The Resonance Peak in Sr2_2RuO4_4: Signature of Spin Triplet Pairing

We study the dynamical spin susceptibility, $\chi({\bf q}, \omega)$, in the normal and superconducting state of Sr$_2$RuO$_4$. In the normal state, we find a peak in the vicinity of ${\bf Q}_i\simeq (0.72\pi,0.72\pi)$ in agreement with recent inelastic neutron scattering (INS) experiments. We predict that for spin triplet pairing in the superconducting state a {\it resonance peak} appears in the out-of-plane component of $\chi$, but is absent in the in-plane component. In contrast, no resonance peak is expected for spin singlet pairing.Comment: 4 pages, 4 figures, final versio

Lagrangian and Hamiltonian for the Bondi-Sachs metrics

We calculate the Hilbert action for the Bondi-Sachs metrics. It yields the Einstein vacuum equations in a closed form. Following the Dirac approach to constrained systems we investigate the related Hamiltonian formulation.Comment: 8 page

Probing single molecule orientations in model lipid membranes with near-field scanning optical microscopy

This is the published version, also available here: http://dx.doi.org/10.1063/1.481367.Single molecule near-field fluorescence measurements are utilized to characterize the molecular level structure in Langmuir–Blodgett monolayers of L-α-dipalmitoylphosphatidylcholine (DPPC).Monolayers incorporating 3×10−4 mol % of the fluorescent lipid analog N-(6-tetramethylrhodaminethiocarbamoyl)-1,2-dihexadecanoyl-sn- glycero-3-phosphoethanolamine, triethylammonium salt (TRITC–DHPE) are transferred onto a freshly cleaved mica surface at low (π=8 mN/m) and high (π=30 mN/m)surfacepressures. The near-field fluorescence images exhibit shapes in the single molecule images that are indicative of the lipid analog probe orientation within the films. Modeling the fluorescence patterns yields the single molecule tilt angle distribution in the monolayers which indicates that the majority of the molecules are aligned with their absorption dipole moment pointed approximately normal to the membrane plane. Histograms of the data indicate that the average orientation of the absorption dipole moment is 2.2° (σ=4.8°) in monolayers transferred at π=8 mN/m and 2.4° (σ=5.0°) for monolayers transferred at π=30 mN/m. There is no statistical difference in the mean tilt angle or distribution for the two monolayer conditions studied. The insensitivity of tilt angle to filmsurfacepressure may arise from small chromophore doped domains of trapped liquid-expanded lipid phase remaining at high surfacepressure. There is no evidence in the near-field fluorescence images for probe molecules oriented with their dipole moment aligned parallel with the membrane plane. We do, however, find a small but significant population of probe molecules (∼13%) with tilt angles greater than 16°. Comparison of the simultaneously collected near-field fluorescence and force images suggests that these large angle orientations are not the result of significant defects in the films. Instead, this small population may represent a secondary insertion geometry for the probe molecule into the lipidmonolayer

Mathisson-Papapetrou equations in metric and gauge theories of gravity in a Lagrangian formulation

We present a simple method to derive the semiclassical equations of motion for a spinning particle in a gravitational field. We investigate the cases of classical, rotating particles (pole-dipole particles), as well as particles with intrinsic spin. We show that, starting with a simple Lagrangian, one can derive equations for the spin evolution and momentum propagation in the framework of metric theories of gravity and in theories based on a Riemann-Cartan geometry (Poincare gauge theory), without explicitly referring to matter current densities (spin and energy-momentum). Our results agree with those derived from the multipole expansion of the current densities by the conventional Papapetrou method and from the WKB analysis for elementary particles.Comment: 28 page

Lightcone reference for total gravitational energy

We give an explicit expression for gravitational energy, written solely in terms of physical spacetime geometry, which in suitable limits agrees with the total Arnowitt-Deser-Misner and Trautman-Bondi-Sachs energies for asymptotically flat spacetimes and with the Abbot-Deser energy for asymptotically anti-de Sitter spacetimes. Our expression is a boundary value of the standard gravitational Hamiltonian. Moreover, although it stands alone as such, we derive the expression by picking the zero-point of energy via a ``lightcone reference.''Comment: latex, 7 pages, no figures. Uses an amstex symbo

Post-Newtonian extension of the Newton-Cartan theory

The theory obtained as a singular limit of General Relativity, if the reciprocal velocity of light is assumed to tend to zero, is known to be not exactly the Newton-Cartan theory, but a slight extension of this theory. It involves not only a Coriolis force field, which is natural in this theory (although not original Newtonian), but also a scalar field which governs the relation between Newtons time and relativistic proper time. Both fields are or can be reduced to harmonic functions, and must therefore be constants, if suitable global conditions are imposed. We assume this reduction of Newton-Cartan to Newton`s original theory as starting point and ask for a consistent post-Newtonian extension and for possible differences to usual post-Minkowskian approximation methods, as developed, for example, by Chandrasekhar. It is shown, that both post-Newtonian frameworks are formally equivalent, as far as the field equations and the equations of motion for a hydrodynamical fluid are concerned.Comment: 13 pages, LaTex, to appear in Class. Quantum Gra

On ``hyperboloidal'' Cauchy data for vacuum Einstein equations and obstructions to smoothness of ``null infinity''

Various works have suggested that the Bondi--Sachs--Penrose decay conditions on the gravitational field at null infinity are not generally representative of asymptotically flat space--times. We have made a detailed analysis of the constraint equations for ``asymptotically hyperboloidal'' initial data and find that log terms arise generically in asymptotic expansions. These terms are absent in the corresponding Bondi--Sachs--Penrose expansions, and can be related to explicit geometric quantities. We have nevertheless shown that there exists a large class of ``non--generic'' solutions of the constraint equations, the evolution of which leads to space--times satisfying the Bondi--Sachs--Penrose smoothness conditions.Comment: 8 pages, revtex styl

A Non - Singular Cosmological Model with Shear and Rotation

We have investigated a non-static and rotating model of the universe with an imperfect fluid distribution. It is found that the model is free from singularity and represents an ever expanding universe with shear and rotation vanishing for large value of time.Comment: 10 pages, late

An Estimate of the Energy Gap of InN from Measurements of the Fundamental Absorption Edge

Optical absorption between 0.4 and 4.5 eV of an InN layer grown by metalorganic vapour phase epitaxy on sapphire was measured at 296 and 12 K. The layer was also characterized by measurements of the Hall effect and of infrared reflectivity in the region of the plasma edge, which determined the concentration, mobility, and effective mass of electrons in the conduction band. The energy gap of InN was estimated to be equal to 0.9 ± 0.2 eV. It was obtained from the spectral position of the fundamental absorption edge. Corrections to the energy gap resulting from the broadening of the fundamental absorption edge, from the Burstein-Moss shift, and from a band-gap shrinkage due to the impurity potential were included

Plane torsion waves in quadratic gravitational theories

The definition of the Riemann-Cartan space of the plane wave type is given. The condition under which the torsion plane waves exist is found. It is expressed in the form of the restriction imposed on the coupling constants of the 10-parametric quadratic gravitational Lagrangian. In the mathematical appendix the formula for commutator of the variation operator and Hodge operator is proved. This formula is applied for the variational procedure when the gravitational field equations are obtained in terms of the exterior differential forms.Comment: 3 May 1998. - 11