Related papers: Constraints on Disconnected Contributions in $\pi\…
The spontaneous breaking of chiral symmetry in QCD is known to be linked to a non-zero density of eigenvalues of the massless Dirac operator near the origin. Numerical studies of two-flavour QCD now suggest that the low quark modes are…
Decoupling of heavy quarks at low energies can be described by means of an effective theory as shown by S. Weinberg in Ref. [1]. We study the decoupling of the charm quark by lattice simulations. We simulate a model, QCD with two degenerate…
An overview of Chiral Perturbation Theory calculations in the mesonic sector at the two Loop level is given. Discussed in some detail are the partially quenched case relevant for lattice QCD, the general fitting procedures and $\pi\pi$,$\pi…
Coupled-channel $\pi K$ and $\eta K$ scattering amplitudes are determined by studying the finite-volume energy spectra obtained from dynamical lattice QCD calculations. Using a large basis of interpolating operators, including both those…
Lattice QCD using fermions whose Dirac operator obeys the Ginsparg-Wilson relation, is perhaps the best known formulation of QCD with a finite cutoff. It reproduces all the low energy QCD phenomenology associated with chiral symmetry at…
The nonperturbative approach to soft high-energy hadron-hadron scattering, based on the analytic continuation of Wilson-loop correlation functions from Euclidean to Minkowskian theory, allows to investigate the asymptotic energy dependence…
We use chiral perturbation theory to investigate twisted and partially twisted boundary conditions which allow access to momenta other than integer multiples of 2pi/L on a lattice with spatial volume L^3. For K -> pi pi decays we show that…
The Schwinger model with two massive fermions is a nontrivial theory for which no analytical solution is known. The strong coupling limit of the theory allows for different semiclassical approximations to extract properties of its low-lying…
Many of the quantities of interest at the precision frontier in particle physics require a good understanding of the strong interaction at low energies. The present talk reviews the theoretical framework used in this context. In particular,…
Using lattice QCD we study the spectrum of low-lying fermion eigenmodes. According to the Banks-Casher relation, accumulation of the low-mode is responsible for the spontaneous breaking of chiral symmetry in the QCD vacuum. On the lattice…
We extract the statistical uncertainties for the pion-nucleon ($\pi N$) low energy constants (LECs) up to fourth order $\mathcal{O}(Q^4)$ in the chiral expansion of the nuclear effective Lagrangian. The LECs are optimized with respect to…
The quark-connected leading-order hadronic contributions to the running of the electromagnetic fine structure constant, $\alpha_{\rm QED}$, and the weak mixing angle, $\theta_W$, are determined by a four-flavour lattice QCD computation with…
The nonperturbative approach to soft high-energy hadron-hadron scattering, based on the analytic continuation of Euclidean Wilson-loop correlation functions, makes possible the investigation of the problem of the asymptotic energy…
Within a multi-channel formulation of $\pi\pi$ scattering, we investigate the use of the finite-volume Hamiltonian approach to resolve scattering observables from lattice QCD spectra. The asymptotic matching of the well-known L\"uscher…
We show how to compute electromagnetic polarizabilities of charged hadrons using four-point functions in lattice QCD. The low-energy behavior of Compton scattering amplitude is matched to matrix elements of current-current correlation…
We discuss how methods developed in the context of perturbation theory can be applied to the computation of lattice correlation functions, in particular in the non perturbative regime. The techniques we consider are integration-by-parts…
An exploratory study is made of the nucleon-nucleon $s$-wave scattering lengths in quenched lattice QCD with the Wilson quark action. The $\pi$-$N$ and $\pi$-$\pi$ scattering lengths are also calculated for comparison. The calculations are…
The electric ($\alpha_\pi$) and magnetic ($\beta_\pi$) Compton polarizabilities of both the charged and the neutral pion are of fundamental interest in the low-energy sector of quantum chromodynamics (QCD). Pion polarizabilities affect the…
Focusing on three-pion states with maximal isospin ($\pi^+\pi^+\pi^+$), we present the first non-perturbative determination of an energy-dependent three-hadron scattering amplitude from first-principles QCD. The calculation combines…
This talk presents a lattice study of spontaneous chiral symmetry breaking performed by the JLQCD and TWQCD collaborations with dynamical overlap fermions. Our lattice configurations are generated in a fixed topological sector. Since finite…