High Energy Physics Lattice

Contrary to the common wisdom, local bosonizations of fermionic systems exist in higher dimensions. Interestingly, resulting bosonic variables must satisfy local constraints of a gauge type. They effectively replace long distance exchange interactions. In this work we study in detail the properties of such a system which was proposed a long time ago. In particular, dependence of the constraints on lattice geometry and fermion multiplicity is further elaborated and is now classified for all two dimensional, rectangular lattices with arbitrary sizes. For few small systems the constraints are solved analytically and the complete spectra of reduced spin hamiltonias are shown to agree with the original fermionic ones. The equivalence is extended to fermions in an external WegnerZ2field. It is also illustrated by an explicit calculation for a particular configuration of Wegner variables. Finally, a possible connection with the recently proposed web of dualities is discussed.

We present the first lattice QCD calculation of the charm quark contribution to the nucleon electromagnetic form factorsGcE,M(Q2)in the momentum transfer range0≤Q2≤1.4GeV2. The quark mass dependence, finite lattice spacing and volume corrections are taken into account simultaneously based on the calculation on three gauge ensembles including one at the physical pion mass. The nonzero value of the charm magnetic momentμcM=−0.00127(38)stat(5)sys, as well as the Pauli form factor, reflects a nontrivial role of the charm sea in the nucleon spin structure. The nonzeroGcE(Q2)indicates the existence of a nonvanishing asymmetric charm-anticharm sea in the nucleon. Performing a nonperturbative analysis based on holographic QCD and the generalized Veneziano model, we study the constraints on the[c(x)−c¯(x)]distribution from the lattice QCD results presented here. Our results provide complementary information and motivation for more detailed studies of physical observables that are sensitive to intrinsic charm and for future global analyses of parton distributions including asymmetric charm-anticharm distribution.

We constructbbu¯d¯states on lattice using NRQCD action for bottom and HISQ action for the light up/down quarks. The NRQCD-HISQ tetraquark operators are constructed for "bound"[bb][u¯d¯]and "molecular"[bu¯][bd¯]states. Corresponding to these different operators, two different appropriately tuned light quark masses are needed to obtain the desired spectra. We explain this requirement of differentmu/din the light of relativised quark model involving Hartree-Fock calculation. The mass spectra of double bottom tetraquark states are obtained on MILCNf=2+1Asqtad lattices at three different lattice spacings. Variational analysis has been carried out to obtain the relative contribution of "bound" and "molecular" states to the energy eigenstates.

InN=1supersymmetric Yang-Mills theory, regularised on a space-time lattice, in addition to the breaking by the gluino mass term, supersymmetry is broken explicitly by the lattice regulator. In addition to the parameter tuning in the theory, the supersymmetric Ward identities can be used as a tool to investigate lattice artefacts as well as to check whether supersymmetry can be recovered in the chiral and continuum limits. In this paper we present the numerical results of an analysis of the supersymmetric Ward identities for our available gauge ensembles at different values of the inverse gauge couplingβand of the hopping parameterκ. The results clearly indicate that the lattice artefacts vanish in the continuum limit, confirming the restoration of supersymmetry.

We summarize our investigations of several aspects ofN=1supersymmetric Yang-Mills (SYM) theory. We present our final results for SU(3)N=1SYM simulated with Wilson fermions. We also discuss the first test of the simulations of the theory with overlap gluinos. Finally, we present some recent progresses concerning the phase structure of the compactified theory onR3×S1.

Non-perturbative renormalization using the regularization independent momentum subtraction (RI/MOM) scheme has achieved great success in dealing with local operators under the lattice regularization, while a high accuracy and systematic examination on its validity of the non-local operator likes the quasi-PDF operator, such as the quark bi-linear operator with Wilson link which suffers from the linear divergence, is still absent. In this work, we compute the pion unpolarized quasi-PDF matrix element in the rest frame at 11 lattice spacings from 0.032 to 0.121 fm, using the discretized fermion actions with or without additive chiral symmetry breaking, on 3 kinds of dynamical gauge ensembles. The result shows that RI/MOM renormalization cancels all the linear divergence for the chiral fermion at least up to Wilson link lengthz∼1.2 fm. But in the case of the clover action which has additive chiral symmetry breaking, there is still a conspicuous residual linear divergence when the lattice spacing is much smaller than 0.1 fm.

We study the contributions from the connected and disconnected contraction diagrams to the pion-kaon scattering amplitude within the framework of SU(4|1)partially-quenched chiral perturbation theory. Combining this with a finite-volume analysis, we demonstrate that a lattice calculation of the easier computable connected correlation functions is able to provide valuable information of the noisier disconnected correlation functions, and may serve as a theory guidance for the future refinement of the corresponding lattice techniques.

We present a calculation of the contribution of the?-term to the neutron and proton electric dipole moments using seven 2+1+1-flavor HISQ ensembles. We also estimate the topological susceptibility for the 2+1+1 theory to be?Q=(66(9)(4)MeV)4in the continuum limit atM?=135MeV. The calculation of the nucleon three-point function is done using Wilson-clover valence quarks. The CP-violating form factorF3is calculated by expanding in small?. We show that lattice artifacts introduce a term proportional toathat does not vanish in the chiral limit, and we include this in our chiral-continuum fits. A chiral perturbation theory analysis shows that theN(0)?(0)state should provide the leading excited state contribution, and we study the effect of such a state. Detailed analysis of the contributions to the neutron and proton electric dipole moment using two strategies for removing excited state contamination are presented. Using the excited state spectrum from fits to the two-point function, we findd?nis small,|d?n|??.01?¯¯¯¯efm, whereas for the proton we get|d?p|??.02?¯¯¯¯efm. On the other hand, if the dominant excited-state contribution is from theN?state, then|d?n|could be as large as0.05?¯¯¯¯efm and|d?p|??.07?¯¯¯¯efm. Our overall conclusion is that present lattice QCD calculations do not provide a reliable estimate of the contribution of the?-term to the nucleon electric dipole moments, and a factor of ten higher statistics data are needed to get better control over the systematics and possibly a3?result.

Extending the successes of lattice quantum chromodynamics(QCD) at zero as well as nonzero temperatures to nonzero density is extremely desirable in view of the quest for the QCD phase diagram both theoretically and experimentally. It turns out though to give rise to some conundrums whose resolution may assist progress in this exciting but difficult area, and should therefore be sought actively.

The hadron resonance gas (HRG) model is often believed to correctly describe the confined phase of QCD. This assumption is the basis of many phenomenological works on QCD thermodynamics and of the analysis of hadron yields in relativistic heavy ion collisions. We use first-principle lattice simulations to calculate corrections to the ideal HRG. Namely, we determine the sub-leading fugacity expansion coefficients of the grand canonical free energy, receiving contributions from processes like kaon-kaon or baryon-baryon scattering. We achieve this goal by performing a two dimensional scan on the imaginary baryon number chemical potential (μB) - strangeness chemical potential (μS) plane, where the fugacity expansion coefficients become Fourier coefficients. We carry out a continuum limit estimation of these coefficients by performing lattice simulations with temporal extents ofN?=8,10,12using the 4stout-improved staggered action. We then use the truncated fugacity expansion to extrapolate ratios of baryon number and strangeness fluctuations and correlations to finite chemical potentials. Evaluating the fugacity expansion along the crossover line, we reproduce the trend seen in the experimental data on net-proton fluctuations by the STAR collaboration.