arXiv subjects

Andrea Shindler

Publications and source records attributed to Andrea Shindler.

49 records · Page 3Linked to original sources

arXiv2014

Chiral Ward identities, automatic O(a) improvement and the gradient flow

Non-singlet chiral Ward identities for fermionic operators at positive flow-time are derived using standard techniques based on local chiral variations of the action and of local operators. The gradient flow formalism is applied to twisted mass fermions and it is shown that automatic O(a) improvement for Wilson twisted mass fermions at maximal twist is a property valid also at positive flow-time. A definition of the chiral condensate that is multiplicatively renormalizable and automatically O(a) improved is then derived.

hep-lat↗

arXiv2013

Computation of the chiral condensate using $N_f=2$ and $N_f=2+1+1$ dynamical flavors of twisted mass fermions

We apply the spectral projector method, recently introduced by Giusti and Lüscher, to compute the chiral condensate using $N_f=2$ and $N_f=2+1+1$ dynamical flavors of maximally twisted mass fermions. We present our results for several quark masses at three different lattice spacings which allows us to perform the chiral and continuum extrapolations. In addition we report our analysis on the $O(a)$ improvement of the chiral condensate for twisted mass fermions. We also study the effect of the dynamical strange and charm quarks by comparing our results for $N_f=2$ and $N_f=2+1+1$ dynamical flavors.

hep-lat↗

arXiv2013

Topological susceptibility from twisted mass fermions using spectral projectors

We discuss the computation of the topological susceptibility using the method of spectral projectors and dynamical twisted mass fermions. We present our analysis concerning the O(a)-improvement of the topological susceptibility and we show numerical results for Nf=2 and Nf=2+1+1 flavours, performing a study of the quark mass dependence in terms of leading order chiral perturbation theory.

hep-lat↗

arXiv2010

The continuum limit of the static-light meson spectrum

We investigate the continuum limit of the low lying static-light meson spectrum using Wilson twisted mass lattice QCD with N_f = 2 dynamical quark flavours. We consider three values of the lattice spacing a ~ 0.051 fm, 0.064 fm, 0.080 fm and various values of the pion mass in the range 280 MeV < m_PS < 640 MeV. We present results in the continuum limit for light cloud angular momentum j = 1/2, 3/2, 5/2 and for parity P = +, -. We extrapolate our results to physical quark masses, make predictions regarding the spectrum of B and B_s mesons and compare with available experimental results.

hep-lat↗

arXiv2009

Chirally rotated Schroedinger functional: non-perturbative tuning in the quenched approximation

The use of chirally rotated boundary conditions provides a formulation of the Schroedinger functional that is compatible with automatic O(a)-improvement of Wilson fermions in the bulk. The elimination of bulk O(a) terms requires the non-perturbative tuning of the critical mass and one additional boundary counterterm. We present the results of such a tuning in the quenched approximation at three values of the renormalised gauge coupling and for a range of lattice spacings.

hep-lat↗

arXiv2009

Observations on the Wilson fermions in the epsilon regime

We make several observations concerning the low quark mass region with Wilson fermions and how this is connected with the epsilon regime in the continuum. A transition from tiny cutoff effects to rather large discretization errors would take place in general with Wilson fermions if we lower the quark mass at finite lattice spacing. We argue that these two regions exhibit rather different behaviours concerning the coupling between cutoff effects and zero-modes. We interpolate between these two regimes adding to the continuum epsilon regime formulae, in the spirit of the Symanzik expansion, the relevant operators parametrising the leading cutoff effects. We compute the partition function, the chiral condensate, scalar and pseudo-scalar correlation functions. The final formulae can be used to fit lattice data to extract physical low energy constants, and to estimate systematic uncertainties coming from discretization errors. Moreover they suggest ways on how to remove these cutoff effects, the core of which are captured by the continuum zero modes.

hep-lat↗

arXiv2008

The static-light meson spectrum from twisted mass lattice QCD

We compute the static-light meson spectrum with N_f = 2 flavours of sea quarks using Wilson twisted mass lattice QCD. We consider five different values for the light quark mass corresponding to 300 MeV < m_PS < 600 MeV and we present results for angular momentum j = 1/2, j = 3/2 and j = 5/2 and for parity P = + and P = -. We extrapolate our results to physical quark masses and make predictions regarding the spectrum of B and B_s mesons.

hep-lat↗

arXiv2008

Static-light meson masses from twisted mass lattice QCD

We compute the static-light meson spectrum using two-flavor Wilson twisted mass lattice QCD. We have considered five different values for the light quark mass corresponding to 300 MeV < m_PS < 600 MeV. We have extrapolated our results, to make predictions regarding the spectrum of B and B_s mesons.

hep-lat↗

arXiv2006

Lattice QCD with light twisted quarks: first results

I report on first results of the ETMC obtained simulating lattice QCD with two degenerate flavours of Wilson twisted mass fermions, for which physical observables are automatically O(a) improved. Recent improvements of the HMC algorithm allow simulations of pseudoscalar masses below 300 MeV on volumes L^3 x 2L with L>2 fm and at values of the lattice spacing a<0.1 fm.

hep-ph↗

arXiv2005

Twisted mass lattice QCD: Recent developments and results

I review recent theoretical developments and numerical results of twisted mass QCD. I argue that, combined with an efficient algorithm, twisted mass QCD can be an attractive QCD lattice action, to perform large scale simulations at small pion masses, where a matching with chiral perturbation theory can be performed. Open issues like flavour breaking effects are also addressed.

hep-lat↗

arXiv2005

On lattice actions for static quarks

We introduce new discretizations of the action for static quarks. They achieve an exponential improvement (compared to the Eichten-Hill regularization) on the signal to noise ratio in static-light correlation functions. This is explicitly checked in a quenched simulation and it is understood quantitatively in terms of the self energy of a static quark and the lattice heavy quark potential at zero distance. We perform a set of scaling tests in the Schroedinger functional and find scaling violations in the O(a) improved theory to be rather small -- for one observable significantly smaller than with the Eichten-Hill regularization. In addition we compute the improvement coefficients of the static light axial current up to O(g_0^4) corrections and the corresponding renormalization constants non-perturbatively. The regularization dependent part of the renormalization of the b-quark mass in static approximation is also determined.

hep-lat↗

arXiv2004

Scaling test for Wilson twisted mass QCD

We present a first scaling test of twisted mass QCD with pure Wilson quarks for a twisting angle of pi/2. We have computed the vector meson mass and the pseudoscalar decay constant for different values of beta at fixed value of r_0 m_PS. The results obtained in the quenched approximation are compared with data for pure Wilson and non-perturbatively O(a) improved Wilson computations. We show that our results from Wilson twisted mass QCD show clearly reduced lattice spacing errors, consistent with O(a) improvement and without the need of any improvement terms added. These results thus provide numerical evidence of the prediction in ref. [1].

hep-lat↗

arXiv1999

Renormalization constants of local operators within the Schrödinger functional scheme

We define, within the Schrödinger functional (SF) scheme, the matrix elements of the twist-2 operators corresponding to the first two moments of non-singlet parton density, and the first moment of singlet parton densities. We perform a lattice one-loop calculation that fixes the relation between the SF scheme and other common schemes and shows the main source of lattice artefacts. Few remarks on the improvement case are added.

hep-lat↗