tag:blogger.com,1999:blog-2846514233477399562.post7151909693689646884..comments2024-01-08T09:37:04.406+01:00Comments on RÉSONAANCES: Weekend Plot: axion hunting Jesterhttp://www.blogger.com/profile/08947218566941608850noreply@blogger.comBlogger8125tag:blogger.com,1999:blog-2846514233477399562.post-31219083334963735292015-01-29T23:30:42.669+01:002015-01-29T23:30:42.669+01:00It's fine and all that axions might start with...It's fine and all that axions might start with no momentum, but won't they acquire momentum as they interact with other particles and between themselves. <br /><br />The point of dark matter is that it clumps together in the universe. If an axion has a mass of <10^-5 eV/c2, then it will gain momentum as it gravitationally attracts, and it will soon be relativistic...but this then stops the clumpiness.<br /><br />How does a <10^-5 eV/c2 rest-mass axion remain non-relativistic while it clumps together?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-7040031704456833082015-01-12T17:55:48.415+01:002015-01-12T17:55:48.415+01:00It is needed another post summarizing pros and con...It is needed another post summarizing pros and cons of current dark matter candidates: axions, wimps & sterile neutrinos.<br />Antonio (AKA "Un fĂsico")noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-24337587796554333222015-01-12T14:12:42.846+01:002015-01-12T14:12:42.846+01:00does the coupling say "gay" on purpose ?...does the coupling say "gay" on purpose ? xDAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-42680623737406541152015-01-11T19:36:58.401+01:002015-01-11T19:36:58.401+01:00It's been a long time, but as I recall, all th...It's been a long time, but as I recall, all the cmb can tell you about axions is that if pq symmetry breaking happens below the inflation scale, there may be a possibility of seeing isocurvature perturbations. So isocurvature perturbations would hint at axions, but the absence of them doesn't say anything about axions at all.<br /><br />Of course, things might have moved on since then. Like I said, it's been a long time.StevieBnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-79389502496566808432015-01-11T03:46:41.705+01:002015-01-11T03:46:41.705+01:00There is the bottom of the barrel, and then here i...There is the bottom of the barrel, and then here is hoping for a miracle in middle earth.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-43726169720231082292015-01-10T23:58:22.983+01:002015-01-10T23:58:22.983+01:00These limits on the dark mater mass depend on how ...These limits on the dark mater mass depend on how it is produced in the early universe. The relic abundance of axions is generated via the vacuum misalignment mechanism, which produces low momentum axions. One can show that QCD axions lighter than ~1 eV behave like cold dark matter from the point of view of the large scale structure. At the end of the day, axions are perfect dark matter candidates, in spite of the tiny mass. Jesterhttps://www.blogger.com/profile/08947218566941608850noreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-84963525658628725872015-01-10T21:08:07.120+01:002015-01-10T21:08:07.120+01:00We know from the CMB measurements and the Lyman Al...We know from the CMB measurements and the Lyman Alpha measurements that dark matter definitely has a rest mass greater than 1 keV, and likely greater than 5 keV. So, axions with rest masses less than 1 keV are not candidates for dark matter.<br />http://arxiv.org/abs/1306.2314<br /><br />The best fit rest mass for dark matter (as far as Lyman Alpha measurements go) is between 14 keV and 100 keV. See article linked above.<br /><br />The best fit 'thermal rest mass' for a fermion dark matter particle (as far as fitting galaxy rotation curves goes) is on the order of 3 keV.<br />http://arxiv.org/abs/1304.0759<br />http://arxiv.org/abs/1401.1214<br /><br />A boson particle with rest mass less than 10 eV is not a viable dark matter particle.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2846514233477399562.post-78894814768453483902015-01-10T19:47:14.746+01:002015-01-10T19:47:14.746+01:00The QCD axion may be the most fascinating dark mat...The QCD axion may be the most fascinating dark matter model out there because the parameters have both minimum and maximum values. Some of those values might be challenging to probe, but at least they're a known target, and this investigation will have a definite endpoint. With WIMPs you can keep on hypothesizing smaller interaction cross-sections.Alexnoreply@blogger.com