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Identifying the Inflaton (new paper Easson et al)

  1. Sep 20, 2010 #1


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    An interesting paper just appeared on arxiv today.

    Identifying the Inflaton
    Damien A. Easson, Brian A. Powell
    5 pages, 2 figures
    (Submitted on 20 Sep 2010)
    "We explore the ability of experimental physics to uncover the underlying structure of the gravitational Lagrangian responsible for inflation. It is a common expectation that improved measurements of the primordial perturbations will result in a better understanding of the nature of the inflaton field. We investigate to what extent this expectation is justifiable within the context of a general inflationary Lagrangian. Our conclusion is that observables beyond the adiabatic and tensor two-point functions on CMB scales are needed; in particular, isocurvature modes or a combination of local non-Gaussiantities and a precision measurement of the tensor spectral index will enable the most successful reconstructions. We show that amongst these observables, the most powerful probe of the inflationary Lagrangian is a precision measurement of the tensor spectral index, as might be possible with a direct detection of primordial gravitational waves."

    I don't have time to comment now but it is always interesting to hear discussion of what it is and is not possible to learn empirically about the early universe (from examining its traces in the CMB).

    We know of Easson in part because of a couple of papers he published this past year with Nobelist George Smoot (about entropic force in cosmology---how it might have a role in understanding either inflation or the present accelerated expansion.) I think of him as doing serious and original work, and willing to take some chances: win or lose. Just a superficial impression but it means I'm moderately alert when I see a new paper by him.

    Maybe someone else will evaluate this and comment.
  2. jcsd
  3. Sep 21, 2010 #2


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    Well, it seems to me that the abstract is a little misleading in that in my experience, it is generally expected that while improved measurements of the temperature power spectrum will improve our knowledge of inflation, the real improvements will come from B-mode polarization measurements (which get at the tensor spectral index mentioned) and potentially non-Gaussianity studies.

    In other words, I'm pretty sure that the general results of this paper are entirely orthodox, at least judging by the abstract, but the abstract seems to be claiming this is new, which makes little sense to me.

    It is always nice, of course, to have these sorts of issues on firmer footing. In particular, moving on from Planck I expect we're going to want to put up another CMB satellite which is capable of measuring the low-ell B-mode power spectrum. Before we can justify the cost, though, we're going to at least need to get a rough handle on the B-mode power spectrum from balloon and ground-based experiments, as well as strong arguments for why such an experiment will help us understand inflation, similar to the analysis presented here.
  4. Sep 21, 2010 #3


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    Hi Guys,

    Thanks for noticing the paper. Chalnoth, in response to your comment: what we emphasize in the paper is the need for a 'precise detection' of n_T of the quality that probably only a direct detection of primordial GWs can afford. A detection of B-mode polarization on CMB scales will be insufficient. We also find that non-Gaussianities are unhelpful for *reconstruction* -- of course, they'll tell us other things. Stay tuned for 2 follow up papers, where we give significant detail behind our analysis and methodology. We briefly mention the benefit of future dedicated B-mode experiments in this paper (first bullet point), and delve into this issue in a bit more detail in a follow up paper due out in a couple days.
  5. Sep 21, 2010 #4


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    Ah, okay, that is quite interesting. Unfortunate, but interesting.

    Interesting, maybe I'll give it a closer look.
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