bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-baryon systems from HAL QCD method and the mirage in the temporal correlation of the direct method
Authors: Iritani Takumi
Published: March 2018

Both direct and HAL QCD methods are currently used to study the hadron interactions in lattice QCD. In the direct method, the eigen-energy of two-particle is measured from the temporal correlation. Due to the contamination of excited states, however, the direct method suffers from the fake eigen-energy problem, which we call the “mirage problem,” while the HAL QCD method can extract information from all elastic states by using the spatial correlation. In this work, we further investigate systematic uncertainties of the HAL QCD method such as the quark source operator dependence, the convergence of the derivative expansion of the non-local interaction kernel, and the single baryon saturation, which are found to be well controlled. We also confirm the consistency between the HAL QCD method and the Lüscher’s finite volume formula. Based on the HAL QCD potential, we quantitatively confirm that the mirage plateau in the direct method is indeed caused by the contamination of excited states.
Lattice QCD studies on baryon interactions in the strangeness -2 sector with physical quark masses
Authors: Sasaki Kenji , Aoki Sinya , Doi Takumi , Gongyo Shinya , Hatsuda Tetsuo , Ikeda Yoichi , Inoue Takashi , Iritani Takumi , Ishii Noriyoshi , Miyamoto Takaya
Published: March 2018

We investigate baryon-baryon (BB) interactions in the strangeness S = −2 sector via the coupled-channel HAL QCD method which enables us to extract the scattering observables from Nambu-Bethe-Salpeter (NBS) wave function on the lattice. The simulations are performed with (almost) physical quark masses (mπ = 146MeV) and a huge lattice volume of La = 8.1fm. We discuss the fate of H-dibaryon state through the ΛΛ and NΞ coupled-channel scatterings
Computation of hybrid static potentials in SU(3) lattice gauge theory
Authors: Reisinger Christian , Capitani Stefano , Philipsen Owe , Wagner Marc
Published: March 2018

We compute hybrid static potentials in SU(3) lattice gauge theory. We present a method to automatically generate a large set of suitable creation operators with defined quantum numbers from elementary building blocks. We show preliminary results for several channels and discuss, which structures of the gluonic flux tube seem to be realized by the ground states in these channels.
Baryon interactions from lattice QCD with physical masses —S = −3 sector: Ξ∑ and Ξ∑-Λ∑—
Authors: Ishii Noriyoshi , Aoki Sinya , Doi Takumi , Gongyo Shinya , Hatsuda Tetsuo , Ikeda Yoichi , Inoue Takashi , Iritani Takumi , Miyamoto Takaya , Nemura Hidekatsu , Sasaki Kenji
Published: March 2018

Hyperon-nucleon and hyperon-hyperon interactions are important in studying the properties of hypernuclei in hypernuclear physics. However, unlike the nucleons which are quite stable, hyperons are unstable so that the direct scattering experiments are difficult, which leads to the large uncertainty in the phenomenological determination of hyperon potentials. In this talk, we use the gauge configurations generated at the (almost) physical point (mπ = 146 MeV) on a huge spatial volume (8:1fm)4 to present our latest result on the hyperon-hyperon potentials in S = −3 sector (Ξ∑ single channel and Ξ∑- ΞΛ; coupled channel) from the Nambu-Bethe-Salpeter wave functions based on the HAL QCD method with improved statistics.
Heavy light tetraquarks from Lattice QCD
Authors: Junnarkar Parikshit , Padmanath M , Mathur Nilmani
Published: March 2018

We present preliminary results from a lattice calculation of tetraquark states in the charm and bottom sector of the type udbb, usbb, udcc and scbb. These calculations are performed on Nf = 2 + 1 + 1 MILC ensembles with lattice spacing of a = 0:12 fm and a = 0:06 fm. A relativistic action with overlap fermions is employed for the light and charm quarks while a non-relativistic action with non-perturbatively improved coefficients is used in the bottom sector. Preliminary results provide a clear indication of presence of energy levels below the relevant thresholds of different tetraquark states in the double bottom sector while a scattering state is observed in the charm sector.
Mass Spectra of Ds and Ωc in Lattice QCD with Nf = 2 + 1 + 1 Domain-Wall Quarks
Authors: Chiu Ting-Wai
Published: March 2018

We perform hybrid Monte Carlo simulation of lattice QCD with Nf = 2+1+1 optimal domain-wall quarks on the 323 × 64 lattice with lattice spacing a ~ 0:06 fm, and generate a gauge ensemble with physical s and c quarks, and pion mass ~ 280 MeV. Using 2-quark (meson) and 3-quark (baryon) interpolating operators, the mass spectra of the lowest-lying states containing s and c quarks (Ds and Ωc) are extracted [1], which turn out in good agreement with the high energy experimental values, together with the predictions of the charmed baryons which have not been observed in experiments. For the five new narrow c states observed by the LHCb Collaboration [2], the lowest-lying Ωc(3000) agrees with our predicted mass 3015(29)(34) MeV of the lowest-lying Ωc with JP = 1/2−. This implies that JP of Ωc(3000) is 1/2−.
Tetraquark resonances computed with static lattice QCD potentials and scattering theory
Authors: Bicudo Pedro , Cardoso Marco , Peters Antje , Pflaumer Martin , Wagner Marc
Published: March 2018

We study tetraquark resonances with lattice QCD potentials computed for two static quarks and two dynamical quarks, the Born-Oppenheimer approximation and the emergent wave method of scattering theory. As a proof of concept we focus on systems with isospin I = 0, but consider different relative angular momenta l of the heavy b quarks. We compute the phase shifts and search for S and T matrix poles in the second Riemann sheet. We predict a new tetraquark resonance for l = 1, decaying into two B mesons, with quantum numbers I(JP) = 0(1−), mass [see formula in PDF] MeV and decay width [see formula in PDF] MeV.
Comparison of different source calculations in two-nucleon channel at large quark mass
Authors: Yamazaki Takeshi , Ishikawa Ken-ichi , Kuramashi Yoshinobu
Published: March 2018

We investigate a systematic error coming from higher excited state contributions in the energy shift of light nucleus in the two-nucleon channel by comparing two different source calculations with the exponential and wall sources. Since it is hard to obtain a clear signal of the wall source correlation function in a plateau region, we employ a large quark mass as the pion mass is 0.8 GeV in quenched QCD. We discuss the systematic error in the spin-triplet channel of the two-nucleon system, and the volume dependence of the energy shift.
Spectroscopy of Charmed and Bottom Hadrons using Lattice QCD
Authors: Mondal Sourav , Padmanath M. , Mathur Nilmani
Published: March 2018

We present preliminary results on the light, charmed and bottom baryon spectra using overlap valence quarks on the background of 2+1+1 flavours HISQ gauge configurations of the MILC collaboration. These calculations are performed on three different gauge ensembles at three lattice spacings (a ∼ 0.12 fm, 0.09 fm and 0.06 fm) and for physical strange, charm and bottom quark masses. The SU(2) heavy baryon chiral perturbation theory is used to extrapolate baryon masses to the physical pion mass and the continuum limit extrapolations are also performed. Our results are consistent with the well measured charmed baryons. We predict the masses of many other states which are yet to be discovered.
The η′ meson at the physical point with Nf = 2 Wilson twisted mass fermions
Authors: Helmes Christopher , Knippschild Bastian , Kostrzewa Bartosz , Liu Liuming , Jost Christian , Ottnad Konstantin , Urbach Carsten , Wenger Urs , Werner Markus
Published: March 2018

We present results for the η′ meson and the topological susceptibility in Nf = 2 flavour lattice QCD. The results are obtained using Wilson twisted mass fermions at maximal twist with pion masses ranging from 340 MeV down to the physical point. A comparison to literature values is performed giving a handle on discretisation effects.
Scattering phaseshift formulas for mesons and baryons in elongated boxes
Authors: Lee Frank X. , Alexandru Andrei
Published: March 2018

We derive Lüscher phaseshift formulas for two-particle states in boxes elongated in one of the dimensions. Such boxes offer a cost-effective way of varying the relative momentum of the particles. Boosted states in the elongated direction, which allow wider access to energies, are also considered. The formulas for the various scenarios (moving and zero-momentum states in cubic and elongated boxes) are compared and relations between them are clarified. The results are applicable to a wide set of meson-meson and meson-baryon elastic scattering processes, with the two-particle system having equal or unequal masses.
Finite continuum quasi distributions from lattice QCD
Authors: Monahan Christopher , Orginos Kostas
Published: March 2018

We present a new approach to extracting continuum quasi distributions from lattice QCD. Quasi distributions are defined by matrix elements of a Wilson-line operator extended in a spatial direction, evaluated between nucleon states at finite momentum. We propose smearing this extended operator with the gradient flow to render the corresponding matrix elements finite in the continuum limit. This procedure provides a nonperturbative method to remove the power-divergence associated with the Wilson line and the resulting matrix elements can be directly matched to light-front distributions via perturbation theory.
Nucleon structure from 2+1 flavor lattice QCD near the physical point
Authors: Tsukamoto Natsuki , Ishikawa Ken-Ichi , Kuramashi Yoshinobu , Sasaki Shoichi , Yamazaki Takeshi
Published: March 2018

We present an update on our results of nucleon form factors measured on a large-volume lattice (8:1fm)4 at almost the physical point in 2+1 flavor QCD. The configurations are generated with the stout-smeared O(a) improved Wilson quark action and Iwasaki gauge action at β = 1:82, which corresponds to the lattice spacing of 0.085 fm. The pion mass at the simulation point is about 145 MeV. We determine the isovector electric radius and magnetic moment from nucleon electric (GE) and magnetic (GM) form factors. We also report on preliminary results of the axial-vector (FA), induced pseudo-scalar (FP) and pseudo-scalar (GP) form factors in order to verify the axial Ward-Takahashi identity in terms of the nucleon matrix elements, which may be called as the generalized Goldberger-Treiman relation.
Bethe-Salpeter wave functions of ηc(1S, 2S) and ψ(1S, 2S) states: local-potential description of the charmonium system revisited
Authors: Nochi Kazuki , Kawanai Taichi , Sasaki Shoichi
Published: March 2018

The quark potential models with an energy-independent central potential have been successful for understanding the conventional charmonium states especially below the open charm threshold. As one might consider, however, the interquark potential is in general energy-dependent, and its tendency gets stronger in higher lying states. Confirmation of whether the interquark potential is energy-independent is also important to verify the validity of the quark potential models. In this talk, we examine the energy dependence of the charmonium potential, which can be determined from the Bethe-Salpeter (BS) amplitudes of cc̅ mesons in lattice QCD.We first calculate the BS amplitudes of radially excited charmonium states, the ηc(2S) and ψ(2S) states, using the variational method and then determine both the quark kinetic mass and the charmonium potential within the HAL QCD method. Through a direct comparison of charmonium potentials determined from both the 1S and 2S states, we confirm that neither the central nor spin-spin potential shows visible energy dependence at least up to 2S state.
Nucleon structure from 2+1-flavor domain-wall QCD
Authors: Ohta Shigemi
Published: March 2018

Nucleon-structure calculations of isovector vector-and axialvector-current form factors, transversity and scalar charge, and quark momentum and helicity fractions are reported from two recent 2+1-flavor dynamical domain-wall fermions lattice-QCD ensembles generated jointly by the RIKEN-BNL-Columbia and UKQCD Collaborations with Iwasaki × dislocation-suppressing-determinatn-ratio gauge action at inverse lattice spacing of 1.378(7) GeV and pion mass values of 249.4(3) and 172.3(3) MeV.
Baryonic and mesonic 3-point functions with open spin indices
Authors: Bali Gunnar S. , Collins Sara , Gläßle Benjamin , Heybrock Simon , Korcyl Piotr , Löffler Marius , Rödl Rudolf , Schäfer Andreas
Published: March 2018

We have implemented a new way of computing three-point correlation functions. It is based on a factorization of the entire correlation function into two parts which are evaluated with open spin-(and to some extent flavor-) indices. This allows us to estimate the two contributions simultaneously for many different initial and final states and momenta, with little computational overhead. We explain this factorization as well as its efficient implementation in a new library which has been written to provide the necessary functionality on modern parallel architectures and on CPUs, including Intel’s Xeon Phi series.
Light meson form factors at high Q2 from lattice QCD
Authors: Koponen Jonna , Zimermmane-Santos André , Davies Christine , Lepage G. Peter , Lytle Andrew
Published: March 2018

Measurements and theoretical calculations of meson form factors are essential for our understanding of internal hadron structure and QCD, the dynamics that bind the quarks in hadrons. The pion electromagnetic form factor has been measured at small space-like momentum transfer |q2| < 0.3 GeV2 by pion scattering from atomic electrons and at values up to 2.5 GeV2 by scattering electrons from the pion cloud around a proton. On the other hand, in the limit of very large (or infinite) Q2 = −q2, perturbation theory is applicable. This leaves a gap in the intermediate Q2 where the form factors are not known.

As a part of their 12 GeV upgrade Jefferson Lab will measure pion and kaon form factors in this intermediate region, up to Q2 of 6 GeV2. This is then an ideal opportunity for lattice QCD to make an accurate prediction ahead of the experimental results. Lattice QCD provides a from-first-principles approach to calculate form factors, and the challenge here is to control the statistical and systematic uncertainties as errors grow when going to higher Q2 values.

Here we report on a calculation that tests the method using an
ηs meson, a ’heavy pion’ made of strange quarks, and also present preliminary results for kaon and pion form factors. We use the nf = 2 + 1 + 1 ensembles made by the MILC collaboration and Highly Improved Staggered Quarks, which allows us to obtain high statistics. The HISQ action is also designed to have small dicretisation errors. Using several light quark masses and lattice spacings allows us to control the chiral and continuum extrapolation and keep systematic errors in check.
Structure of the Nucleon and its Excitations
Authors: Kamleh Waseem , Leinweber Derek , Liu Zhan-wei , Stokes Finn , Thomas Anthony , Thomas Samuel , Wu Jia-jun
Published: March 2018

The structure of the ground state nucleon and its finite-volume excitations are examined from three different perspectives. Using new techniques to extract the relativistic components of the nucleon wave function, the node structure of both the upper and lower components of the nucleon wave function are illustrated. A non-trivial role for gluonic components is manifest. In the second approach, the parity-expanded variational analysis (PEVA) technique is utilised to isolate states at finite momenta, enabling a novel examination of the electric and magnetic form factors of nucleon excitations. Here the magnetic form factors of low-lying odd-parity nucleons are particularly interesting. Finally, the structure of the nucleon spectrum is examined in a Hamiltonian effective field theory analysis incorporating recent lattice-QCD determinations of low-lying two-particle scattering-state energies in the finite volume. The Roper resonance of Nature is observed to originate from multi-particle coupled-channel interactions while the first radial excitation of the nucleon sits much higher at approximately 1.9 GeV.
Parton distribution functions on the lattice and in the continuum
Authors: Karpie Joseph , Orginos Kostas , Radyushkin Anatoly , Zafeiropoulos Savvas
Published: March 2018

Ioffe-time distributions, which are functions of the Ioffe-time ν, are the Fourier transforms of parton distribution functions with respect to the momentum fraction variable x. These distributions can be obtained from suitable equal time, quark bilinear hadronic matrix elements which can be calculated from first principles in lattice QCD, as it has been recently argued. In this talk I present the first numerical calculation of the Ioffe-time distributions of the nucleon in the quenched approximation.
Selected inversion as key to a stable Langevin evolution across the QCD phase boundary
Authors: Bloch Jacques , Schenk Olaf
Published: March 2018

We present new results of full QCD at nonzero chemical potential. In PRD 92, 094516 (2015) the complex Langevin method was shown to break down when the inverse coupling decreases and enters the transition region from the deconfined to the confined phase. We found that the stochastic technique used to estimate the drift term can be very unstable for indefinite matrices. This may be avoided by using the full inverse of the Dirac operator, which is, however, too costly for four-dimensional lattices. The major breakthrough in this work was achieved by realizing that the inverse elements necessary for the drift term can be computed efficiently using the selected inversion technique provided by the parallel sparse direct solver package PARDISO. In our new study we show that no breakdown of the complex Langevin method is encountered and that simulations can be performed across the phase boundary.
Thermal Simulations, Open Boundary Conditions and Switches
Authors: Burnier Yannis , Florio Adrien , Kaczmarek Olaf , Mazur Lukas
Published: March 2018

SU(N) gauge theories on compact spaces have a non-trivial vacuum structure characterized by a countable set of topological sectors and their topological charge. In lattice simulations, every topological sector needs to be explored a number of times which reflects its weight in the path integral. Current lattice simulations are impeded by the so-called freezing of the topological charge problem. As the continuum is approached, energy barriers between topological sectors become well defined and the simulations get trapped in a given sector. A possible way out was introduced by Lüscher and Schaefer using open boundary condition in the time extent. However, this solution cannot be used for thermal simulations, where the time direction is required to be periodic. In this proceedings, we present results obtained using open boundary conditions in space, at non-zero temperature. With these conditions, the topological charge is not quantized and the topological barriers are lifted. A downside of this method are the strong finite-size effects introduced by the boundary conditions. We also present some exploratory results which show how these conditions could be used on an algorithmic level to reshuffle the system and generate periodic configurations with non-zero topological charge.
Anderson localization in sigma models
Authors: Bruckmann Falk , Wellnhofer Jacob
Published: March 2018

In QCD above the chiral restoration temperature there exists an Anderson transition in the fermion spectrum from localized to delocalized modes. We investigate whether the same holds for nonlinear sigma models which share properties like dynamical mass generation and asymptotic freedom with QCD. In particular we study the spectra of fermions coupled to (quenched) CP(N-1) configurations at high temperatures. We compare results in two and three space-time dimensions: in two dimensions the Anderson transition is absent, since all fermion modes are localized, while in three dimensions it is present. Our measurements include a more recent observable characterizing level spacings: the distribution of ratios of consecutive level spacings.
Continuum extrapolation of quarkonium correlators at non-zero temperature
Authors: Ding Heng-Tong , Kaczmarek Olaf , Kruse Anna-Lena , Ohno Hiroshi , Sandmeyer Hauke
Published: March 2018

In the investigation of in-medium modifications of quarkonia and for determining heavy quark diffusion coeffcients, correlation functions play a crucial role. For the first time we perform a continuum extrapolation of charmonium and bottomonium correlators in the vector channel based on non-perturbatively clover-improved Wilson fermions in quenched lattice QCD. Calculations were done at 4 different lattice spacings, spatial extents between 96 and 192, aspect ratio from 1/6 to 1/2, for 5 temperatures between T/Tc = 0:75 and T/Tc = 2:2. We interpolate between different quark masses to match to the same vector meson mass over different lattice setups. Afterwards we extrapolate the renormalized correlators to the continuum. While we find a strong temperature dependence for charmonium, bottomonium states are only slightly affected at higher temperatures.
Unification of the complex Langevin method and the Lefschetzthimble method
Authors: Nishimura Jun , Shimasaki Shinji
Published: March 2018

Recently there has been remarkable progress in solving the sign problem, which occurs in investigating statistical systems with a complex weight. The two promising methods, the complex Langevin method and the Lefschetz thimble method, share the idea of complexifying the dynamical variables, but their relationship has not been clear. Here we propose a unified formulation, in which the sign problem is taken care of by both the Langevin dynamics and the holomorphic gradient flow. We apply our formulation to a simple model in three different ways and show that one of them interpolates the two methods by changing the flow time.
Topological Susceptibility in Nf = 2 QCD at Finite Temperature
Authors: Aoki Sinya , Aoki Yasumichi , Cossu Guido , Fukaya Hidenori , Hashimoto Shoji , Suzuki Kei
Published: March 2018

We study the topological charge in Nf = 2 QCD at finite temperature using Möbius domain-wall fermions. The susceptibility Xt of the topological charge defined either by the index of overlap Dirac operator or a gluonic operator is investigated at several values of temperature T (> Tc) varying the quark mass. A strong suppression of the susceptibility is observed below a certain value of the quark mass. The relation with the restoration of UA(1) is discussed.
Degeneracy of vector-channel spatial correlators in high temperature QCD
Authors: Rohrhofer Christian , Aoki Yasumichi , Cossu Guido , Fukaya Hidenori , Glozman Leonid , Hashimoto Shoji , Lang Christian B. , Prelovsek Sasa
Published: March 2018

We study spatial isovector meson correlators in Nf = 2 QCD with dynamical domain-wall fermions on 323 × 8 lattices at temperatures up to 380 MeV with various quark masses. We measure the correlators of spin-one isovector operators including vector, axial-vector, tensor and axial-tensor. At temperatures above Tc we observe an approximate degeneracy of the correlators in these channels, which is unexpected because some of them are not related under SU(2)L×SU(2)R nor U(1)A symmetries. The observed approximate degeneracy suggests emergent SU(2)CS (chiral-spin) and SU(4) symmetries at high T.
Lattice Study of QCD Phase Structure by Canonical Approach
Authors: Bornyakov V.G. , Boyda D. , Goy V. , Molochkov A. , Nakamura A. , Nikolaev A. , Zakharov V.I.
Published: March 2018

The canonical approach is a powerful tool to circumvent sign problem in LQCD. Although it has its own difficulties it provides opportunity to determine QCD phase transition line. Using improved Wilson fermions we calculated number density at nonzero imaginary chemical potential for confinement and deconfinement phases, restored canonical partition functions Zn and did extrapolation into the real chemical potential region. We computed the higher moments of the baryon number including the kurtosis, and compared our results with information from relativistic heavy ion collision experiments.
Representation of complex probabilities and complex Gibbs sampling
Authors: Salcedo Lorenzo Luis
Published: March 2018

Complex weights appear in Physics which are beyond a straightforward importance sampling treatment, as required in Monte Carlo calculations. This is the wellknown sign problem. The complex Langevin approach amounts to effectively construct a positive distribution on the complexified manifold reproducing the expectation values of the observables through their analytical extension. Here we discuss the direct construction of such positive distributions paying attention to their localization on the complexified manifold. Explicit localized representations are obtained for complex probabilities defined on Abelian and non Abelian groups. The viability and performance of a complex version of the heat bath method, based on such representations, is analyzed.
The ξ/ξ2nd ratio as a test for Effective Polyakov Loop Actions
Authors: Caselle Michele , Nada Alessandro
Published: March 2018

Effective Polyakov line actions are a powerful tool to study the finite temperature behaviour of lattice gauge theories. They are much simpler to simulate than the original (3+1) dimensional LGTs and are affected by a milder sign problem. However it is not clear to which extent they really capture the rich spectrum of the original theories, a feature which is instead of great importance if one aims to address the sign problem. We propose here a simple way to address this issue based on the so called second moment correlation length ξ2nd. The ratio ξ/ξ2nd between the exponential correlation length and the second moment one is equal to 1 if only a single mass is present in the spectrum, and becomes larger and larger as the complexity of the spectrum increases. Since both ξexp and ξ2nd are easy to measure on the lattice, this is an economic and effective way to keep track of the spectrum of the theory. In this respect we show using both numerical simulation and effective string calculations that this ratio increases dramatically as the temperature decreases. This non-trivial behaviour should be reproduced by the Polyakov loop effective action.
Chiral phase transition of three flavor QCD with nonzero magnetic field using standard staggered fermions
Authors: Tomiya Akio , Ding Heng-Tong , Mukherjee Swagato , Schmidt Christian , Wang Xiao-Dan
Published: March 2018

Lattice simulations for (2+1)-flavor QCD with external magnetic field demon-strated that the quark mass is one of the important parameters responsible for the (inverse) magnetic catalysis. We discuss the dependences of chiral condensates and susceptibilities, the Polyakov loop on the magnetic field and quark mass in three degenerate flavor QCD. The lattice simulations are performed using standard staggered fermions and the plaquette action with spatial sizes Nσ = 16 and 24 and a fixed temporal size Nτ = 4. The value of the quark masses are chosen such that the system undergoes a first order chiral phase transition and crossover with zero magnetic field. We find that in light mass regime, the quark chiral condensate undergoes magnetic catalysis in the whole temperature region and the phase transition tend to become stronger as the magnetic field increases. In crossover regime, deconfinement transition temperature is shifted by the magnetic field when quark mass ma is less than 0:4. The lattice cutoff effects are also discussed.
Hadron thermodynamics from imaginary chemical potentials
Authors: Pásztor Attila , Alba Paolo , Bellwied Rene , Borsányi Szabolcs , Fodor Zoltán , Günther Jana N. , Katz Sándor , Ratti Claudia , Mantovani Sarti Valentina , Noronha-Hostler Jacquelyn , Parotto Paolo , Portillo Vazquez Israel , Vovchenko Volodymyr , Stoecker Horst
Published: March 2018

We use 4stout improved staggered lattice data at imaginary chemical potentials to calculate fugacity expansion coefficients in finite temperature QCD. We discuss the phenomenological interpretation of our results within the hadron resonance gas (HRG) model, and the hints they give us about the hadron spectrum. We also discuss features of the higher order coefficients that are not captured by the HRG. This conference contribution is based on our recent papers [1, 2].,
A study of how the particle spectra of SU(N) gauge theories with a fundamental Higgs emerge
Authors: Törek Pascal , Maas Axel , Sondenheimer René
Published: March 2018

In gauge theories, the physical, experimentally observable spectrum consists only of gauge-invariant states. In the standard model the Fröhlich-Morchio-Strocchi mechanism shows that these states can be adequately mapped to the gauge-dependent elementary W, Z, Higgs, and fermions. In theories with a more general gauge group and Higgs sector, appearing in various extensions of the standard model, this has not to be the case. In this work we determine analytically the physical spectrum of SU(N > 2) gauge theories with a Higgs field in the fundamental representation. We show that discrepancies between the spectrum predicted by perturbation theory and the observable physical spectrum arise. We confirm these analytic findings with lattice simulations for N = 3.
Investigating BSM Models with Large Scale Separation
Authors: Hasenfratz Anna , Rebbi Claudio , Witzel Oliver
Published: March 2018

Mass-split systems based on a conformal infrared fixed point provide a lowenergy effective description of beyond the standard model systems with large scale separation. We report results of exploratory investigations with four light and eight heavy flavors using staggered fermions, and up to five different values for the light flavor mass, five different heavy flavor masses, and two values of the bare gauge coupling.
The twelve-flavor β-function and dilaton tests of the sextet scalar
Authors: Fodor Zoltan , Holland Kieran , Kuti Julius , Nogradi Daniel , Him Wong Chik
Published: March 2018

We discuss near-conformal gauge theories beyond the standard model (BSM) where interesting results on the twelve-flavor β-function of massless fermions in the fundamental representation of the SU(3) color gauge group and dilaton tests of the light scalar with two massless fermions in the two-index symmetric tensor (sextet) representation can be viewed as parts of the same BSM paradigm under investigation. The clear trend in the decreasing size of β-functions at fixed renormalized gauge coupling is interpreted as a first indicator how the conformal window (CW) is approached in correlation with emergent near-conformal light scalars. BSM model building close to the CW will be influenced by differing expectations on the properties of the emergent light 0++ scalar either as a σ-particle of chiral symmetry breaking (ΧS B), or as a dilaton of scale symmetry breaking. The twelve-flavor β-function emerges as closest to the CW, perhaps near-conformal, or perhaps with an infrared fixed point (IRFP) at some unexplored strong coupling inside the CW. It is premature to speculate on dilaton properties of the twelveflavor model since the near-conformal realization remains an open question. However, it is interesting and important to investigate dilaton tests of the light sextet scalar whose β-function is closest to the CW in the symmetry breaking phase and emerges as the leading candidate for dilaton tests of the light scalar. We report results from high precision analysis of the twelve-flavor β-function [1] refuting its published IRFP [2, 3]. We present our objections to recent claims [4, 5] for non-universal behavior of staggered fermions used in our analysis. We also report our first analysis of dilaton tests of the light 0++ scalar in the sextet model and comment on related post-conference developments. The dilaton test is the main thrust of this conference contribution including presentation #405 on the nf = 12 β-function and presentation #260 on dilaton tests of the sextet model. They are both selected from the near-conformal BSM paradigm.
SU(3) sextet model with Wilson fermions
Authors: Hansen Martin , Pica Claudio
Published: March 2018

We present our final results for the SU(3) sextet model with the non-improved Wilson fermion discretization. We find evidence for several phases of the lattice model, including a bulk phase with broken chiral symmetry. We study the transition between the bulk and weak coupling phase which corresponds to a significant change in the qualitative behavior of spectral and scale setting observables. In particular the t0 and w0 observables seem to diverge in the chiral limit in the weak coupling phase. We then focus on the study of spectral observables in the chiral limit in the weak coupling phase at infinite volume. We consider the masses and decay constants for the pseudoscalar and vector mesons, the mass of the axial vector meson and the spin-1/2 baryon as a function of the quark mass, while controlling finite volume effects. We then test our data against both the IR conformal and the chirally broken hypotheses.

Preprint: CP3-Origins-2017-49 DNRF90
Update on SU(2) gauge theory with NF = 2 fundamental flavours.
Authors: Drach Vincent , Janowski Tadeusz , Pica Claudio
Published: March 2018

We present a non perturbative study of SU(2) gauge theory with two fundamental Dirac flavours. This theory provides a minimal template which is ideal for a wide class of Standard Model extensions featuring novel strong dynamics, such as a minimal realization of composite Higgs models. We present an update on the status of the meson spectrum and decay constants based on increased statistics on our existing ensembles and the inclusion of new ensembles with lighter pion masses, resulting in a more reliable chiral extrapolation.

Preprint: CP3-Origins-2017-048 DNRF90
Chiral Transition of SU(4) Gauge Theory with Fermions in Multiple Representations
Authors: Ayyar Venkitesh , DeGrand Thomas , Hackett Daniel C. , Jay William I. , T. Neil Ethan , Shamir Yigal , Svetitsky Benjamin
Published: March 2018

We report preliminary results on the finite temperature behavior of SU(4) gauge theory with dynamical quarks in both the fundamental and two-index antisymmetric representations. This system is a candidate to present scale separation behavior, where fermions in different representations condense at different temperature or coupling scales. Our simulations, however, reveal a single finite-temperature phase transition at which both representations deconfine and exhibit chiral restoration. It appears to be strongly first order. We compare our results to previous single-representation simulations. We also describe a Pisarski-Wilczek stability analysis, which suggests that the transition should be first order.
Weakly coupled conformal gauge theories on the lattice
Authors: Fodor Zoltan , Holland Kieran , Kuti Julius , Nogradi Daniel , Him Wong Chik
Published: March 2018

Results are reported for the β-function of weakly coupled conformal gauge theories on the lattice, SU(3) with Nf = 14 fundamental and Nf = 3 sextet fermions. The models are chosen to be close to the upper end of the conformal window where perturbation theory is reliable hence a fixed point is expected. The study serves as a test of how well lattice methods perform in the weakly coupled conformal cases. We also comment on the 5-loop β-function of two models close to the lower end of the conformal window, SU(3) with Nf = 12 fundamental and Nf = 2 sextet fermions.
Wilson and Domainwall Kernels on Oakforest-PACS
Authors: Kanamori Issaku , Matsufuru Hideo
Published: March 2018

We report the performance of Wilson and Domainwall Kernels on a new Intel Xeon Phi Knights Landing based machine named Oakforest-PACS, which is co-hosted by University of Tokyo and Tsukuba University and is currently fastest in Japan. This machine uses Intel Omni-Path for the internode network. We compare performance with several types of implementation including that makes use of the Grid library. The code is incorporated with the code set Bridge++.
openQ*D simulation code for QCD+QED
Authors: Campos Isabel , Fritzsch Patrick , Hansen Martin , Krstić Marinković Marina , Patella Agostino , Ramos Alberto , Tantalo Nazario
Published: March 2018

The openQ*D code for the simulation of QCD+QED with C* boundary conditions is presented. This code is based on openQCD-1.6, from which it inherits the core features that ensure its efficiency: the locally-deflated SAP-preconditioned GCR solver, the twisted-mass frequency splitting of the fermion action, the multilevel integrator, the 4th order OMF integrator, the SSE/AVX intrinsics, etc. The photon field is treated as fully dynamical and C* boundary conditions can be chosen in the spatial directions. We discuss the main features of openQ*D, and we show basic test results and performance analysis. An alpha version of this code is publicly available and can be downloaded from http://rcstar.web.cern.ch/.
Job Management and Task Bundling
Authors: Berkowitz Evan , Jansen Gustav R. , McElvain Kenneth , Walker-Loud André
Published: March 2018

High Performance Computing is often performed on scarce and shared computing resources. To ensure computers are used to their full capacity, administrators often incentivize large workloads that are not possible on smaller systems. Measurements in Lattice QCD frequently do not scale to machine-size workloads. By bundling tasks together we can create large jobs suitable for gigantic partitions. We discuss METAQ and mpi_jm, software developed to dynamically group computational tasks together, that can intelligently backfill to consume idle time without substantial changes to users’ current workflows or executables.
A staggered eigensolver based on sparse matrix bidiagonalization
Authors: Osborn James C. , Jin Xiao-Yong
Published: March 2018

We present a method for calculating eigenvectors of the staggered Dirac operator based on the Golub-Kahan-Lanczos bidiagonalization algorithm. Instead of using orthogonalization during the bidiagonalization procedure to increase stability, we choose to stabilize the method by combining it with an outer iteration that refines the approximate eigenvectors obtained from the inner bidiagonalization procedure. We discuss the performance of the current implementation using QEX and compare with other methods.
Decoupling of charm beyond leading order
Authors: Knechtli Francesco , Korzec Tomasz , Leder Björn , Moir Graham
Published: March 2018

We study the effective theory of decoupling of a charm quark at low energies. We do this by simulating a model, QCD with two mass-degenerate charm quarks. At leading order the effective theory is a pure gauge theory. By computing ratios of hadronic scales we have direct access to the power corrections in the effective theory. We show that these corrections follow the expected leading behavior, which is quadratic in the inverse charm quark mass.
Non-perturbative determination of cV, ZV and ZS/ZP in Nf = 3 lattice QCD
Authors: Heitger Jochen , Joswig Fabian , Vladikas Anastassios , Wittemeier Christian
Published: March 2018

We report on non-perturbative computations of the improvement coefficient cV and the renormalization factor ZV of the vector current in three-flavour O(a) improved lattice QCD with Wilson quarks and tree-level Symanzik improved gauge action. To reduce finite quark mass effects, our improvement and normalization conditions exploit massive chiral Ward identities formulated in the Schrödinger functional setup, which also allow deriving a new method to extract the ratio ZS/ZP of scalar to pseudoscalar renormalization constants. We present preliminary results of a numerical evaluation of ZV and cV along a line of constant physics with gauge couplings corresponding to lattice spacings of about 0:09 fm and below, relevant for phenomenological applications.
αs from the Hadronic Vacuum Polarisation
Authors: Hudspith Renwick , Lewis Randy , Maltman Kim , Shintani Eigo
Published: March 2018

We present our result for the strong coupling constant computed from the u-d vector Hadronic Vacuum Polarisation function. We use nf = 2 + 1 flavours of Domain Wall fermions at 3 lattice spacings, generated by the RBC-UKQCD collaboration. We identify several possible pitfalls in this method for determining the coupling and illustrate how to resolve them.
Wavelets and Lattice Field Theory.
Authors: Neuberger Herbert
Published: March 2018

When continuous fields are expanded in a wavelet basis, a D-dimensional continuum action becomes a (D+1)-dimensional lattice action on the naively discretized Poincare-patch coordinates of an Euclidean AdS(D+1). New possible criteria for acceptable actions open up.
Lattice simulation with the Majorana positivity
Authors: Yamamoto Arata , Hayata Tomoya
Published: March 2018

While the sign problem of the Dirac fermion is conditioned by the semipositivity of a determinant, that of the Majorana fermion is conditioned by the semipositivity of a Pfaffian. We introduce one sufficient condition for the semi-positivity of a Pfaffian. Based on the semi-positivity condition, we study an effective model of the Majorana fermion. We also present the application to the Dirac fermion.
Generating a mass gap using Feynman diagrams in an asymptotically free theory
Authors: Ayyar Venkitesh , Chandrasekharan Shailesh
Published: March 2018

Using the example of a two dimensional four-fermion lattice field theory, we show that Feynman diagrams can generate a mass gap in a theory with massless fermions that interact via a marginally relevant coupling. We show this by introducing an infrared cutoff that makes the perturbation series for the partition function convergent. We use a Monte Carlo approach to sample sufficiently high orders of diagrams and thus expose the presence of the mass gap.
Hubbard-Stratonovich-like Transformations for Few-Body Interactions
Authors: Körber Christopher , Berkowitz Evan , Luu Thomas
Published: March 2018

Through the development of many-body methodology and algorithms, it has become possible to describe quantum systems composed of a large number of particles with great accuracy. Essential to all these methods is the application of auxiliary fields via the Hubbard-Stratonovich transformation. This transformation effectively reduces two-body interactions to interactions of one particle with the auxiliary field, thereby improving the computational scaling of the respective algorithms. The relevance of collective phenomena and interactions grows with the number of particles. For many theories, e.g. Chiral Perturbation Theory, the inclusion of three-body forces has become essential in order to further increase the accuracy on the many-body level. In this proceeding, the an-alytical framework for establishing a Hubbard-Stratonovich-like transformation, which allows for the systematic and controlled inclusion of contact three-and more-body inter-actions, is presented.
One-loop perturbative coupling of A and A★ through the chiral overlap operator
Authors: Makino Hiroki , Morikawa Okuto , Suzuki Hiroshi
Published: March 2018

Recently, Grabowska and Kaplan constructed a four-dimensional lattice formulation of chiral gauge theories on the basis of the chiral overlap operator. At least in the tree-level approximation, the left-handed fermion is coupled only to the original gauge field A, while the right-handed one is coupled only to the gauge field A*, a deformation of A by the gradient flow with infinite flow time. In this paper, we study the fermion one-loop effective action in their formulation. We show that the continuum limit of this effective action contains local interaction terms between A and A*, even if the anomaly cancellation condition is met. These non-vanishing terms would lead an undesired perturbative spectrum in the formulation.
Tensor Network study of the (1+1)-dimensional Thirring Model
Authors: Carmen Bañuls Mari , Cichy Krzysztof , Kao Ying-Jer , David Lin C.-J. , Lin Yu-Ping , Tao-Lin Tan David
Published: March 2018

Tensor Network methods have been established as a powerful technique for simulating low dimensional strongly-correlated systems for over two decades. Employing the formalism of Matrix Product States, we investigate the phase diagram of the massive Thirring model. We also show the possibility of studying soliton dynamics and topological phase transition via the Thirring model.
Large N scaling and factorization in SU(N) Yang-Mills theory
Authors: Vera Miguel García , Sommer Rainer
Published: March 2018

We present results for Wilson loops smoothed with the Yang-Mills gradient flow and matched through the scale t0. They provide renormalized and precise operators allowing to test the 1/N2 scaling both at finite lattice spacing and in the continuum limit. Our results show an excellent scaling up to 1/N = 1/3. Additionally, we obtain a very precise non-perturbative confirmation of factorization in the large N limit.
An Alternative Lattice Field Theory Formulation Inspired by Lattice Supersymmetry-Summary of the Formulation-
Authors: D’Adda Alessandro , Kawamoto Noboru , Saito Jun
Published: March 2018

We propose a lattice field theory formulation which overcomes some fundamental diffculties in realizing exact supersymmetry on the lattice. The Leibniz rule for the difference operator can be recovered by defining a new product on the lattice, the star product, and the chiral fermion species doublers degrees of freedom can be avoided consistently. This framework is general enough to formulate non-supersymmetric lattice field theory without chiral fermion problem. This lattice formulation has a nonlocal nature and is essentially equivalent to the corresponding continuum theory. We can show that the locality of the star product is recovered exponentially in the continuum limit. Possible regularization procedures are proposed.The associativity of the product and the lattice translational invariance of the formulation will be discussed.
RG-inspired machine learning for lattice field theory
Authors: Foreman Sam , Giedt Joel , Meurice Yannick , Unmuth-Yockey Judah
Published: March 2018

Machine learning has been a fast growing field of research in several areas dealing with large datasets. We report recent attempts to use renormalization group (RG) ideas in the context of machine learning. We examine coarse graining procedures for perceptron models designed to identify the digits of the MNIST data. We discuss the correspondence between principal components analysis (PCA) and RG flows across the transition for worm configurations of the 2D Ising model. Preliminary results regarding the logarithmic divergence of the leading PCA eigenvalue were presented at the conference. More generally, we discuss the relationship between PCA and observables in Monte Carlo simulations and the possibility of reducing the number of learning parameters in supervised learning based on RG inspired hierarchical ansatzes.
Stiff self-interacting strings at high temperature QCD
Authors: S Bakry A. , Chen X. , Deliyergiyev M. , Galal A. , Khalaf A. , M Pengming P.
Published: March 2018

We investigate the implications of Nambu-Goto (NG), Lüscher Weisz (LW) and Polyakov-Kleinert (PK) effective string actions for the Casimir energy and the width of the quantum delocalization of the string in 4-dim pure SU(3) Yang-Mills lattice gauge theory. At a temperature closer to the critical point T/Tc=0.9, we found that the next to leading-order (NLO) contributions from the expansion of the NG string in addition to the boundary terms in LW action to decrease the deviations from the lattice data in the intermediate distance scales for both the quark-antiquark QQ̅ potential and broadening of the color tube compared to the free string approximation. We conjecture possible stiffness of the QCD string through studying the effects of extrinsic curvature term in PK action and find a good fitting behavior for the lattice Monte-Carlo data at both long and intermediate quark separations regions.