Symmetry (physics)

About: Symmetry (physics) is a research topic. Over the lifetime, 26435 publications have been published within this topic receiving 500189 citations. The topic is also known as: symmetry (physics) & physical symmetry.

Constraints imposed by CP conservation in the presence of pseudoparticles

Abstract: We elaborate on an earlier discussion of CP conservation of strong interactions which includes the effect of pseudoparticles. We discuss what happens in theories of the quantum-chromodynamics type when we include weak and electromagnetic interactions. We find that strong CP conservation remains a natural symmetry if the full Lagrangian possesses a chiral U(1) invariance. We illustrate our results by considering in detail a recent model of (weak) CP nonconservation.

Theory of symmetry in nuclear magnetic relaxation including applications to high resolution N.M.R. line shapes

Abstract: It is shown in discussing problems involving magnetic relaxation in liquids that, whilst the usual Hilbert space spanned by all the eigenkets of the spin hamiltonian does not reflect any symmetry inherent in the spin system, the vector space (Liouville space) comprising all operators of the spin system does so. The transformation properties of the Liouville operator, as reflected by those of the high resolution spin hamiltonian and relaxation operators whose effects are introduced by means of Redfield relaxation theory, with respect to arbitrary rotations of the coordinate system are investigated. The use of irreducible tensor operators as a set of basis operators spanning Liouville space is stressed, since it is shown that their super-matrix elements of the Liouville operator are given by the Wigner-Eckart theorem provided that relaxation by anisotropy of the chemical shift or anisotropic random fields is absent. These arguments are independent of the fine details of molecular reorientation in the extrem...

Tunable transport with broken space-time symmetries

Abstract: Transport properties of particles and waves in spatially periodic structures that are driven by external time-dependent forces manifestly depend on the space-time symmetries of the corresponding equations of motion. A systematic analysis of these symmetries uncovers the conditions necessary for obtaining directed transport. In this work we give a unified introduction into the symmetry analysis and demonstrate its action on the motion in one-dimensional periodic, both in time and space, potentials. We further generalize the analysis to quasi-periodic drivings, higher space dimensions, and quantum dynamics. Recent experimental results on the transport of cold and ultracold atomic ensembles in ac-driven optical potentials are reviewed as illustrations of theoretical considerations.

Theory of indirect interaction between chemisorbed atoms

Abstract: Progress in the development of the theory of two chemisorbed atoms has been hindered by the very low symmetry of the problem. Mono-layers of adatoms are simplest since they have the full two-dimensional symmetry of the substrate. Going to a (2 × 1) or a (2 × 2) adlayer, which doubles the size of the surface primitive cell, quadruples the size of a secular matrix, raising computer time even more. At the other end of the scale, a single adatom (in a symmetric site) will at least have the point symmetry of the substrate. With jellium as a substrate, this increases to full rotational and translational symmetry. Conserved quantities (“good quantum numbers”), which make calculations simpler, are associated with these symmetries. As a result, a variety of elaborate many-body techniques have been successfully applied to these systems; there are several excellent recent reviews.1,2 For two adatoms on a surface, there is little or no symmetry, typically just a twofold rotation or mirror plane (often leadin...