kimbyd said:
You're really diverging from anything that can be supported by evidence here.
More evidence. Also what other than CMB have dark matter particle theories accurately predicted prospectively in new kinds of phenomena?
Here's a review of the state of dark matter particle research by someone not really known for having any strong advocacy position:
Recent high-resolution simulations that include Cold Dark Matter (CDM) and baryons have shown that baryonic physics can dramatically alter the dark matter structure of galaxies. These results modify our predictions for observed galaxy evolution and structure. Given these updated expectations, it is timely to re-examine observational constraints on the dark matter model. A few observations are reviewed that may indirectly trace dark matter, and may help confirm or deny possible dark matter models. Warm Dark Matter (WDM) and Self-Interacting Dark Matter (SIDM) are currently the favorite alternative models to CDM. Constraints on the WDM particle mass require it to be so heavy that WDM is nearly indistinguishable from CDM. The best observational test of SIDM is likely to be in the dark matter distribution of faint dwarf galaxies, but there is a lack of theoretical predictions for galaxy structure in SIDM that account for the role of baryons.
Alyson Brooks, "
Re-Examining Astrophysical Constraints on the Dark Matter Model" (July 28, 2014). A year later, Brooks is
co-author of an article that compares CDM to SIDM in simulations with baryonic matter feedback and finds that the differences are surprisingly modest.
The problems with conventional Cold Dark Matter models that were used in the formulation of LambdaCDM, requiring a fifth force or some other major revision to the theory have been well known for many years:
Dark matter (DM) self-interactions have important implications for the formation and evolution of structure, from dwarf galaxies to clusters of galaxies. We study the dynamics of self-interacting DM via a light mediator, focusing on the quantum resonant regime where the scattering cross section has a non-trivial velocity dependence. While there are long-standing indications that observations of small scale structure in the Universe are not in accord with the predictions of collisionless DM, theoretical study and simulations of DM self-interactions have focused on parameter regimes with simple analytic solutions for the scattering cross section, with constant or classical velocity (and no angular) dependence. We devise a method that allows us to explore the velocity and angular dependence of self-scattering more broadly, in the strongly-coupled resonant and classical regimes where many partial modes are necessary for the achieving the result. We map out the entire parameter space of DM self-interactions --- and implications for structure observations --- as a function of the coupling and the DM and mediator masses. We derive a new analytic formula for describing resonant s-wave scattering. Finally, we show that DM self-interactions can be correlated with observations of Sommerfeld enhancements in DM annihilation through indirect detection experiments. . . .
As is well known, the collisionless cold DM (CCDM) paradigm has been highly successful in accounting for large scale structure of the Universe. However, it is far from clear that this paradigm can also successfully explain the small scale structure of the Universe. Precision observations of dwarf galaxies show DM distributions with cores, in contrast to cusps predicted by CCDM simulations. It has also been shown that the most massive subhalos in CCDM simulations of Miky Way (MW) size halos are too dense to host the observed brightest satellites of the MW. Lastly, chemo-dynamic measurements in at least two MW dwarf galaxies show that the slopes of the DM density profiles are shallower than predicted by CCDM simulations. These small scale anomalies, taken at face value, may indicate that other interactions besides gravity play a role in structure formation.
Beyond Collisionless Dark Matter: Particle Physics Dynamics for Dark Matter Halo Structure Authors:
Sean Tulin,
Hai-Bo Yu,
Kathryn M. Zurek (Submitted on 15 Feb 2013).
Another examination of conventional cold dark matter models is more vehement. Here are some key quotes from the abstract and body text:
Evidence that Cold Dark Matter (LambdaCDM) and its proposed tailored cures do not work at small scales is staggering. . . .The most troubling signs of the failure of the CDM paradigm have to do with the tight coupling between baryonic matter and the dynamical signatures of DM in galaxies, e.g. the Tully-Fisher relation, the stellar disc-halo conspiracy, the maximum disc phenomenon, the MOdified Newtonian Dynamics (MOND) phenomenon, the baryonic Tully-Fisher relation, the baryonic mass discrepancy-acceleration relation, the 1-parameter dimensionality of galaxies, and the presence of both a DM and a baryonic mean surface density. . . .It should be recalled that the connection between small scale structure features and the mass of the DM particle follows mainly from the value of the free-streaming length lfs. Structures smaller than lfs are erased by free-streaming. WDM particles with mass in the keV scale produce lfs ∼ 100 kpc while 100 GeV CDM particles produce an extremely small lfs ∼ 0.1 pc. While the keV WDM lfs ∼ 100 kpc is in nice agreement with the astronomical observations, the GeV CDM lfs is a million times smaller and produces the existence of too many small scale structures till distances of the size of the Oort’s cloud in the solar system. No structures of such type have ever been observed. Also, the name CDM precisely refers to simulations with heavy DM particles in the GeV scale. . . . The mass of the DM particle with the free-streaming length naturally enters in the initial power spectrum used in the N-body simulations and in the initial velocity. The power spectrum for large scales beyond 100 kpc is identical for WDM and CDM particles, while the WDM spectrum is naturally cut off at scales below 100 kpc, corresponding to the keV particle mass free-streaming length. In contrast, the CDM spectrum smoothly continues for smaller and smaller scales till ∼ 0.1 pc, which gives rise to the overabundance of predicted CDM structures at such scales. . . . Overall, seen in perspective today, the reasons why CDM does not work are simple: the heavy wimps are excessively non-relativistic (too heavy, too cold, too slow), and thus frozen, which preclude them to erase the structures below the kpc scale, while the eV particles (HDM) are excessively relativistic, too light and fast, (its free streaming length is too large), which erase all structures below the Mpc scale; in between, WDM keV particles produce the right answer.
H.J. de Vega and N.G. Sanchez, “Warm dark matter in the galaxies:theoretical and observational progresses. Highlights and conclusions of the chalonge meudon workshop 2011″ (14 Sept 2011)
http://arxiv.org/abs/1109.3187 See also in accord S. Tulin, et al. “Beyond Collisionless Dark Matter: Particle Physics Dynamics for Dark Matter Halo Structure” (15 Feb 2013)
http://arxiv.org/abs/1302.3898:
As is well known, the collisionless cold DM (CCDM) paradigm has been highly successful in accounting for large scale structure of the Universe. . . . Precision observations of dwarf galaxies show DM distributions with cores, in contrast to cusps predicted by CCDM simulations. It has also been shown that the most massive subhalos in CCDM simulations of Miky Way (MW) size halos are too dense to host the observed brightest satellites of the MW. Lastly, chemo-dynamic measurements in at least two MW dwarf galaxies show that the slopes of the DM density profiles are shallower than predicted by CCDM simulations.
Again, the NFW profile predicted for collisionless or almost collisionless dark matter simply does not fit the data.
In cosmological N-body simulations, the baryon effects on the cold dark matter (CDM) halos can be used to solve the small scale problems in ΛCDM cosmology, such as cusp-core problem and missing satellites problem. It turns out that the resultant total density profiles (baryons plus CDM), for halos with mass ranges from dwarf galaxies to galaxy clusters, can match the observations of the rotation curves better than NFW profile. In our previous work, however, we found that such density profiles fail to match the most recent strong gravitational lensing observations. In this paper, we do the converse: we fit the most recent strong lensing observations with the predicted lensing probabilities based on the so-called (α,β,γ) double power-law profile, and use the best-fit parameters (α=3.04,β=1.39,γ=1.88) to calculate the rotation curves. We find that, at outer parts for a typical galaxy, the rotation curve calculated with our fitted density profile is much lower than observations and those based on simulations, including the NFW profile. This again verifies and strengthen the conclusions in our previous works: in ΛCDM paradigm, it is difficult to reconcile the contradictions between the observations for rotation curves and strong gravitational lensing.
Lin Wang, Da-Ming Chen, Ran Li "
The total density profile of DM halos fitted from strong lensing" (July 31, 2017). As the body text explains:
It is now well established that, whatever the manners the baryon effects are included in the collisionless CDM N-body cosmological simulations, if the resultant density profiles can match the observations of rotation curves, they cannot simultaneously predict the observations of strong gravitational lensing (under- or over-predict). And for the case of typical galaxies, the reverse is also true, namely, the SIS profile preferred by strong lensing cannot be supported by the observations of rotation curves near the centers of galaxies.
Brooks, above, suggests that Warm Dark Matter theories don't solve the problems of cold dark matter very well even with baryon effects. Warm dark matter models also have their own problems (in accord see
here).
It has long been known that
small scale structure strongly disfavors a mix of warm and cold dark matter. Warm dark matter models also have
great difficulty forming dwarf galaxies that we know exist (also, see, e.g.
here, and
here).
Recent research constrains warm dark matter models to have masses approximately in the range of 1-2 keV and also tightly bounds their possible self-interactions. The observed Tully-Fisher relation is
inconsistent with lighter warm dark matter particles.
Observations of the Andromeda Galaxy suggest an upper limit on warm dark matter particle sizes of about 2.2 keV.
Long gamma ray burst data imposes similar constraints placing a floor value of about 1.6-1.8 keV for combined limits from the various sources of 1.6-2.2 keV. This is a very narrow window of parameter space in which the a lambdaCDM theory consistent particle could work.
See also deVega and Sanchez, "Dark matter in galaxies: the dark matter particle mass is about 2 keV" (Submitted on 2 Apr 2013)
http://arxiv.org/abs/1304.0759 See also, for example, C. Watso, et al. “Constraining Sterile Neutrino Warm Dark Matter with Chandra Observations of the Andromeda Galaxy”
http://arxiv.org/abs/1111.4217 (10 Jan 2012) (WDM mass capped at 2.2 keV); R. de Souza, A. Mesinger, A. Ferrara, Z. Haiman, R. Perna, N. Yoshida, “Constraints on Warm Dark Matter models from high-redshift long gamma-ray bursts” (17 Apr 2013)
http://arxiv.org/abs/1303.5060 (WMD mass at least 1.6 keV); D. Anderhaldena, et al. “Hints on the Nature of Dark Matter from the Properties of Milky Way Satellites” (12 Dec 2012)
http://arxiv.org/pdf/1212.2967v1.pdf (mixed CDM/WDM models disfavored); J. Viñas, et al. “Typical density profile for warm dark matter haloes” (9 Jul 2012)
http://arxiv.org/abs/1202.2860 (models with more than one WDM species disfavored); Xi Kang, Andrea V. Maccio, aaron A. dutton, "The effect of Warm Dark Matter on galaxy properties: constraints from the stellar mass function and the Tully-Fisher relation" (8 April 2013)
http://arxiv.org/abs/1208.0008 (WDM mass of more than 0.75 keV and consistent with 2 keV).
More on the scatter of the Tully-Fischer relation v. LCDM.
In a LCDM cosmology, the baryonic Tully-Fisher relation (BTFR) is expected to show significant intrinsic scatter resulting from the mass-concentration relation of dark matter halos and the baryonic-to-halo mass ratio. We study the BTFR using a sample of 118 disc galaxies (spirals and irregulars) with data of the highest quality: extended HI rotation curves (tracing the outer velocity) and Spitzer photometry at 3.6 μm (tracing the stellar mass). Assuming that the stellar mass-to-light ratio (M*/L) is nearly constant at 3.6 μm, we find that the scatter, slope, and normalization of the BTFR systematically vary with the adopted M*/L. The observed scatter is minimized for M*/L > 0.5, corresponding to nearly maximal discs in high-surface-brightness galaxies and BTFR slopes close to ~4. For any reasonable value of M*/L, the intrinsic scatter is ~0.1 dex, below general LCDM expectations. The residuals show no correlations with galaxy structural parameters (radius or surface brightness), contrary to the predictions from some semi-analytic models of galaxy formation. These are fundamental issues for LCDM cosmology.
Federico Lelli, Stacy S. McGaugh, and James M. Schombert,
"The small scatter of the baryonic Tully-Fisher relation" (December 14, 2015).
More generally dark matter distributions closely track baryon distributions even though there is no viable mechanism to do so.
See, e.g. Edo van Uitert, et al., "
Halo ellipticity of GAMA galaxy groups from KiDS weak lensing" (October 13, 2016).
The more we go deep into the knowledge of the dark component which embeds the stellar component of galaxies, the more we realize the profound interconnection between them. We show that the scaling laws among the structural properties of the dark and luminous matter in galaxies are too complex to derive from two inert components that just share the same gravitational field. In this paper we review the 30 years old paradigm of collisionless dark matter in galaxies. We found that their dynamical properties show strong indications that the dark and luminous components have interacted in a more direct way over a Hubble Time. The proofs for this are the presence of central cored regions with constant DM density in which their size is related with the disk length scales. Moreover we find that the quantity ρDM(r,L,RD)ρ⋆(r,L,RD) shows, in all objects, peculiarities very hardly explained in a collisionless DM scenario.
Paolo Salucci and Nicola Turini, "
Evidences for Collisional Dark Matter In Galaxies?" (July 4, 2017).
But, this can't simply be remedied by tweaking the cross-section of interaction between ordinary matter and dark matter because XENON1T an LUX and other direct dark matter detection experiments place tight constraints on the maximum cross-section of interaction that dark matter can have with ordinary matter, which limits the extent to which non-gravitational interactions with baryons can account for the tight correlations of baryonic matter and inferred dark matter distributions.
We report the first dark matter search results from XENON1T, a ∼2000-kg-target-mass dual-phase (liquid-gas) xenon time projection chamber in operation at the Laboratori Nazionali del Gran Sasso in Italy and the first ton-scale detector of this kind. The blinded search used 34.2 live days of data acquired between November 2016 and January 2017. Inside the (1042±12) kg fiducial mass and in the [5, 40] keVnr energy range of interest for WIMP dark matter searches, the electronic recoil background was (1.93±0.25)×10−4 events/(kg × day ×keVee), the lowest ever achieved in a dark matter detector. A profile likelihood analysis shows that the data is consistent with the background-only hypothesis. We derive the most stringent exclusion limits on the spin-independent WIMP-nucleon interaction cross section for WIMP masses above 10 GeV/c2, with a minimum of 7.7 ×10−47 cm2 for 35-GeV/c2 WIMPs at 90% confidence level.
From
here. The XENON1T exclusion range is slightly more strict than LUX. Xenon 1T has replicated this exclusion and hence made more robust to all manner of systemic errors. The LHC also provides data that exclude potential dark matter cross-sections of interactions, particularly at lower masses which direct dark matter detection experiments struggle to probe. See e.g.
https://arxiv.org/abs/1709.02304 and
https://arxiv.org/abs/1510.01516
As
Jester at Resonaances explains (a professional physicist and blogger):
One possible scenario is that WIMPs experience one of the Standard Model forces, such as the weak or the Higgs force. The former option is strongly constrained by now. If WIMPs had interacted in the same way as our neutrino does, that is by exchanging a Z boson, it would have been found in the Homestake experiment. Xenon1T is probing models where the dark matter coupling to the Z boson is suppressed by a factor cχ ~ 10^-3 - 10^-4 compared to that of an active neutrino.
Incidentally, the close bounds
emerging at the LHC on deviations from the Standard Model predictions for Higgs boson decays and branching fractions, also increasingly forecloses the possibility of "Higgs portal" dark matter over a wide range of its parameter space, a loophole that might have escaped direct dark matter detection experiments like LUX and XENON1T.
Collisionless bosonic dark matter is likewise excluded over a wide range of parameters.
What about self-interacting dark matter?
We know that self-interactions between dark matter particles with each other with cross-sections of interaction
on the order of 10^-23 to 10^-24 greatly improve the fit to the halo models observed (self-interactions on the order of 10^-22 or more, or of 10^25 or more, clearly do not produce the observed halos). Notably, this cross section of self-interaction is fairly similar to the cross-section of interaction of ordinary matter (e.g. helium atoms) with each other. So, if dark matter halos are explained by self-interaction, the strength of that self-interaction ought to be on the same order of magnitude as electromagnetic interactions.
But, our observations and simulations are now sufficiently precise that we can determine that ultimately, a
simple constant coupling constant between dark matter particles or velocity dependent coupling constant between dark matter particles fails to fit the observed dark matter halos. Generically, these models
generate shallow spherically symmetric halos which are inconsistent with the comparatively dense and ellipsoidal halos that are observed.
Next generation self-interacting dark matter models look at more a general
Yukawa potential generated by dark matter to dark matter forces with massive force carriers (often called "dark photons") that have masses which empirically need to be
on the order of 1 MeV to 100 MeV (i.e. between the mass of an electron and a muon, but less than the lightest hadron, the
pion, which has a mass on the order of 135-140 MeV) to produce dark halos that are a better fit to the dark matter halos that are observed. But, the XENON experiment places
strong limits on interactions between ordinary photons and "dark photons".
Axion Dark Matter
Axion dark matter models are a poor fit to the CMB data that is among the strongest reasons to support a dark matter hypothesis. Renée Hlozek, David J. E. Marsh, Daniel Grin "
Using the Full Power of the Cosmic Microwave Background to Probe Axion Dark Matter" (August 18, 2017).
Galaxy Cluster Bounds For Dark Matter
Galaxy clusters that MOND struggles with are also problematic for a wide range of dark matter particle theories, and suggest hot dark matter neutrino solutions for the discrepancies there, contrary to LambdaCDM models.
Galaxy clusters, employed by Zwicky to demonstrate the existence of dark matter, pose new stringent tests. If merging clusters demonstrate that dark matter is self-interacting with cross section σ/m∼2 cm2/gr, MACHOs, primordial black holes and light axions that build MACHOs are ruled out as cluster dark matter.
Recent strong lensing and X-ray gas data of the quite relaxed and quite spherical cluster A1835 allow to test the cases of dark matter with Maxwell-Boltzmann, Bose-Einstein and Fermi-Dirac distribution, next to Navarro-Frenck-White profiles. Fits to all these profiles are formally rejected at over 5σ, except in the fermionic situation.The interpretation in terms of (nearly) Dirac neutrinos with mass of 1.61+0.19−0.30 eV/c2 is consistent with results on the cluster A1689, with the WMAP, Planck and DES dark matter fractions and with the nondetection of neutrinoless double β-decay. The case will be tested in the 2018 KATRIN experiment.
Theodorus Maria Nieuwenhuizen "
Subjecting dark matter candidates to the cluster test" (October 3, 2017).
A variety of searches for sterile neutrinos have also ruled out this possibility in the relevant mass range. See, e.g.,
https://arxiv.org/abs/1710.06488 and
http://iopscience.iop.org/article/10.1088/1742-6596/718/3/032008/pdf
More Astronomy Evidence Problems with Mass Assembly In LambdaCDM
The speed of the El Gordo galaxy collision (2200 km/second) is a problem for LambdaCDM. See Sandor M. Molnar, Tom Broadhurst.
A HYDRODYNAMICAL SOLUTION FOR THE “TWIN-TAILED” COLLIDING GALAXY CLUSTER “EL GORDO”.
The Astrophysical Journal, 2015; 800 (1): 37 DOI:
10.1088/0004-637X/800/1/37 which notes:
The distinctive cometary X-ray morphology of the recently discovered massive galaxy cluster "El Gordo" (ACT-CT J0102–4915;
z = 0.87) indicates that an unusually high-speed collision is ongoing between two massive galaxy clusters. A bright X-ray "bullet" leads a "twin-tailed" wake, with the Sunyaev-Zel'dovich (SZ) centroid at the end of the northern tail. We show how the physical properties of this system can be determined using our FLASH-based,
N-body/hydrodynamic model, constrained by detailed X-ray, SZ, and Hubble lensing and dynamical data.
The X-ray morphology and the location of the two dark matter components and the SZ peak are accurately described by a simple binary collision viewed about 480 million years after the first core passage. We derive an impact parameter of
300 kpc, and a relative initial infall velocity of 2250 km s–1 when separated by the sum of the two virial radii assuming an initial total mass of 2.15 × 1015 M ☉ and a mass ratio of 1.9. Our model demonstrates that tidally stretched gas accounts for the northern X-ray tail along the collision axis between the mass peaks, and that the southern tail lies off axis, comprising compressed and shock heated gas generated as the less massive component plunges through the main cluster.
The challenge for ΛCDM will be to find out if this physically extreme event can be plausibly accommodated when combined with the similarly massive, high-infall-velocity case of the Bullet cluster and other such cases being uncovered in new SZ based surveys.
As noted earlier in the thread, this is not the only galaxy collision whose details are a poor fit for ΛCDM. One fluke is a fluke. Multiple galaxy collisions with velocities well out of line with ΛCDM predictions is more than a fluke, it is a problem with the theory.
ΛCDM would like to look to galaxy evolution details which are obscure and varied to explain its shortcomings, but they don't, instead, the need to rely on galaxy evolution is a problem because reasonably galaxy evolution hypotheses don't fit the data:
We show that a significant correlation (up to 5sigma) emerges between the bulge index, defined to be larger for larger bulge/disk ratio, in spiral galaxies with similar luminosities in the Galaxy Zoo 2 of SDSS and the number of tidal-dwarf galaxies in the catalogue by Kaviraj et al. (2012). In the standard cold or warm dark-matter cosmological models the number of satellite galaxies correlates with the circular velocity of the dark matter host halo. In generalized-gravity models without cold or warm dark matter such a correlation does not exist, because host galaxies cannot capture in-falling dwarf galaxies due to the absence of dark-matter-induced dynamical friction. However, in such models a correlation is expected to exist between the bulge mass and the number of satellite galaxies, because bulges and tidal-dwarf satellite galaxies form in encounters between host galaxies. This is not predicted by dark matter models in which bulge mass and the number of satellites are a priori uncorrelated because higher bulge/disk ratios do not imply higher dark/luminous ratios. Hence, our correlation reproduces the prediction of scenarios without dark matter, whereas an explanation is not found readily from the a priori predictions of the standard scenario with dark matter. Further research is needed to explore whether some application of the standard theory may explain this correlation.
Martin Lopez-Corredoira and Pavel Kroupa, "
The number of tidal dwarf satellite galaxies in dependence of bulge index" (November 30, 2015).
Occam's Razor
Of course, one of the reasons to favor a dark matter particle approach in the first place was Occam's Razor. Adding one new particle to the mix (when many beyond the Standard Model theories predict that such particles exist and that at least some are stable) would be less of an extension of current theory than a tweak to general relativity. But, when you get into the current system where you start needing not just new particles, but new fundamental forces of Nature and Byzantine constraints on matter assembly in the universe with no obvious physical basis, this becomes much more problematic.
2250 km s–1 when separated by the sum of the two virial radii assuming an initial total mass of 2.15 × 1015 M ☉ and a mass ratio of 1.9. Our model demonstrates that tidally stretched gas accounts for the northern X-ray tail along the collision axis between the mass peaks, and that the southern tail lies off axis, comprising compressed and shock heated gas generated as the less massive component plunges through the main cluster. The challenge for ΛCDM will be to find out if this physically extreme event can be plausibly accommodated when combined with the similarly massive, high-infall-velocity case of the Bullet cluster and other such cases being uncovered in new SZ based surveys.
