Publications (20)31.61 Total impact
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ABSTRACT: SU(3) gauge theory with eight massless flavours is believed to be walking, while the corresponding twelve and fourflavour appear IRconformal and confining respectively. Looking at the simulations performed by the LatKMI collaboration of these theories, we use the topological susceptibility as an additional probe of the IR dynamics. By drawing a comparison with SU(3) pure gauge theory, we see a dynamical quenching effect emerge at larger number of flavours, which is suggestive of emerging nearconformal and conformal behaviour.  [Show abstract] [Hide abstract]
ABSTRACT: In the search for a realistic walking technicolor model, QCD with many flavors is an attractive candidate. From the series of studies by the LatKMI collaboration, we present updated results of the scaling properties of various hadron spectra, including the (pseudo)scalar, vector, and baryon channels, for $N_f=8$ QCD analyzed with the HISQ action. By comparing these with $N_f=12$ QCD, which has properties consistent with conformality, possible signals of walking dynamics are discussed. We also present a preliminary result of the flavorsinglet pseudoscalar mass in manyflavor QCD.  [Show abstract] [Hide abstract]
ABSTRACT: As a part of the project studying large $N_f$ QCD, the LatKMI Collaboration has been investigating the SU(3) gauge theory with four fundamental fermions (fourflavor QCD). The main purpose of studying fourflavor QCD is to provide a qualitative comparison to $N_f= 8$, $12$, $16$ QCD; however, a quantitative comparison to realworld QCD is also interesting. To make such comparisons more meaningful, it is desirable to use the same kind of lattice action consistently, so that qualitative difference of different theories are less affected by artifacts of lattice discretization. Here, we adopt the highlyimproved staggered quark action with the treelevel Symanzik gauge action (HISQ/tree), which is exactly the same as the setup for our simulations for $SU(3)$ gauge theories with $N_f=8$, $12$ and $16$ fundamental fermions~\cite{Aoki:2013xza, Aoki:2012eq, Aoki:2014oma}. In the next section, we show the fermion mass dependence of $F_\pi$, $\langle\bar{\psi}\psi\rangle$, $M_\pi$, $M_\rho$, $M_N$ and their chiral extrapolations. In section 3, preliminary results of the measurement of the mass of the flavorsinglet scalar bound state will be reported.  [Show abstract] [Hide abstract]
ABSTRACT: In the search for a composite Higgs boson in walking technicolor models, many flavor QCD, in particular with $N_f=8$, is an attractive candidate, and has been found to have a composite flavorsinglet scalar as light as the pion. Based on lattice simulations of this theory with the HISQ action, we will present our preliminary results on the scalar decay constant using the fermionic bilinear operator, and on the mass of the lightest baryon state which could be a dark matter candidate. Combining these two results, implications for dark matter direct detection are also discussed.  [Show abstract] [Hide abstract]
ABSTRACT: LatKMI Collaboration discusses the topological insights in manyflavor QCD on the lattice. We explore walking/conformal/confining phase in $N_\mathrm{f}$ = 4, 8 and 12 (in particular $N_\mathrm{f}$ = 8) lattice QCD via the topological charge and susceptibility, eigenvalues and anomalous dimension. 
Article: Conformality in twelveflavour QCD
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ABSTRACT: The spectrum of twelveflavor QCD has been studied in details by the LatKMI collaboration. In this proceeding we present our updated results for the spectrum obtained with the HISQ action at two lattice spacings, several volumes and fermion masses. In particular, we emphasize the existence of a flavorsinglet scalar state parametrically light with respect to the rest of the spectrum, first reported in our paper. This feature is expected to be present for theories in the conformal window, but the lattice calculation of such a state is difficult and requires noisereduction techniques together with large statistics, in order to evaluate disconnected diagrams. Being able to provide a robust observed connection between a light flavorsinglet scalar and (near)conformality is an important step towards observing a light composite Higgs boson in walking technicolor theories on the lattice. We also show updated results for the mass anomalous dimension $\gamma_m$ obtained from various spectral quantities, including the string tension, under the assumption that the theory is inside the conformal window. 
Conference Paper: NonPerturbative Study of 16Flavor QCD
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ABSTRACT: We report the calculation of the flavorsinglet scalar in the SU(3) gauge theory with the degenerate twelve fermions in the fundamental representation using a HISQtype action at a fixed $\beta$. In order to reduce the large statistical error coming from the vacuumsubtracted disconnected correlator, we employ a noise reduction method and a large number of configurations. We observe that the flavorsinglet scalar is lighter than the pion in this theory from the calculations with the fermion bilinear and gluonic operators. This peculiar feature is considered to be due to the infrared conformality of this theory, and it is a promissing signal for a walking technicolor, where a light composite Higgs boson is expected to emerge by approximate conformal dynamics.  [Show abstract] [Hide abstract]
ABSTRACT: We measure glueball masses and the string tension in twelveflavour QCD, aiming at comparing the emerging gluonic spectrum to the mesonic one. When approaching the critical surface at zero quark mass, the hierarchy of masses in the different sectors of the spectrum gives a new handle to determine the existence of an infrared fixed point. We describe the details of our gluonic measurements and the results obtained on a large number of gauge configurations generated with the HISQ action. In particular, we focus on the scalar glueball and its mixing with a flavoursinglet fermionic state, which is lighter than the pseudoscalar (wouldbe pion) state. The results are interesting in view of a light composite Higgs boson in walking technicolor theories.  [Show abstract] [Hide abstract]
ABSTRACT: In search for a composite Higgs boson (technidilaton) in the walking technicolor, we present our preliminary results on the first observation of a light flavorsinglet scalar in a candidate theory for the walking technicolor, the Nf=8 QCD, which was found in our previous paper to have spontaneous chiral symmetry breaking together with remnants of the conformality. Based on simulations with the HISQtype action on several lattice sizes with various fermion masses, we find evidence of a flavorsinglet scalar meson with mass comparable to that of the NambuGoldstone pion in both the small fermionmass region, where chiral perturbation theory works, and the intermediate fermionmass region where the hyperscaling relation holds. We further discuss its chiral limit extrapolation in comparison with other states studied in our previous paper: the scalar has a mass much smaller than that of the vector meson, which is compared to the NambuGoldstone pion having a vanishing mass in that limit.  [Show abstract] [Hide abstract]
ABSTRACT: Based on lattice simulations using highly improved staggered quarks for twelveflavor QCD with several bare fermion masses, we observe a flavorsinglet scalar state lighter than the pion in the correlators of fermionic interpolating operators. The same state is also investigated using correlators of gluonic interpolating operators. Combined with our previous study, that showed twelveflavor QCD to be consistent with being in the conformal window, we infer that the lightness of the scalar state is due to infrared conformality. This result shed some light on the possibility of a light composite Higgs boson ("technidilaton") in walking technicolor theories.  [Show abstract] [Hide abstract]
ABSTRACT: We investigate chiral and conformal properties of the lattice QCD with eight flavors (Nf=8) through meson spectrum using the Highly Improved Staggered Quark (HISQ) action. We also compare our results with those of Nf=12 and Nf=4 which we study on the same systematics. We find that the decay constant F_pi of the pseudoscalar meson "pion" is nonzero, with its mass M_pi consistent with zero, both in the chiral limit extrapolation of the chiral perturbation theory (ChPT). We also measure other quantities which we find are in accord with the pi data results: The rho meson mass is consistent with nonzero in the chiral limit, and so is the chiral condensate, with its value neatly coinciding with that from the GellMannOakesRenner relation in the chiral limit. Thus our data for the Nf=8 QCD are consistent with the spontaneously broken chiral symmetry. Remarkably enough, while the Nf=8 data near the chiral limit are well described by the ChPT, those for the relatively large fermion bare mass m_f away from the chiral limit actually exhibit a finitesize hyperscaling relation, suggesting a large anomalous dimension gamma_m ~ 1. This implies that there exists a remnant of the infrared conformality, and suggests that a typical technicolor ("onefamily model") as modeled by the Nf=8 QCD can be a walking technicolor theory having an approximate scale invariance with large anomalous dimension gamma_m ~ 1.  [Show abstract] [Hide abstract]
ABSTRACT: The LatKMI collaboration is studying systematically the dynamical properties of N_f = 4,8,12,16 SU(3) gauge theories using lattice simulations with (HISQ) staggered fermions. Exploring the spectrum of manyflavour QCD, and its scaling near the chiral limit, is mandatory in order to establish if one of these models realises the Walking Technicolor scenario. Although lattice technologies to study the mesonic spectrum are well developed, scalar flavoursinglet states still require extra effort to be determined. In addition, gluonic observables usually require largestatistic simulations and powerful noisereduction techniques. In the following, we present useful spectroscopic methods to investigate scalar glueballs and scalar flavoursinglet mesons, together with the current status of the scalar spectrum in N_f = 12 QCD from the LatKMI collaboration.  [Show abstract] [Hide abstract]
ABSTRACT: 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 modelbuilding point of view: The typical walking technicolor model with the large anomalous dimension is the socalled onefamily model (FarhiSusskind model). Thus we explore the walking behavior in LQCD with 8 HISQ quarks by comparing with the 4flavor case (in which the chiral symmetry is spontaneously broken). We report preliminary results on the spectrum, analyzed through the chiral perturbation theory and the finitesize hyperscaling, and we discuss the availability of the Nf=8 QCD to the phenomenology.  [Show abstract] [Hide abstract]
ABSTRACT: We present our result of the manyflavor QCD. Information of the phase structure of manyflavor SU(3) gauge theory is of great interest, since the gauge theories with the walking behavior near the infrared fixed point are candidates of new physics for the origin of the dynamical electroweak symmetry breaking. We study the SU(3) gauge theories with 12 and 16 fundamental fermions. Utilizing the HISQ type action which is useful to study the continuum physics, we analyze the lattice data of the mass and the decay constant of the pseudoscalar meson and the mass of the vector meson as well at several values of lattice spacing and fermion mass. The finite size scaling test in the conformal hypothesis is also performed. Our data is consistent with the conformal scenario for Nf=12. We obtain the mass anomalous dimension $\gamma_m \sim 0.40.5$. An update of $N_f=16$ study is also shown. 
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ABSTRACT: We study infrared conformality of the twelveflavor QCD on the lattice. Utilizing the highly improved staggered quarks (HISQ) type action which is useful to study the continuum physics, we analyze the lattice data of the mass and the decay constant of a pseudoscalar meson and the mass of a vector meson as well at several values of lattice spacing and fermion mass. Our result is consistent with the conformal hypothesis for the mass anomalous dimension $\gamma_m \sim 0.40.5$. 
Article: Many flavor QCD with N_f=12 and 16
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ABSTRACT: Information of the phase structure of many flavor SU(3) gauge theory is of great interest for finding a theory which dynamically breaks the electroweak symmetry. We study the SU(3) gauge theory with fermions for $N_f=12$ and 16 in fundamental representation. Both of them, through perturbation theory, reside in the conformal phase. We try to determine the phase of each theory nonperturbatively with lattice simulation and to find the characteristic behavior of the physical quantities in the phase. HISQ type staggered fermions are used to reduce the discretization error which could compromise the behavior of the physical quantity to determine the phase structure at nonzero lattice spacings. Spectral quantities such as bound state masses of meson channel and meson decay constants are investigated with careful finite volume analysis. Our data favor the conformal over chiral symmetry breaking scenario for both $N_f=12$ and 16.  [Show abstract] [Hide abstract]
ABSTRACT: We present the first report of the LatKMI collaboration on the the lattice QCD simulation performed at the KMI computer, "$\varphi$", for the cases of 4 flavors and 8 flavors, the latter being expected to be a candidate for the walking technicolor having an approximate scale invariance near the infrared fixed point. The simulation was carried out based on the highly improved staggered quark (HISQ) action. In this proceedings, we report preliminary results on the spectrum, analyzed through the chiral perturbation theory and the finitesize hyperscaling. We observe qualitatively different behavior of the 8flavor case in contrast to the 4flavor case which shows clear indication of the hadronic phase as in the usual QCD.  [Show abstract] [Hide abstract]
ABSTRACT: We study corrections to the conformal hyperscaling relation in the conformal window of the large Nf QCD by using the ladder SchwingerDyson (SD) equation as a concrete dynamical model. From the analytical expression of the solution of the ladder SD equation, we identify the form of the leading mass correction to the hyperscaling relation. We find that the anomalous dimension, when identified through the hyperscaling relation neglecting these corrections, yields a value substantially lower than the one at the fixed point \gamma_m^* for large mass region. We further study finitevolume effects on the hyperscaling relation, based on the ladder SD equation in a finite spacetime with the periodic boundary condition. We find that the finitevolume corrections on the hyperscaling relation are negligible compared with the mass correction. The anomalous dimension, when identified through the finitesize hyperscaling relation neglecting the mass corrections as is often done in the lattice analyses, yields almost the same value as that in the case of the infinite spacetime neglecting the mass correction, i.e., a substantially lower value than \gamma_m^* for large mass. We also apply the finitevolume SD equation to the chiralsymmetrybreaking phase and find that when the theory is close to the critical point such that the dynamically generated mass is much smaller than the explicit breaking mass, the finitesize hyperscaling relation is still operative. We also suggest a concrete form of the modification of the finitesize hyperscaling relation by including the mass correction, which may be useful to analyze the lattice data.
Publication Stats
147  Citations  
31.61  Total Impact Points  
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Institutions

20122015

Nagoya University
 KobayashiMaskawa Institute for the Origin of Particles and the Universe (KMI)
Nagoya, Aichi, Japan
