Universal behavior in complex-mediated reactions: Dynamics of S(1D)+ o-D2 --> D + SD at low collision energies

Reactive and elastic cross-sections, and rate coefficients, have been calculated for the S(1D)+ D2 (v=0, j=0) reaction using a modified hyperspherical quantum reactive scattering method. The considered collision energy ranges from the ultracold regime, where only one partial wave is open, up to the Langevin regime, where many of them contribute. This work presents the extension of the quantum calculations, which were compared with the experimental results in a previous work, down to energies in the cold and ultracold domains. Results are analyzed and compared with the universal case of the quantum defect theory by Jachymski et al. [Phys. Rev. Lett. 110, 213202 (2013)]. State-to-state integral and differential cross sections are also shown covering the ranges of low-thermal, cold and ultracold collision energy regimes. It is found that at E/k_B T < 1 K there are substantial departures from the expected statistical behavior, and that dynamical features become increasingly important with decreasing collision energy, leading to vibrational excitation.Comment: Submitted to Journal of Chemical Physic

Strings at future singularities

We discuss the behaviour of strings propagating in spacetimes which allow future singularities of either a sudden future or a Big-Rip type. We show that in general the invariant string size remains finite at sudden future singularities while it grows to infinity at a Big-Rip. This claim is based on the discussion of both the tensile and null strings. In conclusion, strings may survive a sudden future singularity, but not a Big-Rip where they are infinitely stretched.Comment: REVTEX 4.0, 4 pages, no figures, references adde

Beyond universality: parametrizing ultracold complex-mediated reactions using statistical assumptions

We have calculated accurate quantum reactive and elastic cross-sections for the prototypical barrierless reaction D$^{+}$ + H$_2$($v$=0, $j$=0) using the hyperspherical scattering method. The considered kinetic energy ranges from the ultracold to the Langevin regimes. The availability of accurate results for this system allows to test the quantum theory by Jachymski et al. [Phys. Rev. Lett. 110, 213202 (2013)] in a nonuniversal case. The short range reaction probability is rationalized using statistical model assumptions and related to a statistical factor. This provides a means to estimate one of the parameters that characterizes ultracold processes from first principles. Possible limitations of the statistical model are considered

From geodesics of the multipole solutions to the perturbed Kepler problem

A static and axisymmetric solution of the Einstein vacuum equations with a finite number of Relativistic Multipole Moments (RMM) is written in MSA coordinates up to certain order of approximation, and the structure of its metric components is explicitly shown. From the equation of equatorial geodesics we obtain the Binet equation for the orbits and it allows us to determine the gravitational potential that leads to the equivalent classical orbital equations of the perturbed Kepler problem. The relativistic corrections to Keplerian motion are provided by the different contributions of the RMM of the source starting from the Monopole (Schwarzschild correction). In particular, the perihelion precession of the orbit is calculated in terms of the quadrupole and 2$^4$-pole moments. Since the MSA coordinates generalize the Schwarzschild coordinates, the result obtained allows measurement of the relevance of the quadrupole moment in the first order correction to the perihelion frequency-shift

Exterior Differential System for Cosmological G2 Perfect Fluids and Geodesic Completeness

In this paper a new formalism based on exterior differential systems is derived for perfect-fluid spacetimes endowed with an abelian orthogonally transitive G2 group of motions acting on spacelike surfaces. This formulation allows simplifications of Einstein equations and it can be applied for different purposes. As an example a singularity-free metric is rederived in this framework. A sufficient condition for a diagonal metric to be geodesically complete is also provided.Comment: 27 pages, 0 figures, LaTeX2e, to be published in Classical and Quantum Gravit

Spacetime averaging of exotic singularity universes

Taking a spacetime average as a measure of the strength of singularities we show that big-rips (type I) are stronger than big-bangs. The former have infinite spacetime averages while the latter have them equal to zero. The sudden future singularities (type II) and $w-$singularities (type V) have finite spacetime averages. The finite scale factor (type III) singularities for some values of the parameters may have an infinite average and in that sense they may be considered stronger than big-bangs.Comment: 5 pages, no figures, REVTEX4-1, minor improvement