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.