arXiv subjects

Stephan Durr

Publications and source records attributed to Stephan Durr.

51 records · Page 3Linked to original sources

arXiv2012

The ratio m_c/m_s with Wilson fermions

We determine the quark mass ratio m_c/m_s on the lattice, using Wilson-type fermions. Configurations with N_f=2 dynamical clover-improved fermions by the QCDSF collaboration are used, which were made available through the ILDG. In the valence sector we use a sophisticated, mass-independently O(a)-improved Wilson-type action with small cut-off effects even in the charm mass region. After an extrapolation to the physical pion mass, to zero lattice spacing and to infinite box volume, we find m_c/m_s=11.27(30)(26).

hep-lat↗

arXiv2011

SU(2) chiral perturbation theory low-energy constants from staggered 2+1 flavor simulations

We measure the pion mass and decay constant on ensembles generated by the Wuppertal-Budapest Collaboration, and extract the NLO low-energy constants l_3 and l_4 of SU(2) chiral perturbation theory. The data are generated in 2+1 flavor simulations with Symanzik glue and 2-fold stout-smeared staggered fermions, with pion masses varying from 135 MeV to 400 MeV, lattice scales between 0.7 GeV and 2.0 GeV, and m_s kept at its physical value. Furthermore, by excluding the lightest mass points, we are able to test the reliability of SU(2) chPT as a tool to extrapolate towards the physical point from higher pion masses.

hep-lat↗

arXiv2011

Review of lattice results concerning low energy particle physics

We review lattice results relevant for pion and kaon physics with the aim of making them easily accessible to the particle physics community. Specifically, we review the determination of the light-quark masses, the form factor f_+(0), relevant for the semileptonic K -> pi transition at zero momentum transfer as well as the ratio f_K/f_pi of decay constants and discuss the consequences for the elements V_{us} and V_{ud} of the CKM matrix. Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of SU(2)_LxSU(2)_R and SU(3)_LxSU(3)_R Chiral Perturbation Theory and review the determination of the B_K parameter of neutral kaon mixing. We introduce quality criteria and use these when forming averages. Although subjective and imperfect, these criteria may help the reader to judge different aspects of current lattice computations. Our main results are summarized in section 1.2, but we stress the importance of the detailed discussion that underlies these results and constitutes the bulk of the present review.

hep-lat↗

arXiv2010

Scaling study for 2 HEX smeared fermions: hadron and quark masses

The goal of this study is to investigate the scaling behaviour of our 2 HEX action. For this purpose, we compute the $N_f=3$ spectrum and compare the results to our 6 EXP action. We find a large scaling window up to $\sim 0.15\,\mathrm{fm}$ along with small scaling corrections at the 2%-level and full compatibility with our previous study. As a second important observable to be tested for scaling, we chose the non-perturbatively renormalized quenched strange quark mass. Here we find a fairly flat scaling with a broad scaling range up to $\simeq 0.15\,\mathrm{fm}$ and perfect agreement with the literature.

hep-lat↗

arXiv2009

Logarithmic link smearing for full QCD

A Lie-algebra based recipe for smoothing gauge links in lattice field theory is presented, building on the matrix logarithm. With or without hypercubic nesting, this LOG/HYL smearing yields fat links which are differentiable w.r.t. the original ones. This is essential for defining UV-filtered ("fat link") fermion actions which may be simulated with a HMC-type algorithm. The effect of this smearing on the distribution of plaquettes and on the residual mass of tree-level O(a)-improved clover fermions in quenched QCD is studied.

hep-lat↗

arXiv2008

Heavy-strange meson decay constants in the continuum limit of quenched QCD

We improve a previous quenched result for heavy-light pseudoscalar meson decay constants with the light quark taken to be the strange quark. A finer lattice resolution (a ~ 0.05 fm) in the continuum limit extrapolation of the data computed in the static approximation is included. We also give further details concerning the techniques used in order to keep the statistical and systematic errors at large lattice sizes L/a under control. Our final result, obtained by combining these data with determinations of the decay constant for pseudoscalar mesons around the D_s, follows nicely the qualitative expectation of the 1/m-expansion with a (relative) 1/m-term of about -0.5 GeV/m_PS. At the physical b-quark mass we obtain F_{B_s} = 193(7) MeV, where all errors apart from the quenched approximation are included.

hep-lat↗

arXiv2007

Rationale for UV-filtered clover fermions

We study the contributions Sigma_0 and Sigma_1, proportional to a^0 and a^1, to the fermion self-energy in Wilson's formulation of lattice QCD with UV-filtering in the fermion action. We derive results for m_{crit} and the renormalization factors Z_S, Z_P, Z_V, Z_A to 1-loop order in perturbation theory for several filtering recipes (APE, HYP, EXP, HEX), both with and without a clover term. The perturbative series is much better behaved with filtering, in particular tadpole resummation proves irrelevant. Our non-perturbative data for m_{crit} and Z_A/(Z_m*Z_P) show that the combination of filtering and clover improvement efficiently reduces the amount of chiral symmetry breaking -- we find residual masses am_{res}=O(10^{-2}).

hep-lat↗

arXiv2007

Precision study of the SU(3) topological susceptibility in the continuum

We determine the topological susceptibility in the SU(3) pure gauge theory. We perform a series of high-statistics lattice studies and take the combined continuum and infinite volume limit. We find chi_{top}r_0^4=0.0524(7)(6) which translates into chi_{top}^{1/4}=193(1)(8)MeV with the second error exclusively due to the intrinsic scale ambiguity.

hep-lat↗

arXiv2006

Testing UV-filtered ("fat-link") clover fermions

We investigate filtered clover fermions, built from fat gauge links, both in one-loop perturbation theory and in numerical simulations. We use a variety of filtering recipes (APE, HYP, EXP, HEX), some of which are suitable for a HMC with dynamical fermions. A generic filtering together with a (fat-link) clover term yields fermions with much reduced chiral symmetry breaking.

hep-lat↗

arXiv2006

Lattice fermions with complex mass

We present evidence in the Schwinger model that rooted staggered fermions may correctly describe the m<0 sector of a theory with an odd number of flavors. We point out that in QCD-type theories with a complex-valued quark mass every non-chiral action essentially "borrows" knowledge about the theta-transformation properties from the overlap action.

hep-lat↗

arXiv2005

Physics prospects of UV-filtered overlap quarks

Some key features of the overlap operator with a UV-filtered Wilson kernel are discussed. The first part concerns spectral properties of the underlying shifted hermitean Wilson operator and the relation to the observed speedup of the overlap construction. Next, the localization of the filtered overlap and its axial-vector renormalization constant are discussed. Finally, results of an exploratory scaling study for $m_{ud}, m_s$ and $f_π, f_K$ are presented.

hep-lat↗

arXiv2005

Continuum physics with quenched overlap fermions

We calculate $m_{ud}=(m_u+m_d)/2$, $m_s$, $f_π$ and $f_K$ in the quenched continuum limit with UV-filtered overlap fermions. We see rather small scaling violations on lattices as coarse as $a^{-1} \simeq 1 \mathrm{GeV}$ and conjecture that similar advantages would be manifest in unquenched studies.

hep-ph↗

arXiv2005

Theoretical issues with staggered fermion simulations

The legality of the "rooting trick" in dynamical staggered fermion simulations is discussed, i.e. whether the theory with the Boltzmann weight $\det^{1/4}(D_\mathrm{st})$ yields the right continuum limit. Since the problem is unsolved, pieces of evidence in favor and against are collected and examined.

hep-lat↗

arXiv2005

Finite volume effects for meson masses and decay constants

We present a detailed numerical study of finite volume effects for masses and decay constants of the octet of pseudoscalar mesons. For this analysis we use chiral perturbation theory and asymptotic formulae a la Luscher and propose an extension of the latter beyond the leading exponential term. We argue that such a formula, which is exact at the one-loop level, gives the numerically dominant part at two loops and beyond. Finally, we discuss the possibility to determine low energy constants from the finite volume dependence of masses and decay constants.

hep-lat↗

arXiv2005

Filtered overlap: speedup, locality, kernel non-normality and Z_A~1

We investigate the overlap operator with a UV filtered Wilson kernel. The filtering leads to a better localization of the operator even on coarse lattices and with the untuned choice $ρ=1$. Furthermore, the axial-vector renormalization constant $Z_A$ is much closer to 1, reducing the mismatch with perturbation theory. We show that all these features persist over a wide range of couplings and that the details of filtering prove immaterial. We investigate the properties of the kernel spectrum and find that the kernel non-normality is reduced. As a side effect we observe that for certain applications of the filtered overlap a speed-up factor of 2-4 can be achieved.

hep-lat↗