arXiv subjects
Publications and source records attributed to Arnon Dar.
We show that cosmic rays in external galaxies, groups and clusters rich in gas, with an average flux similar to that observed in the Milky Way, could have produced the observed extragalactic diffuse gamma radiation.
The most simple observed cases of gravitational lensing of distant quasars and galaxies by galaxies and clusters of galaxies are used to test Einstein's theory of General Relativity and Newtonian Gravity over galactic and intergalactic distances. They extend the distance range over which Newton-Einstein Gravity has been tested by 10 orders of magnitude. Although the precision of the tests are far from the precision of the solar system tests of EGR and those from pulsar timing in close binary systems, they confirm quite accurately the validity of Einstein's General Relativity and its weak field limit, Newtonian Gravity, over galactic and intergalactic distances and the existence of large quantities of dark matter in galaxies and clusters of galaxies. Future observations can improve the accuracy of the tests and reduce the possibilities for systematic errors.
Striking similarities exist between high energy gamma ray emission from active galactic nuclei (AGN) and gamma ray bursts (GRBs). They suggest that GRBs are generated by inverse Compton scattering from highly relativistic electrons in transient jets. Such jets may be produced along the axis of an accretion disk formed around stellar black holes (BH) or neutron stars (NS) in BH-NS and NS-NS mergers and in accretion induced collapse of magnetized white dwarfs (WD) or neutron stars in close binary systems. Such events may produce the cosmological GRBs. Transient jets formed by single old magnetized neutron stars in an extended Galactic halo may produce a local population of GRBs. Here we show that jet production of GRBs by inverse Compton scattering can explain quite simply the striking correlations that exist between various temporal features of GRBs, their duration histogram, the power spectrum of their complex multipeak light curves, their power-law high energy spectra and other features of GRBs. Some additional predictions are made including the expected polarization of gamma-rays in the bursts.
The enclosed paper was submitted for publication in Ap.J Lett. in February 1992. It has been rejected on the grounds that it predicts primordial Deuterium abundance which is contradicted by observations and because it disagreed with published analysis and conclusions of previous authors. However, in a recent article in NATURE (14 April 1994) Vol. 368 pp. 599-603, Songalia, Cowie, Hogan and Rugers describe a recent measurement (November 1993) with the Keck 10-m Telescope, of the Deuterium abundance in a high redshift cloud between us and a distant quasar. They find D/H\approx 1.9-2.5 x10^{-4} in good agreement with our prediction D/H=(2.1+\- 0.35)x10^{-4}, which is larger by an order of magnitude than believed before. Songalia et al. found that the baryon density inferred from Big Bang Nucleosynthesis is "consistent with the amount of presently observed luminous matter comprising all the baryons in the Universe" while we found the same. We post here our unpublished 1991 paper, which was reported in international conferences and was distributed only as a preprint, mainly because of its physics and its sad moral: If you submit for publication a correct paper with important results that contradict the "party line" it has only slim chances to be accepted for publication.
In a recent paper Dar and Shaviv (1994) presented results of calculations with an improved standard solar model (SSM) that suggest a standard physics solution to the solar neutrino problem. In a subsequent publication with a similar title Bahcall et al. (1994) have claimed to refute the results obtained by Dar and Shaviv. Here we show that the criticism and conclusions of Bahcall et al. are unjustified. In particular, their attempts to reproduce the results of Dar and Shaviv failed because they did not use the same nuclear cross sections and did not include in their calculations major physics improvements which were included in the improved SSM code used by Dar and Shaviv.
An imroved standard solar model, with more accurate input parameters and more accurate treatment of plasma physics effects, predicts a solar neutrino flux which is consistent within experimental uncertainties with the solar neutrino observations after 1986.
We show that recent $γ$-ray observations of the Small Magellanic Cloud with EGRET rule out a universal cosmic ray flux only at energies below $\approx 10$ GeV, while the observed diffuse X-ray and $γ$-ray background radiations have already ruled out, by more than three orders of magnitude, a universal extragalactic cosmic ray flux identical to that observed in the local solar neighborhood at energies below $10^6$ GeV.