tag:blogger.com,1999:blog-7315236707728759521.post1307277769041211222..comments2024-03-28T21:52:52.100-06:00Comments on Dispatches From Turtle Island: More Dark Matter Exclusions (Updated August 20, 2014)Andrew Oh-Willekehttp://www.blogger.com/profile/02537151821869153861noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-7315236707728759521.post-2838051015319448202014-12-22T15:47:17.276-07:002014-12-22T15:47:17.276-07:00The DAMA direct dark matter experiment claims to h...The DAMA direct dark matter experiment <a href="http://arxiv.org/abs/1412.6524" rel="nofollow">claims to have detected an annual variation in potential 2-6 keV energy dark matter hits at the 9.3 sigma level</a>, although the interpretation of the signal as DM is not well established.andrewhttps://www.blogger.com/profile/08172964121659914379noreply@blogger.comtag:blogger.com,1999:blog-7315236707728759521.post-31461781940736393972014-08-26T15:34:19.758-06:002014-08-26T15:34:19.758-06:00See also 1408.3531 "Constraints on 3.55 keV l...See also 1408.3531 "Constraints on 3.55 keV line emission from stacked observations of dwarf spheroidal galaxies" by D. Malyshev, A. Neronov, D. Eckert, which seems to make the DM interpretation of the 3.55 keV line unlikely.andrewhttps://www.blogger.com/profile/08172964121659914379noreply@blogger.comtag:blogger.com,1999:blog-7315236707728759521.post-80819295270510821002014-08-21T17:38:57.214-06:002014-08-21T17:38:57.214-06:00There are published papers that put floors on WDM ...There are published papers that put floors on WDM particle masses that are higher than the ceilings on WDM particle masses in other papers.<br /><br />So far, the overlaps are very small (1-2 keV differences), and can be massaged away with experimental uncertainties (both statistical and systemmic) and theoretical distinctions such as DeVega's recognition that the definition of DM mass for thermal relic freeze out purposes, and the definition of DM mass for purposes of interpreting a 3.5 keV X-ray signal may be different and require a conversion factor that reflects those differences.<br /><br />Still, it isn't hard to imagine some new data point from astronomy observations or particle physics that conclusively establishes a new upper or lower bound that is impossible to reconcile with the existing mass constraints on WDM which are already tight.<br /><br />For example, one could imagine some future observation of ultra-low frequency gravity waves measured with precision space based observatories to get a sufficiently large effective measurement distance to require that WDM have more than 20 keV, a value contradicted by other observational measurements.<br /><br />Also, the questions of DM particle formation are even more vexing than those of leptogenesis and baryongenesis. We have no process that takes us from the Big Bang to a universe dominated by DM relative to baryonic matter, while at a minimum, we do have Standard Model processes by which the existing fundamental particle content of the universe can be derived from a point after the Big Bang with the existing aggregate baryon number and lepton number o the universe from any arbitrary mix of baryons and leptons in the universe. Indeed, this follows very naturally from the fact that every form of fermion (and Higgs bosons, W bosons and Z bosons) except protons, neutrons, electrons, and three kinds of neutrinos are unstable in time frames of 10^-6 seconds or less, and that gluons effectively operate only at short ranges that give them equally short effective lifetimes.<br /><br />Moreover, we have processes like pair production from highly energetic photons that can create all of the Standard Model baryons and leptons from pure energy, but simply fails to produce the non-zero baryon number and lepton number for the universe that we would expect.<br /><br />In contrast, we have not identified any fundamental process of any kind that produces dark matter particles, or even meaningfully certain amounts of invisible products - there are places like J/psi decays to photons and invisible products where there could be production of DM particles in the gaps that arise due to lack of experimental precision, but none where they actually exist.<br /><br />Now, the pre-nucleosynthesis phase of the post-Big Bang period is distinct from the region which our most extreme experiments can probe because it has much higher energies, so it could be that DM production (and perhaps B and L number variations as well), are exclusively high energy processes, perhaps only taking place at a GUT scale, for example.<br /><br />But, the bounds the energies of those processes are getting tighter as well.andrewhttps://www.blogger.com/profile/08172964121659914379noreply@blogger.comtag:blogger.com,1999:blog-7315236707728759521.post-5445210172775978342014-08-21T15:50:05.904-06:002014-08-21T15:50:05.904-06:00Thanks for finding the pre-print by Anderson et a...Thanks for finding the pre-print by Anderson et al.<br />It seems like it's pretty strong evidence against a 7.1 keV sterile neutrino as dark matter. The 3.55 keV X-ray signal should have been in the halos of the galaxies where they were looking. (Of course, there's dark matter throughout the Milky Way Galaxy, so it has always been tough to determine signal from background.)<br /><br />As you state it in your post, there's only a very narrow range of possible dark matter candidates left to rule out. The astrophysical data set still leans towards a 2-10 keV fermion dark matter particle that is virtually-completely sterile to every force exempt gravity.<br />But what that particle might be is nearly anyone's guess.<br /><br />One might assume that a particle with no "E&M/Weak/orStrong charge" would have a mass less than the mass of a neutrino. (Because heavier particles tend to have more types of "charges." But we know (from the Lyman Alpha Forest) that dark matter can't have a mass below ~1 keV. <br /><br />So, you're absolutely right that we're right back to square one. We have no clue what is dark matter.Anonymousnoreply@blogger.com