The path to dark matter and other fundamental enigmas may be through a warped extra dimension, according to a new study that proposes a new theory of the universe.
By Becky Ferreira
Scientists want to search for a hypothetical particle that can act as a portal to a warped fifth dimension that mediates the cosmic realms of light and dark.
You would be forgiven for assuming that sentence is a science fiction synopsis, but it is actually the mind-boggling upshot of a recent study that seeks to illuminate some of the most persistent enigmas in science.
The existence of this speculative particle could “provide a natural explanation” for the abundance of dark matter, an unidentified substance that accounts for most of the universe’s mass, and resolve intractable problems about subatomic particles known as fermions, according to the new research, which was published last month in The European Physical Journal C.
The study adds that “the presence of new physics” can explain these fundamental mysteries by presenting a model of the universe with a fifth dimension that can be traversed by particles.
The study was authored by Javier Castellano and Matthias Neubert, theoretical physicists at the PRISMA+ Cluster of Excellence at Johannes Gutenberg University Mainz, and Adrián Carmona, an Athenea3i fellow at the department of theoretical physics and the cosmos at the University of Granada.
“We have been working on a similar topic for quite some time,” said the team in an email.
“Our initial motivation was to explain the possible origin of fermion masses in theories with a warped extra dimension.”
“We knew that the masses of these constituents had some special features, which were crying out for an explanation,” they said.
The researchers are part of a long scientific tradition that questions whether the four dimensions that humans can comprehend—3D space and time—are really all the universe has to offer. This line of research has produced 5-dimensional field equations that express the implications an extra dimension would have on the universe, and reality itself.
While researching these equations in relation to fermion masses, the team sketched out the existence of a new scalar field associated with a speculative particle that is roughly similar to the Higgs field associated with the famous Higgs boson particle.
“We found that the new scalar field had an interesting, non-trivial behavior along the extra dimension,” the team explained. “Since this new particle has very similar quantum properties as the Higgs boson, it was very natural to assume that the two particles should mix with each other, meaning that their quantum-mechanical wave functions are intertwined.”
“Studying this mixing was one of the original motivations of this work,” the researchers added.
As they probed this hypothesis, the physicists realized that the heavy particle could offer “a unique window” into dark matter because it would be able to mediate a new force connecting dark matter and its more familiar visible counterpart, which takes the form or stars, planets, and everything else we can detect with traditional light-based astronomy.
“If this heavy particle exists, it would necessarily connect the visible matter that we know and that we have studied in detail with the constituents of the dark matter, assuming that dark matter is composed out of fundamental fermions, which live in the extra dimension,” the physicists explained.
“This is not a far-fetched idea, since we know that ordinary matter is made of fermions and that, if this extra dimension exists, they will very likely propagate into it,” they noted.
Models of the hypothetical particle did not conflict with real observational evidence of dark matter abundance in the universe. This general agreement with empirical evidence, along with the hefty mathematical work in the study, demonstrates that the particle could be “a possible new messenger to the dark sector,” the researchers said.
“Therefore, confirming the existence of such a new scalar particle will open an exciting path towards the possible discovery of dark matter,” the team said. “This will give us in particular very useful information about the possible mass range of dark matter and its interactions with the particles we know nowadays.”
Now that scientists have a lead on this hypothetical particle and its 5th dimension, they have to actually look for it. The Higgs boson was eventually spotted by the Large Hadron Collider (LHC) in Switzerland in 2012, an achievement that earned the Nobel Prize in Physics. However, the LHC would not be equipped to search for the particle proposed in the new paper, as it would be too heavy to be generated in any current facility.
Though the particle might be detectable for a new generation of proposed colliders, such as the International Linear Collider, the Compact Linear Collider (CLIC), and the Future Circular Collider, the researchers said that “due to its large mass the prospects for such a direct discovery seem very challenging even at the high energies discussed for such a machine (100 TeV).”
Even so, the researchers believe that the particle could be detected more indirectly, such as through observing gravitational waves, which are ripples in spacetime.
“Another possibility, which we did not explore yet, is that this new particle could play an important role in the cosmological history of the universe, and might produce gravitational waves that can be searched for with future gravitational-wave detectors,” the researchers added.
Future studies of dark matter could also help to constrain the odds of the particle’s existence, so the team is optimistic that their 5th-dimensional concept will develop alongside advances in particle physics and cosmology. Beyond its implications for understanding dark matter, the particle, if it exists, could shed light on longstanding scientific dilemmas such as the flavor puzzle or the hierarchy problem, while also opening a new window into the early universe.
“One could study the potential role played by the new scalar particle in stabilizing the extra dimension,” the team said. “This could also eventually lead to an interesting cosmological history of the universe and might lead to the production of gravitational waves. This is an interesting line of research, which we plan to follow in the months ahead.”
“One could also try to find new ways of probing this particle at future hadron colliders,” the researchers concluded. “As you can see, there are really plenty of things one can think of!”