Kei-ichi Nagai

Many flavor QCD as exploration of the walking behavior with the approximate IR fixed point

Computing Research Center, High Energy Accelerator Research Organization (KEK), Tsukuba,305-0801, JapanWe present the first report of the LatKMI collaboration on the the lattice QCD simulation per-formed at the KMI computer, “ϕ”, for the cases of 4 flavors and 8 flavors, the latter being ex-pected to be a candidate for the walking technicolor having an approximate scale invariance nearthe infrared fixed point. The simulation was carried out base d on the highly improved staggeredquark (HISQ) action. In this proceedings,we report preliminaryresults on the spectrum, analyzedthrough the chiral perturbation theory and the finite-size hyperscaling. We observe qualitativelydifferent behavior of the 8-flavor case in contrast to the 4-flavor case which shows clear indicationof the hadronic phase as in the usual QCD.The XXIX International Symposium on Lattice Field Theory - Lattice 2011July 10-16, 2011Squaw Valley, Lake Tahoe, California

Exploring walking behavior in SU(3) gauge theory with 4 and 8 HISQ quarks

Yasumichi Aokia, Tatsumi Aoyamaa, Masafumi Kurachia, Toshihide Maskawaa, Kei-ichi Nagai∗ a, Hiroshi Ohkia, Akihiro Shibatab, Koichi Yamawakia and Takeshi Yamazakia LatKMI Collaboration aKobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University, Nagoya, 464-8602, Japan bComputing Research Center, High Energy Accelerator Research Organization (KEK), Tsukuba, 305-0801, Japan E-mail: keiichi.nagai@kmi.nagoya-u.ac.jp

Flavor-singlet spectrum in multi-flavor QCD

Studying SU(3) gauge theories with increasing number of light fermions is relevant both for understanding the strong dynamics of QCD and for constructing strongly interacting extensions of the Standard Model (e.g. UV completions of composite Higgs models). In order to contrast these many-flavors strongly interacting theories with QCD, we study the flavor-singlet spectrum as an interesting probe. In fact, some composite Higgs models require the Higgs boson to be the lightest flavor-singlet scalar in the spectrum of a strongly interacting new sector with a well defined hierarchy with the rest of the states. Moreover, introducing many light flavors at fixed number of colors can influence the dynamics of the lightest flavor-singlet pseudoscalar. We present the on-going study of these flavor-singlet channels using multiple interpolating operators on high-statistics ensembles generated by the LatKMI collaboration and we compare results with available data obtained by the Lattice Strong Dynamics collaboration. For the theory with 8 flavors, the two collaborations have generated configurations that complement each others with the aim to tackle the massless limit using the largest possible volumes.

Walking signals in eight-flavor QCD on the lattice

We investigate walking signals of Nf = 8 QCD through the meson spectrum, using the HISQ action. Our data for Nf = 8 QCD are consistent with chiral perturbation theory (ChPT) in their chiral extrapolations, hence with the theory exhibiting spontaneous chiral symmetry breaking. Remarkably, while the Nf = 8 data near the chiral limit are well described by the ChPT, those for the relatively large fermion bare mass mf away from the chiral limit actually exhibit a finite-size hyperscaling relation, suggesting a large anomalous dimension g m � 1. This implies that there exists a remnant of the infrared conformality, and suggests that a typical “one-family technicolor model, as modeled by Nf = 8 QCD, can be a walking technicolor theory.

Lattice simulation of SU(2) gauge theory with chirally symmetric fermions

We numerically study the SU(2) gauge theory with two dynamical flavors of the domain-wall fermions in fundamental representation. The meson spectra and the residual mass are measured on three lattice volumes and at two values of gauge coupling so as to investigate the finite volume effect. On generated configurations, eigenvalues of the overlap fermion operator are determined and compared to the random matrix theory. To quantify the effect of violation of the exact chiral symmetry, we measure the correlation between the eigenvectors of the domain-wall and the overlap operators.

The KMI Lattice Project — Exploring for Technicolor from QCD

It is well known that the SU(3) gauge theory with the fundamental 16-flavor fermion is governed by a nontrivial infrared fixed point in the 2-loop perturbation theory, while the theory has not been well investigated by non-perturbative lattice simulations. We investigate properties of 16-flavor QCD by lattice simulation with highly improved action setup(HISQ/tree) at two lattice spacings. We present preliminary results for the mass of the lightest pseudoscalar meson, and its decay constant at non-zero fermion mass. We discuss the finitemass and finite-volume scaling of the quantities, the mass anomalous dimension extracted from the scaling, and comparison of the anomalous dimension with the perturbation theory.

Schwinger-Dyson Study for Walking/Conformal Dynamics with IR Cutoffs

Motivated by recent progress on many flavor QCD on a lattice, we investigate conformal/walking dynamics by using Schwinger-Dyson (SD) equation within an improved ladder approximation for two-loop running coupling. By numerically solving the SD equation, we obtain a pole mass

SU(2) gauge theory with domain-wall fermions in fundamental and adjoint representations

m_{p}

KMI project on many flavor QCD with N_f=12 and 16

, pion decay constant

Lattice Study of SU(3) Gauge Theory with Four Fundamental Fermions

f_{pi}