MIT’s new axion detector, in cross-section, designed to simulate an astrophysical magnetar/Courtesy of the researchers
Cosmology today would certainly seem to be at a standstill. Yesterday we looked at the quadrillion dubious rescues for string theory, reasons for believing that they are “pure, unadulterated hype,” and the fact that insiders are now leaning hard on theoretical physicist Sabine Hossenfelder for calling it out.
So, how is another frustrating topic, dark matter doing? From ScienceDaily:
Physicists from MIT and elsewhere have performed the first run of a new experiment to detect axions — hypothetical particles that are predicted to be among the lightest particles in the universe. If they exist, axions would be virtually invisible, yet inescapable; they could make up nearly 85 percent of the mass of the universe, in the form of dark matter.
Axions are particularly unusual in that they are expected to modify the rules of electricity and magnetism at a minute level. In a paper published today in Physical Review Letters, the MIT-led team reports that in the first month of observations the experiment detected no sign of axions within the mass range of 0.31 to 8.3 nanoelectronvolts. This means that axions within this mass range, which is equivalent to about one-quintillionth the mass of a proton, either don’t exist or they have an even smaller effect on electricity and magnetism than previously thought…
While they are thought to be everywhere, axions are predicted to be virtually ghost-like, having only tiny interactions with anything else in the universe. …
The researchers reasonably hoped to find axions around magnetars, “ a type of neutron star that churns up a hugely powerful magnetic field.” They designed and carried out an experiment:
In 2018, the team carried out ABRACADABRA’s first run, continuously sampling between July and August. After analyzing the data from this period, they found no evidence of axions within the mass range of 0.31 to 8.3 nanoelectronvolts that change electricity and magnetism by more than one part in 10 billion.
The experiment is designed to detect axions of even smaller masses, down to about 1 femtoelectronvolts, as well as axions as large as 1 microelectronvolts.
The team will continue running the current experiment, which is about the size of a basketball, to look for even smaller and weaker axions. Meanwhile, Winslow is in the process of figuring out how to scale the experiment up, to the size of a compact car — dimensions that could enable detection of even weaker axions. Paper. (open access) – Jonathan L. Ouellet, Chiara P. Salemi, Joshua W. Foster, Reyco Henning, Zachary Bogorad, Janet M. Conrad, Joseph A. Formaggio, Yonatan Kahn, Joe Minervini, Alexey Radovinsky, Nicholas L. Rodd, Benjamin R. Safdi, Jesse Thaler, Daniel Winklehner, Lindley Winslow. First Results from ABRACADABRA-10 cm: A Search for Sub-μeV Axion Dark Matter. Physical Review Letters, March 29, 2019; DOI: 10.1103/PhysRevLett.122.121802 More.
A ghost indeed. “It is a challenging experiment because the expected signal is less than 20
Is it theoretically possible that the axion be so small that it is not individually measurable by any foreseeable technique but the mass of axions has an enormous effect?
See also: At Forbes: The “miracle” hope for finding the dark matter of the universe is dead
and
Astrophysicist: photons with mass wouldn’t solve the dark matter puzzle
Before you go: Discover: Even the best dark matter theories are crumbling
Researcher: The search for dark matter has become a “quagmire of confirmation bias” So many research areas in science today are hitting hard barriers that it is reasonable to think that we are missing something.
Physicists devise test to find out if dark matter really exists
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Largest particle detector draws a blank on dark matter
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and
Proposed dark matter solution: “Gravity is not a fundamental governance of our universe, but a reaction to the makeup of a given environment.”