Search Results

Since molecules consist of positive and negative particles, they can have electric dipole moments when oriented in electric fields and a molecular beam can be deflected in a non-uniform electric field. Theoretical discussions of the energies, deflections, and resonance transitions are given. From experimental measurements of the electric resonance spectrum, various molecular properties, such as the electric dipole moment of the molecule, hyperfine structure, and contributions from different molecular vibrational states are obtained.

The evaporation of an alkali metal halide (MX) yields a mixture of monomers and smaller amounts of dimers, trimers, and tetramers. This chapter describes the monomers in terms of their electric dipole moments, dissociation energies, and bond distances. The spherical ion model is used to construct potential energy curves and to calculate dissociation energies in reasonable agreement with their experimental counterparts from the experimental bond distances. Similar calculations on the dimers and on crystals with rock salt structure indicate that the M-X bond distances should be 5% and 15%, respectively, longer than in the monomers. The polarizable ion model leads to significantly better agreement between experimental and calculated electric dipole moments than the spherical ion model. Finally, the crystal structures of compounds containing a negatively charge alkali metal atom or even an isolated electron as cations are described.

These lectures aim to explain how certain types of atomic, molecular, and optical physics experiments can have a substantial impact in modern particle physics. A central pedagogical goal is to describe, using only concepts familiar to atomic experimentalists, how new particles can lead to new terms in the atomic or molecular Hamiltonian. Well-motivated examples are discussed, including potential dark matter candidates known as “dark photons”, known and as-yet unknown Higgs bosons, and supersymmetric particles leading to CP violation. The observable effects of new Hamiltonian terms associated with these phenomena are worked out, and state-of-the-art strategies for detecting them, using atomic and molecular experiments, are described for some cases. Remarkably, the sensitivity of atomic/molecular experiments can make it possible to detect new particles even more massive than those that can be created directly at the largest high-energy colliders.

The last chapter of the volume addresses the question of dipolar gases, which exhibit peculiar long-range and anisotropic two-body interactions. Dipolar interactions of both magnetic and electric nature are discussed. The long-range nature of the force and its anisotropic behaviour affect the conditions of stability of the gas in the presence of harmonic trapping in a peculiar way, giving rise to stable as well as to metastable configurations. The long-range and anisotropic nature of the dipolar interaction is also the origin of a series of novel dynamic phenomena, such as the anisotropic propagation of sound and the possible emergence of rotonic excitations in quasi-two-dimensional configurations. Some key features of dipolar Fermi gases, like the deformation of the Fermi surface, are also outlined.

Lattice vibrations which involve a fluctuating electric dipole have quite different properties from non-polar vibrations. In particular, they couple directly via the dipole moment to the radiation field in the crystal to form mixed phonon-photon modes which have a characteristic dispersion relation and are known as polaritons. Their frequencies generally depend on wavevector and on their polarization, and can be readily explored by direct absorption of infrared radiation or by the inelastic scattering of light. In this chapter, soft modes are viewed as damped harmonic oscillators with possibly temperature-dependent descriptive parameters. The effects of electronic contributions to electric dipole moment are discussed and represented by a single damped harmonic oscillator describing electron-shell vibrations about the ionic cores. The chapter also looks at the dielectric function and linear response, infrared spectra, Raman spectroscopy, some experimental studies, and Rayleigh scattering and critical opalescence.

Chapter 2 describes experiments searching for CP symmetry violations that might account for the matter–antimatter imbalance in our universe. It describes the historical discovery of mesons and quantum-mechanical oscillations between particle and antiparticle (i.e., particle–antiparticle oscillations) in the neutral K meson and heavier meson systems. It introduces quarks and quark flavor. The chapter relates CP violation to violations of time reversal invariance that might be revealed by a spatial separation of positive and negative electric charge within or around the fundamental constituent particles of matter. It describes a halfcentury of experimental searches, including ongoing projects, for the particle electric dipole moments that would characterize such a charge separation. Technological advances (such as ultra-cold neutron beams) and theoretical concepts (such as vacuum polarization) relevant to these searches are introduced. While some CP violation has been clearly observed, its extent remains insufficient to account for the universe’s matter–antimatter imbalance.

This chapter describes particle reactions that violate CP and T symmetry, the decay of the neutral K meson and the neutral B meson. It presents the Kobayashi-Maskawa model that explains how the Standard Model can provide a theory of CP and T violation and describes experimental tests of that model.