Tidal stability of giant molecular clouds in the Large Magellanic Cloud

Star formation does not occur until the onset of gravitational collapse inside giant molecular clouds. However, the conditions that initiate cloud collapse and regulate the star formation process remain poorly understood. Local processes such as turbulence and magnetic fields can act to promote or prevent collapse. On larger scales, the galactic potential can also influence cloud stability and is traditionally assessed by the tidal and shear effects. In this paper, we examine the stability of giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC) against shear and the galactic tide using CO data from the Magellanic Mopra Assessment (MAGMA) and rotation curve data from the literature. We calculate the tidal acceleration experienced by individual GMCs and determine the minimum cloud mass required for tidal stability. We also calculate the shear parameter, which is a measure of a clouds susceptibility to disruption via shearing forces in the galactic disk. We examine whether there are correlations between the properties and star forming activity of GMCs and their stability against shear and tidal disruption. We find that the GMCs are in approximate tidal balance in the LMC, and that shear is unlikely to affect their further evolution. GMCs with masses close to the minimal stable mass against tidal disruption are not unusual in terms of their mass, location, or CO brightness, but we note that GMCs with large velocity dispersion tend to be more sensitive to tidal instability. We also note that GMCs with smaller radii, which represent the majority of our sample, tend to more strongly resist tidal and shear disruption. Our results demonstrate that star formation in the LMC is not inhibited by to tidal or shear instability.Comment: 18 pages, 10 Figures, Accepted in PAS

Implementation of uniform perturbation method for potential flow past axisymmetric and two-dimensional bodies

The aerodynamic characteristics of potential flow past an axisymmetric slender body and a thin airfoil are calculated using a uniform perturbation analysis method. The method is based on the superposition of potentials of point singularities distributed inside the body. The strength distribution satisfies a linear integral equation by enforcing the flow tangency condition on the surface of the body. The complete uniform asymptotic expansion of its solution is obtained with respect to the slenderness ratio by modifying and adapting an existing technique. Results calculated by the perturbation analysis method are compared with the existing surface singularity panel method and some available analytical solutions for a number of cases under identical conditions. From these comparisons, it is found that the perturbation analysis method can provide quite accurate results for bodies with small slenderness ratio. The present method is much simpler and requires less memory and computation time than existing surface singularity panel methods of comparable accuracy

Heavy Quarkonium Dissociation Cross Sections in Relativistic Heavy-Ion Collisions

Many of the hadron-hadron cross sections required for the study of the dynamics of matter produced in relativistic heavy-ion collisions can be calculated using the quark-interchange model. Here we evaluate the low-energy dissociation cross sections of $J/\psi$, $\psi'$, $\chi$, $\Upsilon$, and $\Upsilon'$ in collision with $\pi$, $\rho$, and $K$, which are important for the interpretation of heavy-quarkonium suppression as a signature for the quark gluon plasma. These comover dissociation processes also contribute to heavy-quarkonium suppression, and must be understood and incorporated in simulations of heavy-ion collisions before QGP formation can be established through this signature.Comment: 38 pages, in LaTe

Constraints on Dark Photon from Neutrino-Electron Scattering Experiments

A possible manifestation of an additional light gauge boson $A^\prime$, named as Dark Photon, associated with a group $U(1)_{\rm B-L}$ is studied in neutrino electron scattering experiments. The exclusion plot on the coupling constant $g_{\rm B-L}$ and the dark photon mass $M_{A^\prime}$ is obtained. It is shown that contributions of interference term between the dark photon and the Standard Model are important. The interference effects are studied and compared with for data sets from TEXONO, GEMMA, BOREXINO, LSND as well as CHARM II experiments. Our results provide more stringent bounds to some regions of parameter space.Comment: 22 pages, 6 figures, 2 tables, text improved, fig.6 updated, references adde

Covariant hamiltonian dynamics

We discuss the covariant formulation of the dynamics of particles with abelian and non-abelian gauge charges in external fields. Using this formulation we develop an algorithm for the construction of constants of motion, which makes use of a generalization of the concept of Killing vectors and tensors in differential geometry. We apply the formalism to the motion of classical charges in abelian and non-abelian monopole fieldsComment: 15 pages, no figure