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No WIMPS! Heavy particles don’t clarify gravitational lensing oddities

No WIMPS! Heavy particles don’t clarify gravitational lensing oddities

2023-04-24 02:54:21

Image of many galaxies, with some distorted streaks near the center.
Enlarge / The purple arcs on the proper of heart are background galaxies distorted by gravitational lensing. The quantity, location, and diploma of distortion of those pictures relies on the distribution of darkish matter within the foreground.

Many years after it turned clear that the seen Universe is constructed on a framework of darkish matter, we nonetheless do not know what darkish matter truly is. On giant scales, a wide range of proof factors towards what are referred to as WIMPs: weakly interacting huge particles. However there are a number of particulars which can be troublesome to elucidate utilizing WIMPs, and a long time of trying to find the particles have turned up nothing, leaving folks open to the concept one thing aside from a WIMP contains darkish matter.

One of many many candidates is something called an axion, a force-carrying particle that was proposed to resolve an issue in an unrelated space of physics. They are much lighter than WIMPs however produce other properties which can be in step with darkish matter, which has sustained low-level curiosity in them. Now, a brand new paper argues that there are options in a gravitational lens (largely the product of darkish matter) which can be finest defined by axion-like properties.

Particle or wave?

So, what’s an axion? On the best degree, it is an especially gentle particle with no spin that acts as a power service. They had been initially proposed to make sure that quantum chromodynamics, which describes the habits of the sturdy power that holds protons and neutrons collectively, would not break the conservation of cost parity. Sufficient work was executed to verify axions had been suitable with different theoretical frameworks, and a few searches had been executed to attempt to detect them. However axions have largely languished as considered one of numerous potential options to an issue that we’ve not discovered resolve.

They’ve, nonetheless, attracted some consideration as potential options to darkish matter. However the habits of darkish matter was higher defined by a heavy particle—particularly a weakly interacting huge particle. Axions had been anticipated to be on the lighter facet and will probably be as gentle because the near-massless neutrino. The searches that had been executed for axions tended to rule out most of the heavier lots, as effectively, making the issue much more pronounced.

However axions could also be making a comeback, or no less than holding regular whereas WIMPs faceplant. There have been numerous detectors constructed to attempt to catch indications of the weak interactions of WIMPs, they usually’ve come up empty. If WIMPs are Normal Mannequin particles, we may have inferred their presence based mostly on lacking mass in particle colliders. No proof of that has been forthcoming. That has triggered folks to reexamine whether or not WIMPs are one of the best answer to darkish matter.

On cosmological scales, WIMPs proceed to suit the info extraordinarily effectively. However when you get all the way down to the degrees of particular person galaxies, there are some oddities that do not work fairly as effectively until the darkish matter halo surrounding a galaxy has an advanced construction. Comparable issues appear to be true once you attempt to map the darkish matter of particular person galaxies based mostly on its capability to create a gravitational lens that warps area in order that it magnifies and distorts background objects.

WIMP-based dark matter, modeled at left, leads to a smooth distribution from high (red) to low (blue) as you move farther from a galaxy's core. With axions (right), quantum interference creates a far more irregular pattern.

WIMP-based darkish matter, modeled at left, results in a easy distribution from excessive (purple) to low (blue) as you progress farther from a galaxy’s core. With axions (proper), quantum interference creates a much more irregular sample.

See Also

Amruth, et. al.

The brand new work makes an attempt to narrate these potential oddities to a distinction between the properties of WIMPS and axions. As their identify implies, WIMPs ought to behave like discrete particles, interacting virtually totally by means of gravity. In contrast, axions ought to work together with one another by means of quantum interference, creating wave-like patterns of their frequency all through a galaxy. So, whereas the frequency of WIMPs ought to gently decline with distance from the core of a galaxy, axions ought to type a standing wave (technically, a soliton) that enhances their frequency close to the galactic core. Farther out, complicated interference patterns ought to create areas the place there are primarily no axions and different areas the place they’re current at twice the common density.

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