Cold or warm dark matter or a mixture

[wolram]

This paper favors a mixture, but there are many papers that predict Cold dark matter, is there a particle that can be ruled out, or pushed to the back of favored particles.

arXiv:1611.09362 [pdf, other]
Hints against the cold and collisionless nature of dark matter from the galaxy velocity function
Aurel Schneider, Sebastian Trujillo-Gomez, Emmanouil Papastergis, Darren S. Reed, George Lake
Comments: 17 pages, 10 figures, comments welcome
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

The observed number of dwarf galaxies as a function of rotation velocity is significantly smaller than predicted by the ΛCDM model. This discrepancy cannot be simply solved by assuming strong baryonic processes, since they would violate the observed relation between maximum circular velocity (vmax) and baryon mass of galaxies. A speculative but tantalising possibility is that the mismatch between observation and theory points towards the existence of non-cold or non-collisionless dark matter (DM). In this paper, we investigate the effects of warm, mixed (i.e warm plus cold), and self-interacting DM scenarios on the abundance of dwarf galaxies and the relation between observed HI line-width and maximum circular velocity. Both effects have the potential to alleviate the apparent mismatch between the observed and theoretical abundance of galaxies as a function of vmax. For the case of warm and mixed DM, we show that the discrepancy disappears, even for luke-warm models that evade stringent bounds from the Lyman-α forest. Self-interacting DM scenarios can also provide a solution as long as they lead to extended (≳1.5 kpc) dark matter cores in the density profiles of dwarf galaxies. Only models with velocity-dependent cross sections can yield such cores without violating other observational constraints at larger scales.

 

[Chalnoth]

This paper favors a mixture, but there are many papers that predict Cold dark matter, is there a particle that can be ruled out, or pushed to the back of favored particles.

arXiv:1611.09362 [pdf, other]
Hints against the cold and collisionless nature of dark matter from the galaxy velocity function
Aurel Schneider, Sebastian Trujillo-Gomez, Emmanouil Papastergis, Darren S. Reed, George Lake
Comments: 17 pages, 10 figures, comments welcome
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

The observed number of dwarf galaxies as a function of rotation velocity is significantly smaller than predicted by the ΛCDM model. This discrepancy cannot be simply solved by assuming strong baryonic processes, since they would violate the observed relation between maximum circular velocity (vmax) and baryon mass of galaxies. A speculative but tantalising possibility is that the mismatch between observation and theory points towards the existence of non-cold or non-collisionless dark matter (DM). In this paper, we investigate the effects of warm, mixed (i.e warm plus cold), and self-interacting DM scenarios on the abundance of dwarf galaxies and the relation between observed HI line-width and maximum circular velocity. Both effects have the potential to alleviate the apparent mismatch between the observed and theoretical abundance of galaxies as a function of vmax. For the case of warm and mixed DM, we show that the discrepancy disappears, even for luke-warm models that evade stringent bounds from the Lyman-α forest. Self-interacting DM scenarios can also provide a solution as long as they lead to extended (≳1.5 kpc) dark matter cores in the density profiles of dwarf galaxies. Only models with velocity-dependent cross sections can yield such cores without violating other observational constraints at larger scales.

As far as I'm aware, there isn't anything definitive that points to cold dark matter specifically. Hot dark matter is ruled out pretty conclusively, but those observations only place an upper limit on the dark matter temperature.

From a model selection standpoint, warm dark matter is very exciting because it should be at least a little bit easier to measure its properties. But the kind of measurements described in the paper above are very difficult, and it's not easy at all to show conclusively that the problem isn't some other effect. So what we would need, as with most things in physics, is an independent check that uses a different type of observational evidence to get at the temperature of the dark matter. Direct detection of the particles would be ideal, but that may take a long time (if ever).