A Massive Renormalizable Abelian Gauge Theory in 2+1 Dimensions

The standard formulation of a massive Abelian vector field in $2+1$ dimensions involves a Maxwell kinetic term plus a Chern-Simons mass term; in its place we consider a Chern-Simons kinetic term plus a Stuekelberg mass term. In this latter model, we still have a massive vector field, but now the interaction with a charged spinor field is renormalizable (as opposed to super renormalizable). By choosing an appropriate gauge fixing term, the Stuekelberg auxiliary scalar field decouples from the vector field. The one-loop spinor self energy is computed using operator regularization, a technique which respects the three dimensional character of the antisymmetric tensor $\epsilon_{\alpha\beta\gamma}$. This method is used to evaluate the vector self energy to two-loop order; it is found to vanish showing that the beta function is zero to two-loop order. The canonical structure of the model is examined using the Dirac constraint formalism.Comment: LaTeX, 17 pages, expanded reference list and discussion of relationship to previous wor

Testing spatial noncommutativiy via the Aharonov-Bohm effect

The possibility of detecting noncommutative space relics is analyzed using the Aharonov-Bohm effect. We show that, if space is noncommutative, the holonomy receives non-trivial kinematical corrections that will produce a diffraction pattern even when the magnetic flux is quantized. The scattering problem is also formulated, and the differential cross section is calculated. Our results can be extrapolated to high energy physics and the bound $\theta \sim [ 10 {TeV}]^{-2}$ is found. If this bound holds, then noncommutative effects could be explored in scattering experiments measuring differential cross sections for small angles. The bound state Aharonov- Bohm effect is also discussed.Comment: 16 pp, Revtex 4, 2 fig, new references added. To appear in PR

Nuclear level densities and γ -ray strength functions of 180,181Ta and neutron capture cross sections

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Resonances in odd-odd 182Ta

Abstract: Enhanced γ -decay on the tail of the giant electric dipole resonance, such as the scissors or pygmy resonances, can have significant impact on (n,γ ) reaction rates. These rates are important input for modeling processes that take place in astrophysical environments and nuclear reactors. Recent results from the University of Oslo indicate the existence of a significant enhancement in the photon strength function for nuclei in the actinide region due to the scissors resonance. Further, the M1 strength distribution of the scissors resonances in rare earth nuclei has been studied extensively over the years. To investigate the evolution and persistence of the scissor resonance in other mass regions, an experiment was performed utilizing the NaI(Tl) γ -ray detector array (CACTUS) and silicon particle telescopes (SiRi) at the University of Oslo Cyclotron laboratory. Particle-γ coincidences from the 181Ta(d,p)182Ta and 181Ta(d,d’)181Ta reactions were used to measure the nuclear level density and photon strength function of the well-deformed 181Ta and 182Ta systems, to investigate the existence of resonances below the neutron separation energy

Non-Boltzmann behavior from the Boltzmann equation

We compute the stress autocorrelation function in a two- and three-dimensional system by using the lattice-Boltzmann method. The algebraic long-time behavior ∼t-d/2 in the stress correlation function is clearly observed. The amplitude of this tail is compared with the mode-coupling expression for the long-time tail in the stress correlation function. Agreement is found between the mode-coupling theory and simulation in both two and three dimensions

Rotational diffusion in dense suspensions

We have computed the rotational diffusion coefficient for a suspension of hard spheres. We find excellent agreement with experimental results over a density range up to, and including, the colloidal crystal. However, we find that theories derived to second order in the volume fraction overestimate the rotational diffusion coefficient for volume fractions exceeding 25%. To investigate the sensitivity of the rotational diffusion coefficient to the pair distribution function we also consider a perfect FCC crystal with negligible thermal motion. We show that, in line with theoretical predictions, the first term in the expansion of the rotational diffusion coefficient in powers of the volume fraction becomes quadratic. Relative to the random distribution, the rotational diffusion coefficient in this case is significantly larger. By studying the decay of angular velocity fluctuations, we examined the time dependence of the rotational diffusion coefficient. We find that for rotation the situation is similar to that reported for translation. The suspension behaves like an "effective fluid", i.e. the rotational dynamics of a particle in the suspension can be described by the isolated particle result, but with the suspension viscosity replacing the fluid viscosity. As with translation, this picture only holds for times long compared to the time it takes transverse momentum to diffuse over a distance of the order of a particle radius