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 $m_{p}$, pion decay constant $f_{\pi}$, and investigate the chiral symmetry breaking and mass anomalous dimension $\gamma_{m}$ in the presence of IR cutoffs $\Lambda_{\mathrm{IR}}$. We find that the chiral symmetry breaking is suppressed \ if IR cutoff $\Lambda_{\mathrm{IR}}$ becomes larger than the critical \ value near the dynamical mass ($\Lambda_{\mathrm{IR}}$ $\simeq m_{D}$) In the conformal phase the $\gamma_{m}$ is strongly suppressed by IR cutoffs for $\Lambda _{\mathrm{IR}}$ $\simeq m_{p}$. We, then, obtain finite size hyperscaling (FSS) relation by adapting a linearized approximation for the SD equation, and examine the $\gamma_{m}$ The results offer valuable insight and suggestion for analyses in lattice gauge theories.Comment: 5 pages,2 figures; Presented at Sakata Memorial KMI Workshop on "Origin of Mass and Strong Coupling Gauge Theories" (SCGT15

Domain-wall fermions with U(1) dynamical gauge fields in (4+1)-dimensions

We carry out a numerical simulation of a domain-wall model in (4+1) dimensions, in the presence of a quenched U(1) dynamical gauge field only in an extra dimension, corresponding to the weak coupling limit of a (4-dimensional) physical gauge coupling. Our numerical data suggest that the zero mode seems absent in the symmetric phase, so that it is difficult to construct a lattice chiral gauge theory in the continuum limit.Comment: 3 pages, latex, 5 figures, Talk presented at LATTICE96(chiral gauge) by K. Naga

Lattice Gross-Neveu model with domain-wall fermions

We investigate the two-dimensional lattice Gross-Neveu model, using the domain-wall fermion formulation, as a toy model of lattice QCD. We study features of the phase diagram related to the mechanism of chiral symmetry restoration, and find that the parity-broken phase (Aoki phase) exists for finite extent in the extra dimension ($N_s$). We also find that O(a) scaling violation terms vanishes in the limit of $N_s\to\infty$.Comment: LATTICE99 (Chiral Fermions), 3 pages, 4 figure

Residual mass effects in improved domain wall fermions

In order to improve simulations with domain wall fermions (DWFs), it has been suggested to project out a number of low-lying eigenvalues of the 4-dimensional Dirac operator that generates the transfer matrix of DWF. We investigate how this projection method affects chiral properties of quenched DWF. In particular, we study the behaviour of the residual mass as a function of the size of the extra dimension.Comment: 3 pages, 2 figures, Lattice2002(chiral

Phase structure and Higgs boson mass in a Higgs-Yukawa model with a dimension-6 operator

We investigate the impact of a $\lambda_6 \varphi^6$ term included in a chirally invariant lattice Higgs-Yukawa model. Such a term could emerge from BSM physics at some larger energy scale. We map out the phase structure of the Higgs-Yukawa model with positive $\lambda_6$ and negative quartic self coupling of the scalar fields. To this end, we evaluate the constraint effective potential in lattice perturbation theory and also determine the magnetization of the model via numerical simulations which allow us to reach also non-perturbative values of the couplings. As a result, we find a complex phase structure with first and second order phase transitions identified through the magnetization. Further we analyze the effect of such a $\varphi^6$ term on the lower Higgs boson mass bound to see, whether the standard model lower mass bound can be altered.Comment: proceedings for The 32nd International Symposium on Lattice Field Theor

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

We present the report of the LatKMI collaboration on the lattice QCD simulation for the cases of 4 and 8 flavors. The Nf=8 in particular is interesting from the model-building point of view: The typical walking technicolor model with the large anomalous dimension is the so-called one-family model (Farhi-Susskind model). Thus we explore the walking behavior in LQCD with 8 HISQ quarks by comparing with the 4-flavor case (in which the chiral symmetry is spontaneously broken). We report preliminary results on the spectrum, analyzed through the chiral perturbation theory and the finite-size hyperscaling, and we discuss the availability of the Nf=8 QCD to the phenomenology.Comment: 7 pages, Proceedings of 30th International Symposium on Lattice Field Theory, June 24-29, 2012, Cairns, Australi