A
bstract
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
+
K
π
(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
→ π decays for a determination of the CKM-matrix element for which we predict |
V
us
| = 0
.
2233(5)(9) where the first error is from experiment and the second error from the lattice computation.
Domain wall QCD with near-physical pions Arthur, R.; Blum, T.; Boyle, P. A. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
05/2013, Letnik:
87, Številka:
9
Journal Article
Odprti dostop
We present physical results for a variety of light hadronic quantities obtained via a combined analysis of three 2 + 1 flavour domain wall fermion ensemble sets. In this analysis we include a third ...ensemble set that makes use of the novel Iwasaki + DSDR with a lattice size of 24sup 3 x 64 and subs = 32 to reach down to partially-quenched pion masses as low as 143(1) MeV and a unitary pion mass of 171(1) MeV, while retaining good chiral symmetry and topological tunneling. We also obtain values for the SU(2) chiral perturbation theory effective couplings, (ProQuest: Formulae and/or non-USASCII text omitted).
Observation of neutrinoless double beta decay, a lepton number violating process that has been proposed to clarify the nature of neutrino masses, has spawned an enormous world-wide experimental ...effort. Relating nuclear decay rates to high-energy, beyond the Standard Model (BSM) physics requires detailed knowledge of non-perturbative QCD effects. Using lattice QCD and taking advantage of effective field theory methods, we compute the model-independent leading-order matrix elements of short-range operators, which arise due to heavy BSM mediators, that contribute to this decay. Contributions from short-range operators may thus prove to be equally important to or even more important than those from long-range Majorana neutrino exchange.
The axial coupling of the nucleon, gA, is the strength of its coupling to the weak axial current of the standard model of particle physics, in much the same way as the electric charge is the strength ...of the coupling to the electromagnetic current. This axial coupling dictates the rate at which neutrons decay to protons, the strength of the attractive long-range force between nucleons and other features of nuclear physics. Precision tests of the standard model in nuclear environments require a quantitative understanding of nuclear physics that is rooted in quantum chromodynamics, a pillar of the standard model. The importance of g A makes it a benchmark quantity to determine theoretically - a difficult task because quantum chromodynamics is non-perturbative, precluding known analytical methods. Lattice quantum chromodynamics provides a rigorous, non-perturbative definition of quantum chromodynamics that can be implemented numerically. It has been estimated that a precision of two per cent would be possible by 2020 if two challenges are overcome: contamination of gA from excited states must be controlled in the calculations and statistical precision must be improved markedly. Here we use an unconventional method 11 inspired by the Feynman-Hellmann theorem that overcomes these challenges. We calculate a g A value of 1.271 ± 0.013, which has a precision of about one per cent.
We have performed fits of the pseudoscalar masses and decay constants, from a variety of the RBC-UKQCD Collaboration's domain wall fermion ensembles, to SU(2) partially quenched chiral perturbation ...theory at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO). We report values for nine NLO and eight linearly independent combinations of NNLO partially quenched low-energy constants, which we compare to other lattice and phenomenological determinations. We discuss the size of successive terms in the chiral expansion and use our large set of low-energy constants to make predictions for mass splittings due to QCD isospin-breaking effects and the S-wave pipi scattering lengths. We conclude that, for the range of pseudoscalar masses explored in this work, 115MeV <, ~ m sub(PS) <, ~ 430MeV, the NNLO SU(2) expansion is quite robust and can fit lattice data with percent-scale accuracy.
We report the first lattice QCD calculation of the complex kaon decay amplitude AO with physical kinematics, using a 323x64 lattice volume and a single lattice spacing a, with 1/a=1.3784(68) GeV. We ...find Re(A0)=4.66(1.00)(1.26)x10-7 GeV and lm(A0)=-1.90(1.23)(1.08)x10-11 GeV, where the first error is statistical and the second systematic. The first value is in approximate agreement with the experimental result: Re(A0)=3.3201(18)x10-7 GeV, while the second can be used to compute the direct CP-violating ratio Re( epsilon '/ epsilon )=1.38(5.15)(4.59)x10-4, which is 2.1sigma below the experimental value 16.6(2.3)x10-4. The real part of A0 is CP conserving and serves as a test of our method while the result for Re( epsilon '/ epsilon ) provides a new test of the standard model theory of CP violation, one which can be made more accurate with increasing computer capability.
We show that the running of operators which mix under renormalization can be computed fully nonperturbatively as a product of continuum step-scaling matrices. These step-scaling matrices are obtained ...by taking the "ratio" of Z matrices computed at different energies in an RI-MOM type scheme for which twisted boundary conditions are an essential ingredient. Our method allows us to relax the bounds of the Rome-Southampton window. We also explain why such a method is important in view of the light quark physics program of the RBC-UKQCD Collaborations. To illustrate our method, using n sub(functionof) = 2 + 1 domain-wall fermions, we compute the nonperturbative running matrix of four-quark operators needed in K arrow right pipi decay and neutral kaon mixing. Our results are then compared to perturbation theory.
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