meetingsandtelecons:april10.08 [PPPDT Wiki]

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==== Discussion Topics for Telecon of April 10, 2008 ====

  * Release of Epic Report 
  * Discussion of Strategy Statement

=== Draft Strategy Statement ===

The polarization of the cosmic microwave background radiation contains a wealth of information about the physics of the early universe, the growth of structures, and properties of the fundamental particles of physics. Much of this information is accessible only through detailed mapping of the CMB polarization. A polarization map of the galaxy at millimeter and sub-millimeter wavelengths also contains information about properties of galactic dust, sources of synchrotron radiation, and magnetic field strength and structure, all of which are of strong interest for the astrophysical community. 

We believe that the most effective way to probe the abundant cosmological and astrophysical information that is encoded in the polarization at these wavelengths is with a dedicated satellite. A CMB Polarization satellite would provide a full sky map of the CMB polarization, probing scales not accessible from the ground. It would have unprecedented sensitivity, a result of the absence of the atmosphere or a warm Telescope. It is widely acknowledged that the most critical component of a polarization experiment, namely the control of sources of systematic errors, can best be achieved on a satellite platform. 

The Primordial Polarization Program Definition Team and the scientists signed below endorse a program of technology development and sub-orbital experiments that will lead to a CMB Polarization satellite as soon as feasible. We urge NASA and other agencies to fund this program to its fullest. 


=== Strategy for Decadal Panel: Recap ===

Two approaches that bracket the range of possibilities.

(a) While B-mode science is compelling, no case can be made for a satellite any time soon and perhaps never. 

(b) A strong case for a satellite can and should be made to the decadal panel even as of today because the science return, even with a null detection, is compelling. Not only a satellite is justified, it is critical to the health of our field. 

== Charles Lawrence ==

B-mode science is compelling, and must be pursued by a program of technology development, suborbital experiments, and a space mission (whose ultimate need and configuration will depend critically on the outcome of the suborbital experiments).

== Jamie Bock ==

As to your question if we should bring to the decadal panel a) a satellite to detect B-modes or b) a plan for a satellite once B-modes are detected from the ground, I have an alternative.  What if we instead bring forth the comprehensive science satellite to study all aspects of the CMB in temperature and polarization, and then say if the B-modes are detected from the ground at a high level we can come back with a cheaper small satellite option.  This strategy gets all of our science on the table, puts the issue of B-mode amplitude in the most favorable light, and keeps CMB in a favorable position programmatically at NASA.

== The 'no case now' argument ==

  * A satellite is justified when the science can not be done from sub-orbital platforms.
  * CMB Polarization has been measured by sub-orbital experiments. There is no reason to assume that B-modes can not be measured by such experiments as well. 
  * At the moment there is no compelling argument to go to space.
  * A compelling case for space may present itself when we know more about sub-orbital measurements, but this is not the case now. 

== Al Kogut ==

I expect it will take at least one telecon to come to some consensus
on the issue of whether a CMBPOL satellite is justified.  I also expect
that this will turn on issues of politics and semantics, not technical
capabilities.  I don't think anyone argues against the notion that anything
a ground-based or suborbital experiment can do, a satellite can do better,
so the question of whether a satellite is necessary or not will depend
on what the defined mission for that satellite is.  If the primary mission
is a statistical detection of non-zero B-mode power, consistent with inflation
and inconsistent with lensing or foregrounds (in analogy to the initial
COBE-DMR detection of CMB anisotropy) then a satellite is hard to justify.
If the mission is something beyond a statistical detection (e.g. measuring
the primordial B-mode power spectrum in some detail, in analogy to WMAP or
Planck and the unpolarized anisotropy) then the requirements of very long
integration times and substantially lower systematic error limits make a
satellite much more attractive.

There are two sticking points.  The first is that a primary mission to
map the B-mode power spectrum may not be a high priority once the initial
statistical detection has been verified (at least that's one take from
the series of theory telecons).  The second is that "more attractive"
is not the same as "absolutely required".  A telecon might help sharpen
our arguments to go beyond the simple "satellites are better" reasoning
to give specific examples of what we expect the limiting factors to be
from ground-based or suborbital missions and why a satellite would avoid
these limits.

Playing Devil's advocate, we might look at the progress measuring the
unpolarized CMB anisotropy to see what limits we would have today if we
ignore all COBE and WMAP data  points.  If the goal had simply been
detection, then clearly COBE was not necessary: we simply could have waited
ten years for the ground-based and suborbital missions to improve.
Extrapolating to B-mode polarization, what limits might we expect
to obtain given 15 years of successively more capable ground-based and
sub-orbital experiments?  Of course, this ignores the positive feedback that
major mission like COBE, WMAP, and Planck have on the field, and this may
well be the best reason to push for a satellite.

== Lyman ==

I believe that "waiting to see what we find from Planck, the ground, and balloon missions"
before moving ahead is the wrong approach to the future of our field. Here is why:

1)I think the science from a CMBPOL mission is as least as interesting as that from any other satellite mission with the exception of LISA.

2)If we do not plan for it it will not happen. A CMB satellite is a long way off no matter what we do.  Unless we make real plans for it now,  we'll all be retired (if not worse), before we see the results.

3)You need a satellite for a full sky census with a comprehensive set of null tests. Though
there were many great experiments before WMAP,  there are at least a couple of orders of magnitude
difference in the control of systematic error with WMAP, not to mention the large improvement in statistical error, full sky coverage, etc.

4)There is a lot of ancillary science. We should take seriously measuring the neutrino mass with a satellite mission. Looking for isocurature modes, cosmic strings, topological defects, and other non-Gaussianities, are all important. We have no a priori reason for excluding these possibilities.  Finding any one of them is as likely as finding w ne -1 (though of course we support a comprehensive science plan!).  I think  Planck  will be at least as exciting for what it will tell us about these new things as for what it will tell us about the current suite of parameters. This is all great physics from the highest energy accelerator we'll ever have a chance to access, the early universe.

5)Though we should look to theory for guidance, we should not plan a mission around it. What's
in vogue in theory changes every couple of years.  We need a longer time scale perspective. For me the view is that the CMB sky is our best hope for finding new "fundamental" physics. It hasn't let us down yet. Let's look at it with all we've got.

6) By seriously planning we will keep NASA, NSF, NIST, and with luck the DOE, engaged.
The quest to understand the CMB has led to fantastic technological development especially on the detector front. It will take years for these developments to percolate but they will.

7)There are a lot of misconceptions about the feasibility of the mission. We can change that.
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