new cosmology stuff

[Ecurb Noselrub]

I was just sort of wrapping my head around the isotropic homogeneous model, and now this. Oh well, we will all die in ignorance. But we certainly know more than the nomads 6000 years ago. I guess it's all relative.

[Recusant]

Far from ignorance, if one has paid attention. In the larger view, yes all we have are flawed stories, products of impressive but limited primate brains.

When it comes to cosmology and astronomy in general, in our day we've been privileged to be able to see things that our grandfathers didn't even imagine. Farther away and in better detail, with new discoveries appearing all the time. We're far from fully understanding what we see. However people continue to enlarge our understanding, which is cheering and for some, pleasantly exciting.

[Icarus]

Heady stuff !

[Recusant]

This is a good one. What if neutrinos (partially defined by their lack of interaction with matter) actually interact with dark matter on some level?  What if? 

"Ghost Particles Interacting With Dark Matter Could Solve a Huge Cosmic Mystery" | Science Alert

A new investigation of the early Universe led by Poland's National Centre for Nuclear Research has just found that there may be an interaction between two of the most elusive components of the cosmos.

By combining different kinds of observations, cosmologists have shown that what we see is more easily explained if neutrinos, aka 'ghost particles', weakly interact with dark matter.

With a vexing certainty of three sigma, the signal isn't strong enough to be definitive, but is also too strong to be a mere hint or noise in the data.

It's a finding that could open the way to a small expansion of the Standard Cosmological Model, relaxing the assumption that dark matter is entirely collisionless and allowing for faint scattering between neutrinos and dark matter.

Neutrinos and dark matter are two components of the Universe that don't interact much with much of anything.

Neutrinos are among the most abundant particles in the Universe. They form in generous quantities under energetic circumstances, such as supernova explosions and the atomic fusion that takes place in the hearts of stars – so they're pretty much everywhere.

However, they have no electric charge, their mass is extremely small, and they barely interact with other particles they encounter. Hundreds of billions of neutrinos are streaming through your body right now. Every now and then, a neutrino collides with another particle, producing a shower of decay particles and photons that we need special underground equipment to detect.

Dark matter, on the other hand, doesn't seem to interact with ordinary matter at all, except gravitationally. The strong evidence for its existence comes from gravitational effects such as galaxy rotation rates and the warping of space-time that cannot be accounted for by normal matter. These effects suggest that roughly 85 percent of the matter in the Universe is made up of 'dark' matter that we cannot see.

[Computer simulations were set up to compare models, including a model in which neutrinos and dark matter interact weakly. The model(s?) with the interaction seemed somewhat closer to observations than models without interaction.]

"If this interaction between dark matter and neutrinos is confirmed, it would be a fundamental breakthrough," says theoretical physicist and cosmologist William Giarè of the University of Hawaiʻi, formerly at the University of Sheffield.

"It would not only shed new light on a persistent mismatch between different cosmological probes, but also provide particle physicists with a concrete direction, indicating which properties to look for in laboratory experiments to help finally unmask the true nature of dark matter."

"If" is doing a lot of heavy lifting there, but these mysteries have been sufficiently perplexing that this avenue of enquiry looks deeply tantalizing.

[Continues . . .]

The paper is open access:

"A solution to the S₈ tension through neutrino–dark matter interactions"  Nature Astronomy

Abstract:

Neutrinos and dark matter (DM) are two of the least understood components of the Universe, yet both play crucial roles in cosmic evolution. Clues about their fundamental properties may emerge from discrepancies in cosmological measurements across different epochs of cosmic history.

Possible interactions between them could leave distinctive imprints on cosmological observables, offering a rare window into dark sector physics beyond the standard ΛCDM framework. Here we present compelling evidence that DM–neutrino interactions can resolve the persistent structure growth parameter discrepancy, [LaTeX enscribed equation, see original to view it], between early and late Universe observations.

By incorporating cosmic shear measurements from current weak lensing surveys, we demonstrate that an interaction strength of u ≈ 10−4 not only provides a coherent explanation for the high-multipole observations from the Atacama Cosmology Telescope, but also alleviates the S₈ discrepancy. Combining early Universe constraints with DES Y3 cosmic shear data yields a nearly 3σ preference for non-zero DM–neutrino interactions.

This strengthens previous observational claims and provides a clear path towards a breakthrough in cosmological research. Our findings challenge the standard ΛCDM paradigm and highlight the potential of future large-scale structure surveys, which can rigorously test this interaction and unveil the fundamental properties of DM.

[Recusant]

Further speculative cosmology. As long as it could give an accurate idea of our Universe, I'll listen. May not buy the idea but there's nothing wrong with some window-shopping. Evidence of an extraordinarily speedy neutrino could indicate the existence of primordial black holes (PBH). More specifically, exploding primordial black holes.

"Did we just see a black hole explode? Physicists think so—and it could explain (almost) everything" | Phys.org

In 2023, a subatomic particle called a neutrino crashed into Earth with such a high amount of energy that it should have been impossible. In fact, there are no known sources anywhere in the universe capable of producing such energy—100,000 times more than the highest-energy particle ever produced by the Large Hadron Collider, the world's most powerful particle accelerator. However, a team of physicists at the University of Massachusetts Amherst recently hypothesized that something like this could happen when a special kind of black hole, called a "quasi-extremal primordial black hole," explodes.

In new research published in Physical Review Letters, the team not only accounts for the otherwise impossible neutrino but shows that the elementary particle could reveal the fundamental nature of the universe.

Black holes exist, and we have a good understanding of their life cycle: an old, large star runs out of fuel, implodes in a massively powerful supernova, and leaves behind an area of spacetime with such intense gravity that nothing, not even light, can escape. These black holes are incredibly heavy and are essentially stable.

But, as physicist Stephen Hawking pointed out in 1970, another kind of black hole—a primordial black hole (PBH), could be created not by the collapse of a star, but from the universe's primordial conditions shortly after the Big Bang. PBHs exist only in theory so far, and, like standard black holes, are so massively dense that almost nothing can escape them—which is what makes them "black." However, despite their density, PBHs could be much lighter than the black holes we have so far observed. Furthermore, Hawking showed that PBHs could slowly emit particles via what is now known as "Hawking radiation" if they got hot enough.

"The lighter a black hole is, the hotter it should be and the more particles it will emit," says Andrea Thamm, co-author of the new research and assistant professor of physics at UMass Amherst. "As PBHs evaporate, they become ever lighter, and so hotter, emitting even more radiation in a runaway process until explosion. It's that Hawking radiation that our telescopes can detect."

[Continues . . .]

The paper is behind a paywall, but I found an open access preprint version. The abstract is from the published version and I nominate its final sentence as an exemplary "big if true":

"Explaining the PeV Neutrino Fluxes at KM3NeT and IceCube with Quasi-Extremal Primordial Black Holes" | arXiv

The KM3NeT experiment has recently observed a neutrino with an energy around 100,PeV, and IceCube has detected five neutrinos with energies above 1,PeV. While there are no known astrophysical sources, exploding primordial black holes could have produced these high-energy neutrinos.

For Schwarzschild black holes this interpretation results in tensions between the burst rates inferred from the KM3NeT and IceCube observations, with indirect constraints from the extragalactic gamma ray background and with the non-observation of an associated gamma ray signal at LHAASO.

In this letter we show that if there is a population of primordial black holes charged under a new dark 𝑢(1) symmetry which spend most of their time in a quasi-extremal state, the neutrino emission at 1,PeV may be more suppressed than at 100,PeV. The burst rates implied by the KM3NeT and IceCube observations and the indirect constraints can then all be consistent at 1𝜎, and no associated gamma-ray signal was expected at LHAASO. Furthermore, these black holes could constitute all of the observed dark matter in the universe.

[Dark Lightning]

I read that this morning. It'll take us the life of the universe to understand it all, but a lot of its life has already passed us by. Well, it's the ride that counts, I guess. I'm liking that story about binary star pairs tossing one star off at stupendous velocities. Wild universe.

[Recusant]

Yeah, the idea of primordial black holes has been around for some time, but by their nature they would be extremely difficult to find. It'd be a cool way to resolve the identity of dark matter though. 

It's true that we see the Universe at a point long past the Big Bang. Still, for life as we know it to exist there has to be a liberal sprinkling of elements heavier than hydrogen, helium, and lithium. For that, a few generations of supernovae have to have come and gone. Takes some time. Most likely there is or has been life in the Universe that started a billion years or two before Earth's, but I don't think we're particularly late to the party. 

[Dark Lightning]

Yeah, hard to say how much longer the party will last. I won't see the end, either. 

[Recusant]

OK, the party being the Universe: <Carl Sagan voice>Billions and billions of years</Carl Sagan voice>. If it's life on this planet, it seems likely to me that there will still be living things of some sort here when Earth is engulfed by Sol in its latter times. There are microorganisms living miles below the surface; tiny interstices in the rocks being large caves to them. Even if the surface gets scoured thoroughly, those deep dwellers will carry on.

A giant impact like the one which is thought to have formed the Moon could do it though. Turn the entire surface molten. Assuming the existence of rogue interstellar planets, the unlucky one out of a few trillion chance of such a visitor could rub out active DNA here before the Big Roasting. I'll see whether I can come up with any other ways it could happen, that'll be good for some cheerful contemplation.

If it's our species or its descendants, that could be several thousand years even after we degrade the planet. Homo sapiens is fairly adaptable. This civilization seems intent on bringing its own downfall but some humans will almost certainly survive that. 

[Dark Lightning]

H. Sap. is certainly a vicious brute, so I expect some longevity.