tag:blogger.com,1999:blog-2846514233477399562.post9008835470591688455..comments2024-01-08T09:37:04.406+01:00Comments on RÉSONAANCES: 21cm to dark matterJesterhttp://www.blogger.com/profile/08947218566941608850noreply@blogger.comBlogger12125tag:blogger.com,1999:blog-2846514233477399562.post-4430225944730791032018-04-01T15:54:40.618+01:002018-04-01T15:54:40.618+01:00Regarding the photon-injection way, should not it ...Regarding the photon-injection way, should not it lead to photon over-abundance at the surrounding regions? It seams that at the respective CMB tail, at cca 1.4 GHz <a href="http://adsabs.harvard.edu/abs/1995ApL%26C..32....3S" rel="nofollow">this</a> && <a href="http://adsabs.harvard.edu/abs/1995ApL%26C..32....7B" rel="nofollow">that</a> suggest otherwise. Even though <a href="https://arxiv.org/abs/0901.0555" rel="nofollow">this</a> says that there is some rise detected, though at above frequencies.<br />May be that the (over)decrease only occurs when the hydrogen line is measured, at the Dawn, now, or for any suitable <i>z</i> value.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-1894182624430561572018-03-23T18:18:39.784+01:002018-03-23T18:18:39.784+01:00Thanks Wildschwein and Louis. I haven't yet st...Thanks Wildschwein and Louis. I haven't yet studied the details of how the spin temperature evolves, so I only wrote a vague sentence in the post. The reference Wildschwein mentions looks very useful to understand it better.Anonymoushttps://www.blogger.com/profile/15251854537700513873noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-76197588939706043392018-03-23T14:19:36.939+01:002018-03-23T14:19:36.939+01:00Das Wildschwein, thank you for clearing this up fo...Das Wildschwein, thank you for clearing this up for me and for the paper reference.<br /><br />Best,<br /><br />LuisAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-50208648794034488212018-03-23T13:52:47.483+01:002018-03-23T13:52:47.483+01:00Dear Jester,
Thank you for posting this nice summ...Dear Jester,<br /><br />Thank you for posting this nice summary. It helps to understand the context of this exciting measurement.<br /><br />Looking at the paper, I noticed that the improvement in residual RMS they get does not look too impressive for such a large signal. The simultaneous match giving residuals in Fig 1c reduces RMS residuals by 0.062 K, while I estimate that adding back the (centered) signal would change RMS by roughly 0.15 K (assuming zero correlation of signal and residuals in Fig 1c). I think this indicates that a significant part of the signal "comes" from the change of foreground parameterization, i.e. the correlation of the signal with the difference of foreground models between Fig 1b and Fig 1c is rather large. That this is plausible is confirmed by Extended Data Fig 8, which shows that the foreground models actually are not too bad at matching the signal. Unfortunately they did not plot the difference in foreground models between Fig 1b and 1c, as far as I see.<br /><br />Therefore I agree with you that a reduction of the signal amplitude with further analysis would not be unexpected. I am a bit surprised that the authors are so confident that they can exclude the Standard Model prediction.<br /><br />Another concern I'd have is that the signal is mostly "in a low Fourier mode" of the observed brightness temperature function as it is wide and close to sinusoidal, so it is not too distinctive. They checked that there is no similar signal in the 90-200 MHz range, though, so that diminishes this concern a bit.Edwin Steinerhttps://www.blogger.com/profile/15616273828572365838noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-18918550414494841532018-03-23T13:28:32.978+01:002018-03-23T13:28:32.978+01:00Luis: the Lyman alpha pumping in this case DECREAS...Luis: the Lyman alpha pumping in this case DECREASES the number of Hydrogen atoms in the triplet state and hence decreases the spin temperature. This is because the Baryon kinetic energy is colder than the CMB and the Lyman alpha "colour temperature" is coupled to the Baryon kinetic energy due to recoils. The spin temperature starts at the CMB temperature before significant numbers of Lyman alpha photons are produced. See 1109.6012.Das Wildschweinhttps://www.blogger.com/profile/05046459957655622184noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-45362024166406198722018-03-23T13:13:16.081+01:002018-03-23T13:13:16.081+01:00Hi, thank you for this very interesting post. I ha...Hi, thank you for this very interesting post. I have a very basic doubt regarding the interpretation of the results and the physical process involved. If you could take a few minutes to resolve it I would be most grateful. <br /><br />As I understand, the absorption of Lyman alpha photons from the first stars by the neutral hydrogen drives electronic transitions that ultimately *increase* the number of hydrogen atoms in which the electron is in the higher energy level of the fundamental level hyperfine structure. This is what is called Lyman alpha pumping, I guess. In the equation for T21 this would correspond to lowering the Ts - i.e., Ts is lower when the higher energy is more populated (weird) - to produce an absorption (negative value for T21). However, pumping should make less hydrogen atoms available to absorb 21cm photons from the CMB and thus absorption of such photons should decrease instead of increasing to form the now observed dip at the expansion corrected frequency between 70-90 MHz. <br /><br />I have some key idea wrong somewhere in this argument but despite some effort have been unable to pin it down.<br /><br />Thank you in advance for your time.<br /><br />Best regards,<br />LuisAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-14550649803488709282018-03-22T00:51:01.308+01:002018-03-22T00:51:01.308+01:00so you've not found any problems with McGaugh&...so you've not found any problems with McGaugh's equations in the paper I ref and Andrew linked, good.<br /><br />regarding BBN - dark matter has lithium 7 problem ref<br />http://www.astro.umd.edu/~ssm/mond/BBNLCDMMOND.jpg<br /><br />this paper https://arxiv.org/abs/1803.02804 suggests EDGES eliminates most of the parameter space for viable dark matter models<br /><br />btw was there any new LHC physics results presented in Moriond EW 2018neohttps://www.blogger.com/profile/17318664916557810347noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-65820708399817715892018-03-21T23:23:50.388+01:002018-03-21T23:23:50.388+01:00CMB and BBN in the first place. Then the entire co...CMB and BBN in the first place. Then the entire cosmological history. OmegaM = OmegaB does not work unless you add more particles and/or interactions. Then you have to satisfy constraints on the particles and forces you introduced (just like DM models with milli-charged particles have to satisfy the supernovae and direct detection constraints). You need a complete model, otherwise you cannot even fail. Anonymoushttps://www.blogger.com/profile/15251854537700513873noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-79357377594824860892018-03-21T22:11:26.756+01:002018-03-21T22:11:26.756+01:00What other existing constrains do you have in mind...What other existing constrains do you have in mind? There was another paper which shows a chart how incredibly difficult it is to get that value from any DM value. Andrew can provide the link. neohttps://www.blogger.com/profile/17318664916557810347noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-68625588464892902412018-03-21T21:20:19.720+01:002018-03-21T21:20:19.720+01:00Stacy's paper observes that one would get the ...Stacy's paper observes that one would get the correct amplitude of the EDGES signal if the total matter density in the universe were equal to the baryonic density measured in CMB and BBN, OmegaM = OmegaB = 0.05. This is an interesting fact to keep in mind. However, the challenge here is not to explain one data point, but to provide an explanation consistent with all existing experimental constraints. Just fixing OmegaM = OmegaB = 0.05 without modifying other physics does not give you a complete model satisfying the existing constraints. So the paper is not at the same footing as the other ones. Anonymoushttps://www.blogger.com/profile/15251854537700513873noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-32277128433679813352018-03-21T20:11:29.077+01:002018-03-21T20:11:29.077+01:00The link to the paper mentioned by neo is https://...The link to the paper mentioned by neo is https://arxiv.org/pdf/1803.02365.pdfandrewhttps://www.blogger.com/profile/08172964121659914379noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-5600126307032445632018-03-21T19:34:47.977+01:002018-03-21T19:34:47.977+01:00can you comment on Stacy McGaugh's explanation...can you comment on Stacy McGaugh's explanation of an all baryon no dark matter universe as the explanation?<br /><br />Strong Hydrogen Absorption at Cosmic Dawn: the Signature of a Baryonic Universe<br />Stacy McGaugh neohttps://www.blogger.com/profile/17318664916557810347noreply@blogger.com