What is the connection between dark matter and ordinary baryonic matter?

[Garth]

There are several pieces of evidence to suggest that DM is a real artifact of the universe.
1. Nearly flat rotation curves of spiral galaxies suggest they are embedded in a massive unseen halo of some kind. (Although the mass of these haloes may be affected by GR gravitational effects and over-estimated by ~30% Over estimate of dark matter).
2. $\gamma$-ray emission from galactic cores may be a marker of DM annihilation.
3. Galactic cluster dynamics likewise require large unseen masses in between the individual galactic haloes. This mass is also detected by gravitational lensing effects.
4. Unseen mass is required to explain the formation of large scale structure early in the universe's history.
5. The observed mass density of the universe, from cluster lensing of distant quasars, seems to be about 30% of the closure density $\Omega_M \sim 0.3$, whereas the visible mass density is only $\Omega_v \sim 0.003$.

The standard model allows a maximum baryon density of around $\Omega_b \sim 0.04$ created by nucleosynthesis in the Big Bang. The WMAP data is consisitent with this and a $\Omega_M = 0.27$, so it requires a component of $\Omega_{DM} \sim 0.23$, and also, if that data is interpreted as evidence of a spatially flat universe, then it also requires Dark energy with $\Omega_{DE} \sim 0.73$.

Note that this standard model still requires a lot of unseen (dark) baryonic matter, the difference between $\Omega_b \sim 0.04$ and $\Omega_v \sim 0.003$, i.e. in the standard model there is an OOM greater amount of unseen baryonic matter than that which is visible as stars and nebulae.

But what is the rest of the DM?

There are numerous alternative proposals including, e.g. Self-Interacting dark matter, Self-Annihilating dark matter, Decaying dark matter, and many others. But a recent paper Cold Dark Matter as Compact Composite Objects suggests

However, a general idea that DM could be an object strongly interacting with ordinary baryons ( in view of many hints coming from very different unrelated observations, see some highlights above) still remains to be a very attractive idea.

In fact, it was recently suggested a natural reason why the dark matter objects might be closely related to the ordinary baryons [18], [19]. Our original argument suggesting the necessity of such kind of connection was based on the observation that $\Omega_B \sim \Omega_{DM}$. Indeed, these two contributions to $\Omega$ could be in general very different because (according to the canonical view) they are originated from fundamentally different physics at very different cosmological epoch. Therefore, the observed relation $\Omega_B \sim \Omega_{DM}$ between the two very different contributions to $\Omega$ is extremely difficult to explain in models that invoke a DM candidate not related to the ordinary quark/baryon degrees of freedom.

We shall see in what follows, that a resolution of the puzzle $\Omega_B \sim \Omega _{DM}$ within our framework might be linked
to a number of other problems highlighted above. We are not claiming, of course, to have these problems solved in our framework. Rather, we want to present some arguments suggesting that many apparently unrelated problems might be in fact closely related.

The idea is that the dark matter consists of very dense (few times the nuclear density) macroscopic droplets of ordinary light quarks ( or/and antiquarks) [18], [19] which however are formed not in ordinary hadronic phase, but rather in color superconducting phase.

The paper then explains how this might have happened in the "color superconducting phase" of the BBN and that today DM particles are strongly interacting composite macroscopically large objects which made of well known light quarks (or even antiquarks).

Whatever the merits of this model, the interesting idea from my POV is the concept that a link between the nature of DM and baryonic matter may resolve some problems with the standard mainstream model. IMHO this DM is baryonic in nature.

Garth

 

[Greg Bernhardt]

@Garth did you find any more insight on this topic?