Finding the hypothetical particle axion could mean discovering for the first time what happened in the Universe a second after the Big Bang, suggests a new study published in Physical examination D June 7.
How far can we go back in the past of the Universe today? In the electromagnetic spectrum, observations of the cosmic diffuse background – commonly known as CMB – allow us to go back almost 14 billion years until the Universe cooled enough for protons and electrons to combine. and form neutral hydrogen. The CMB has taught us a lot about the evolution of the cosmos, but the photons from the CMB were released 400,000 years after the Big Bang, making it extremely difficult to learn the history of the universe before that time.
To open a new window, a trio of theoretical researchers, including Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Principal Investigator, University of California, Berkeley, MacAdams Professor of Physics and Lawrence Berkeley National Laboratory principal researcher Hitoshi Murayama, Lawrence Berkeley National Laboratory physics researcher and University of California, Berkeley, postdoctoral fellow Jeff Dror (now at University of California, Santa Cruz) and UC Berkeley Miller researcher Nicholas Rodd, looked beyond photons and into the domain of hypothetical particles known as axions, which may have been emitted in the first second of the history of the Universe.
In their paper, they suggest the possibility of looking for an axion analogue of CMB, which is called a cosmic axion background or CaB.
Although hypothetical, there are many reasons to suspect that the axion could exist in our Universe.
On the one hand, axions are a generic prediction of string theory, one of today’s best hopes for a theory of quantum gravity. The existence of an axion could further help solve the long-standing puzzle of why we have yet to measure an electric dipole moment for the neutron, a problem more officially known as ” strong CP problem ”. More recently, the axion has become a promising candidate for dark matter, and as a result, researchers are rapidly looking for dark matter for the axion.
In their paper, the researchers point out that as experimenters develop more sensitive instruments to search for dark matter, they may come across another sign of axions in the form of CaB. But since CaB shares similar properties with dark matter axions, there is a risk that the experiments will reject the CaB signal as noise.
Finding the CaB on one of these instruments would be a double discovery. Not only would this confirm the existence of the axion, but researchers around the world would immediately have a new fossil from the First Universe. Depending on how CaB was produced, researchers could learn more about various aspects of the evolution of the Universe never before possible (Figure).
“What we have proposed is that by changing the way current experiments analyze data, we may be able to research the remaining axions of the early universe. Then we may be able to learn more about it. the origin of dark matter, phase transition or inflation at the beginning of the Universe. There are already experimental groups that have expressed interest in our proposal, and I hope we can discover something new about the early Universe that was not known before, ”says Murayama.
“The evolution of the universe can produce axions with a characteristic energy distribution. By detecting the energy density of the universe currently composed of axions, experiments such as MADMAX, HAYSTAC, ADMX and DMRadio could us give answers to some of the most important puzzles in cosmology, such as “How hot has our universe become?”, “What is the nature of dark matter?”, “Has our universe suffered a period of rapid expansion known as ‘phase transition’ inflation, ”explains Dror.
The new study gives reason to be excited about the dark matter axion program. Even though dark matter is not made up of axions, these instruments can provide a picture of the Universe when it was less than a second.