# Mass parameter for quintessence

1. Sep 8, 2011

Dear all,

As u know, one of the best potentials for quintessence is
V=[M]^[4+$\alpha$] [$\phi$]^[-$\alpha$]

They usually call M, THE MASS PARAMETER.

Who knows what is the value of M for now?

2. Sep 8, 2011

### marcus

I have never heard any evidence that "quintessence" is real. Have you?

If it is not a real thing, then there would be no correct value of the parameter M.

My impression is that quintessence is an idea that people used to talk about back around 2003---over 5 years ago anyway. And it turned out to be an unnecessary complication. So it went out of style.

So the professional cosmologists don't talk about quintessence very much, except to rule it out or show it is unnecessary to the model when they get some new data.
(Every time you get a new batch of data, it is one of the things you consider, and check to see that it still is unnecessary.)

Have you seen some recent scientific journal articles about it? Have I missed something?

3. Sep 8, 2011

Dear Marcus,
I agree with you and I am trying to rule it out and show this is completely unneccessary.
But for doing that I really need to find out what is the value for the parameter mass they are using...
unfortunately I could just find one article about it -steinhardt- which says
M=([$\rho$][m] * [planck mass][$\alpha$])^(1/(4+$\alpha$))

But I don't know which units are they working in...

4. Sep 9, 2011

### marcus

Dear Shadi, I probably won't be able to help but others might. The first thing is to post the name of the Steinhardt article, if possible a link. Then we can see what you are talking about in context.

Oh! I think you may mean this one:
http://arxiv.org/abs/astro-ph/9807002
Quintessence, Cosmic Coincidence, and the Cosmological Constant
Ivaylo Zlatev (1), Limin Wang (1), Paul J. Steinhardt (1 and 2) ((1) University of Pennsylvania, (2) Princeton University)
(Submitted on 1 Jul 1998 (v1), last revised 21 Oct 1998 (this version, v2))
Recent observations suggest that a large fraction of the energy density of the universe has negative pressure. One explanation is vacuum energy density; another is quintessence in the form of a scalar field slowly evolving down a potential. In either case, a key problem is to explain why the energy density nearly coincides with the matter density today. The densities decrease at different rates as the universe expands, so coincidence today appears to require that their ratio be set to a specific, infinitessimal value in the early universe. In this paper, we introduce the notion of a "tracker field", a form of quintessence, and show how it may explain the coincidence, adding new motivation for the quintessence scenario.
4 pages, 4 figures

Is that the paper? My guess is that it is dead letter. Over 10 years old. But someone else here may know better. If this is it, then at least they have something to look at.

Last edited: Sep 9, 2011
5. Sep 9, 2011