Topological susceptibility from the twisted mass Dirac operator spectrum

We present results of our computation of the topological susceptibility with N f = 2 and N f = 2 + 1 + 1 flavours of maximally twisted mass fermions, using the method of spectral projectors. We perform a detailed study of the quark mass dependence and discretization effects. We make an attempt to confront our data with chiral perturbation theory and extract the chiral condensate from the quark mass dependence of the topological susceptibility. We compare the value with the results of our direct computation from the slope of the mode number. We emphasize the role of autocorrelations and the necessity of long Monte Carlo runs to obtain results with good precision. We also show our results for the spectral projector computation of the ratio of renormalization constants Z P / Z S

Short distance singularities and automatic O(a) improvement: the cases of the chiral condensate and the topological susceptibility

Short-distance singularities in lattice correlators can modify their Symanzik expansion by leading to additional O( a ) lattice artifacts. At the example of the chiral condensate and the topological susceptibility, we show how to account for these lattice artifacts for Wilson twisted mass fermions and show that the property of automatic O( a ) improvement is preserved at maximal twist

Topological susceptibility and the sampling of field space in N f = 2 lattice QCD simulations

We present a measurement of the topological susceptibility in two flavor QCD. In this observable, large autocorrelations are present and also sizable cutoff effects have to be faced in the continuum extrapolation. Within the statistical accuracy of the computation, the result agrees with the expectation from leading order chiral perturbation theory

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

Decay constants of B-mesons from non-perturbative HQET with two light dynamical quarks

We present a computation of B-meson decay constants from lattice QCD simulations within the framework of Heavy Quark Effective Theory for the b-quark. The next-to-leading order corrections in the HQET expansion are included non-perturbatively. Based on <math altimg="si1.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>N</mi></mrow><mrow><mi mathvariant="normal">f</mi></mrow></msub><mo>=</mo><mn>2</mn></math> gauge field ensembles, covering three lattice spacings <math altimg="si2.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mi>a</mi><mo>≈</mo><mo stretchy="false">(</mo><mn>0.08</mn><mtext>–</mtext><mn>0.05</mn><mo stretchy="false">)</mo><mtext> </mtext><mtext>fm</mtext></math> and pion masses down to <math altimg="si3.gif" xmlns="http://www.w3.org/1998/Math/MathML"><mn>190</mn><mtext> </mtext><mtext>MeV</mtext></math> , a variational method for extracting hadronic matrix elements is used to keep systematic errors under control. In addition we perform a careful autocorrelation analysis in the extrapolation to the continuum and to the physical pion mass limits. Our final results read <math altimg="si4.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>f</mi></mrow><mrow><mi mathvariant="normal">B</mi></mrow></msub><mo>=</mo><mn>186</mn><mo stretchy="false">(</mo><mn>13</mn><mo stretchy="false">)</mo><mtext> </mtext><mtext>MeV</mtext></math> , <math altimg="si5.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>f</mi></mrow><mrow><msub><mrow><mi mathvariant="normal">B</mi></mrow><mrow><mi mathvariant="normal">s</mi></mrow></msub></mrow></msub><mo>=</mo><mn>224</mn><mo stretchy="false">(</mo><mn>14</mn><mo stretchy="false">)</mo><mtext> </mtext><mtext>MeV</mtext></math> and <math altimg="si6.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>f</mi></mrow><mrow><msub><mrow><mi mathvariant="normal">B</mi></mrow><mrow><mi mathvariant="normal">s</mi></mrow></msub></mrow></msub><mo stretchy="false">/</mo><msub><mrow><mi>f</mi></mrow><mrow><mi mathvariant="normal">B</mi></mrow></msub><mo>=</mo><mn>1.203</mn><mo stretchy="false">(</mo><mn>65</mn><mo stretchy="false">)</mo></math> . A comparison with other results in the literature does not reveal a dependence on the number of dynamical quarks, and effects from truncating HQET appear to be negligible

Simulation of QCD with N f = 2 + 1 flavors of non-perturbatively improved Wilson fermions

We describe a new set of gauge configurations generated within the CLS effort. These ensembles have N f = 2 + 1 flavors of non-perturbatively improved Wilson fermions in the sea with the Lüscher-Weisz action used for the gluons. Open boundary conditions in time are used to address the problem of topological freezing at small lattice spacings and twisted-mass reweighting for improved stability of the simulations. We give the bare parameters at which the ensembles have been generated and how these parameters have been chosen. Details of the algorithmic setup and its performance are presented as well as measurements of the pion and kaon masses alongside the scale parameter t 0

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 $$\frac{{\left\langle x\right\rangle}^{(3)}}{{\left\langle x\right\rangle}^{(8)}}=0.39(1)(4)$$

Review of lattice results concerning low-energy particle physics

We review lattice results related to pion, kaon D - and B -meson physics with the aim of making them easily accessible to the particle-physics community. More specifically, we report on the determination of the light-quark masses, the form factor f+(0) arising in semileptonic K→π transition at zero momentum transfer, as well as the decay-constant ratio fK/fπ of decay constants and its consequences for the CKM matrix elements Vus and Vud . Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of SU(2)L×SU(2)R and SU(3)L×SU(3)R Chiral Perturbation Theory and review the determination of the BK parameter of neutral kaon mixing. The inclusion of heavy-quark quantities significantly expands the FLAG scope with respect to the previous review. Therefore, we focus here on D - and B -meson decay constants, form factors, and mixing parameters, since these are most relevant for the determination of CKM matrix elements and the global CKM unitarity-triangle fit. In addition we review the status of lattice determinations of the strong coupling constant αs