Quantum evolution across singularities: the case of geometrical resolutions

We continue the study of time-dependent Hamiltonians with an isolated singularity in their time dependence, describing propagation on singular space-times. In previous work, two of us have proposed a "minimal subtraction" prescription for the simplest class of such systems, involving Hamiltonians with only one singular term. On the other hand, Hamiltonians corresponding to geometrical resolutions of space-time tend to involve multiple operator structures (multiple types of dependence on the canonical variables) in an essential way. We consider some of the general properties of such (near-)singular Hamiltonian systems, and further specialize to the case of a free scalar field on a two-parameter generalization of the null-brane space-time. We find that the singular limit of free scalar field evolution exists for a discrete subset of the possible values of the two parameters. The coordinates we introduce reveal a peculiar reflection property of scalar field propagation on the generalized (as well as the original) null-brane. We further present a simple family of pp-wave geometries whose singular limit is a light-like hyperplane (discontinuously) reflecting the positions of particles as they pass through it.Comment: 25 pages, 1 figur

Haldane-gap excitations in the low-H_c 1-dimensional quantum antiferromagnet NDMAP

Inelastic neutron scattering on deuterated single-crystal samples is used to study Haldane-gap excitations in the new S=1 one-dimensional quantum antiferromagnet NDMAP, that was recently recognized as an ideal model system for high-field studies. The Haldane gap energies $\Delta_x=0.42$ meV, $\Delta_y=0.52$ meV and $\Delta_z=1.86$ meV, for excitations polarized along the a, b, and c crystallographic axes, respectively, are directly measured. The dispersion perpendicular to the chain axis c is studied, and extremely weak inter-chain coupling constants $J_y=1.8\cdot 10^{-3}$ meV and $J_x=3.5\cdot 10^{-4}$ meV, along the a and b axes, respectively, are determined. The results are discussed in the context of future experiments in high magnetic fields.Comment: 5 pages, 4 figures, submitted to Phys. Rev.

Structure and conformational dynamics of molecules in the excited electronic states: theory and experiment

The structure of conformational non-rigid molecules in the excited electronic states are investigated by joint theoretical and experimental methods. The theoretical part of work consist of two stages. In first stage the ab initio quantum-chemical calculations are carried out using high level methods. In second stage the vibrational problems of the various dimensions are solved by variational method for vibrations of large amplitude. In experimental part of work the vibronic spectra are investigated: gas-phase absorption and also, fluorescence excitation spectra of jet-cooled molecules. Some examples are considered

Structure and conformational dynamics of molecules in the excited electronic states: theory and experiment

The structure of conformational non-rigid molecules in the excited electronic states are investigated by joint theoretical and experimental methods. The theoretical part of work consist of two stages. In first stage the ab initio quantum-chemical calculations are carried out using high level methods. In second stage the vibrational problems of the various dimensions are solved by variational method for vibrations of large amplitude. In experimental part of work the vibronic spectra are investigated: gas-phase absorption and also, fluorescence excitation spectra of jet-cooled molecules. Some examples are considered

Peculiarities in fragment mass distribution in the 238U\bf{^{238}U} + 40Ar\bf{^{40}Ar} (243 MeV) reaction

A pronounced fine structure (FS) in the form of distinct peaks was observed in neutron gated mass spectra from the decay of the $^{278}$110 composite system produced in the reaction $\mathsf{^{238}U}$ + $\mathsf{^{40}Ar}$ (243 MeV) at an initial excitation energy $E^*> 70$ MeV. The FS peaks are located in the vicinity of mass numbers 70-80, 100, and 130, which correspond to those of magic nuclei (clusters). In the data there is also evidence for a new type of decay -collinear cluster tripartition of an excited nucleus