The table below has all of the physical constants of the Standard Model of Particle Physics and General Relativity (which are collectively called "Core Theory" in physics) in one place. The data is as of September 2021, although little research since then has been incorporated into the sources cited yet. This version of the table has also been edited from prior versions for greater clarity and stylistic consistency.
Has something happened with the neutrino masses recently? I remember them having an upper limit on sum of masses plus known differences in square of mass with a huge range allowed.
ReplyDeleteDirect measurements limit the smallest neutrino mass to about 0.8 eV. But indirect measurements from cosmology limit the sum of the three neutrino masses to about 0.012 eV. The table incorporates that limitation.
ReplyDeleteSee https://pdglive.lbl.gov/Particle.action?node=S066&init=0 and https://pdglive.lbl.gov/Particle.action?node=S067&init=0
ReplyDeleteOk, looks like the cosmology upper limit has been pushed down a lot. Last time I looked at those numbers I think the upper limit was about 0.2 eV. Given that the squared mass differences give a min of about 0.06, halving the upper limit gives a much narrower interval.
ReplyDeleteThanks!
ReplyDeleteAstrophysics > Astrophysics of Galaxies
[Submitted on 26 Sep 2022]
Dwarf galaxies with central cores in modified Newtonian dynamics (MOND) gravity
J. Sanchez Almeida (1 and 2) ((1) Instituto de Astrofisica de Canarias, La Laguna, Spain, (2) Departamento de Astrofisica, Universidad de La Laguna, Spain)
Some dwarf galaxies are within the Mondian regime at all radii, i.e., the gravitational acceleration provided by the observed baryons is always below the threshold of g†≃1.2×10−10ms−2. These dwarf galaxies often show cores, in the sense that assuming Newton's gravity to explain their rotation curves, the total density profile ρ(r) presents a central plateau or {\em core} (dlogρ/dlogr→0 when r→0). Here we show that under MOND gravity, the existence of this core implies a baryon content whose density gbar must decrease toward the center of the gravitational potential (gbar→0 when r→0). Such drop of baryons toward the central region is neither observed nor appears in numerical simulations of galaxy formation following MOND gravity. We analyze the problem posed for MOND as well as possible workarounds.
Comments: Accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2209.12547 [astro-ph.GA]
@neo
ReplyDeleteI'll take a look at it (in due time).
@JollyJoker
ReplyDeleteThe most aggressive cosmology limit in PDG claims a sum of three neutrino mass limit of just 0.09 eV which would definitively rule out the inverted hierarchy of neutrino masses and tighten the limits even further.
As I note, the neutrino mass limits are not Gaussian because most of the uncertainty is 100% shares between the three neutrino masses based upon their sum, and because the limit on the sum of the neutrino masses is one sided, from the top only, rather than on both sides of a best fit value. The lower limit is the one from the neutrino mass differences in the oscillation context taking the lowest neutrino mass to be zero. Only the variation in the masses due to uncertainty in the oscillation based mass differences in Gaussian.
At 0.09 eV, you have a per mass species uncertainty due to uncertainty in the mass scale of 0.01 eV each, which cut in half is plus or minus 0.005 eV (i.e. 5 meV) only that isn't really right since 0.09 eV or 0.12 eV for the sum of the three neutrino masses is a 95% (two sigma) confidence interval in a measurement bound by zero, and not a one sigma 68% confidence interval in a measurement bounded by 0.06 eV. So the best fit value is actually much closer to 0.06 eV than my crude combination suggests.
Taking all of that into account, I doubt that the lowest neutrino mass is much more than 4-5 meV and is probably closer to 1 meV or less.
There are good theoretical reasons, however (not least of which the fact that everything that interacts via the weak force has non-zero mass and everything that doesn't has zero mass), to believe it is non-zero even though this isn't strictly required by oscillation data or the cosmological data. Also if the neutrino has Majorana mass if must be non-zero, and if the neutrino has Dirac mass the same mechanism that give the other two neutrino mass eigenstates non-zero masses should also give some mass to the lightest one.