A&C reference library

marcus

http://arxiv.org/abs/astro-ph/0406139
A Quantum Approach to Dark Matter
Authors: A. D. Ernest
Comments: To be published in "Progress in Dark Matter Research" Nova Science Inc. New York

"This work develops and explores a quantum-based theory which enables the nature and origin of cold dark matter (CDM) to be understood without need to introduce exotic particles. The quantum approach predicts the existence of certain macroscopic quantum structures that are WIMP-like even when occupied by traditional baryonic particles. These structures function as dark matter candidates for CDM theory on large scales where it has been most successful, and retain the potential to yield observationally compliant predictions on galactic cluster and sub-cluster scales. Relatively pure, high angular momentum, eigenstate solutions obtained from Schrodinger's equation in weak gravity form the structural basis. They have no classical analogue, and properties radically different from those of traditional localised matter (whose eigenstate spectra contain negligible quantities of such states). Salient features include radiative lifetimes that can exceed the age of the universe, energies and 'sizes' consistent with galactic halos, and negligible interaction rates with radiation and macroscopic galactic objects. This facilitates the formation of sparsely populated macroscopic quantum structures that are invisible and stable. Viable structure formation scenarios are based on the seed potential wells of primordial black holes formed at the e+/e- phase transition. The structures can potentially produce suitable internal density distributions and have capacity to accommodate the required amount of halo dark matter. The formation scenarios show that it is possible to incorporate structures into universal evolutionary scenarios without significantly compromising the results of WMAP or the measurements of elemental BBN ratios."

meteor

Grzegorz Wardziñski offers all the abstracts of the latest papers in Astro-ph in Arxiv, all in the same page. The section is called Astro-ph for busy people. Wonderful!
http://www.camk.edu.pl/~gwar/astro-ph.html

marcus

turbo points out that Aunt Nettie
has an explanation for why grass is green---
it is trying to get a message back to its home planet.
http://www.dearauntnettie.com/archiv...hives-0105.htm
(dont believe this! it may be intended as a joke)

marcus

Quantum Gravity Phenomenology

http://ws2004.ift.uni.wroc.pl/html.html

WS-2004 symposium, Feb 4-14
notes for all the talks are online, click on "lectures"
for a listing
a number of the talks are also on arxiv. search under author name.

marcus

Chronos supplied this link
http://www.astrosociety.org/pubs/mer...2/nothing.html
to a non-technical discussion by Filippenko and Pasachoff of
how the universe can have zero total energy
(positive mass-energy of matter balanced by negative gravitational potential)

marcus

sol put this curvegraphing applet link
which is good

but we somehow dont have a good post about the Friedmann eqns.
on this sticky thread and we should. I will try to get something

but please if anybody has a better discussion of the basic equations of cosmology, showing the Lambda which has become so important, please
post it

marcus

in an earlier post on this thread we had a little bit about the Friedmann eqns. but this is better and also here is a link to a Sean Carroll piece in LivingReviews. the people at Albert Einstein Institute-Potsdam MPI asked Carroll to do the piece on "Cosmological Constant" for LivingReviews

http://relativity.livingreviews.org/...1-1/node3.html

Sean Carroll is a blogger as well as one of the worlds foremost cosmologists. he's at chicago. check out his blog sometime--it can be entertaining---the name is "preposterousuniverse"
------------------

In what follows I am using the same notation Sean Carroll uses in
LivingReviews which is pretty standard.

First here is a version of the Friedmann equations which conceals the cosmological constant as "dark energy" added into the rho term as another kind of energy density. So you dont see the Lambda explicitly in this version. This is how a lot of people do it nowadays, and the dark energy fraction is given as 73 percent of total energy density rho.

[tex](\frac{a'}{a})^2 = \frac{8\pi G}{3}\rho - \frac{k}{a^2}[/tex]

[tex]\frac{a''}{a}= -\frac{4\pi G}{3}(\rho + 3p)[/tex]

Now I'm going to separate the cosmological constant part out as Lamda, an inverse distance squared term. Now rho is all the other stuff, not counting dark energy, and the equations are:

[tex](\frac{a'}{a})^2 = \frac{8\pi G}{3}\rho - \frac{k}{a^2} + \frac{\Lambda}{3}[/tex]

[tex]\frac{a''}{a}= -\frac{4\pi G}{3}(\rho + 3p)+\frac{\Lambda}{3}[/tex]

EXPLAINING THE NOTATION
this is with c = 1 units, which simplifies things some.
the scale factor of the metric (whose increase is the expansion of the universe) is denoted by the letter a.
k is a spatial curvature parameter used to distinguish three cases
k = -1, 0, +1 for negative curvature, spatially flat, positive curvature

rho is an energy density, and easy to confuse with p pressure

the universe appears to be spatially flat, the critical density rho_crit is that needed for it to be perfectly flat with k = 0

HOW THE HUBBLE PARAMETER COMES IN
the Hubble parameter H is defined to be the time derivative a' of the scale parameter a, divided by a.
[tex]H^2 = (\frac{a'}{a})^2 [/tex]
for the time being assume we've included the Lambda term in rho as "dark energy, because this is a convenient way to set things up for calculating stuff, like the critical density. In the case of a spatially flat universe the first Friedmann equation boils down to

[tex]H^2 = \frac{8\pi G}{3}\rho_{crit}[/tex]

algebraically that turns into the formula for the critical density

[tex]\rho_{crit} = \frac{3}{8\pi G}H^2[/tex]

the Hubble parameter has been measured really accurately at 71 km/s per Mpc
and this lets us calculate the critical density at 0.83 joule per cubic km.since the U tests out flat or very nearly so, this is taken to be the
density of all the stuff, stars galaxies, light, dark matter, dust, dark energy etc. It all amounts to 0.83 joule per cubic km.

And the dark energy being 73 percent (from supernova data) means that its share is 0.6 joule per cubic km.

sol2

http://hyperphysics.phy-astr.gsu.edu...tro/fried.html

This is a good link Marcus as well, and will lead you to many of the equations.

Marcus, part of this journey for me, was recognizng how the universe could move from our past, to our now, and if we could not look beyond to the hyper geometries, how could we have ever accepted any views in cosmology like Reimann's?

What comes next? Omega?

marcus

Pete contributed this to the "Dark Energy" thread. this shows the cosm. const. Lambda in the context of the full GR equation.
I have usually been discussing this in the simplified context of the Friedmann equations, derived from the full Einstein equation. What Pete has taken the trouble to put in LaTex is a useful reference, so I'll just copy it here:
---exerpt from Pete---
The term Dark Energy is given to that matter which is causing the universe to expand at an accelerating rate. This is what some call "anti-gravity" since this is clearly gravity acting in a repulsive manner.
Back in Einstein's day nobody knew of any kind of matter which could produce such an effect. since Einstein assumed that the universe was static he added a term to his field equations to allow for this repulsive effect. Einstein's equations changed from

[tex]G^{\alpha\beta} = \frac{8\pi G}{c^4}T^{\alpha\beta}[/tex]

to

[tex]G^{\alpha\beta} + \Lambda g^{\alpha\beta} = \frac{8\pi G}{c^4}T^{\alpha\beta}[/tex]

[itex]\Lambda[/itex] is called the cosmological constant. In modern terms the cosmological constant is also called "Dark Energy." This is the term which, for normal matter, allows for anti-gravity when [itex]\Lambda[/itex] > 0....
---endquote---
for full post see
http://www.physicsforums.com/showthr...180#post301180

some more links for good measure
http://math.ucr.edu/home/baez/gr/outline1.html
http://math.ucr.edu/home/baez/einstein/einstein.html

marcus

Correction to previous post (too late to edit)
where one of the links was wrong

Ned Wright's balloon animation
http://www.astro.ucla.edu/~wright/balloon0.html
Cartoon strip about the particle horizon being 3X what you naively expect
http://www.astro.ucla.edu/~wright/photons_outrun.html
Microlensing by a star
http://www.astro.ucla.edu/~wright/microlensing.html
Cluster of galaxies lensing animation
http://www.astro.ucla.edu/~wright/cluster-lensing.html
Inflation animation
http://www.astro.ucla.edu/~wright/CM...ng_bubble.html
Animation of what "Equal Power on All Scales" means---part of
understanding the fluctuations shown by the Microwave Background
http://www.astro.ucla.edu/~wright/CMB-MN-03/epas.html

turbo

Here's a nice non-technical overview of the state of quantum gravity research, including some basic information about how studying cosmic rays and gamma ray bursts might help probe the structure of spacetime.

http://arxiv.org/abs/physics/0311037

marcus

Here is an introductions to cosmology, in about 60 pages:

http://arxiv.org/abs/astro-ph/0409426

An overview of Cosmology
Authors: Julien Lesgourgues
Lecture notes for the Summer Students Programme of CERN (2002-2004). 62 pages, 30 figures.

Very basic conceptual introduction to Cosmology, aimed at undergraduate students with no previous knowledge of General Relativity

---abstract---
While purely philosophical in the early times, and still very speculative at the beginning of the twentieth century, Cosmology has gradually entered into the realm of experimental science over the past eighty years. It has raised some fascinating questions like: is the Universe static or expanding ? How old is it and what will be its future evolution ? Is it flat, open or closed ? Of what type of matter is it composed ? How did structures like galaxies form ? In this course, we will try to give an overview of these questions, and of the partial answers that can be given today. In the first chapter, we will introduce some fundamental concepts, in particular from General Relativity. In the second chapter, we will apply these concepts to the real Universe and deal with concrete results, observations, and testable predictions.
---end quote---

meteor

Helioseismology: the study of the interior of the sun by observing the oscillations on its surface. This is a 60 pages paper that offers an introduction to the subject, also includes an historical review. All that you want to know about f-modes, g-modes, ring-diagram analysis, helioseismic holography,...can be found here. Title of the paper: "Helioseismology"
http://arxiv.org/abs/astro-ph/0207403

marcus

Sean Carroll online Cosmology Primer

good FAQ
http://pancake.uchicago.edu/%7Ecarro...rimer/faq.html

rest of Primer is probably very good also, but havent reviewed it yet.
see what you think

meyer_lev3

New member, first post

Streaming video of lectures/talks on current topics by Hawking, Weinberg, others.

Especially good is "Brane New World" (2003) By Steven Hawking.

http://www.phys.cwru.edu/events/cerca_video_archive.php

Enjoy .

marcus

thanks for the link, meyer_lev, and welcome.
Personally, I wasn't aware of this Case Western Reserve archive of public lectures on cosmology topics. Impressive list of speakers and panelists.

turbo

My apologies if this has been posted previously. It is a fascinating overview of Physics papers from the last 110 years or so. You can browse by field, author, decade, etc.

http://fangio.magnet.fsu.edu/~vlad/pr100/