HEP Lattice·hep-lat

Thu·Nov 4, 2021Thursday·November 4, 2021

12 papers—9 primary·3 cross-listed·reconstructed*

01*
Conjecture about the QCD phase diagram
José Antonio García-Hernández🇲🇽 · Edgar López-Contreras🇲🇽 · Elías Natanael Polanco-Euán🇲🇽 · Wolfgang Bietenholz🇲🇽
We present a phase diagram study of the O(4) model as an effective theory for 2-flavor QCD. In the chiral limit, both theories perform spontaneous symmetry breaking with isomorphic groups, which suggests that they belong to the same universality class. Since we are interested in high temperature, we further assume dimensional reduction to the 3d O(4) model, which implies topological sectors. According to Skyrme and others, the corresponding topological charge represents the baryon number. Hence the baryon chemical potential $μ_{B}$ appears as an imaginary vacuum angle, which can be included in the lattice simulations without any sign problem. We present simulation results for the critical line in the chiral limit, and for the crossover in the presence of light quark masses. The shapes of these lines are compatible with other conjectures, but up to about $μ_{B} \approx 300$ MeV we do not find a Critical Endpoint, although there are indications for it to be near-by.
hep-latPoS(2022)·4 citations
02*
Lattice QED in external electromagnetic fields
D. K. Sinclair🇺🇸 · J. B. Kogut🇺🇸
We study QED in external electromagnetic fields using methods developed for simulating lattice QCD. Our first project is to simulate QED in a constant (in space and time) external magnetic field on a euclidean space-time lattice using the Rational Hybrid Monte Carlo (RHMC) method. Observables we measure include the condensate $⟨ ψ ˉ ψ ⟩$ and the effective electron action after integrating out the fermion fields. We look for evidence that the combined effect of the magnetic field and the electron-positron attraction from QED produces a non-zero condensate in the limit of zero electron mass, a non-perturbative effect analogous to spontaneous chiral symmetry breaking. Very preliminary evidence is that such a condensate exists, at least for strong external magnetic fields and unphysically large electric charge. In addition, we are storing field configurations to measure the expected distortions and screenings of the coulomb field of a charged particle due to the vacuum polarization asymmetries produced by the magnetic field. We hope also to measure the dynamical contribution to the electron mass produced by the same mechanism that produces a finite condensate in the zero input mass limit.
hep-latPoS(2022)·3 citations
03*
Numerical simulation of self-dual U(1) lattice field theory with electric and magnetic matter
Maria Anosova🇦🇹 · Christof Gattringer🇦🇹 · Nabil Iqbal🇬🇧 · Tin Sulejmanpasic🇬🇧
We study a recently proposed formulation of U(1) lattice field theory with electric and magnetic matter based on the Villain formulation. This discretization allows for a duality that gives rise to relations between weak and strong gauge coupling. There exists a self-dual value of the gauge coupling where one may study the model as a function of the remaining matter coupling. Using Monte Carlo simulations based on a worldline/worldsheet representation of the system we evaluate order parameters for spontaneous breaking of self-duality. We find that in some interval of the matter coupling self-duality becomes broken spontaneously. We determine the endpoints of this interval and study the nature of the corresponding critical points. Finally we explore the system away from the self-dual gauge coupling and show that when crossing the self-dual point a first order jump is seen in the order parameters.
hep-latPoS(2022)·5 citations
04*
What is chiral susceptibility probing?
JLQCD collaboration: S. Aoki🇯🇵 · Y. Aoki🇯🇵 · H. Fukaya🇯🇵 · S. Hashimoto🇯🇵 · C. Rohrhofer🇯🇵 · K. Suzuki🇯🇵
In the early days of QCD, the axial $U (1)$ anomaly was considered as a trigger for the breaking of the $S U (2)_{L} \times S U (2)_{R}$ symmetry through topological excitations of gluon fields. However, it has been a challenge for lattice QCD to quantify the effect. In this work, we simulate QCD at high temperatures with chiral fermions. The exact chiral symmetry enables us to separate the contribution from the axial $U (1)$ breaking from others among the susceptibilities in the scalar and pseudoscalar channels. Our result in two-flavor QCD indicates that the chiral susceptibility, which is conventionally used as a probe for $S U (2)_{L} \times S U (2)_{R}$ breaking, is actually dominated by the axial $U (1)$ breaking at temperatures $T \geq 165$ MeV.
hep-lathep-phPoS(2022)·3 citations
05*
A spin-charge flip symmetric fixed point in 2+1d with massless Dirac fermions
Hanqing Liu🇺🇸
We study a quantum phase transition of electrons on a two-dimensional square lattice. Our lattice model preserves the full $O (4)$ symmetry of free spin- $\frac{1}{2}$ Dirac fermions on a bipartite lattice. In particular, it not only preserves the usual $SO (4)$ (spin-charge) symmetry like in the half-filling Hubbard model, but also preserves a $Z_{2}$ spin-charge flip symmetry. Using sign-problem-free Monte Carlo simulation, we find a second order quantum phase transition from a massless Dirac phase to a massive phase with spontaneously chosen spin order or charge order, which become simultaneously critical at the critical point. We analyze all the possible 4-fermion couplings in the continuum respecting the lattice symmetry, and identify the terms whose effective potential in the broken phase is consistent with the numerical results. Using renormalization group calculations in the continuum, we show the existence of the new spin-charge flip symmetric fixed point and calculate its critical exponents.
hep-latcond-mat.str-elhep-thPoS(2022)·3 citations
06*
3+1D $θ$ -Term on the Lattice from the Hamiltonian Perspective
Angus Kan🇨🇦 · Lena Funcke🇺🇸 · Stefan Kühn🇨🇾 · Luca Dellantonio🇨🇦 · Jinglei Zhang🇨🇦 · Jan F. Haase🇨🇦 · Christine A. Muschik🇨🇦 · Karl Jansen🇩🇪
Quantum and tensor network simulations have emerged as prominent sign-problem free approaches to lattice gauge theories. Unlike conventional Markov chain Monte Carlo methods, they are based on the Hamiltonian formulation. In this talk, we fill a gap in the literature and present the first derivation of the Hamiltonian 3+1D $θ$ -term -- which is an important sign-problem afflicted term -- for Abelian and non-Abelian lattice gauge theories. Furthermore, we perform exact diagonalization for a 3+1D U(1) lattice gauge theory including the $θ$ -term on a unit periodic cube. Our numerical results reveal a novel phase transition at fixed values of $θ$ in the strong-coupling regime. The transition is evidenced by an avoided level crossing in the ground state energy, as well as sudden changes in the plaquette expectation value, the electric energy density, and the topological charge density. Extensions of our work to larger lattices can be readily performed using state-of-the-art tensor network simulations. Moreover, our work provides a concrete starting point for an eventual quantum simulation of the $θ$ -dependent phase structure and dynamics of lattice gauge theories in 3+1D. This talk is mainly based on [1]. We expand beyond [1] by including a derivation of the (non-)Abelian fixed-length Higgs term in the Hamiltonian formulation for future studies of (non-)Abelian-Higgs models with a $θ$ -term.
hep-latPoS(2022)·7 citations
07*
With complex Langevin towards the QCD phase diagram
Felipe Attanasio🇩🇪 · Benjamin Jäger · Felix P.G. Ziegler🇩🇰
We use complex Langevin simulations to explore the QCD phase diagram over a large range of chemical potentials and temperatures. For our simulations, we use two flavours of dynamical Wilson fermions with a pion mass of approximately $480$ MeV with a spatial volume of $2 4^{3}$ . Here we report on consistency checks at zero chemical potentials and present our results for the fermion density and the Polyakov loop. We find that at the lowest temperature the fermion density remains zero until $m_{N} /3$ , in line with the expectations from the Silver Blaze phenomenon.
hep-latPoS(2022)·4 citations
08*
The static energy in 2+1+1-flavor QCD
Sebastian Steinbeißer🇩🇪 · Nora Brambilla🇩🇪 · Rafael L. Delgado🇪🇸 · Andreas S. Kronfeld🇺🇸 · Viljami Leino🇩🇪 · Peter Petreczky🇺🇸 · Antonio Vairo🇩🇪 · Johannes Heinrich Weber🇩🇪
We report on the status of the analysis of the static energy in $2 + 1 + 1$ -flavor QCD. The static energy is obtained by measuring Wilson line correlators in Coulomb gauge using the HISQ action, yielding the scales $r_{0} / a$ , $r_{1} / a$ , $r_{2} / a$ , their ratios, and the string tension $σ r_{i}^{2}$ . We put emphasis on the possible effects due to the dynamical charm-quark by comparing the lattice results to continuum results of the static energy with and without a massive flavor at two-loop accuracy. We employ gauge-field ensembles from the HotQCD and MILC Collaborations.
hep-lathep-phhep-thPoS(2022)·2 citations
09*
The asymptotic approach to the continuum of lattice QCD spectral observables
Nikolai Husung🇩🇪 · Peter Marquard🇩🇪 · Rainer Sommer🇩🇪
We consider spectral quantities in lattice QCD and determine the asymptotic behavior of their discretization errors. Wilson fermion with O $(a)$ -improvement, (Möbius) Domain wall fermion (DWF), and overlap Dirac operators are considered in combination with the commonly used gauge actions. Wilson fermions and DWF with domain wall height $M_{5} = 1 + O (g_{0}^{2})$ have the same, approximate, form of the asymptotic cutoff effects: $K a^{2} [g ˉ^{2} (a^{- 1})]^{0.760}$ . A domain wall height $M_{5} = 1.8$ , as often used, introduces large mass-dependent $K^{'} (m) a^{2} [g ˉ^{2} (a^{- 1})]^{0.518}$ effects. Massless twisted mass fermions have the same form as Wilson fermions when the Sheikholeslami-Wohlert term [1] is included. For their mass-dependent cutoff effects we have information on the exponents $Γ^_{i}$ of $g ˉ^{2} (a^{- 1})$ but not for the pre-factors. For staggered fermions there is only partial information on the exponents. We propose that tree-level $O (a^{2})$ improvement, which is easy to do [2], should be used in the future -- both for the fermion and the gauge action. It improves the asymptotic behavior in all cases.
hep-latPLB(2022)·38 citations
10*
Determination of the generalized parton distributions through the analysis of the world electron scattering data considering two-photon exchange corrections
Hadi Hashamipour🇮🇷 · Muhammad Goharipour🇮🇷 · K. Azizi🇮🇷 · S.V. Goloskokov🇷🇺
We determine the valence generalized parton distributions (GPDs) $H_{v}^{q}$ and $E_{v}^{q}$ with their uncertainties at zero skewness by performing a $χ^{2}$ analysis of the world electron scattering data considering two-photon exchange corrections. The data include a wide and updated range of the electric and magnetic form factors (FFs) of the proton and neutron. As a result, we find that there are no enough constraints on GPDs $E_{v}^{q}$ from FFs data solely though $H_{v}^{q}$ are well constrained. By including the new data of the charge and magnetic radius of the nucleon in the analysis, we show that they put new constraints on the final GPDs, especially on $E_{v}^{q}$ . Moreover, we calculate the gravitational FF $M_{2}$ and the total angular momentum $J^{q}$ using the extracted GPDs and compare them with the FFs obtained from the light-cone QCD sum rules (LCSR) and Lattice QCD. We show that our results are interestingly in a good consistency with the pure theoretical predictions.
↳ hep-phhep-exhep-latPRD(2022)·30 citations
11*
Cancellation of IR Divergences in 3d Abelian Gauge Theories
Giovanni Galati🇮🇹 · Marco Serone🇮🇹
Three dimensional abelian gauge theories classically in a Coulomb phase are affected by IR divergences even when the matter fields are all massive. Using generalizations of Ward-Takahashi identities, we show that correlation functions of gauge-invariant operators are IR finite to all orders in perturbation theory. Gauge invariance is sufficient but not necessary for IR finiteness. In particular we show that specific gauge-variant correlators, including the two-point function of matter fields, are also IR finite to all orders in perturbation theory. Possible applications of these results are briefly discussed.
↳ hep-thcond-mat.stat-mechcond-mat.str-elhep-lat+1JHEP(2022)·4 citations
12*
Introduction to Monte Carlo for Matrix Models
Raghav G. Jha🇨🇦
We consider a wide range of matrix models and study them using the Monte Carlo technique in the large $N$ limit. The results we obtain agree with exact analytic expressions and recent numerical bootstrap methods for models with one and two matrices. We then present new results for several unsolved multi-matrix models where no other tool is yet available. In order to encourage an exchange of ideas between different numerical approaches to matrix models, we provide programs in Python that can be easily modified to study potentials other than the ones discussed. These programs were tested on a laptop and took between a few minutes to several hours to finish depending on the model, $N$ , and the required precision.
↳ hep-thhep-latphysics.comp-phSciPost Phys.Lect.Notes(2022)·17 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.