From massive gravity to modified general relativity II

We continue our investigation of massive gravity in the massless limit of vanishing graviton mass. From gauge invariance we derive the most general coupling between scalar matter and gravity. We get further couplings beside the standard coupling to the energy-momentum tensor. On the classical level this leads to a further modification of general relativity.Comment: 12 pages, no figur

Exoplanet Transit Parallax

The timing and duration of exoplanet transits has a dependency on observer position due to parallax. In the case of an Earth-bound observer with a 2 AU baseline the dependency is typically small and slightly beyond the limits of current timing precision capabilities. However, it can become an important systematic effect in high-precision repeated transit measurements for long period systems due to its relationship to secular perspective acceleration phenomena. In this short paper we evaluate the magnitude and characteristics of transit parallax in the case of exoplanets using simplified geometric examples. We also discuss further implications of the effect, including its possible exploitation to provide immediate confirmation of planetary transits and/or unique constraints on orbital parameters and orientations.Comment: 12 Pages, 3 Figures, Accepted for publication in Ap

Gauge Independence of the S-Matrix in the Causal Approach

The gauge dependence of the time-ordered products for Yang-Mills theories is analysed in perturbation theory by means of the causal method of Epstein and Glaser together with perturbative gauge invariance. This approach allows a simple inductive proof of the gauge independence of the physical S-matrix.Comment: 19 pages, latex, 1 figur

The Chandra Fornax Survey - I: The Cluster Environment

We present the first results of a deep Chandra survey of the inner 1 degree of the Fornax cluster of galaxies. Ten 50 ksec pointings were obtained in a mosaic centered on the giant elliptical galaxy NGC 1399 at the nominal cluster center. Emission and temperature maps of Fornax are presented, and an initial study of 771 detected X-ray point sources is made. Regions as small as 100pc are resolved. The intra-cluster gas in Fornax exhibits a highly asymmetric morphology and temperature structure, dominated by a 180 kpc extended ``plume'' of low surface brightness, cool, ~1 keV) gas to the North-East of NGC 1399 with a sharper edge to the South West. The elliptical galaxy NGC 1404 also exhibits a cool halo of X-ray gas within the cluster, with a highly sharpened leading edge as it presumably falls into the cluster, and a cometary-like tail. We estimate that some ~200-400 point sources are physically associated with Fornax. Confirming earlier works, we find that the globular cluster population in NGC 1399 is highly X-ray active, extending to globulars which may in fact be intra-cluster systems. We have also found a remarkable correlation between the location of giant and dwarf cluster galaxies and the presence of X-ray counterparts, such that systems inhabiting regions of low gas density are more likely to show X-ray activity. Not only does this correlate with the asymmetry of the intra-cluster gas but also with the axis joining the center of Fornax to an infalling group 1 Mpc to the South-West. We suggest that Fornax may be experiencing an intergalactic ``headwind'' due to motion relative to the surrounding large-scale structure.Comment: 35 pages, 15 figures, submitted to ApJ. Most figures not included owing to severe compression degradation - we strongly recommend downloading the full resolution paper from http://www.astro.columbia.edu/~caleb/ms_highres.pdf (1.9Mb

Massive gravity from descent equations

Both massless and massive gravity are derived from descent equations (Wess-Zumino consistency conditions). The massive theory is a continuous deformation of the massless one.Comment: 8 pages, no figur

The Standard Model and its Generalizations in Epstein-Glaser Approach to Renormalization Theory II: the Fermion Sector and the Axial Anomaly

We complete our study of non-Abelian gauge theories in the framework of Epstein-Glaser approach to renormalization theory including in the model an arbitrary number of Dirac Fermions. We consider the consistency of the model up to the third order of the perturbation theory. In the second order we obtain pure group theoretical relations expressing a representation property of the numerical coefficients appearing in the left and right handed components of the interaction Lagrangian. In the third order of the perturbation theory we obtain the the condition of cancellation of the axial anomaly.Comment: 38 pages, LATEX 2e, extensive rewritting, some errors eliminate

The Interaction of Quantum Gravity with Matter

The interaction of (linearized) gravitation with matter is studied in the causal approach up to the second order of perturbation theory. We consider the generic case and prove that gravitation is universal in the sense that the existence of the interaction with gravitation does not put new constraints on the Lagrangian for lower spin fields. We use the formalism of quantum off-shell fields which makes our computation more straightforward and simpler.Comment: 25 page

Electron-positron pair production in the external electromagnetic field of colliding relativistic heavy ions

The results concerning the $e^+e^-$ production in peripheral highly relativistic heavy-ion collisions presented in a recent paper by Baltz {\em{et al.}} are rederived in a very straightforward manner. It is shown that the solution of the Dirac equation directly leads to the multiplicity, i.e. to the total number of electron-positron pairs produced by the electromagnetic field of the ions, whereas the calculation of the single pair production probability is much more involved. A critical observation concerns the unsolved problem of seemingly absent Coulomb corrections (Bethe-Maximon corrections) in pair production cross sections. It is shown that neither the inclusion of the vacuum-vacuum amplitude nor the correct interpretation of the solution of the Dirac equation concerning the pair multiplicity is able the explain (from a fundamental point of view) the absence of Coulomb corrections. Therefore the contradiction has to be accounted to the treatment of the high energy limit.Comment: 6 pages, 4 Postscript figures, uses svjour.cls/svepj.cl

A Fully Self-Consistent Treatment of Collective Fluctuations in Quantum Liquids

The problem of calculating collective density fluctuations in quantum liquids is revisited. A fully quantum mechanical self-consistent treatment based on a quantum mode-coupling theory [E. Rabani and D.R. Reichman, J. Chem. Phys.116, 6271 (2002)] is presented. The theory is compared with the maximum entropy analytic continuation approach and with available experimental results. The quantum mode-coupling theory provides semi-quantitative results for both short and long time dynamics. The proper description of long time phenomena is important in future study of problems related to the physics of glassy quantum systems, and to the study of collective fluctuations in Bose fluids.Comment: 9 pages, 4 figure