A generalized p-form model in D=3

A topological model in three dimensions is proposed. It combines the Chern-Simons action with a BFK-model which was investigated recently by the authors of hep-th/9906146. The finiteness of the model to all orders of perturbation theory is shown in the framework of algebraic renormalization procedure.Comment: 15 page

Tilted axis rotation, candidates for chiral bands, and wobbling motion in 138Nd

High-spin states in 138Nd were investigated using the reaction 94Zr(48Ca,4n), detecting coincident γ rays with the gasp spectrometer. A rich level scheme was constructed including four bands of negative parity at low spins, eight bands of dipole transitions, and eight bands of quadrupole transitions at medium spins. The cranked shell model and the tilted-axis cranking model are used to assign configurations to the observed bands, where zero pairing is assumed. For selected configurations the case of finite pairing is also considered. A consistent notation for configuration assignment that applies for both zero and finite pairing is introduced. The observed bands are interpreted as rotation around the short and long principal axes (quadrupole bands), as well as around a tilted axis (dipole bands). The dipole bands have an intermediate character, between magnetic and collective electric rotation. A pair of dipole bands is identified as candidates for chiral partners. The possible existence of the wobbling mode at low deformation and medium spins is discussed. The consistent interpretation of the multitude of observed bands strongly supports the existence of stable triaxial deformation at medium spins in 138Nd. ©2012 American Physical Societ

Anisotropic colloids through non-trivial buckling

We present a study on buckling of colloidal particles, including experimental, theoretical and numerical developments. Oil-filled thin shells prepared by emulsion templating show buckling in mixtures of water and ethanol, due to dissolution of the core in the external medium. This leads to conformations with a single depression, either axisymmetric or polygonal depending on the geometrical features of the shells. These conformations could be theoretically and/or numerically reproduced in a model of homogeneous spherical thin shells with bending and stretching elasticity, submitted to an isotropic external pressure.Comment: submitted to EPJ

Algebraic structure of gravity in Ashtekar variables

The BRST transformations for gravity in Ashtekar variables are obtained by using the Maurer-Cartan horizontality conditions. The BRST cohomology in Ashtekar variables is calculated with the help of an operator $\delta$ introduced by S.P. Sorella, which allows to decompose the exterior derivative as a BRST commutator. This BRST cohomology leads to the differential invariants for four-dimensional manifolds.Comment: 19 pages, report REF. TUW 94-1

Low-lying octupole isovector excitation in Nd-144

International audienceThe nature of low-lying 3− levels in Nd144 was investigated in the Nd143(n,γγ) cold neutron-capture reaction. The combination of the high neutron flux from the research reactor at the Institut Laue-Langevin and the high γ-ray detection efficiency of the EXILL setup allowed the recording of γγ coincidences. From the coincidence data precise branching ratios were extracted. Furthermore, the octagonal symmetry of the setup allowed angular-distribution measurements to determine multipole-mixing ratios. Additionally, in a second measurement the ultra-high resolution spectrometer GAMS6 was employed to conduct lifetime measurements using the gamma-ray induced Doppler-shift technique (GRID). The confirmed strong M1 component in the 33−→31− decay strongly supports the assignment of the 33− level at 2779keV as low-lying isovector octupole excitation. Microscopic calculations within the quasiparticle phonon model confirm an isovector component in the wave function of the 33− level, firmly establishing this fundamental mode of nuclear excitation in near-spherical nuclei

3D Brownian Diffusion of Submicron-Sized Particle Clusters

We report on the translation and rotation of particle clusters made through the combination of spherical building blocks. These clusters present ideal model systems to study the motion of objects with complex shape. Because they could be separated into fractions of well-defined configurations on a sufficient scale and their overall dimensions were below 300 nm, the translational and rotational diffusion coefficients of particle duplets, triplets and tetrahedrons could be determined by a combination of polarized dynamic light scattering (DLS) and depolarized dynamic light scattering (DDLS). The use of colloidal clusters for DDLS experiments overcomes the limitation of earlier experiments on the diffusion of complex objects near surfaces because the true 3D diffusion can be studied. When the exact geometry of the complex assemblies is known, different hydrodynamic models for calculating the diffusion coefficient for objects with complex shapes could be applied. Because hydrodynamic friction must be restricted to the cluster surface the so-called shell model, in which the surface is represented as a shell of small friction elements, was most suitable to describe the dynamics. A quantitative comparison of the predictions from theoretical modeling with the results obtained by DDLS showed an excellent agreement between experiment and theory