tag:blogger.com,1999:blog-6976071487922527618.post6712178988706064047..comments2024-03-27T05:38:30.610+01:00Comments on Blank On The Map: New BICEP rumours: nothing to see hereSesh Nadathurhttp://www.blogger.com/profile/07155102110438904961noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-6976071487922527618.post-92061846270632331492014-05-19T02:19:45.818+02:002014-05-19T02:19:45.818+02:00Thank you. Re a third frequency, there's an a...Thank you. Re a third frequency, there's an amusing back-and-forth in Flauger's presentation (at 1:08) where he tries and fails to get a date for 220 GHz data from BICEP3 (?) (later that 2015?) from someone in the audience. I think the audience member says "no 220 GHz receivers exist right now"...Art Brownhttps://www.blogger.com/profile/07475756299132780448noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-90415081639427404102014-05-18T17:36:44.542+02:002014-05-18T17:36:44.542+02:00By the way, thanks for asking that question: it ma...By the way, thanks for asking that question: it made me go and look up the answer, and in the process I learned some things I didn't know! Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-43734721862637110332014-05-18T17:35:18.483+02:002014-05-18T17:35:18.483+02:00This is a tricky question, the answer to which dep...This is a tricky question, the answer to which depends a little on whether there is any primordial signal to be seen, or whether it is all due to dust. So if there is a large primordial $r$ out there (say with a value 0.1 or larger) and Planck eventually manage to sort out all the systematics issues that having been holding back their polarization maps, then it will be Planck that should confirm the BICEP result, within a few months. (They have a couple of conferences scheduled in December to present their results, we should know one way or another by then.)<br /><br />If Planck either cannot resolve their systematics, or does not have the sensitivity to unambiguously confirm a primordial signal, then we are in a difficult grey zone, because it seems they are also not going to provide a clear statement about dust in the BICEP window. In this case I think the Keck Array data at 100 GHz will be the first information we get - this data is already being collected, so we should not need to wait too long. Having two frequencies is better than one, and will give some indication of possible dust levels, but may still not be conclusive. Eventually I believe Keck will also work at 220 GHz.<br /><br />There are also several other polarization experiments currently in operation or just about to start. SPTPol, POLARBEAR and ACTPol are sensitive to much smaller, arcminute angular scales than the degree scales (or larger) on which the GW signal shows up; they're much better for looking for B-modes from lensing. I also don't think they look at the same patch of sky as BICEP, so not sure whether they can say anything useful about the dust there. There's the ABS experiment in Chile, which should be starting about now, targeting primordial B-modes, but they're also only one frequency (145 GHz). There's a balloon-borne experiment called SPIDER which should provide multi-frequency data in something like 2-3 years (I believe it has been launched already, though their website isn't clear!), and another one due to launch soon called PIPER.<br /><br />But for the short term, let's hope Planck provides the answers quickly! Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-56136366389299191632014-05-16T23:05:45.280+02:002014-05-16T23:05:45.280+02:00Thanks for the discussion of Liu et al, and especi...Thanks for the discussion of Liu et al, and especially for the figure overlaying the BICEP2 area. If not Planck, who will clean up the dust, and when?Art Brownhttps://www.blogger.com/profile/07475756299132780448noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-25564037104471001802014-05-15T10:25:58.577+02:002014-05-15T10:25:58.577+02:00Hello and thanks for the comment. I read your blog...Hello and thanks for the comment. I read your blog post, but I don't really agree with you. Firstly, there's no justification for assuming the polarization fraction is the same, or even roughly the same, across the sky. The same goes for the total intensity of dust emission. Therefore extrapolating from the areas Planck did not mask to the areas they did is likely to give you a number that has nothing much to do with reality. The only numbers that really matter to this discussion are (a) how much dust emission is there <i>in the BICEP window</i>, and (b) what is the polarization fraction of that dust? <br /><br />Since that window lies in the region masked by Planck, the answer to both of those questions is "we don't know". What we do know is that since Planck chose to mask the region, either (i) there isn't a lot of dust emission in that windowl, even at 353 GHz (and therefore even less at 150 GHz), or (ii) the error in determining the polarization fraction is large, or (iii) both.<br /><br />It seems likely to me that option (iii) is correct (if (i) is true, (ii) probably follows as well). This is not bad news for BICEP; it may even be good news. The option that would be bad news for BICEP would be if (i) were not true but somehow (ii) were - there is a lot of dust, we're just not sure how polarized it is - I don't think that is likely given how measurements work, but only Planck people would know for sure.<br /><br />Incidentally, the "revision" to the old polarization fraction map is basically due to subtracting out the (unpolarized) cosmic infrared background (CIB), which isn't to do with dust. This is quite an elementary step, so people think it is unlikely that the BICEP team forgot to do something so straightforward themselves! (For instance, see <a href="http://telescoper.wordpress.com/2014/05/14/that-bicep-rumour/" rel="nofollow">Peter Coles' blog</a>.)Sesh Nadathurhttps://www.blogger.com/profile/07155102110438904961noreply@blogger.comtag:blogger.com,1999:blog-6976071487922527618.post-56366882614901037172014-05-15T01:43:26.163+02:002014-05-15T01:43:26.163+02:00Sesh, the new Planck paper says "The data are...Sesh, the new Planck paper says "The data are not shown in the grey areas where the dust emission is not dominant or where residuals were identified comparing individual surveys." The term residuals refers to uncertainties. Later they say, "we only show the Planck polarization data and derived quantities, where the systematic uncertainties are small, and where the dust signal dominates total emission." So there is no reason for assuming that this is "good news" as you claim. It could be that they are not showing the BICEP2 region because the systematic uncertainties are high. <br /><br />In fact, far from being "good news" for BICEP2, I think the paper you cite is actually bad news, for reasons I explain in this blog post:<br /><br />http://futureandcosmos.blogspot.com/2014/05/why-new-planck-paper-casts-grave-doubts.html <br /><br />The new paper is bad news for BICEP2 because the new, revised polarized fraction graph (with lots of yellow regions now showing as red, with a higher 20 percent polarization fraction) now shows a lot higher polarization fraction than the previous version used by BICEP2. Mark Mahinhttps://www.blogger.com/profile/17230591038352645520noreply@blogger.com