Partially quenched chiral perturbation theory and numerical simulations

Farchioni, F.; Gebert, C.; Montvay, I.; Scholz, Enno E.; Scorzato, L.

doi:10.1016/s0370-2693(03)00386-1

Cited by 18 publications

(15 citation statements)

References 23 publications

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“…On the other hand, our current data do not show the clear quark mass dependence expected from ChPT in the continuum: the chiral logarithm may appear only below m P S /m V ∼ 0.4. This result contrasts with that of the qq+q collaboration [22] based on unimproved plaquette glue and Wilson quark actions, but is not dissimilar to that of UKQCD [24].…”

Section: Discussioncontrasting

confidence: 95%

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Light hadron spectroscopy in two-flavor QCD with small sea quark masses

et al. 2004

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We extend the study of the light hadron spectrum and the quark mass in two-flavor QCD to smaller sea quark mass, corresponding to mP S /mV = 0.60-0.35. Numerical simulations are carried out using the RG-improved gauge action and the meanfield-improved clover quark action at β = 1.8 (a = 0.2 fm from ρ meson mass). We observe that the light hadron spectrum for small sea quark mass does not follow the expectation from chiral extrapolations with quadratic functions made from the region of mP S /mV = 0.80-0.55. Whereas fits with either polynomial or continuum chiral perturbation theory (ChPT) fails, the Wilson ChPT (WChPT) that includes a 2 effects associated with explicit chiral symmetry breaking successfully fits the whole data: In particular, WChPT correctly predicts the light quark mass spectrum from simulations for medium heavy quark mass, such as mP S /mV ∼ > 0.5. Reanalyzing the previous data with the use of WChPT, we find the mean up and down quark mass being smaller than the previous result from quadratic chiral extrapolation by approximately 10%, m MS ud (µ = 2 GeV) = 3.11 (17) [MeV] in the continuum limit.

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Section: Discussioncontrasting

confidence: 95%

“…We first examine the one-loop formulae from continuum ChPT, which have already been tested in [11,22]. We then attempt a fit based on WChPT including effects of O(a 2 ) chiral symmetry violation due to the Wilson term.…”

Section: Chiral Extrapolation Based On Chptmentioning

confidence: 99%

Light hadron spectroscopy in two-flavor QCD with small sea quark masses

et al. 2004

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“…The fit formulae for N f = 2 are derived starting from [6], too, as has been done, for instance, in [13]. Combined fits to a f xy and (am xy ) 2 from the two lightest ensembles with a mass cut of am avg ≤ 0.01 are shown in Fig.…”

Section: Su(2)×su(2) Chiral Fitsmentioning

confidence: 99%

Chiral Limit and Light Quark Masses in 2+1 Flavor Domain Wall QCD

Lin¹,

Scholz²

2008

Proceedings of the XXV International Symposium on Lattice Field Theory — PoS(LATTICE 2007)

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We present results for meson masses and decay constants measured on 24 3 × 64 lattices using the domain wall fermion formulation with an extension of the fifth dimension of L s = 16 for N f = 2 + 1 dynamical quark flavors. The lightest dynamical meson mass in our set-up is around 331 MeV, while partially quenched mesons reach masses as low as 250 MeV. The applicability of SU(3) × SU(3) and SU(2) × SU(2) (partially quenched) chiral perturbation theory will be compared and we quote values for the low-energy constants from both approaches. We will extract the average light quark and strange quark masses and use a non-perturbative renormalization technique (RI/MOM) to quote their physical values. The pion and kaon decay constants are determined at those values from our chiral fits and their ratio is used to obtain the CKM-matrix element |V us |. The results presented here include statistical errors only.Lattice QCD allows us to study QCD phenomenology from first principles by using Monte Carlo techniques. Recent developments in both the computer technology and numerical algorithms have made possible lattice simulations with the correct number of fermion flavors in the vacuum polarization, which are essential for establishing direct connections between lattice simulations and the underlying low-energy QCD. However, the computational cost increases dramatically as one decreases the quark masses in the simulations towards the chiral limit. As such, current lattice simulations still work with quark masses heavier than their physical values, and extrapolations are necessary to obtain meaningful physical results from the simulations with heavy quark masses.Chiral perturbation theory (χPT) is a low-energy effective theory which connects physical observables to quark masses in explicit functional forms, and is a useful tool to guide the extrapolations for the lattice QCD simulations. Since it is based on the approximate chiral symmetry of QCD, it is important to have a chiral fermion formulation on the lattice in order to make direct use of the continuum χPT for the sake of the extrapolations. The domain wall fermion (DWF) formulation is well-suited in this regard, since it preserves exact flavor symmetry, and chiral symmetry is only mildly broken. Its chiral symmetry breaking effect can be quantitatively described by a small additive mass shift called the residual mass, m res . Recent work has shown [1, 2] that, to do chiral extrapolations for domain wall fermions, the only modification to the continuum χPT is to replace the input quark mass by the sum of the input quark mass and m res , leaving the number of low energy constants unchanged, at least up to terms of O(ma) which can be viewed as next-to-next-to-leading order (NNLO). This is in contrast to the cases of Wilson fermions or staggered fermions, where, at next-to-leading order, a few new low-energy constants need to be introduced to account for the chiral symmetry (Wilson) or flavor symmetry (staggered) breaking effects.One of the challenges of chiral extrapolations...

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“…Fits of present PQ lattice data require NNLO terms [12,13,14]. Full non-analytic NNLO calculations in PQχPT are not available, so, as an intermediate step, we have determined the form of the analytic NNLO mass and decay constant corrections for charged mesons.…”

Section: Analytic Nnlo Mass and Decay Constant Correctionsmentioning

confidence: 99%

“…Fits in Ref. [13] to PQ lattice data with It is interesting to consider the contributions to the α i from the three unphysical operators. We find that these operators do contribute to the α i (in fact, to all five of them in the basis we use), i.e.…”

Section: Analytic Nnlo Mass and Decay Constant Correctionsmentioning

confidence: 99%

Unphysical operators in partially quenched QCD

Sharpe

Water²

2004

Phys. Rev. D

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We point out that the chiral Lagrangian describing pseudo-Goldstone bosons in partially quenched QCD has one more four-derivative operator than that for unquenched QCD with three flavors. The new operator can be chosen to vanish in the unquenched sector of the partially quenched theory. Its contributions begin at next-to-leading order in the chiral expansion. At this order it contributes only to unphysical scattering processes, and we work out some examples. Its contributions to pseudo-Goldstone properties begin at next-to-next-to-leading order, and we determine their form. We also determine all the zero and two derivative operators in the O(p 6 ) partially quenched chiral Lagrangian, finding three more than in unquenched QCD, and use these to give the general form of the analytic next-to-next-to-leading order contributions to the pseudo-Goldstone mass and decay constant. We discuss the general implications of such additional operators for the utility of partially quenched simulations.

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Partially quenched chiral perturbation theory and numerical simulations

Cited by 18 publications

References 23 publications

Light hadron spectroscopy in two-flavor QCD with small sea quark masses

Light hadron spectroscopy in two-flavor QCD with small sea quark masses

Chiral Limit and Light Quark Masses in 2+1 Flavor Domain Wall QCD

Unphysical operators in partially quenched QCD

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