A recent investigation into the nascent stages of the Universe, spearheaded by Poland’s National Centre for Nuclear Research, has brought to light a potential nexus between two of the cosmos’s most enigmatic constituents.
By synthesizing a variety of observational data, cosmologists have deduced that our observed reality is more readily interpreted if neutrinos, often referred to as ‘ghost particles’, engage in subtle interactions with dark matter.
While the indicated signal exhibits a concerning certainty of three sigma, it falls short of being conclusive. Nevertheless, it transcends the realm of a mere hint or background noise within the collected data.
This particular finding holds the potential to facilitate a modest amplification of the Standard Cosmological Model, by loosening the tenet that dark matter is entirely non-interacting and permitting feeble scattering events between neutrinos and dark matter.
Neutrinos and dark matter represent two cosmic components that exhibit minimal engagement with most forms of matter and energy.
Among the most prolific particles in the Universe, neutrinos are generated in substantial quantities under highly energetic conditions, such as during supernova explosions and the nuclear fusion processes occurring within stellar cores, rendering them ubiquitously present.
However, their lack of electric charge, exceptionally minuscule mass, and their propensity to interact sparsely with other particles they encounter mean that they pass through us unnoticed. Billions of neutrinos are traversing your body at this very moment. On infrequent occasions, a neutrino may collide with another particle, instigating a cascade of decay products and photons that necessitate specialized subterranean detection apparatus.
Conversely, dark matter appears to have no discernible interaction with baryonic matter, save for its gravitational influence. The compelling evidence for its existence stems from gravitational phenomena like the rotational velocities of galaxies and the curvature of spacetime, neither of which can be explained by visible matter alone. These observable effects suggest that approximately 85 percent of the universe’s matter comprises invisible ‘dark’ matter.
The hypothesis that these two remarkably elusive entities might interact is not novel; theoretical frameworks proposing their potential association, in ways yet undetected, have been put forth since the early 2000s.
Over the past few years, scientific publications have offered several indications, albeit tentative, that neutrino-dark matter interactions might be occurring. This latest research, spearheaded by physicist Lei Zu—who conducted the work at Poland’s National Centre for Nuclear Research and is now affiliated with the National Astronomical Observatory of Japan—aimed to advance this concept beyond theoretical speculation with the objective of addressing a significant enigma in cosmology.
This challenge arises when we juxtapose observations of the universe’s primordial epoch, as captured by the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO), with data from the more recent cosmos.
The CMB is an enduring signature of the initial light that traversed the universe unimpeded approximately 380,000 years post-Big Bang; BAO represent vast cosmic structures that originated from acoustic waves propagating through the early universe, effectively frozen in time when the medium became too sparse to sustain them.
Projecting the CMB and BAO data forward to the current age of the universe—13.8 billion years—using the standard cosmological model results in a universe that appears considerably more aggregated than the one we observe.
“This discrepancy does not invalidate the standard cosmological model, but it may imply its incompleteness,” explains cosmologist Eleonora Di Valentino from the University of Sheffield in the UK. “Our study suggests that interactions between dark matter and neutrinos could account for this divergence, offering novel insights into the mechanisms of structure formation in the universe.”
In a unified effort, the research team compiled one of the most comprehensive integrated datasets to date for evaluating neutrino-dark matter interactions across both the early and late universe. Their compilation included two distinct CMB observations, three BAO datasets, and data from the ongoing Dark Energy Survey, which is systematically mapping the distribution of dark matter and dark energy.
Subsequently, they conducted cosmological simulations utilizing each of the CMB and BAO datasets independently, prior to their amalgamation. Their analysis incorporated an additional element: the inclusion of neutrino-dark matter scattering events.
The outcomes indicated a moderate inclination towards scattering within the individual datasets, portraying a universe that bore a somewhat closer resemblance to our present-day cosmos in simulations incorporating scattering compared to those without. However, this inclination was significantly more pronounced when the combined datasets were analyzed, achieving a confidence level of 3 sigma.
While far from definitive, this result aligns with prior findings and is sufficiently robust to warrant further scrutiny.
“Should this interaction between dark matter and neutrinos be substantiated, it would represent a fundamental paradigm shift,’ states theoretical physicist and cosmologist William Giarè of the University of Hawaiʻi, who was formerly associated with the University of Sheffield.
“It would not only illuminate a persistent divergence between disparate cosmological probes but also furnish particle physicists with a concrete avenue for inquiry, specifying the characteristics to investigate in laboratory experiments to finally unveil the true nature of dark matter.”
The word “if” carries significant weight in this context, yet the profound perplexity of these unresolved issues renders this line of investigation exceptionally compelling.
“To elucidate and rigorously scrutinize such a distinct effect necessitates venturing beyond the conventional approximations employed in particle cosmology,” concludes theoretical physicist Sebastian Trojanowski of the Polish National Centre for Nuclear Research, “which will constitute the focus of subsequent research endeavors.”
These findings have been disseminated in the esteemed journal Nature Astronomy.
