Search results for "lattice field theory"
showing 10 items of 150 documents
The Soliton Concept in Lattice Dynamics
1996
In previous chapters we have considered nonlinear waves in the macroworld. We have examined different systems which provide the simplest examples of onedimensional systems or devices, where the localized waves or pulses called solitons can be simply and coherently created, easily observed, and manipulated on a macroscopic scale. At the microscopic level the localized nonlinear wave modes have a spatial extension ranging from less than a few microns to a few angstroms. These excitations, which correspond to large-amplitude atomic or molecular motions, are mainly created by thermal processes, sometimes by some external stimulus; their experimental manifestation is indirect; their observation …
Lattice quantum hadrodynamics
1992
Quantum corrections to the mean-field equation of state for nuclear matter are estimated in a lattice simulation of quantum hadrodynamics. In contrast with the standard coordinate-space methods used in lattice QCD, the calculations are carried out here in momentum space and on nonhypercubic (irregular) lattices. The quantum corrections to the known mean-field equation of state were found to be considerable.
Thermal field theories and shifted boundary Conditions
2014
The analytic continuation to an imaginary velocity of the canonical partition function of a thermal system expressed in a moving frame has a natural implementation in the Euclidean path-integral formulation in terms of shifted boundary conditions. The Poincare' invariance underlying a relativistic theory implies a dependence of the free-energy on the compact length L_0 and the shift xi only through the combination beta=L_0(1+xi^2)^(1/2). This in turn implies that the energy and the momentum distributions of the thermal theory are related, a fact which is encoded in a set of Ward identities among the correlators of the energy-momentum tensor. The latter have interesting applications in latti…
Extracting three-body observables from finite-volume quantities
2015
Scattering and transition amplitudes with three-hadron final states play an important role in nuclear and particle physics. However, predicting such quantities using numerical Lattice QCD is very difficult, in part because of the effects of Euclidean time and finite volume. In this review we highlight recent formal developments that work towards overcoming these issues. We organize the presentation into three parts: large volume expansions, non-relativistic nonperturbative analyses, and nonperturbative studies based in relativistic field theory. In the first part we discuss results for ground state energies and matrix elements given by expanding in inverse box length, $1/L$. We describe com…
Energy relaxation in a? 4 with long range interactions
1995
We investigate the influence of long range interactions on the relaxation behaviour of a lattice model with an on-site potential ofϕ 4-type and “infinite” range harmonic interactions. For finite number of particlesN, it is shown that the autocorrelation functions of the fluctuations of the one-particle energiesE n(t) decays exponentially. The corresponding relaxation time τ is proportional toN and is given by τ(T, N) =Nτ0(T). The temperature dependent time scale τ0 can explicitly be related to the dynamics of a one-particle correlator of the noninteracting system. The results are derived using Mori-Zwanzig projection formalism. The corresponding memory kernel is calculated within a mode cou…
Quantum simulation of gauge potentials with cold atoms in optical lattices: a tunable platform for relativistic fermions and axions
2014
We offer here a brief introduction to the idea of quantum simulations with cold atomic gases, with focus on the recent efforts towards artificial gauge potentials and fields. This is mainly intended as a sort of “pedestrian guide” for people not yet working in the field, but curious to get a first contact with it; longer and deeper reviews are addressed for deeper details. As a special case, we focus here on reviewing some own previous contributions about a flexible toolbox based on bichromatic optical lattices and Raman assisted tunnelling. Such a scheme would allow good control on the mass and kinetic terms of a lattice Hamiltonian in different effective dimensions. If realized with fermi…
Hamiltonian lattice QCD at finite density: equation of state in the strong coupling limit
2001
The equation of state of Hamiltonian lattice QCD at finite density is examined in the strong coupling limit by constructing a solution to the equation of motion corresponding to an effective Hamiltonian describing the ground state of the many body system. This solution exactly diagonalizes the Hamiltonian to second order in field operators for all densities and is used to evaluate the vacuum energy density from which we obtain the equation of state. We find that up to and beyond the chiral symmetry restoration density the pressure of the quark Fermi sea can be negative indicating its mechanical instability. Our result is in qualitative agreement with continuum models and should be verifiabl…
Nucleon isovector charges and twist-2 matrix elements with Nf=2+1 dynamical Wilson quarks
2019
We present results from a lattice QCD study of nucleon matrix elements at vanishing momentum transfer for local and twist-2 isovector operator insertions. Computations are performed on gauge ensembles with nonperturbatively improved ${N}_{f}=2+1$ Wilson fermions, covering four values of the lattice spacing and pion masses down to ${M}_{\ensuremath{\pi}}\ensuremath{\approx}200\text{ }\text{ }\mathrm{MeV}$. Several source-sink separations (typically $\ensuremath{\sim}1.0$ to $\ensuremath{\sim}1.5\text{ }\text{ }\mathrm{fm}$) allow us to assess excited-state contamination. Results on individual ensembles are obtained from simultaneous two-state fits across all observables and all available sou…
Finite size effects at phase transitions
2008
For many models of statistical thermodynamics and of lattice gauge theory computer simulation methods have become a valuable tool for the study of critical phenomena, to locate phase transitions, distinguish whether they are of first or second order, and so on. Since simulations always deal with finite systems, analysis of finite size effects by suitable finite size scaling concepts is a key ingredient of such applications. The phenomenological theory of finite size scaling is reviewed with emphasis on the concept of probability distributions of order parameter and/or energy. Attention is also drawn to recent developments concerning anisotropic geometries and anisotropic critical behavior, …
Chiral Instabilities and the Onset of Chiral Turbulence in QED Plasmas
2020
We present a first principles study of chiral plasma instabilities and the onset of chiral turbulence in QED plasmas far from equilibrium. By performing classical-statistical lattice simulations of the microscopic theory, we show that the generation of strong helical magnetic fields from a helicity imbalance in the fermion sector proceeds via three distinct phases. During the initial linear instability regime the helicity imbalance of the fermion sector causes an exponential growth(damping) of magnetic field modes with right(left) handed polarization, for which we extract the characteristic growth (damping) rates. Secondary growth of unstable modes accelerates the helicity transfer from fer…