The Weyl tensor two-point function in de Sitter spacetime

We present an expression for the Weyl-Weyl two-point function in de Sitter spacetime, based on a recently calculated covariant graviton two-point function with one gauge parameter. We find that the Weyl-Weyl two-point function falls off with distance like r^{-4}, where r is spacelike coordinate separation between the two points.Comment: 9 pages, no figure

Waveforms for Gravitational Radiation from Cosmic String Loops

We obtain general formulae for the plus- and cross- polarized waveforms of gravitational radiation emitted by a cosmic string loop in transverse, traceless (synchronous, harmonic) gauge. These equations are then specialized to the case of piecewise linear loops, and it is shown that the general waveform for such a loop is a piecewise linear function. We give several simple examples of the waveforms from such loops. We also discuss the relation between the gravitational radiation by a smooth loop and by a piecewise linear approximation to it.Comment: 16 pages, 6 figures, Revte

Compressing nearly hard sphere fluids increases glass fragility

We use molecular dynamics to investigate the glass transition occurring at large volume fraction, phi, and low temperature, T, in assemblies of soft repulsive particles. We find that equilibrium dynamics in the (phi, T) plane obey a form of dynamic scaling in the proximity of a critical point at T=0 and phi=phi_0, which should correspond to the ideal glass transition of hard spheres. This glass point, `point G', is distinct from athermal jamming thresholds. A remarkable consequence of scaling behaviour is that the dynamics at fixed phi passes smoothly from that of a strong glass to that of a very fragile glass as phi increases beyond phi_0. Correlations between fragility and various physical properties are explored.Comment: 5 pages, 3 figures; Version accepted at Europhys. Let

Thermal decomposition of a honeycomb-network sheet - A Molecular Dynamics simulation study

The thermal degradation of a graphene-like two-dimensional triangular membrane with bonds undergoing temperature-induced scission is studied by means of Molecular Dynamics simulation using Langevin thermostat. We demonstrate that the probability distribution of breaking bonds is highly peaked at the rim of the membrane sheet at lower temperature whereas at higher temperature bonds break at random anywhere in the hexagonal flake. The mean breakage time $\tau$ is found to decrease with the total number of network nodes $N$ by a power law $\tau \propto N^{-0.5}$ and reveals an Arrhenian dependence on temperature $T$. Scission times are themselves exponentially distributed. The fragmentation kinetics of the average number of clusters can be described by first-order chemical reactions between network nodes $n_i$ of different coordination. The distribution of fragments sizes evolves with time elapsed from a $\delta$-function through a bimodal one into a single-peaked again at late times. Our simulation results are complemented by a set of $1^{st}$-order kinetic differential equations for $n_i$ which can be solved exactly and compared to data derived from the computer experiment, providing deeper insight into the thermolysis mechanism.Comment: 21pages, 9 figures, LaTeX, revised versio

Spin swap vs. double occupancy in quantum gates

We propose an approach to realize quantum gates with electron spins localized in a semiconductor that uses double occupancy to advantage. With a fast (non-adiabatic) time control of the tunnelling, the probability of double occupancy is first increased and then brought back exactly to zero. The quantum phase built in this process can be exploited to realize fast quantum operations. We illustrate the idea focusing on the half-swap operation, which is the key two-qubit operation needed to build a CNOT gate.Comment: 5 pages, 2 figure

Spinor Parallel Propagator and Green's Function in Maximally Symmetric Spaces

We introduce the spinor parallel propagator for maximally symmetric spaces in any dimension. Then, the Dirac spinor Green's functions in the maximally symmetric spaces R^n, S^n and H^n are calculated in terms of intrinsic geometric objects. The results are covariant and coordinate-independent.Comment: 7 page

The Mauna Kea Observatories Near-Infrared Filter Set. I: Defining Optimal 1-5 μ\mum Bandpasses

A new MKO-NIR infrared filter set is described, including techniques and considerations given to designing a new set of bandpasses that are useful at both mid- and high-altitude sites. These filters offer improved photometric linearity and in many cases reduced background, as well as preserve good throughput within the JHKLM atmospheric windows. MKO-NIR filters have already been deployed with a number of instruments around the world as part of a filter consortium purchase to reduce the unit cost of filters. Through this effort we hope to establish, for the first time, a single standard set of infrared fitlers at as many observatories as possible.Comment: PASP, in press; 32 pages, 11 figures, 3 Table

Recovering hidden Bloch character: Unfolding Electrons, Phonons, and Slabs

For a quantum state, or classical harmonic normal mode, of a system of spatial periodicity "R", Bloch character is encoded in a wavevector "K". One can ask whether this state has partial Bloch character "k" corresponding to a finer scale of periodicity "r". Answering this is called "unfolding." A theorem is proven that yields a mathematically clear prescription for unfolding, by examining translational properties of the state, requiring no "reference states" or basis functions with the finer periodicity (r,k). A question then arises, how should one assign partial Bloch character to a state of a finite system? A slab, finite in one direction, is used as the example. Perpendicular components k_z of the wavevector are not explicitly defined, but may be hidden in the state (and eigenvector |i>.) A prescription for extracting k_z is offered and tested. An idealized silicon (111) surface is used as the example. Slab-unfolding reveals surface-localized states and resonances which were not evident from dispersion curves alone.Comment: 11 pages, 7 figure