I strongly suspect that baryon number and lepton number are not violated outside of Standard Model sphaleron interactions (which conserve B-L). So far, even they have not been observed at the LHC.
I am not confident that even sphaleron interactions actually happen, although whether or not they do at very high energies (which are far beyond what can be reproduced at the current LHC and are limited predominately to the first microsecond after the Big Bang) is largely irrelevant to the larger conclusions about the source of baryon asymmetry in the universe, because the effect size is too small.
A sphaleron requires a roughly 9 TeV energy to be concentrated at a density of about 1000 times that of the mass-energy density of a proton (i.e., a radius of about 8.4 * 10^-17 meters). The Schwarzschild radius of a 9 TeV sphaleron is about 2.4 * 10^-50 meters. The Planck length is about 1.6 * 10^-35 meters. A Planck length black hole, arguably the least massive possible black hole, has a mass of about 1.2 * 10^16 TeV (22 micrograms).
Creating a sphaleron would probably require a collider at least 100 times as powerful as the LHC, if it is possible at all. This is probably something that the next generation of more powerful particle colliders will not achieve.
Creating a sphaleron would require a mass-energy density more than nine million times greater than a neutron star, i.e. 10^17 kg/m^3, or the mass-energy density of a minimum sized stellar collapse black hole. A mass-energy density this great has never been observed.
This concentrated a mass-energy may not be possible. It is possible and plausible that instead, there is a minimum mass-energy density in the universe, something that might provide a fixed point that makes an asymptotically safe theory of quantum gravity possible. If this threshold existed, it would prevent the non-conservation of baryon number and lepton number from occurring at all. It would also make primordial black holes not merely impossible to produce in practice in the modern era, but theoretically impossible.
This isn't necessarily inconsistent with the observed baryon asymmetry of the universe. The baryon asymmetry of the universe could arise from a scenario in which the birth of the universe arises from a pair of universes, one the CPT image of the other, living in pre- and post-big bang epochs. The CPT-invariance strictly constrains the vacuum states of the quantized fields. Thus, before the Big Bang is a predominantly antimatter universe in which time runs backwards relative to our universe. See also here and here.
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Dark matter is slowing the spin of the Milky Way's galactic bar
The researchers found that the stars in the stream carry a chemical fingerprint—they are richer in heavier elements (called metals in astronomy), proving that they have traveled away from the galactic center, where stars and star-forming gas are about 10 times as rich in metals compared to the outer galaxy.
Using this data, the team inferred that the bar—made up of billions of stars and trillions of solar masses—had slowed down its spin by at least 24% since it first formed.
Co-author Dr. Ralph Schoenrich (UCL Physics & Astronomy) said, "Astrophysicists have long suspected that the spinning bar at the center of our galaxy is slowing down, but we have found the first evidence of this happening.
"The counterweight slowing this spin must be dark matter. Until now, we have only been able to infer dark matter by mapping the gravitational potential of galaxies and subtracting the contribution from visible matter.
"Our research provides a new type of measurement of dark matter—not of its gravitational energy, but of its inertial mass (the dynamical response), which slows the bar's spin."
Co-author and Ph.D. student Rimpei Chiba, of the University of Oxford, said, "Our finding offers a fascinating perspective for constraining the nature of dark matter, as different models will change this inertial pull on the galactic bar.
"Our finding also poses a major problem for alternative gravity theories—as they lack dark matter in the halo, they predict no or significantly too little slowing of the bar."
The Milky Way, like other galaxies, is thought to be embedded in a "halo" of dark matter that extends well beyond its visible edge.
Dark matter is invisible and its nature is unknown, but its existence is inferred from galaxies behaving as if they were shrouded in significantly more mass than we can see. There is thought to be about five times as much dark matter in the Universe as ordinary, visible matter.
Alternative gravity theories such as modified Newtonian dynamics reject the idea of dark matter, instead seeking to explain discrepancies by tweaking Einstein's theory of general relativity.
The Milky Way is a barred spiral galaxy, with a thick bar of stars in the middle and spiral arms extending through the disc outside the bar. The bar rotates in the same direction as the galaxy.
https://phys.org/news/2021-06-dark-milky-galactic-bar.html
As always, thanks for the link. Phys.org is know for overblowing or distorting results, however. MOND actually has an inertial mass rather than dynamical mass formulation, and non-modified gravity scientists statements about what modified gravity theories can and cannot do are frequently wrong.
Still, deserves further attention as any independent methodology does.
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