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Researchers find way to show how the tiniest particles in ouruniverse saved us from complete annihilation

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Researchers find way
to show how thetiniest particles in ouruniverse saved us
from completeannihilation

TRIUMF Innovations
30 January 2020

[with notes from the Kavli IPMU publication]
Recently discovered ripples of spacetime called
gravitational waves could contain evidence to prove thetheory that life survived the Big Bang because of aphase transition that allowed neutrino particles toreshuﬄe matter and anti-matter, explains a new study by

an international team of researchers.
How we were saved from a complete annihilation is not aquestion in science fiction or a Hollywood movie.
According to the Big Bang theory of modern cosmology,
matter was created with an equal amount of anti-matter.
If it had stayed that way, matter and anti-matter shouldhave eventually met and annihilated one to one, leading
up to a complete annihilation.

But our existence contradicts this theory. To overcome acomplete annihilation, the Universe must have turned asmall amount of anti-matter into matter creating animbalance between them. The imbalance needed is only
a part in a billion. But it has remained a complete
mystery when and how the imbalance was created.
“The Universe becomes opaque to light once we lookback to around a million years after its birth. This makes
the fundamental question of ‘why are we here?’ diﬃcult
to answer,” says paper co-author Jeﬀ Dror, postdoctoral
fellow at the University of California, Berkeley.
Since matter and anti-matter have the opposite electricalcharges, they cannot turn into each other, unless they
are electrical neutral. Neutrinos are the only electricalneutral matter particles we know, and they are thestrongest contender to do this job. A theory many
researchers support is that the Universe went through aphase transition so that neutrinos could reshuﬄe matterand anti-matter.
“A phase transition is like boiling water to vapor, orcooling water to ice. The behavior of matter changes at
specific temperatures called critical temperature. When acertain metal is cooled to a low temperature, it loses
electrical resistance completely by a phase transition,
becoming a superconductor. It is the basis of Magnetic
Resonance Imaging (MRI) for cancer diagnosis ormaglev technology that floats a train so that it can run at
300 miles an hour without causing dizziness. Just like asuperconductor, the phase transition in the early
Universe may have created a very thin tube of magnetic
fields called cosmic strings,” explains paper co-author
Hitoshi Murayama, MacAdams Professor of Physics at
the University of California, Berkeley, and Principal
Investigator at the Kavli Institute for the Physics andMathematics of the Universe, University of Tokyo.
Dror and Murayama are part of a team of researchers
from Japan, US and Canada who believe the cosmic
strings then try to simplify themselves, leading up to tiny
wobbling of spacetime called gravitational waves. These
could be detected by future space-borne observatories
such as LISA, BBO (European Space Agency) or
DECIGO (Japanese Astronautical Exploration Agency) fornearly all possible critical temperatures.

(TRIUMF postdoctoral fellow Graham White)“The recent discovery of gravitational waves opens up a
new opportunity to look back further to a time, as the
Universe is transparent to gravity all the way back to thebeginning. When the Universe might have been a trillion
to a quadrillion times hotter than the hottest place in the
Universe today, neutrinos are likely to have behaved injust the way we require to ensure our survival. We
demonstrated that they probably also left behind abackground of detectable gravitational ripples to let us
know,” says paper co-author Graham White, apostdoctoral fellow at TRIUMF.
“Cosmic strings used to be popular as a way of creatingsmall variations in mass densities that eventuallybecame stars and galaxies, but it died because recent
data excluded this idea. Now with our work, the idea
comes back for a diﬀerent reason. This is exciting!” says
Takashi Hiramatsu, a postdoctoral fellow at the Institutefor Cosmic Ray Research, University of Tokyo, whichruns Japan’s gravitational wave detector KAGRA andHyper-Kamiokande experiments.
“Gravitational wave from cosmic strings has a spectrum
very diﬀerent from astrophysical sources such as mergerof black holes. It is quite plausible that we will becompletely convinced the source is indeed cosmic

strings,” says Kazunori Kohri, Associate Professor at theHigh Energy Accelerator Research Organization Theory
Center in Japan.
“It would be really exciting to learn why we exist at all,”says Murayama. “This is the ultimate question inscience.”
The paper was published as an Editor’s Suggestion in
Physical Review Letters online on 28 January, 2020.

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