A lattice study of a chirally invariant Higgs–Yukawa model including a higher dimensional Φ6 -term

We discuss the non-thermal phase structure of a chirally invariant Higgs–Yukawa model on the lattice in the presence of a higher dimensional Φ6 -term. For the exploration of the phase diagram we use analytical, lattice perturbative calculations of the constraint effective potential as well as numerical simulations. We also present first results of the effects of the Φ6 -term on the lower Higgs boson mass bounds

Non-perturbative test of the Witten-Veneziano formula from lattice QCD

We compute both sides of the Witten-Veneziano formula using lattice techniques. For the one side we perform dedicated quenched simulations and use the spectral projector method to determine the topological susceptibility in the pure Yang-Mills theory. The other side we determine in lattice QCD with N f = 2 + 1 + 1 dynamical Wilson twisted mass fermions including for the first time also the flavour singlet decay constant. The Witten-Veneziano formula represents a leading order expression in the framework of chiral perturbation theory and we also employ leading order chiral perturbation theory to relate the flavor singlet decay constant to the relevant decay constant parameters in the quark flavor basis and flavor non-singlet decay constants. After taking the continuum and the SU(2) chiral limits we compare both sides and find good agreement within uncertainties

Four-flavour leading-order hadronic contribution to the muon anomalous magnetic moment

We present a four-flavour lattice calculation of the leading-order hadronic vacuum polarisation contribution to the anomalous magnetic moment of the muon, $a_{\mu}^{\mathrm{hvp}}$ , arising from quark-connected Feynman graphs. It is based on ensembles featuring N f = 2 + 1 + 1 dynamical twisted mass fermions generated by the European Twisted Mass Collaboration (ETMC). Several light quark masses are used in order to yield a controlled extrapolation to the physical pion mass. We employ three lattice spacings to examine lattice artefacts and several different volumes to check for finite-size effects. Incorporating the complete first two generations of quarks allows for a direct comparison with phenomenological determinations of $a_{\mu}^{\mathrm{hvp}}$ . Our final result including an estimate of the systematic uncertainty $a_{\mu}^{\mathrm{hvp}}$ = 6 . 74(21)(18) · 10 −8 shows a good overall agreement with these computations

First moment of the flavour octet nucleon parton distribution function using lattice QCD

We perform a lattice computation of the flavour octet contribution to the average quark momentum in the nucleon, x μ 2 = 4 GeV 2 8 $${\left\langle x\right\rangle}_{\mu^2=4\kern0.5em {\mathrm{GeV}}^2}^{\left((8)\right.}$$ . In particular, we fully take the disconnected contributions into account in our analysis for which we use a generalization of the technique developed in [1]. We investigate systematic effects with particular emphasis on the excited states contamination. We find that in the renormalization free ratio x 3 x 8 $$\frac{{\left\langle x\right\rangle}^{(3)}}{{\left\langle x\right\rangle}^{(8)}}$$ (with 〈x〉 (3) the non-singlet moment) the excited state contributions cancel to a large extent making this ratio a promising candidate for a comparison to phenomenological analyses. Our final result for this ratio is in agreement with the phenomenological value and we find, including systematic errors, x 3 x 8 = 0.39 1 4 $$\frac{{\left\langle x\right\rangle}^{(3)}}{{\left\langle x\right\rangle}^{(8)}}=0.39(1)(4)$$