Latest News from the Universe: CDM vs WDM and the Future of Dark Matter Models

[wolram]

http://chalonge.obspm.fr/colloque2015.html

After more than twenty five years, and as often in big-sized science, CDM research (CDM+ baryon simulations, direct and indirect WIMP experimental research and model building),has by now its own internal inertia and own organized community, without reproducing the astronomical observations and failing to provide any experimental signal of wimps (except signals compatible with experimental noise). Growing CDM + baryon galactic simulations involve ever increasing large super-computers and large number of people working with, CDM particle wimp search involved (and involve) large and long-time planned experiments, huge number of people and huge budgets. One should not to be surprised then if a strategic scientific change have not yet operated in the CDM + baryon research and in the wimp research, given the way in which the organization operates, although their real scientific situation is of decline. Wimps are not the DM particle, DM is not Cold because the right DM particle is at the keV scale, DM is Warm.
See also.
http://arxiv.org/abs/1201.1617PURPOSE AND TOPICS

1. The new concordance model in agreement with observations: ΛWDM (Lambda-dark energy- Warm Dark Matter). Recently, Warm (keV scale) Dark Matter emerged impressively over CDM (Cold Dark Matter) as the leading Dark Matter candidate. Astronomical evidence that Cold Dark Matter (LambdaCDM) and its proposed tailored baryonic cures do not work at galactic and small scales is staggering. LambdaWDM solves naturally the problems of LambdaCDM and agrees remarkably well with the observations at galactic and small scales as well as large and cosmological scales. In contrast, LambdaCDM simulations only agree with observations at large scales.

In the context of this new Dark Matter situation, which implies novelties in the astrophysical, cosmological, particle and nuclear physics context, the 19th Paris Colloquium 2015 is devoted to the Latest News from the Universe.

So is CDM now ruled out, what difference will it make to or models?

 

[wabbit]

What are the relevant papers behind this presentation ? I looked at the site and didn't find the bibliography.

 

[wolram]

This is another paper on the subject:

http://arxiv.org/abs/1201.1617

ABSTRACT We investigate for the first time the effects of a Warm Dark Matter (WDM) power spectrum on the statistical properties of galaxies using a semi-analytic model of galaxy formation. The WDM spectrum we adopt as a reference case is suppressed - compared to the standard Cold Dark Matter (CDM) case - below a cut-off scale ≈ 1 Mpc corresponding (for thermal relic WDM particles) to a mass mX = 0.75 keV. This ensures consistency with present bounds provided by the microwave background WMAP data and by the comparison of hydrodynamical N-body simulations with observed Lyman-α forest. We run our fiducial semi-analytic model with such a WDM spectrum to derive galaxy luminosity functions (in B, UV, and K bands) and the stellar mass distributions over a wide range of cosmic epochs, to compare with recent observations and with the results in the CDM case. The predicted color distribution of galaxies in the WDM model is also checked against the data. When compared with the standard CDM case, the luminosity and stellar mass distributions we obtain assuming a WDM spectrum are characterized by: i) a flattening of the faint end slope and ii) a sharpening of the cutoff at the bright end for z . 0.8. We discuss how the former result is directly related to the smaller number of low-mass haloes collapsing in the WDM scenario, while the latter is related to the smaller number of satellite galaxies accumulating in massive haloes at low redshift, thus suppressing the accretion of small lumps on the central, massive galaxies. These results shows how a adopting a WDM power spectrum may contribute to solve two major problems of CDM galaxy formation scenarios, namely, the excess of predicted faint (low mass) galaxies at low and - most of all - high redshifts, and the excess of bright (massive) galaxies at low redshifts.

 

[wabbit]

Thanks. At first sight it seems strange that they can make such strong claims - if this is correct I would expect many published papers since 2012, if only checking against newer Planck data.

Lets hear from the experts here.

 

[Chronos]

There exists a possibility both warm and cold DM may play a role, as suggested in this paper http://arxiv.org/abs/1503.07867. It would be extraordinary, IMO, if a single species of DM particles can satisfy all cosmological constraints.

 

[Chalnoth]

It would be really amazing to be able to measure the temperature of dark matter, as that would provide another constraint which we could use to limit the available parameter space for dark matter particles.

But it's certainly not a slam-dunk just yet. For one, at the low-mass end, galaxies tend to expel most of their normal (baryonic) matter early in formation. This makes such galaxies much dimmer than you would expect just based upon observing the luminosity to mass ratios of larger galaxies. So it's very possible that the reason we're not seeing very many galaxies at the low-mass end is just that they are too dim for us to observe. It's really, really hard to demonstrate that the observations aren't biased at the low-mass end.

So I think it's best to wait until there is another, independent line of evidence before concluding that WDM is the reality.