tag:blogger.com,1999:blog-2846514233477399562.post8680124875825296095..comments2024-01-08T09:37:04.406+01:00Comments on RÉSONAANCES: How many neutrinos in the sky? Jesterhttp://www.blogger.com/profile/08947218566941608850noreply@blogger.comBlogger32125tag:blogger.com,1999:blog-2846514233477399562.post-65867010701003514952013-02-28T10:44:27.686+01:002013-02-28T10:44:27.686+01:00Rather than discussing interpretations of Neff=3.5...Rather than discussing interpretations of Neff=3.5 it's better to wait 3 more weeks for the Planck results, as they will seriously change the experimental situation. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-1979851467273210322013-02-18T05:05:31.972+01:002013-02-18T05:05:31.972+01:00What this new data can say about the NuMSM devised...What this new data can say about the NuMSM devised by Shaposhnikov?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-85237240741608644542013-02-17T20:11:43.806+01:002013-02-17T20:11:43.806+01:00What a 3.5 value would imply in terms of particle ...What a 3.5 value would imply in terms of particle content of Dark Matter? Is there a kind of Dark Matter that seems already prefered by this data (e.g. axions, etc)?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-89801742028734005492013-02-12T12:38:57.983+01:002013-02-12T12:38:57.983+01:00A new CMB data combination is in Calabrese et al....A new CMB data combination is in <a href="http://arxiv.org/abs/1302.1841/" rel="nofollow"> Calabrese et al. </a> <br /><br />They find mild tension between ACT + SPT on the ell > 1500 tail: from the CMB power spectrum alone they find Neff:<br /> 2.90 +/- 0.53 (WMAP9 + ACT) <br /> 3.75 +/- 0.47 (WMAP9 + SPT) <br /> 3.34 +/- 0.4 (WMAP9 + ACT + SPT) <br /><br />Adding in also the 4-point function from CMB lensing , they get 3.24 +/- 0.39. <br /><br />This is all CMB without BAO+HO, which probably tend to pull Neff slightly upwards. <br />So, basically the preference between ~ 3 or 4 is fuzzy, but 5 looks strongly disfavoured. As noted elsewhere, Planck should give a substantial improvement (but if the true value were 3.5 it may not settle the question).Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-11504931404885658302013-02-08T05:09:42.771+01:002013-02-08T05:09:42.771+01:00@abbyyorker, yes LEP used the invisible width of t...@abbyyorker, yes LEP used the invisible width of the Z to beautifully constrain Nnu~3.0+epsilon, but that only applies to particles coupling to the Z. The constraints from cosmology are ~30X less precise but more generic (thereby constraining axions, light sterile neutrinos, etc.).Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-87372695063070946482013-02-07T03:02:01.657+01:002013-02-07T03:02:01.657+01:00I could have sworn that light neutrino bounds were...I could have sworn that light neutrino bounds were also made by ee collider luminosity, and that they suggested 3 generations years ago.abbyyorkernoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-66918182871237730452013-02-06T02:12:42.001+01:002013-02-06T02:12:42.001+01:00 Neff~ 3.16 +- 0.4 from CMB lensing... Neff~ 3.16 +- 0.4 from CMB lensing...Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-86055449790210556572013-02-04T21:35:34.809+01:002013-02-04T21:35:34.809+01:00No attempt by WMAP to admit fault or explain the &...No attempt by WMAP to admit fault or explain the 'slight alteration', though. What are they playing at?Thomas Denthttps://www.blogger.com/profile/16355010444546331416noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-39899504412583465682013-02-03T21:29:57.417+01:002013-02-03T21:29:57.417+01:00Foster, the usual assumption is that the right-han...Foster, the usual assumption is that the right-handed sterile neutrinos are very heavy, in which case Neff=3 (only light particles contribute to Neff). But it is possible that some of these sterile neutrino are light and get populated in the early universe, which may explain why Neff is measured somewhat higher than 3. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-73477630607348096092013-02-03T21:23:04.244+01:002013-02-03T21:23:04.244+01:00Thanks! Thanks! Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-47945318727421792282013-01-31T18:52:21.867+01:002013-01-31T18:52:21.867+01:00The bug-fixed WMAP9 papers have appeared on the ar...The bug-fixed WMAP9 papers have appeared on the arxiv, and, as the rumors suggested, the Neff constraint that uses BAO data went up: the new WMAP9+CMB+H0+BAO constraint is Neff = 3.84 +/- 0.40, 2-sigma higher than the standard value of 3.046. This constraint is consistent with and slightly broader than the SPT+WMAP7+H0+BAO constraint of Neff = 3.71 +/- 0.35 presented in 1212.6267.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-62611760324509794872013-01-30T22:06:50.724+01:002013-01-30T22:06:50.724+01:00Doesn't the existence of neutrino masses doubl...Doesn't the existence of neutrino masses double Neff, even though the right-handed nu's don't couple to anything? Their existence doubles the number of relativistic d.o.f. <br /><br />Doesn't that mean Neff should be 6? Or is that factor of 2 already incorporated into the LCDM and nucleosynthesis calculations?Foster Boondogglenoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-88013060488922810772013-01-24T06:05:37.972+01:002013-01-24T06:05:37.972+01:00Right, what I said above was confusing: only parti...Right, what I said above was confusing: only particles below eV mass will contribute to Neff measured in the CMB. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-53817671106461289962013-01-23T18:50:41.601+01:002013-01-23T18:50:41.601+01:00(Different Anonymous) to George, Andrew, Jester: t...(Different Anonymous) to George, Andrew, Jester: there are some confusions above about mass scales. <br /><br />Basically N_eff is the energy density in anything which was relativistic in the few e-foldings before the CMB era, excluding photons; and measured in units of one very light neutrino. <br /><br />So, keV-scale warm dark matter does not count because it went non-relativistic way before the CMB era. Warm DM is indistinguishable from cold DM as far as the microwave background is concerned, but does affect very small-scale structure i.e. dwarf galaxies due to free-streaming at much earlier times. <br /><br />Neutrinos at < 0.2eV are almost identical to massless ones in the CMB, though they are non-relativistic today and have subtle effects on large-scale structure. <br /><br />Anything at ~ 1 eV is an intermediate case because it goes non-relativistic just before the CMB era, so the effects are more complicated than just a change in N_eff (but popular CMB codes can handle that). This is disfavoured anyway by large-scale structure.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-10152326493137041492013-01-23T04:35:48.074+01:002013-01-23T04:35:48.074+01:00George, what makes neutrinos special is that they ...George, what makes neutrinos special is that they decoupled from the rest of the thermal plasma when they were still relativistic, around T~MeV. That would be true for any neutrino masses below MeV (and we know the masses are below eV). Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-16987485277532414762013-01-23T04:24:05.188+01:002013-01-23T04:24:05.188+01:00Zachariah, in more laymen's terms, here's ...Zachariah, in more laymen's terms, here's a short explanation I'm borrowing from Cosmic Variance: "...In the early universe, dark matter just collapses under the pull of gravity, while ordinary matter also feels pressure, and therefore oscillates. As a result, the two components are out of phase in the even-numbered peaks in the CMB spectrum. In English: dark matter pushes up the first and third peak in the CMB spectrum, while suppressing the second and fourth peak. That would be extremely hard to mimic in a theory without dark matter..." Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-32258293338291151922013-01-22T23:32:30.781+01:002013-01-22T23:32:30.781+01:00Why do only neutrinos of all massive particles con...Why do only neutrinos of all massive particles contribute to a radiation energy density? Is this independent of what a neutrino mass might be?curious georgehttps://www.blogger.com/profile/10772402605458395530noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-83751855494016272342013-01-22T20:54:55.936+01:002013-01-22T20:54:55.936+01:00Would it be possible to explain in layman's te...Would it be possible to explain in layman's terms how the detailed map of the CMB provides strong evidence for dark matter?Zachariahhttps://www.blogger.com/profile/01113742343822288721noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-79178301133601520982013-01-22T11:44:53.377+01:002013-01-22T11:44:53.377+01:00Andrew: tooting my own trumpet but that would seem...Andrew: tooting my own trumpet but that would seem to me to favour axions as part of the DM. They can be light and erase structure like WDM, but the non-thermal production means they never show up in Neff.Tories Smellhttps://www.blogger.com/profile/15622660682213487917noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-4427719526223959852013-01-22T11:41:36.731+01:002013-01-22T11:41:36.731+01:00It's worth noting something Jester says in sli...It's worth noting something Jester says in slightly more detail: Neff bounds come from the effect on CMB damping, but only if one fixes the low \ell stuff, like the angular diameter distance to last scattering. So, if you just blindly went onto LAMBDA's CAMB web app and upped Neff, the Silk damping actually increases. As for 3+1 models: it's still easy to accommodate a light sterile neutrino as these guys only thermalise through mixing and, again as Jester said, don't have to contribute anywhere near a "whole" neutrino species to the CMB.<br /><br />Finally, WMAP+ACT on Neff is in marginal tension with WMAP+SPT, with the ACT combination being lower. Being full sky, Planck should clear this up. The new lower values of Neff come form enforcing consistency with standard BBN, so if you want more neutrinos you can always mess with BBN (!) or introduce late decays in the intermediate epochs.Tories Smellhttps://www.blogger.com/profile/15622660682213487917noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-43374097970382558292013-01-22T05:17:33.170+01:002013-01-22T05:17:33.170+01:00It should also be pointed out that the new SPT dat...It should also be pointed out that the new SPT data described in Story et al (1210.7231) and Hou et al (1212.6267) provides, in conjunction with WMAP7 data, the tightest current constraint on Neff: Neff = 3.62 +/- 0.48, or Neff = 3.71 +/- 0.35 when Hubble constant and BAO data are included (and there's no (known) bug in the SPT papers). The latter is 1.9-sigma higher than the standard value of 3.046. Even though these new SPT papers used WMAP7 data, the WMAP7 vs WMAP9 change is outweighed by the big improvement in the SPT data (which the WMAP9 paper didn't use). It will be interesting to see what Planck sees, with Planck-only errors forecasted to be sigma(Neff)~0.2.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-52338667158691705492013-01-22T03:24:04.841+01:002013-01-22T03:24:04.841+01:00"All these peaks and wiggles are predicted by..."All these peaks and wiggles are predicted by the standard cosmological model, the so-called ΛCDM model (black line)."<br /><br />Meanwhile, the Neff data simultaneously removes many of the main remaining dark matter candidates (since different experimental data suggests that cold dark matter produces more large scale structure in the universe than we observe, and that warm dark matter with keV scale particles would be a better fit. Yet, keV scale dark matter particles ought to produce a Neff of at least 4, which the numbers cited disfavor by about 4-1 (and a Neff of 5+ is disfavored by about 4.97 sigma). So, Marnie, hold onto the 3+1 papers for a bit, but ditch the 3+2 papers for sure.<br /><br />Direct dark matter searches also strongly disfavor heavy WIMPS that wouldn't show up in Neff.<br /><br />Thus, the same measurement simultaneously confirms CDM and denies it a mechanism.andrewhttps://www.blogger.com/profile/08172964121659914379noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-5461597245162095602013-01-22T01:12:18.841+01:002013-01-22T01:12:18.841+01:00There are rumors that the WMAP9 papers contain a b...There are rumors that the WMAP9 papers contain a bug in their Neff analysis. They are revising their Neff constraint to something more consistent with the more recent SPT and ACT results, i.e., Neff = 3.6 +/- 0.3. Keep your eyes open for the revised WMAP9 result.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-90788897604382290702013-01-21T23:37:57.268+01:002013-01-21T23:37:57.268+01:00In general no. The bounds on Neff constrain very l...In general no. The bounds on Neff constrain very light particles (MeV or less). As for SUSY particles, theorists usually imagine them at the TeV scale. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-46520646103771130352013-01-21T13:51:15.586+01:002013-01-21T13:51:15.586+01:00A layperson doubt: Do those results have any effec...A layperson doubt: Do those results have any effect on supersymmetric models?<br /><br />[]s,<br /><br />Roberto Takatanonehttps://www.blogger.com/profile/00205668953897582538noreply@blogger.com