NEQNET: The world of theoretical physics

For physicts by physicists

  • Archives
  • Best posts
  • Contact us
  • How to subscribe
  • Newcomer?
  • Open problems
  • Home
  • APPLIED
  • ASTRO
  • COND-MAT
  • HEP-TH/PH

Subscribe via email

or connect via

179. Followup on ekpyrosis and phoenix universe

ASTRO, HEP-TH/PH — By Dmitry Podolsky on January 13, 2009 at 11:30 pm
Print This Post Print This Post   Save This Post as PDF

Dmitry Podolsky has got his PhD from Landau Institute for Theoretical Physics. He currently works as postdoc at Case Western Reserve University. He is also one of the editors of NEQNET.

As follows from the title, this is a followup on the guest post “The return of the phoenix universe” by Jean-Luc Lehners. Jean-Luc kindly agreed to answer to a couple of questions related to physics behind ekpyrosis for NEQNET. In what follows D. – me, J. – Jean-Luc.

D. It is interesting that about a year ago I was talking to Andrei Linde (he was preparing his paper on ekpyrosis with Mukhanov at that time) and eventually asked him whether it is possible to construct an analogue of eternal inflation for ekpyrotic cosmology. His answer was negative at that time, but now it seems to be that your phoenix universe is exactly this analogue of eternal inflation – you are trying to find a balance between expanding (inflating in inflationary cosmology) and collapsing (AdS sinks in inflationary cosmology) patches. The only difference is that your phoenix universe seems to be dominated by large patches with small effective CC.

J. Yes, I guess you could say that in some sense what we did is the ekpyrotic equivalent to eternal inflation, however with a very different global structure as a result!

D. It looks like the actual distribution of patches will strongly depend on boundary conditions near the AdS crunch – in particular, it will determine the actual probability to live in a 60-efold-large patch at a given moment of time. Why do you choose them in such a way that the bounce is allowed at all (179. Followup on ekpyrosis and phoenix universe at the point of bounce)? Can’t you choose them in some different way – for example, that evolution always ends up with an AdS crunch? The reason I ask is that once I have found a general solution of Einstein equations near the AdS crunch singularity. It turns out the asymptotic behavior of the metric components is quasi-isotropic – AdS crunch always happens in all points of 3d space, but in different moments of time.

J. Unfortunately, I don’t really understand what you are asking in your first question. We did not impose 179. Followup on ekpyrosis and phoenix universe at the bounce as a boundary condition, although 179. Followup on ekpyrosis and phoenix universe is much smaller for those trajectories corresponding to a long ekpyrotic phase than for general trajectories with a short and insufficient ekpyrotic phase.

D. Sorry for asking a confusing question and let me reformulate it better.

Let us foliate the ekpyrotic Universe with constant 179. Followup on ekpyrosis and phoenix universe hypersurfaces (or constant 179. Followup on ekpyrosis and phoenix universe, if you want). To quantitatively understand the causal structure of the Universe, I would like to learn how to calculate the probability 179. Followup on ekpyrosis and phoenix universe that the given Hubble patch will have size 179. Followup on ekpyrosis and phoenix universe (for given 179. Followup on ekpyrosis and phoenix universe) at a given moment of time t.

I understand that this probability depends on details of physics near the bounce. For example, if there is no 179. Followup on ekpyrosis and phoenix universe in Eq. (6) of your paper, then there is simply no bounce – Universe will reach AdS Big Crunch in finite time (so after some time the probability 179. Followup on ekpyrosis and phoenix universe will be equal to zero).

Now, what I know from my paper is that the solution with AdS crunch is a general solution of the Einstein equations in ekpyrotic models – that is, for any initial conditions and any ordinary matter present in the Universe apart of scalar fields driving ekpyrosis the AdS crunch should be achieved in finite time. This picture is different from yours, as you understand (you say instead that causal structure is dominated by large Hubble patches at late times).

So, my question is really is – what is the physics behind 179. Followup on ekpyrosis and phoenix universe in your model? Do you have some not-so-ordinary matter (like, say, ghost condensate) that provides 179. Followup on ekpyrosis and phoenix universe?

J. 179. Followup on ekpyrosis and phoenix universe arises due to ordinary matter on the negative-tension brane. Neil Turok and I have analyzed this in our paper. However, this reflection in moduli space (which is described in more detail in my papers with Turok and McFadden) occurs before the collision of the boundary orbifold branes, in other words, it does not correspond to the moment of the big bang. Probably I did not make this clear. In the 4d effective theory, the moment of the big bang is still singular, and from the higher-dimensional point of view it corresponds to the momentary shrinking to zero size of the orbifold direction. In the so-called “new” ekpyrotic models, this is different. There they put in a null energy-condition-violating type of matter so that the big bang is non-singular and corresponds to a bounce at a finite value of the scale factor.

D. Thanks! Did I understand correctly that you actually still need inflation (well, dark energy) in order for make patches large enough?

J. Yes, dark energy is absolutely essential in this minimal model in its role as a stabilizer. One could in fact imagine other stabilization mechanisms, such as for example a localizing potential for the s field at present times. In that case less efolds of dark energy would be needed. What we looked at here is the model without any additions, and for this model 60 efolds of dark energy domination are necessary to produce large habitable patches. However, I would not call this inflation, even though the mathematices is of course analogous: first of all, the relevant density perturbations are not produced by this dark energy phase. Secondly, the energy scale is 100 orders of magnitude lower than for inflation. This is crucial, as the large Hubble parameter during inflation is what causes all the problems of eternal inflation. Lastly, dark energy has been observed, and inflation not!

D. Thanks for the very interesting interview!

0 Comments

You can be the first one to leave a comment.

Leave a Comment

Click here to cancel reply.


For LaTeX in your comment, please use tags [tex] and [/tex]. Also, you may use the following HTML tags: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong> .

Login with Facebook:

or subscribe me to comments RSS feed

Trackback responses to this post

Related Posts

  • No Related Post
  • Comments
  • Login
  • Search
  • Large non-Gaussianity from axion inflation Large non-Gaussianity from axion inflation
    January 31, 2012 14:01
  • On strong disorder renormalization On strong disorder renormalization
    March 18, 2011 20:03
  • Relaunching NEQNET
    January 20, 2011 21:01
  • Saturday’s photoguess: what does this monkey symbolize?
    June 20, 2009 19:06
  • Dynamics of space storm
    June 19, 2009 12:06
  • Micro: Can 2 question provide a common solution? Black holes, information loss paradox and Ultra high energy cosmic rays. ...
  • James Ph. Kotsybar: SAGITTARIUS A* -- James Ph. Kotsybar Mysteriously cloaked, obscure despite Interior illuminating glare, Long ...
  • cad: The presentation can be found in several formats at http://pirsa.org/08110051/...
  • James Ph. Kotsybar: COMMENTS FOR THIS ENTRY ARE CLOSED -- James Ph. Kotsybar When the general public hears about A breakthrough in...
  • James Ph. Kotsybar: FEARFUL SYMMETRY (from Songs Of Experiments) -- James Ph. Kotsybar Beyond notice, out of sight in dimensions c...
  • James Ph. Kotsybar: OFF THE SCALE -- James Ph. Kotsybar The young lady known simply as Bright, who could travel at speeds f...
  • James Ph. Kotsybar: COSMIC PREDICTION -- James Ph. Kotsybar Betelgeuse is gonna blow! It?s just a matter of time It?s only ten...
  • Leo: Ok I have a question: if a black hole is supermassive, say 100 billion solar mass, let's suppose Alice fells int...
  • James Ph. Kotsybar: HIGHER DIMENSIONS -- James Ph. Kotsybar From point to line to plane to sphere there?s only three dimensi...
  • superkuh: I am glad you are back! No more disapointing weekly refreshings of that monkey....
  • Dmitry: Thank you James, beautiful and inspiring as usual :)...
  • Dmitry: Yes, renormalization group should still be applicable, but crit. exponents have to be different. By the way, if we ...
  • James Ph. Kotsybar: UNIQUE PARAMETERS -- James Ph. Kotsybar There is only one answer to creation. Though we don?t nearly understan...
  • Ariel Amir: Very interesting, thanks. It indeed seems to be very close to what we discuss here. I wonder whether the distributi...
  • Dmitry: Hi Ariel, thanks for the explanation! Let me now discuss a bit the application I had in mind. It has to do w...
    Register,
    login with your NEQNET profile
    or login with Facebook:

    • 226. Top ten open problems in physics
      • 33 comments
    • 353. Vortex line representation. Cauchy invariant
      • 33 comments
    • The very meaning of socialism
      • 26 comments
    • 377. Temporal and spatial dependence of quantum entanglement
      • 26 comments
    • Biocentrism: book review
      • 24 comments

Facebook: Community

Facebook: Your Friends

Google Friend Connect

Links: Journals

Links: Resources

Links: Blogs

  • Lubos Motl's Reference Frame
Copyright © NEQNET: The world of theoretical physics 2008-2011. All Rights Reserved.