Search results for "lattice [space-time]"

Broad excitations in a 2+1D overoccupied gluon plasma

2021

Motivated by the initial stages of high-energy heavy-ion collisions, we study excitations of far-from-equilibrium 2+1 dimensional gauge theories using classical-statistical lattice simulations. We evolve field perturbations over a strongly overoccupied background undergoing self-similar evolution. While in 3+1D the excitations are described by hard-thermal loop theory, their structure in 2+1D is nontrivial and nonperturbative. These nonperturbative interactions lead to broad excitation peaks in spectral and statistical correlation functions. Their width is comparable to the frequency of soft excitations, demonstrating the absence of soft quasiparticles in these theories. Our results also su…

Ab initio simulations of silver film adhesion on α-Al2O3 (0 0 0 1) and MgO (1 0 0) surfaces

1998

The atomic and electronic structure of the Ag/MgO (1 0 0) and Ag/alpha-Al2O3(0 0 0 1) interfaces are calculated by means of the ab initio Hartree-Fock approach combined with a supercell model. The electronic density distribution and the interface binding energy/equilibrium distance for both interfaces are analyzed. For a complete (1:1) surface coverage of the MgO surface the energetically most favorable adsorption position for the Ag atom is above the O atom. For the Ag/alpha-Al2O3 interface the preferable adsorption positions for the Ag atom are over centers of either large equilateral oxygen triangles (in Al-substituted sites of Al-terminated corundum surface) or isosceles oxygen triangle…

Properties of the ground-state baryons in chiral perturbation theory

2010

15th High Energy Physics International Conference on Quantum Chromodynamics. Montpellier (FRANCE). JUN 28-JUL 02, 2010

Unitarized Chiral Perturbation Theory in a finite volume: scalar meson sector

2011

We develop a scheme for the extraction of the properties of the scalar mesons f0(600), f0(980), and a0(980) from lattice QCD data. This scheme is based on a two-channel chiral unitary approach with fully relativistic propagators in a finite volume. In order to discuss the feasibility of finding the mass and width of the scalar resonances, we analyze synthetic lattice data with a fixed error assigned, and show that the framework can be indeed used for an accurate determination of resonance pole positions in the multi-channel scattering.

Vacuum correlators at short distances from lattice QCD

2021

Non-perturbatively computing the hadronic vacuum polarization at large photon virtualities and making contact with perturbation theory enables a precision determination of the electromagnetic coupling at the $Z$ pole, which enters global electroweak fits. In order to achieve this goal ab initio using lattice QCD, one faces the challenge that, at the short distances which dominate the observable, discretization errors are hard to control. Here we address challenges of this type with the help of static screening correlators in the high-temperature phase of QCD, yet without incurring any bias. The idea is motivated by the observations that (a) the cost of high-temperature simulations is typica…

Systematic T1 improvement for hyperpolarized 129xenon

2015

The spin-lattice relaxation time T1 of hyperpolarized (HP)-(129)Xe was improved at typical storage conditions (i.e. low and homogeneous magnetic fields). Very long wall relaxation times T(1)(wall) of about 18 h were observed in uncoated, spherical GE180 glass cells of ∅=10 cm which were free of rubidium and not permanently sealed but attached to a standard glass stopcock. An "aging" process of the wall relaxation was identified by repeating measurements on the same cell. This effect could be easily removed by repeating the initial cleaning procedure. In this way, a constant wall relaxation was ensured. The Xe nuclear spin-relaxation rate 1/T1(Xe-Xe) due to van der Waals molecules was invest…

Dynamics of supercooled liquids and glassy solids

2001

Hardening and long-range stress formation in lithium fluoride induced by energetic ions

2003

Abstract LiF crystals were irradiated with Au, Pb, Bi and S ions in the energy range 400–2300 MeV and studied by means of Vickers microindentation. Remarkable hardening effects are observed which depend on the applied fluence and ion species, and correlate with the ion energy loss along the ion path. Structural investigations reveal irradiation-induced stress extending deep into the adjacent non-irradiated crystal and leading to the formation of dislocations. X-ray diffraction measurements of the irradiated crystals show a decrease of the lattice constant indicating the presence of internal stress.

Neutron irradiation influence on magnesium aluminium spinel inversion

2002

Abstract Grown by the Verneuil method MgO · nAl2O3 single crystals and natural spinel crystal have been studied using X-ray diffraction and photoluminescence spectra. The fast neutron irradiation of magnesium aluminium spinel leads to the lattice parameter decrease. The bond lengths of Mg–O and Al–O vary with the u-parameter and the lattice parameter. On the other hand, the bond lengths are related with the inversion parameter. Using changes of the lattice parameter during irradiation we have calculated the inversion parameter, which is 15–20%. In the luminescence spectra, the fast neutron radiation (fluence 1016 cm−2) produces an increase in the intensity ratio of the N- to R-lines by 5–20…

The subtraction contribution to the muonic-hydrogen Lamb shift: a point for lattice QCD calculations of the polarizability effect

2020

The proton-polarizability contribution to the muonic-hydrogen Lamb shift is a major source of theoretical uncertainty in the extraction of the proton charge radius. An empirical evaluation of this effect, based on the proton structure functions, requires a systematically improvable calculation of the "subtraction function", possibly using lattice QCD. We consider a different subtraction point, with the aim of accessing the subtraction function directly in lattice calculations. A useful feature of this subtraction point is that the corresponding contribution of the structure functions to the Lamb shift is suppressed. The whole effect is dominated by the subtraction contribution, calculable o…