[en] 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 → ∞

[en] 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

[en] We calculate one-loop renormalization factors and mixing coefficients of bilinear quark operators for a class of gluon actions with six-link loops and O(a)-improved quark action. The calculation is carried out by evaluating on-shell Green's functions of quarks and gluons in the standard perturbation theory. We find a general trend that finite parts of one-loop coefficients are reduced approximately by a factor two for the renormalization-group improved gluon actions compared with the case of the standard plaquette gluon action

[en] The amount of u-bar and that of d-bar in the proton were assumed to be the same based on the flavor symmetry. However, previous experiments found that d-bar is dominant in the proton. In particular, d-bar/u-bar is as asymmetric as 1.7 at Bjorken x ∼ 0.2. The SeaQuest experiment at Fermilab aims to measure the flavor asymmetry at higher x region (0.15 < x < 0.45). The ratio d-bar/u-bar is derived from the cross section ratio of proton-deuteron to proton-proton Drell-Yan processes. We analyzed the data taken in 2015 and obtained the preliminary result. We found that the d-bar/u-bar > 1 at higher x. (author)

[en] The amounts of d-bar and u-bar in the proton were expected to be the same based on the flavor independence of gluon splitting. However, muon deep inelastic scattering experiment NMC at CERN found that the amount of d-bar is larger than u-bar in the proton. Bjorken x dependence of the sea quark flavor asymmetry can be studied in Drell-Yan experiments. The E866 experiment at Fermilab showed that d-bar(x)/u-bar(x) > 1.0 at 0.015 < x < 0.20. SeaQuest at Fermilab measures the light-antiquark flavor asymmetry d-bar/u-bar precisely in a large x range (0.15 < x < 0.45) including the unrevealed region in E866. It uses a 120 GeV proton beam extracted from Fermilab Main Injector colliding with liquid hydrogen and deuterium targets to measure the Drell-Yan process. The light-antiquark flavor asymmetry d-bar(x)/u-bar(x) is derived from the cross section ratio of proton-deuteron to proton-proton Drell-Yan processes. SeaQuest released the preliminary result in 2016. The analyses toward final results are in progress. (author)

[en] SeaQuest is an experiment to measure Drell-Yan reaction q + q-bar → Y^* → μ⁺ + μ^- using 120 GeV proton beams and magnetic spectrometers at the Fermi National Accelerator Laboratory. With a focus on the fact that this reaction is sensitive to antiquark distribution in the nucleon, the authors compared the cross section of the proton target and the deuteron target to measure the flavor asymmetry d-bar(x)/u-bar(x) in the range between 0.10 and 0.58 of Bjorken x. As a result, it was shown that d d-bar(x) is larger than u-bar(x) in the measured range of Bjorken x. (A.O.)

[en] We explore aspects of the phase structure of SU(2) and SU(3) lattice gauge theories at strong coupling with many flavors N_f of Wilson fermions in the fundamental representation. The pseudoscalar meson mass as a function of hopping parameter is observed to deviate from the expected analytic dependence, at least for sufficiently large N_f. Implications of this effect are discussed, including the relevance to recent searches for an infrared fixed point.

[en] It has been suggested to project out a number of low-lying eigenvalues of the four-dimensional Wilson-Dirac operator that generates the transfer matrix of domain-wall fermions in order to improve simulations with domain-wall fermions. We investigate how this projection method reduces the residual chiral symmetry-breaking effects for a finite extent of the extra dimension. We use the standard Wilson as well as the renormalization- group-improved gauge action. In both cases we find a substantially reduced residual mass when the projection method is employed. In addition, the large fluctuations in this quantity disappear. (author)

[en] We study the two-dimensional lattice Gross-Neveu model with Wilson twisted mass fermions in order to explore the phase structure in this setup. In particular, we investigate the behaviour of the phase transitions found earlier with standard Wilson fermions as a function of the twisted mass parameter μ. We find that qualitatively the dependence of the phase transitions on μ is very similar to the case of lattice QCD

[en] We derive finite-size scaling formulae for four-dimensional Higgs-Yukawa models near the Gaussian fixed point. These formulae will play an essential role in future, detailed investigation of such models. In particular, they can be used to determine the nature of the observed phase transitions, and confirm or rule out the possibility of having non-trivial fixed points in the Higgs-Yukawa models. Our scaling formula for Binder's cumulant is tested against lattice simulations carried out at weak couplings, and good agreement is found. As a separate project, we also present preliminary results from our study of a chirally-invariant Higgs-Yukawa model including a dimension-six operator at finite temperature. Our work provides first indications of first-order temperature-induced phase transitions near the infinite cutoff limit in this model.