Publications (28)66.68 Total impact
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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.  [Show abstract] [Hide abstract]
ABSTRACT: The composition of nucleons has long been known to be subatomic particles called quarks and gluons, which interact through the strong force and theoretically can be described by Quantum Chromodynamics (QCD). Lattice QCD (LQCD), in which the continuous spacetime is translated into grid points on a fourdimensional lattice and ab initio Monte Carlo simulations are performed, is by far the only modelindependent method to study QCD with controllable errors. We report the successful application of a novel algorithm, AllModeAveraging, in the LQCD calculations of nucleon internal structure on the Gordon supercomputer our award of roughly 6 million service units through XSEDE. The application of AMA resulted in as much as a factor of 30 speedup in computational efficiency.  [Show abstract] [Hide abstract]
ABSTRACT: Neutral $B$ meson mixing matrix elements and $B$ meson decay constants are calculated. Static approximation is used for $b$ quark and domainwall fermion formalism is employed for light quarks. The calculations are carried out on $2+1$ flavor dynamical ensembles generated by RBC/UKQCD Collaborations with lattice spacings $0.086$fm ($a^{1}\sim 2.3$GeV) and $0.11$fm ($1.7$GeV), and a fixed physical spatial volume of about $(2.7{\rm fm})^3$. In the static quark action, linksmearings are used to improve the signaltonoise ratio. We employ two kinds of linksmearings, HYP1 and HYP2, and their results are combined in taking the continuum limit. For the matching between the lattice and the continuum theory, oneloop perturbative $O(a)$ improvements are made to reduce discretization errors. As the most important quantity of this work, we obtain SU(3) breaking ratio $\xi=1.208(60)$, where the error includes statistical and systematic one. We also find other neutral $B$ meson mixing quantities $f_B\sqrt{\hat{B}_B}=240(22)$MeV, $f_{B_s}\sqrt{\hat{B}_{B_s}}=290(22)$MeV, $\hat{B}_B=1.17(22)$, $\hat{B}_{B_s}=1.22(13)$ and $B_{B_s}/B_B=1.028(74)$, $B$ meson decay constants $f_B=219(17)$MeV, $f_{B_s}=264(19)$MeV and $f_{B_s}/f_B=1.193(41)$, in the static limit of $b$ quark.Physical Review D 06/2014; 91(11). DOI:10.1103/PhysRevD.91.114505 · 4.64 Impact Factor 
Conference Paper: NonPerturbative Study of 16Flavor QCD
Proceedings of KMIGCOE Workshop; 03/2014  [Show abstract] [Hide abstract]
ABSTRACT: Neutral B meson mixing matrix elements and B meson decay constants are calculated. Static approximation is used for b quark and domainwall fermion formalism is employed for light quarks. The calculations are done on 2+1 flavor dynamical ensembles, whose lattice spacings are 0.086 fm and 0.11 fm with a fixed physical spatial volume of about (2.7 fm)^3. In the static quark action, linksmearings are used to improve the signaltonoise ratio. We employ two kinds of linksmearings and their results are combined in taking a continuum limit. For the matching between the lattice and the continuum theory, oneloop perturbative calculations are used including O(a) improvements to reduce discretization errors. We obtain SU(3) braking ratio \xi=1.222(60) in the static limit of b quark.  [Show abstract] [Hide abstract]
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 review lattice results related to pion, kaon, D and Bmeson physics with the aim of making them easily accessible to the particle physics community. More specifically, we report on the determination of the lightquark masses, the form factor f+(0), arising in semileptonic K > pi transition at zero momentum transfer, as well as the decay constant ratio fK/fpi of decay constants and its consequences for the CKM matrix elements Vus and Vud. Furthermore, we describe the results obtained on the lattice for some of the lowenergy constants of SU(2)LxSU(2)R and SU(3)LxSU(3)R Chiral Perturbation Theory and review the determination of the BK parameter of neutral kaon mixing. The inclusion of heavyquark quantities significantly expands the FLAG scope with respect to the previous review. Therefore, for this review, we focus on D and Bmeson decay constants, form factors, and mixing parameters, since these are most relevant for the determination of CKM matrix elements and the global CKM unitaritytriangle fit.European Physical Journal C 10/2013; 74(9). DOI:10.1140/epjc/s1005201428907 · 5.08 Impact Factor  [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.Physical Review D 09/2013; 89(11). DOI:10.1103/PhysRevD.89.111502 · 4.64 Impact Factor  [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.Physical Review Letters 05/2013; 111(16). DOI:10.1103/PhysRevLett.111.162001 · 7.51 Impact Factor  [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.Physical review D: Particles and fields 02/2013; 87(9). DOI:10.1103/PhysRevD.87.094511 · 4.86 Impact Factor  [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.  Physical review D: Particles and fields 09/2012; 86(5). DOI:10.1103/PhysRevD.86.059903 · 4.86 Impact Factor

Conference Paper: Proton decay matrix elements from lattice QCD
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ABSTRACT: We report on the calculation of the matrix elements of nucleon to pseudoscalar decay through a three quark operator, a part of the lowenergy, fourfermion, baryonnumberviolating operator originating from grand unified theories. The direct calculation of the form factors using domainwall fermions on the lattice, incorporating the u, d and s seaquarks effects yields the results with all the relevant systematic uncertainties controlled for the first time.Workshop on GUT; 07/2012  [Show abstract] [Hide abstract]
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 $\gamma_m \sim 0.40.5$.Physical review D: Particles and fields 07/2012; 86(5). DOI:10.1103/PhysRevD.86.054506 · 4.86 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the masses of bottom mesons using an improved relativistic action for the bquarks and the RBC/UKQCD Iwasaki gauge configurations with 2+1 flavors of dynamical domainwall light quarks. We analyze configurations with two lattice spacings: a^{1} = 1.729 GeV (a ~ 0.11 fm) and a^{1} = 2.281 GeV (a ~ 0.086 fm). We use an anisotropic, cloverimproved Wilson action for the bquark, and tune the three parameters of the action nonperturbatively such that they reproduce the experimental values of the B_s and B_s* heavylight meson states. The masses and masssplittings of the lowlying bottomonium states (such as the eta_b and Upsilon) can then be computed with no additional inputs, and comparison between these predictions and experiment provides a test of the validity of our method. We obtain bottomonium masses with total uncertainties of ~0.50.6% and finestructure splittings with uncertainties of ~3545%; for all cases we find good agreement with experiment. The parameters of the relativistic heavyquark action tuned for bquarks presented in this work can be used for precise calculations of weak matrix elements such as Bmeson decay constants and mixing parameters with lattice discretization errors that are of the same size as in light pseudoscalar meson quantities. This general method can also be used for charmed meson masses and matrix elements if the parameters of the heavyquark action are appropriately tuned.Physical review D: Particles and fields 06/2012; 86(11). DOI:10.1103/PhysRevD.86.116003 · 4.86 Impact Factor
Publication Stats
357  Citations  
66.68  Total Impact Points  
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Institutions

20112015

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


2009

Brookhaven National Laboratory
New York, New York, United States
