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Register a new userHadron-Hadron Interactions from $N_f=2+1+1$ Lattice QCD: $I=3/2$ $pi K$ Scattering Length
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In this paper we report on results for the s-wave scattering length of the $pi$-$K$ system in the $I=3/2$ channel from $N_f=2+1+1$ Lattice QCD. The calculation is based on gauge configurations generated by the European Twisted Mass Collaboration with pion masses ranging from about $230$ to $450,text{MeV}$ at three values of the lattice spacing. Our main result reads $M_{pi},a_0^{3/2,text{phys}} = -0.059(2)$. Using chiral perturbation theory we are also able to estimate $M_{pi},a_0^{1/2,text{phys}} = 0.163(3)$. The error includes statistical and systematic uncertainties, and for the latter in particular errors from the chiral and continuum extrapolations.
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We present results for the $I=2$ $pipi$ scattering length using $N_f=2+1+1$ twisted mass lattice QCD for three values of the lattice spacing and a range of pion mass values. Due to the use of Laplacian Heaviside smearing our statistical errors are reduced compared to previous lattice studies. A detailed investigation of systematic effects such as discretisation effects, volume effects, and pollution of excited and thermal states is performed. After extrapolation to the physical point using chiral perturbation theory at NLO we obtain $M_pi a_0=-0.0442(2)_mathrm{stat}(^{+4}_{-0})_mathrm{sys}$.
We present results for the interaction of two kaons at maximal isospin. The calculation is based on $N_f=2+1+1$ flavour gauge configurations generated by the European Twisted Mass Collaboration with pion masses ranging from about $230$ to $450,textrm{MeV}$ at three values of the lattice spacing. The elastic scattering length $a_0^{I=1}$ is calculated at several values of the bare strange and light quark masses. We find $M_K a_0 = -0.385(16)_{textrm{stat}} (^{+0}_{-12})_{m_s}(^{+0}_{-5})_{Z_P}(4)_{r_f}$ as the result of a combined extrapolation to the continuum and to the physical point, where the first error is statistical, and the three following are systematical. This translates to $a_0 = -0.154(6)_{textrm{stat}}(^{+0}_{-5})_{m_s} (^{+0}_{-2})_{Z_P}(2)_{r_f},textrm{fm}$.
We present an investigation of the Rho-meson from Nf=2+1+1 flavour lattice QCD. The calculation is performed based on gauge configuration ensembles produced by the ETM collaboration with three lattice spacing values and pion masses ranging from 230 MeV to 500 MeV. Applying the Luscher method phase shift curves are determined for all ensembles separately. Assuming a Breit-Wigner form, the Rho-meson mass and width are determined by a fit to these phase shift curves. Mass and width combined are then extrapolated to the chiral limit, while lattice artefacts are not detectable within our statistical uncertainties. For the Rho-meson mass extrapolated to the physical point we find good agreement with experiment. The corresponding decay width differs by about two standard deviations from the experimental value.
The $I=1$ $p$-wave and $I=2$ $s$-wave elastic $pi$-$pi$ scattering amplitudes are calculated from a first-principles lattice QCD simulation using a single ensemble of gauge field configurations with $N_{mathrm{f}} = 2+1$ dynamical flavors of anisotropic clover-improved Wilson fermions. This ensemble has a large spatial volume $V=(3.7mathrm{fm})^3$, pion mass $m_{pi} = 230mathrm{MeV}$, and spatial lattice spacing $a_s = 0.11mathrm{fm}$. Calculation of the necessary temporal correlation matrices is efficiently performed using the stochastic LapH method, while the large volume enables an improved energy resolution compared to previous work. For this single ensemble we obtain $m_{rho}/m_{pi} = 3.350(24)$, $g_{rhopipi} = 5.99(26)$, and a clear signal for the $I=2$ $s$-wave. The success of the stochastic LapH method in this proof-of-principle large-volume calculation paves the way for quantitative study of the lattice spacing effects and quark mass dependence of scattering amplitudes using state-of-the-art ensembles.
We compute various (generalized) isovector charges of the octet baryons. These include $g_A$, $g_T$ and $g_S$ as well as the unpolarized, polarized and transversity parton distribution function (PDF) momentum fractions $langle xrangle_{u^+-d^+}$, $langle xrangle_{Delta u^--Delta d^-}$ and $langle xrangle_{delta u^+-delta ^+}$. The simulations are carried out on a subset of the (isospin symmetric) $N_f=2+1$ flavour Coordinated Lattice Simulations (CLS) gauge ensembles with lattice spacings ranging from $aapprox 0.086,$fm down to $aapprox 0.050,$fm. First results on the breaking of flavour symmetry and the low energy constants $F$ and $D$ are presented. While SU(3) flavour symmetry violations are found to be sizeable for $g_A=langle 1rangle_{Delta u^+-Delta d^+}$, these are quite small for $g_T=langle 1rangle_{delta u^--delta d^-}$ and $langle xrangle_{u^+-d^+}$.
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