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

In a recent paper, Kaplinghat and Turner (2001) (KT) advertise that MOND canbe derived naturally in the CDM paradigm. They actually proceed to produce amore limited result: Every galaxy should have a transition radius, $r_t$, belowwhich baryons dominate, and above which dark matter (DM) takes over; theacceleration at $r_t$ is nearly the same for all galaxies; and due to acoincidences this is of order $a_0\sim cH_0$. This follows from their tacit,intermediate result, whereby CDM halos of galaxies have a very nearly universalacceleration profile $a(r)\approx v^2(r)/r\approx A\hat a(r/\ell)$, where A isuniversal, and only the scale $\ell$ varies from halo to halo. (This remains sowhen baryons are added because they assume a universal baryon-collapse factor.)The KT scenario is phenomenologically wrong--observed galaxies are simply notlike that. For example, it precludes altogether the existence of LSB galaxies,in which the acceleration is everywhere smaller than $a_0$. Thephenomenologically sound outcome--i.e., the role of $a_0$ as a transitionacceleration in high-surface-brightness galaxies--pertains to only a small partof the statement of MOND. There are several other, independent roles that$a_0\sim cH_0$ plays in MOND phenomenology, and other predictions of MOND, notrelated to the value of $a_0$, that are not explainable in the KT scenario. The results of KT also disagree with those of CDM simulations, which, as theynow stand, do not reproduce any aspect of MOND phenomenology.Comment: 6 page