378 research outputs found
Precision computation of the kaon bag parameter
Indirect CP violation in K \rightarrow {\pi}{\pi} decays plays a central role
in constraining the flavor structure of the Standard Model (SM) and in the
search for new physics. For many years the leading uncertainty in the SM
prediction of this phenomenon was the one associated with the nonperturbative
strong interaction dynamics in this process. Here we present a fully controlled
lattice QCD calculation of these effects, which are described by the neutral
kaon mixing parameter B_K . We use a two step HEX smeared clover-improved
Wilson action, with four lattice spacings from a\approx0.054 fm to
a\approx0.093 fm and pion masses at and even below the physical value.
Nonperturbative renormalization is performed in the RI-MOM scheme, where we
find that operator mixing induced by chiral symmetry breaking is very small.
Using fully nonperturbative continuum running, we obtain our main result
B_K^{RI}(3.5GeV)=0.531(6)_{stat}(2)_{sys}. A perturbative 2-loop conversion
yields B_K^{MSbar-NDR}(2GeV)=0.564(6)_{stat}(3)_{sys}(6)_{PT}, which is in good
agreement with current results from fits to experimental data.Comment: 10 pages, 7 figures. v2: Added one reference and one figure, replaced
2 figures for better readability and updated ensembles, conclusions
unchanged. Final, published versio
Full QED+QCD Low-Energy Constants through Reweighting
The effect of sea quark electromagnetic charge on meson masses is
investigated, and first results for full QED+QCD low-energy constants are
presented. The electromagnetic charge for sea quarks is incorporated in
quenched QED+full QCD lattice simulations by a reweighting method. The
reweighting factor, which connects quenched and unquenched QED, is estimated
using a stochastic method on 2+1 flavor dynamical domain-wall quark ensembles.Comment: 5 pages, 9 figures, REVTeX 4.1, v2: published versio
Universal Fluctuations of the Danube Water Level: a Link with Turbulence, Criticality and Company Growth
A global quantity, regardless of its precise nature, will often fluctuate
according to a Gaussian limit distribution. However, in highly correlated
systems, other limit distributions are possible. We have previously calculated
one such distribution and have argued that this function should apply
specifically, and in many instances, to global quantities that define a steady
state. Here we demonstrate, for the first time, the relevance of this
prediction to natural phenomena. The river level fluctuations of the Danube are
observed to obey our prediction, which immediately establishes a generic
statistical connection between turbulence, criticality and company growth
statistics.Comment: 5 pages, 1 figur
Electromagnetic corrections to light hadron masses
At the precision reached in current lattice QCD calculations, electromagnetic
effects are becoming numerically relevant. We will present preliminary results
for electromagnetic corrections to light hadron masses, based on simulations in
which a degree of freedom is superimposed on QCD
configurations from the BMW collaboration.Comment: 7 pages, 2 figures, The XXVIII International Symposium on Lattice
Field Theory, June 14-19,2010, Villasimius, Sardinia Ital
Prospects for a lattice calculation of the rare decay
We present a strategy for calculating the rare decay of a
baryon to a proton and di-lepton pair using lattice QCD. To determine
this observable one needs to numerically evaluate baryonic two-, three-, and
four-point correlation functions related to the target process. In particular,
the four-point function arises from the insertion of incoming and outgoing
baryons, together with a weak Hamiltonian mediating the transition
and an electromagnetic current creating the outgoing leptons. As is described
in previous work in other contexts, this four-point function has a highly
non-trivial relation to the physical observable, due to nucleon and
nucleon-pion intermediate states. These lead to growing Euclidean time
dependence and, in the case of the nucleon-pion states, to power-like volume
effects. We discuss how to treat these issues in the context of the
decay and, in particular, detail the
relation between the finite-volume estimator and the physical, complex-valued
amplitude. In doing so, we also make connections between various approaches in
the literature
Electromagnetic finite-size effects to the hadronic vacuum polarization
In order to reduce the current hadronic uncertainties in the theory
prediction for the anomalous magnetic moment of the muon, lattice calculations
need to reach sub-percent accuracy on the hadronic-vacuum-polarization
contribution. This requires the inclusion of
electromagnetic corrections. The inclusion of electromagnetic interactions in
lattice simulations is known to generate potentially large finite-size effects
suppressed only by powers of the inverse spatial extent. In this paper we
derive an analytic expression for the finite-volume
corrections to the two-pion contribution to the hadronic vacuum polarization at
next-to-leading order in the electromagnetic coupling in scalar QED. The
leading term is found to be of order where is the spatial extent.
A term is absent since the current is neutral and a photon far away
thus sees no charge and we show that this result is universal. Our analytical
results agree with results from the numerical evaluation of loop integrals as
well as simulations of lattice scalar gauge theory with stochastically
generated photon fields. In the latter case the agreement is up to
exponentially suppressed finite-volume effects. For completeness we also
calculate the hadronic vacuum polarization in infinite volume using a basis of
2-loop master integrals.Comment: 42 pages, 11 figure
First exploratory calculation of the long-distance contributions to the rare kaon decays <i>K</i> →π ℓ<sup>+</sup>ℓ<sup>-</sup>
The rare decays of a kaon into a pion and a charged lepton/antilepton pair
proceed via a flavour changing neutral current and therefore may only be
induced beyond tree level in the Standard Model. This natural suppression makes
these decays sensitive to the effects of potential New Physics. The CP
conserving decay channels however are dominated by a
single photon exchange; this involves a sizeable long-distance hadronic
contribution which represents the current major source of theoretical
uncertainty. Here we outline our methodology for the computation of the
long-distance contributions to these rare decay amplitudes using lattice QCD
and present the numerical results of the first exploratory studies of these
decays in which all but the disconnected diagrams are evaluated. The domain
wall fermion ensembles of the RBC and UKQCD collaborations are used, with a
pion mass of and a kaon mass of . In particular we determine the form factor, , of the
decay from the lattice at small values of
, obtaining for the
three values of respectively.Comment: 40 pages, 14 figures, 4 table
Statistics of extremal intensities for Gaussian interfaces
The extremal Fourier intensities are studied for stationary
Edwards-Wilkinson-type, Gaussian, interfaces with power-law dispersion. We
calculate the probability distribution of the maximal intensity and find that,
generically, it does not coincide with the distribution of the integrated power
spectrum (i.e. roughness of the surface), nor does it obey any of the known
extreme statistics limit distributions. The Fisher-Tippett-Gumbel limit
distribution is, however, recovered in three cases: (i) in the non-dispersive
(white noise) limit, (ii) for high dimensions, and (iii) when only
short-wavelength modes are kept. In the last two cases the limit distribution
emerges in novel scenarios.Comment: 15 pages, including 7 ps figure
Domain wall QCD with physical quark masses
We present results for several light hadronic quantities (, ,
, , , , ) obtained from simulations of 2+1
flavor domain wall lattice QCD with large physical volumes and nearly-physical
pion masses at two lattice spacings. We perform a short, O(3)%, extrapolation
in pion mass to the physical values by combining our new data in a simultaneous
chiral/continuum `global fit' with a number of other ensembles with heavier
pion masses. We use the physical values of , and to
determine the two quark masses and the scale - all other quantities are outputs
from our simulations. We obtain results with sub-percent statistical errors and
negligible chiral and finite-volume systematics for these light hadronic
quantities, including: = 130.2(9) MeV; = 155.5(8) MeV; the
average up/down quark mass and strange quark mass in the scheme
at 3 GeV, 2.997(49) and 81.64(1.17) MeV respectively; and the neutral kaon
mixing parameter, , in the RGI scheme, 0.750(15) and the
scheme at 3 GeV, 0.530(11).Comment: 131 pages, 30 figures. Updated to match published versio
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