Do Modified Newtonian Dynamics Follow from the Cold Dark Matter Paradigm?

Abstract

In a recent paper, Kaplinghat & Turner (KT) advertised that modified Newtonian dynamics (MOND) could be derived naturally in the cold dark matter (CDM) paradigm. They actually proceeded to produce a more limited result: Every galaxy should have a transition radius below which baryons dominate and above which dark r t matter takes over; the acceleration at is nearly the same for all galaxies, and owing to coincidences, this is on r t the order of . This follows from their tacit, intermediate result, whereby CDM halos of galaxies have a ∼ cH varies from halo to halo. (This remains so when baryons are added because KT assume a universal baryoncollapse factor.) The KT scenario is phenomenologically wrong-observed galaxies are simply not like that. For example, their scenario precludes altogether the existence of low surface brightness galaxies, in which the acceleration is everywhere smaller than . The phenomenologically sound outcome-i.e., the role of as a a a 0 0 transition acceleration in high surface brightness galaxies-pertains to only a small part of the statement of MOND. There are several other independent roles that plays in MOND phenomenology and other a ∼ cH 0 0 predictions of MOND, not related to the value of , that are not explainable in the KT scenario. The results of a 0 KT also disagree with those of CDM simulations, which, as they now stand, do not reproduce any aspect of MOND phenomenology.

Modified Newtonian Dynamics (MOND): Observational Phenomenology and Relativistic Extensions

“…Then with a fixed collapse factor for the baryonic material, the transition from dominance of dark over baryonic occurs at a universal acceleration, which by numerical coincidence, is of the order of cH 0 and thus of a 0 (see also [412]). While, still today, it remains to be seen whether this scenario would quantitatively hold in numerical simulations, it was noted by Milgrom [307] that this scenario only explained the role of a 0 as a transition radius between baryon and dark matter dominance in high-surface brightness (HSB) galaxies, precluding altogether the existence of low-surface brightness (LSB) galaxies where dark matter dominates everywhere. The real challenge for ΛCDM is rather to explain all the different roles played by a 0 in galaxy dynamics, different roles that can all be summarized within the single law proposed by Milgrom, just like Kepler's laws are unified under Newton's law.…”

Dipolar dark matter and dark energy

“…In contrast to modified gravity theories, the model should be viewed as a modified matter theory. The idea that the phenomenology of MOND could arise from the CDM paradigm has been previously discussed [38,39]. However here we shall consider a true modification of the physics of dark matter, drastically different from CDM (see also [40] for an alternative approach in a related spirit).…”

Astrophysics in 2002

“…In comparison, the following are practically old friends: (1) conformal gravity (Mannheim 2001), (2) non-cosmological redshifts (Arp 2002a for;Sembach et al 2001 against), (3) quantized redshifts (Roscoe 2002), and (4) modified Newtonian dynamics (MOND) as an alternative to dark matter (Milgrom 2002).…”