Search arXiv⌕ Search

arXiv · 0708.1295

Why rooting fails

Abstract

I explore the origins of the unphysical predictions from rooted staggered fermion algorithms. Before rooting, the exact chiral symmetry of staggered fermions is a flavored symmetry among the four "tastes." The rooting procedure averages over tastes of different chiralities. This averaging forbids the appearance of the correct 't Hooft vertex for the target theory.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Michael Creutz. 2007-11-16. Why rooting fails. https://arxiv.org/abs/0708.1295

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

Unpolarized quasi- and pseudo-distributions at one loop: gluon correlator decomposition, matching, and the region $|x|>1$

We compute one-loop unpolarized quark and gluon quasi- and pseudo-distributions in $\overline{\mathrm{MS}}$ and match them to light-cone PDFs. Decomposing the gluon correlator into six covariant form factors, we derive the $6\times6$ renormalization mixing matrix: its eigenvectors classify multiplicatively renormalizable combinations, and any lattice operator choice projects onto our results without a further loop calculation. Evaluating all Fourier transforms in $d$ dimensions, we resolve the structure of the exterior $|x|>1$ in quasi-distributions. The correlator carries a short-distance logarithm with a branch cut at $ν=0$. By the Paley-Wiener theorem, the analytic part transforms into $|x|\le1$, so the exterior is generated solely by this branch cut. At leading power, the exterior carries no independent non-perturbative physics: it is fixed by the light-cone PDF through the renormalization group. In the gluon channel, the matching kernel of Balitsky, Morris and Radyushkin differs from our $\overline{\mathrm{MS}}$ result by a finite polynomial, identical across index choices. We trace this to contracting an internal loop index over two instead of $d-2$ transverse directions, omitting an evanescent operator on the collinear pole. Using our basis, we show that the independent kernel of Yao, Ji and Zhang agrees with ours, separated from Balitsky et al. by the same polynomial. While the ratio scheme protects the momentum fraction $\langle x\rangle_g$, this kernel difference suppresses the extracted normalized second and third gluon moments by $11\%$ and $13\%$ at $α_s=0.3$, so the true $\overline{\mathrm{MS}}$ gluon is systematically harder than reported.

hep-lat↗

Equation of state of hot and dense QCD using the complex Langevin equation

We present continuum-extrapolated lattice results for the QCD equation of state at high temperatures and unprecedentedly large baryon chemical potentials. These results were obtained by performing the first complex Langevin simulations at the physical value of the pion mass. We work in a strangeness-neutral, charm-neutral, and isospin-symmetric setup and show results for the baryon density, pressure, and trace anomaly as a function of baryon chemical potential and temperature, respectively.

hep-lat↗

RG-Invariant Symmetry Ratio for QCD: A Study of $U(1)_A$ and Chiral Symmetry Restoration

We introduce a renormalization-group-invariant (RGI), scheme-independent symmetry ratio $κ_{AB}$, for the quantitative characterization of symmetry breaking in QCD. As a first application, we employ $κ_{AB}$ to investigate the relative strength of $SU(2)_L \times SU(2)_R$ chiral symmetry and $U(1)_A$ axial symmetry breaking in $N_f=2+1+1$ lattice QCD using optimal domain-wall fermions at the physical point. Our study covers three lattice spacings and twelve temperatures in the range 164--385~MeV. We examine three independent symmetry-breaking channels in the nonsinglet sector with quark-connected correlators: the $U(1)_A$-sensitive scalar--pseudoscalar channel ($κ_{PS}$), probing the $π$--$δ$ system; the $SU(2)_L \times SU(2)_R$-sensitive vector--axial-vector channel ($κ_{VA}$), probing the $ρ$--$a_1$ system; and an additional $U(1)_A$-sensitive tensor vector--axial-tensor vector channel ($κ_{TX}$), probing the $ρ_T$--$b_1$ system. At each lattice spacing we observe a clear hierarchy $κ_{PS} > κ_{VA} > κ_{TX}$. Since temperature and lattice spacing are not varied independently in the present ensembles, the lattice-spacing dependence of the hierarchy cannot be isolated, and a controlled continuum extrapolation is deferred to future work.

hep-lat↗