What Are the Six Puzzles Challenging LCDM Cosmology?

[wolram]

[37] arXiv:0811.4684 [ps, pdf, other]
Title: Six Puzzles for LCDM Cosmology
Authors: L. Perivolaropoulos
Comments: 9 pages, 3 figures. Invited article to the TSPU anniversary volume "The Problems of Modern Cosmology" on the occasion of the 50th birthday of Prof. S. D. Odintsov
Subjects: Astrophysics (astro-ph)
Quote.
The LCDM cosmological model is a well defined, simple and predictive model which is consistent with the majority of current cosmological observations. Despite of these successes there are specific cosmological observations which differ from the predictions of LCDM at a level of 2\sigma or higher. These observations include the following: 1. Large Scale Velocity Flows (LCDM predicts significantly smaller amplitude and scale of flows than what observations indicate), 2. Brightness of Type Ia Supernovae (SnIa) at High Redshift z (LCDM predicts fainter SnIa at High z), 3. Emptiness of Voids (LCDM predicts more dwarf or irregular galaxies in voids than observed), 4. Profiles of Cluster Haloes (LCDM predicts shallow low concentration and density profiles in contrast to observations which indicate denser high concentration cluster haloes) 5. Profiles of Galaxy Haloes (LCDM predicts halo mass profiles with cuspy cores and low outer density while lensing and dynamical observations indicate a central core of constant density and a flattish high dark mass density outer profile), 6. Sizable Population of Disk Galaxies (LCDM predicts a smaller fraction of disk galaxies due to recent mergers expected to disrupt cold rotationally supported disks). Even though the origin of some of the above challenges may be astrophysical or related to dark matter properties, it should be stressed that even on galactic and cluster scales, the effects of dark energy on the equilibrium and stability of astrophysical systems are not negligible and they may play a key role in the resolution of the above puzzles. Here, I briefly review these six challenges of LCDM and discuss the possible dark energy properties required for their resolution.

 

[wolram]

Are the six challenges acknowledged as genuine in the community?

 

[marcus]

Are the six challenges acknowledged as genuine in the community?

Sure. They are puzzles, as he says. Things to think about. The paper is a summary of questions people would like to get answers for (or if they already have answers they will be eager to tell you about them)

At least in my humble opinion. I spotted the paper yesterday and put in bibliography because I thought it might be useful.

Let's make a more legible list of these six problems so anybody who looks can see easily:

1. Large Scale Velocity Flows (LCDM predicts significantly smaller amplitude and scale of flows than what observations indicate),

2. Brightness of Type Ia Supernovae (SnIa) at High Redshift z (LCDM predicts fainter SnIa at High z),

3. Emptiness of Voids (LCDM predicts more dwarf or irregular galaxies in voids than observed),

4. Profiles of Cluster Haloes (LCDM predicts shallow low concentration and density profiles in contrast to observations which indicate denser high concentration cluster haloes)

5. Profiles of Galaxy Haloes (LCDM predicts halo mass profiles with cuspy cores and low outer density while lensing and dynamical observations indicate a central core of constant density and a flattish high dark mass density outer profile),

6. Sizable Population of Disk Galaxies (LCDM predicts a smaller fraction of disk galaxies due to recent mergers expected to disrupt cold rotationally supported disks).

There may be other anomalous observations that people can think of, and would like to add to the list, but this list already seems pretty interesting. I assume these puzzles have been or will be answered---it is part of the give and take that surrounds any dominant model. Nothing is ever really settled until a model has finally gone into honorable retirement and been replaced by a new football (i.e. a new dominant model.)

Wolram, I can't speak will entire confidence here because there are plenty of things I don't understand the details of. But let's look at his main article and his references, and get an idea of how things stand:
http://arxiv.org/abs/0811.4684

BTW 45-year-old Leandros Perivolaropoulos postdoc'd at Harvard in the early 1990s and has 79 publications on Spires with some excellent citation numbers and a respectable publication track-record with most of his articles accepted by Physical Review D, or something equally solid.

He's reliably mainstream, I'd say. Here's his homepage:
http://leandros.physics.uoi.gr/home/

 

[oldman]

Question about dark matter structures

A feature of large-scale structure formation that puzzles me (but must have long since been understood by those who model structure formation with a mixture of dark and luminous matter) is the formation of filaments, sheets, ropes and knots of clustered galaxies --- the kind of structures seen in the computer simulations accessible from, say, http://astro.uchicago.edu/~andrey/" .

The reason I find them puzzling is this: One might expect structures which are the result of gravitation attraction to reflect the symmetry of the underlying physical law of gravity. For example the spherical shape of stars and planets reflects the symmetry of the inverse square law. The morphology of galaxies reflects the same symmetry, often modified by the uniaxial symmetry of angular momentum conservation. Although these are structures made of luminous matter one expects dark matter structures, like galaxy haloes, to also reflect the symmetry of the law of gravitational attraction, which they do.

But large scale filaments etc. don't seem to have any obvious symmetries. Is this because they are just too big for their formation to be influenced by the symmetry of gravity? or is there some difference between the gravitational collapse of dark matter and luminous matter? if so, what is this difference? Do those who model structure formation treat the formation of filaments etc. just as an emergent phenomenon, or do they somewhere describe the physical reasons why the symmetry of gravity is unimportant in this case?

 

[wolram]

Marcus, i am only interested in Peculiar velocities and large scale structure, apart from the brightness of sn, i think the other issues could tentatively be put aside for now.
I think we need to understand how the above fit with the two (forces) gravity and dark energy, and dark matter in LCDM model.

 

[wolram]

This may be silly, but would pre collapse galactic angular momentum be retained in the collapsed medium? assuming the universe (bounced).

 

[marcus]

This may be silly, but would pre collapse galactic angular momentum be retained in the collapsed medium? assuming the universe (bounced).

Astute question. I haven't seen it treated yet, in the QG literature. It may have been...should have been. But I don't remember seeing a treatment.

I can't resist hazarding a guess: angular momentum will turn out to be retained in the loop quantum cosmology bounce. But until I see a research paper explicitly dealing with that question I can't really say anything definite.