Instabilities in the nonsymmetric theory of gravitation

We consider the linearized nonsymmetric theory of gravitation (NGT) within the background of an expanding universe and near a Schwarzschild metric. We show that the theory always develops instabilities unless the linearized nonsymmetric lagrangian reduces to a particular simple form. This theory contains a gauge invariant kinetic term, a mass term for the antisymmetric metric-field and a coupling with the Ricci curvature scalar. This form cannot be obtained within NGT. Next we discuss NGT beyond linearized level and conjecture that the instabilities are not a relic of the linearization, but are a general feature of the full theory. Finally we show that one cannot add ad-hoc constraints to remove the instabilities as is possible with the instabilities found in NGT by Clayton.Comment: 29 page

Shelf-ocean exchange and hydrography west of the Antarctic Peninsula: A review

The West Antarctic Peninsula (WAP) is a highly productive marine ecosystem where extended periods of change have been observed in the form of glacier retreat, reduction of sea-ice cover and shifts in marine populations, among others. The physical environment on the shelf is known to be strongly influenced by the Antarctic Circumpolar Current flowing along the shelf slope and carrying warm, nutrient-rich water, by cold waters flooding into the northern Bransfield Strait from the Weddell Sea, by an extensive network of glaciers and ice shelves, and by strong seasonal to inter-annual variability in sea-ice formation and air–sea interactions, with significant modulation by climate modes like El Niño–Southern Oscillation and the Southern Annular Mode. However, significant gaps have remained in understanding the exchange processes between the open ocean and the shelf, the pathways and fate of oceanic water intrusions, the shelf heat and salt budgets, and the long-term evolution of the shelf properties and circulation. Here, we review how recent advances in long-term monitoring programmes, process studies and newly developed numerical models have helped bridge these gaps and set future research challenges for the WAP system

Problems and hopes in nonsymmetric gravity

We consider the linearized nonsymmetric theory of gravitation (NGT) within the background of an expanding universe and near a Schwarzschild mass. We show that the theory always develops instabilities unless the linearized nonsymmetric lagrangian reduces to a particular simple form. This form contains a gauge invariant kinetic term, a mass term for the antisymmetric metric-field and a coupling with the Ricci curvature scalar. This form cannot be obtained within NGT. Based on the linearized lagrangian we know to be stable, we consider the generation and evolution of quantum fluctuations of the antisymmetric gravitational field (B-field) from inflation up to the present day. We find that a B-field with a mass m ~ 0.03(H_I/10^(13)GeV)^4 eV is an excellent dark matter candidate.Comment: 9 pages, 1 figure. Based on two talks by the authors at the 2nd International Conference on Quantum Theories and Renormalization Group in Gravity and Cosmology (IRGAC) 2006, Barcelon

Multimetric extension of the PPN formalism: experimental consistency of repulsive gravity

Recently we discussed a multimetric gravity theory containing several copies of standard model matter each of which couples to its own metric tensor. This construction contained dark matter sectors interacting repulsively with the visible matter sector, and was shown to lead to cosmological late-time acceleration. In order to test the theory with high-precision experiments within the solar system we here construct a simple extension of the parametrized post-Newtonian (PPN) formalism for multimetric gravitational backgrounds. We show that a simplified version of this extended formalism allows the computation of a subset of the PPN parameters from the linearized field equations. Applying the simplified formalism we find that the PPN parameters of our theory do not agree with the observed values, but we are able to improve the theory so that it becomes consistent with experiments of post-Newtonian gravity and still features its promising cosmological properties.Comment: 19 pages, no figures, journal versio

Gravitational solution to the Pioneer 10/11 anomaly

A fully relativistic modified gravitational theory including a fifth force skew symmetric field is fitted to the Pioneer 10/11 anomalous acceleration. The theory allows for a variation with distance scales of the gravitational constant G, the fifth force skew symmetric field coupling strength omega and the mass of the skew symmetric field mu=1/lambda. A fit to the available anomalous acceleration data for the Pioneer 10/11 spacecraft is obtained for a phenomenological representation of the "running" constants and values of the associated parameters are shown to exist that are consistent with fifth force experimental bounds. The fit to the acceleration data is consistent with all current satellite, laser ranging and observations for the inner planets.Comment: 14 pages, 3 figures, 3 tables. typo's were corrected at Equations (4) and (12) and a third table including our predictions for the anomalous perihelion advance of the planets was adde

Fluctuation Spectrum from a Scalar-Tensor Bimetric Gravity Theory

Predictions of the CMB spectrum from a bimetric gravity theory (gr-qc/0101126) are presented. The initial inflationary period in BGT is driven by a vanishingly small speed of gravitational waves v_g in the very early universe. This initial inflationary period is insensitive to the choice of scalar field potential and initial values of the scalar field. After this initial period of inflation, v_g will increase rapidly and the effects of a potential will become important. We show that a quadratic potential introduced into BGT yields an approximately flat spectrum with inflation parameters: n_s=0.98, n_t=-0.027, alpha_s=-3.2e-4 and alpha_t=-5.0e-4, with r >= 0.014.Comment: 14 pages, uses amsmath, amssym

Experimental data and model for the turbulent boundary layer on a convex, curved surface

Experiments were performed to determine how boundary layer turbulence is affected by strong convex curvature. The data gathered on the behavior of the Reynolds stress suggested the formulation of a simple turbulence model. Data were taken on two separate facilities. Both rigs had flow from a flat surface, over a convex surface with 90 deg of turning and then onto a flat recovery surface. The geometry was adjusted so that, for both rigs, the pressure gradient along the test surface was zero. Two experiments were performed at delta/R approximately 0.10, and one at weaker curvature with delta/R approximately 0.05. Results show that after a sudden introduction of curvature the shear stress in the outer part of the boundary layer is sharply diminished and is even slightly negative near the edge. The wall shear also drops off quickly downstream. When the surface suddenly becomes flat again, the wall shear and shear stress profiles recover very slowly towards flat wall conditions. A simple turbulence model, which was based on the theory that the Prandtl mixing length in the outer layer should scale on the velocity gradient layer, was shown to account for the slow recovery

Time Delay Predictions in a Modified Gravity Theory

The time delay effect for planets and spacecraft is obtained from a fully relativistic modified gravity theory including a fifth force skew symmetric field by fitting to the Pioneer 10/11 anomalous acceleration data. A possible detection of the predicted time delay corrections to general relativity for the outer planets and future spacecraft missions is considered. The time delay correction to GR predicted by the modified gravity is consistent with the observational limit of the Doppler tracking measurement reported by the Cassini spacecraft on its way to Saturn, and the correction increases to a value that could be measured for a spacecraft approaching Neptune and Pluto.Comment: 5 pages, LaTex file, no figures. Corrections to Table