Search results for "lattice [space-time]"
showing 10 items of 692 documents
Meson interactions at large $N_c$ from Lattice QCD
2019
We report on the computation of the scaling of QCD observables with the number of colours, $N_c$. For this, we use dynamical configurations with four active flavours, $N_f=4$, and values of $N_c=3-6$. We study the meson masses and decay constants, and compute the leading and subleading contributions to the Low Energy Constants (LECs) of the chiral Lagrangian. We also explore $\pi \pi$ scattering in the $I=2$ channel, and compute the $K \to \pi $ weak decay matrix elements. We comment on the relation of the latter to $K \to \pi\pi$ processes and the $\Delta I=1/2$ rule.
Hadronic light-by-light scattering amplitudes from lattice QCD versus dispersive sum rules
2017
The hadronic contribution to the eight forward amplitudes of light-by-light scattering ($\gamma^*\gamma^*\to \gamma^*\gamma^*$) is computed in lattice QCD. Via dispersive sum rules, the amplitudes are compared to a model of the $\gamma^*\gamma^*\to {\rm hadrons}$ cross sections in which the fusion process is described by hadronic resonances. Our results thus provide an important test for the model estimates of hadronic light-by-light scattering in the anomalous magnetic moment of the muon, $a_\mu^{\rm HLbL}$. Using simple parametrizations of the resonance $M\to \gamma^*\gamma^*$ transition form factors, we determine the corresponding monopole and dipole masses by performing a global fit to …
Hadronic light-by-light scattering in the anomalous magnetic moment of the muon
2018
15th International Workshop on Tau Lepton Physics, Amsterdam, The Netherlands, 24 Sep 2018 - 28 Sep 2018; SciPost physics 1, 031 (2019). doi:10.21468/SciPostPhysProc.1.031
Hadronic Contributions to the Anomalous Magnetic Moment of the Muon from Lattice QCD
2021
The Standard Model of Particle Physics describes three of the four known fundamental interactions: the strong interaction between quarks and gluons, the electromagnetic interaction, and the weak interaction. While the Standard Model is extremely successful, we know that it is not a complete description of nature. One way to search for physics beyond the Standard Model lies in the measurement of precision observables. The anomalous magnetic moment of the muon \(a_\mu \equiv \frac{1}{2}(g-2)_\mu \), quantifying the deviation of the gyromagnetic ratio from the exact value of 2 predicted by the Dirac equation, is one such precision observable. It exhibits a persistent discrepancy of 3.5 standar…
Doubly heavy baryon spectra guided by lattice QCD
2016
This paper provides results for the ground state and excited spectra of three-flavored doubly heavy baryons, $bcn$ and $bcs$. We take advantage of the spin-independent interaction recently obtained to reconcile the lattice SU(3) QCD static potential and the results of nonperturbative lattice QCD for the triply heavy baryon spectra. We show that the spin-dependent potential might be constrained on the basis of nonperturbative lattice QCD results for the spin splittings of three-flavored doubly heavy baryons. Our results may also represent a challenge for future lattice QCD work, because a smaller lattice error could help in distinguishing between different prescriptions for the spin-dependen…
Hadron structure from lattice QCD
2014
Recent progress in lattice QCD calculations of nucleon structure will be presented. Calculations of nucleon matrix elements and form factors have long been difficult to reconcile with experiment, but with advances in both methodology and computing resources, this situation is improving. Some calculations have produced agreement with experiment for key observables such as the axial charge and electromagnetic form factors, and the improved understanding of systematic errors will help to increase confidence in predictions of unmeasured quantities. The long-omitted disconnected contributions are now seeing considerable attention and some recent calculations of them will be discussed.
Spectroscopy, leptonic decays and the nature of heavy quarkonia
2008
We examine the electronic width ratios of Upsilon resonances below the BBbar threshold by means of an effective (Cornell-type) QCD potential incorporating 1/m_b corrections obtained from a prior fit to the bottomonium spectrum. From our analysis we conclude that the Upsilon(2S) and Upsilon(3S) states should belong to the strong-coupling (nonperturbative) regime while the Upsilon(1S) state should belong to the weak-coupling (perturbative) regime, in agreement with a previous study based on radiative decays.
Lattice calculations of the leading hadronic contribution to g-2
2012
We report on our ongoing project to calculate the leading hadronic contribution to the anomalous magnetic moment of the muon aHLO μ using two dynamical flavours of non-perturbatively O(a) improved Wilson fermions. In this study, we changed the vacuum polarisation tensor to a combination of local and point-split currents which significantly reduces the numerical effort. Partially twisted boundary conditions allow us to improve the momentum resolution of the vacuum polarisation tensor and therefore the determination of the leading hadronic contribution to (g− 2)μ . We also extended the range of ensembles to include a pion mass below 200MeV which allows us to check the non-trivial chiral behav…
Relativistic corrections to the static potential at O(1/m) and O(1/m^2)
2007
We investigate the relativistic corrections to the static potential, i.e. the O(1/m) potential and the O(1/m^2) velocity-dependent potentials, in SU(3) lattice gauge theory. They are important ingredients of potential nonrelativistic QCD for heavy quarkonium. Utilizing the multi-level algorithm, we obtain remarkably clean signals of these potentials up to r=0.9 fm. We observe long range nonperturbative contributions to these corrections.
QCD at non-zero temperature from the lattice
2015
I review the status of lattice QCD calculations at non-zero temperature. After summarizing what is known about the equilibrium properties of strongly interacting matter, I discuss in more detail recent results concerning the quark-mass dependence of the thermal phase transition and the status of calculations of non-equilibrium properties.