in Phys. Rev.
- …