[Shape-univ] Re: loose thoughts on topology and nongaussianity

[Boud Roukema]

hi Bartek, shape-univ,

On Thu, 1 Jun 2006, blew wrote:

> > Hajian & Souradeep (2006) measure the bispectrum from several different
> > version of WMAP-1st-year and claim no significant deviations from
> gaussianity:
> > http://arxiv.org/abs/astro-ph/0501001
>
> This is definitelly interesting paper. They deal with tests od SI

SI = statistical isotropy (for people who didn't read the paper).

> violation and what are possible sources of such violation - eg.
> nonuniform sky noice. This is of particular interest to me recently since,
> I was calculating the variance (related to power spectrum amplidute) in
> separate region on the sky of WMAP and clearly I see nonuniform pattern of
> even with small scale signal removed. So I don;t quite understand that no
> strong IS violation was found, unless they mean the primordial SI is not
> viiolated after accounting for non-uniform noice in the map.
> BTW. they calculate Bipolar power spectrum, NOT bispectrum IMHO.
> and where is it about gaussianity ? are you talking about astro-ph/0501001
> ? well maybye a bit but they sure don't test it.

i haven't looked closely at either the bispectrum nor the bipolar
power spectrum, so you're presumably correct: these are (presumably)
two completely different statistics.

My error, sorry. :(


> > But they don't model the *expected* signature of the PDS (poincare
> dodecahedral
> > space) in 0501001.
> >
> > In Hajian & Souradeep (2003), they model the expected signature from various
> > specific versions of the T^3 model:
> > http://arxiv.org/abs/astro-ph/0301590
>
> again, this is not about the bispectrum.
> In any case with BiPS it's not possible to detect NG (non-Gaussainity),
> now is it ? it's on;y a measure of SI.

True: statistical isotropy and non-gaussianity do not imply each other.

> I have to stick with NG I guess not SI.

Sure, there are dozens of people around the world working on these subjects,
so better continue to focus on one topic and do it properly than try to do
too much...

> however there is so much independent sources of NG...
> my primary target is to deal with NG as an one of the observales (currently
> achievable) to constrain inflationary models. But seems to me that also
> A ans n_s and tensors are of very high competitive interest.
> I'm not yet sure which of these are better way of doing that, sure they are
> independent and NG will continoue to be sexy in cosmology for many years. :)

:)

> BUT... since topo-stuff can also be a source of NG - which is primordial - so
> it surly is within my interest.

pozdr
boud