A New interpretation of MOND based on Mach principle and an Unruh like effect

A new interpretation is introduced for MOND based on the Sciama's interpretation of Mach principle and an Unruh like effect, in the context of a generalized equivalence principle. It is argued that in a locally accelerated frame with acceleration $a$ the appearance of a Rindler horizon may give rise to a constant acceleration $a_0$ as the local properties of cosmological horizon or Hubble length. The total gravitational acceleration inside this frame becomes the combination of $a$ with $a_0$. For $a\gg a_0$, the conventional gravitational mass $m_g$ interacts with the dominant acceleration as $m_g a$ and application of Sciama's interpretation leads to the standard Newtonian dynamics. For $a\ll a_0$, however, a reduced gravitational mass $\bar{m}_g$ interacts with the dominant acceleration as $\bar{m}_g a_0$ and the application of Sciama's interpretation on this reduced gravitational mass leads to MOND. This introduces a third proposal for MOND: {\it The modification of gravitational mass}.Comment: 11 pages, throughout revisio

IN VITRO STUDIES ON STRAIN-DEPENDENT PRODUCTION OF THYMUS-SPECIFIC AUTOANTIBODIES

In vitro cultures of spleen cells (S) from normal 8–10-wk-old DBA/2J mice were shown to develop a small number of plaque-forming cells (PFC) that released antibodies lytic to syngenic and autologous thymus cells as well as to syngenic lymphoma L5178Y cells used as the target in the PFC assay. A marked increase in the number of PFC detectable on L5178Y target cells was demonstrated on day 4 in the cultures of S cells to which syngenic or autologous thymus cells had been added (S+T) at time 0, whereas the PFC detectable on thymus cells in such cultures remained at a level similar to that in S cultures. This suggested that two populations of PFC participated in the observed phenomena. No PFC developed in the culture of thymus cells (T). The addition of the cell-free supernatants of 24-h cultures of T or of L5178Y cells to syngenic S cultures also caused a specific increase in the number of the PFC detectable on L5178Y, which suggested that certain immunogenic factors released from the T cells stimulated the response observed in the S+T cultures. Antibodies of IgM nature were detected in the supernatants of S+T cultures by means of cytolysis in agar of L5178Y cells. Although such antibodies did not cause lysis of thymus cells, they could be completely removed by absorption with normal adult or fetal thymus cells of syngenic origin. Still, the absorbing capacity of L5178Y was much higher than that of thymus cells. The absorption was more efficient at 4°C than at 22°C, and hardly any absorption occurred at 37°C. The tissue distribution of the antigen under study seemed to be restricted to thymus cells since no other murine tissue cells tested removed the antibodies. The thymic antigen under study was not restricted to strain DBA/2J and could be demonstrated on thymus cells of all other strains tested. On the other hand, the ability of spleen cells to respond in vitro to this antigen has thus far been observed only in DBA/2J mice. Spleen cells of strains C57BL/6J and NZB/BINJ as well as (DBA/2 x NZB)F1 failed to show any significant increase in the PFC response detectable on the L5178Y target when syngenic thymus cells or DBA/2J thymus cells were added. An intravenous injection of syngenic thymus cells to DBA/2J mice also caused the appearance in their spleens of PFC detectable on the L5178Y target. The described in vitro system may provide a good means of studying the cellular basis of generation of self-tolerance and of its breakdown

The Bright Side of Dark Matter

We show that it is not possible in the absence of dark matter to construct a four-dimensional metric that explains galactic observations. In particular, by working with an effective potential it is shown that a metric which is constructed to fit flat rotation curves in spiral galaxies leads to the wrong sign for the bending of light i.e. repulsion instead of attraction. Hence, without dark matter the motion of particles on galactic scales cannot be explained in terms of geodesic motion on a four- dimensional metric. This reveals a new bright side to dark matter: it is indispensable if we wish to retain the cherished equivalence principle.Comment: 7 pages, latex, no figures. Received an honorable mention in the 1999 Gravity research Foundation Essay Competition. Submitted to Phys. Rev. Let

Gaseous drag on a gravitational perturber in Modified Newtonian Dynamics and the structure of the wake

We calculate the structure of a wake generated by, and the dynamical friction force on, a gravitational perturber travelling through a gaseous medium of uniform density and constant background acceleration g_ext, in the context of Modified Newtonian Dynamics (MOND). The wake is described as a linear superposition of two terms. The dominant part displays the same structure as the wake generated in Newtonian gravity scaled up by a factor mu^{-1}(g_ext/a_0), where a_{0} is the constant MOND acceleration and mu the interpolating function. The structure of the second term depends greatly on the angle between g_{ext} and and the velocity of the perturber. We evaluate the dynamical drag force numerically and compare our MOND results with the Newtonian case. We mention the relevance of our calculations to orbit evolution of globular clusters and satellites in a gaseous proto-galaxy. Potential differences in the X-ray emission of gravitational galactic wakes in MOND and in Newtonian gravity with a dark halo are highlighted.Comment: 13 pages, 7 figures, accepted for publication in MNRA

Modified gravity without dark matter

On an empirical level, the most successful alternative to dark matter in bound gravitational systems is the modified Newtonian dynamics, or MOND, proposed by Milgrom. Here I discuss the attempts to formulate MOND as a modification of General Relativity. I begin with a summary of the phenomenological successes of MOND and then discuss the various covariant theories that have been proposed as a basis for the idea. I show why these proposals have led inevitably to a multi-field theory. I describe in some detail TeVeS, the tensor-vector-scalar theory proposed by Bekenstein, and discuss its successes and shortcomings. This lecture is primarily pedagogical and directed to those with some, but not a deep, background in General RelativityComment: 28 pages, 10 figures, lecture given at Third Aegean Summer School, The Invisible Universe: Dark Matter and Dark Energy, minor errors corrected, references update

Tidal dwarf galaxies as a test of fundamental physics

Within the cold dark matter (CDM) framework tidal dwarf galaxies (TDGs) cannot contain dark matter, so the recent results by Bournaud et al. (2007) that 3 rotating TDGs do show significant evidence for being dark matter dominated is inconsistent with the current concordance cosmological theory unless yet another dark matter component is postulated. We confirm that the TDG rotation curves are consistent with Newtonian dynamics only if either an additional dark matter component is postulated, or if all 3 TDGs happen to be viewed nearly edge-on, which is unlikely given the geometry of the tidal debris. We also find that the observed rotation curves are very naturally explained without any free parameters within the modified Newtonian dynamics (MOND) framework if inclinations are adopted as derived by Bournaud et al. We explore different inclination angles and two different assumptions about the external field effect. The results do not change significantly, and we conclude therefore that Newtonian dynamics has severe problems while MOND does exceedingly well in explaining the observed rotation curves of the 3 TDGs studied by Bournaud et al.Comment: Accepted for publication in A&A Letters, 5 pages, 3 figure

Testing quantised inertia on galactic scales

Galaxies and galaxy clusters have rotational velocities apparently too fast to allow them to be gravitationally bound by their visible matter. This has been attributed to the presence of invisible (dark) matter, but so far this has not been directly detected. Here, it is shown that a new model that modifies inertial mass by assuming it is caused by Unruh radiation, which is subject to a Hubble-scale (Theta) Casimir effect predicts the rotational velocity (v) to be: v^4=2GMc^2/Theta (the Tully-Fisher relation) where G is the gravitational constant, M is the baryonic mass and c is the speed of light. The model predicts the outer rotational velocity of dwarf and disk galaxies, and galaxy clusters, within error bars, without dark matter or adjustable parameters, and makes a prediction that local accelerations should remain above 2c^2/Theta at a galaxy's edge.Comment: 7 pages, 1 figure. Accepted for publication in Astrophysics and Space Science on 27/7/201

The shape of "dark matter" halos in disc galaxies according to the modified dynamics

Analyses of halo shapes for disc galaxies are said to give incongruous results. I point out that the modified dynamics (MOND) predicts for disc galaxies a distribution of fictitious dark matter that comprises two components: a pure disc and a rounder halo. The former dominates the true disc in regions of small accelerations, where it controls the z-dynamics in the disc (disc flaring etc.); it has a finite total mass. It also dominates the round component near the centre where the geometry is nearly planar. The second component controls motions far from the plane, has a total enclosed mass that diverges linearly with radius, and determines the rotation curve at large radii. Its ellipticity may be appreciable at small radii but vanishes asymptotically. This prediction of MOND differs from what one expects from galaxy-formation scenarios with dark matter. Analyses to date, which, as they do, assume one component--usually with a constant ellipticity, perforce give conflicting results for the best-value ellipticity, depending on whether they probe the disc or the sphere, small radii or large ones.Comment: 8 page