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An artistic illustration of the mechanism proposed by Professor Stefano Profumo where quantum effects near the rapidly expanding cosmic horizon after the Big Bang gravitationally generate dark matter particles. Credit: Stefano Profumo<\/p>\n
Two recent studies by Professor Stefano Profumo at the University of California, Santa Cruz, propose theories that attempt to answer one of the most fundamental open questions in modern physics: What is the particle nature of dark matter?<\/p>\n
Science has produced overwhelming evidence that the mysterious substance, which accounts for 80% of all matter in the universe, exists. Dark matter’s presence explains what binds galaxies together and makes them rotate. Findings such as the large-scale structure of the universe and measurements of the cosmic microwave background also prove that something as-yet undetermined permeates all that darkness.<\/p>\n
What remains unknown are the origins of dark matter, and hence, what are its particle properties? Those weighty questions primarily fall to theoretical physicists like Profumo. And in two recent papers, he approaches those questions from different directions, but both centered on the idea that dark matter might have emerged naturally from conditions in the very early universe\u2014rather than dark matter being an exotic new particle that interacts with ordinary matter in some detectable way.<\/p>\n
Shadowy origins<\/p>\n
The most recent study<\/a>, published on July 8 in Physical Review D, explores whether dark matter could have formed in a hidden sector\u2014a kind of “mirror world” with its own versions of particles and forces. While completely invisible to humans, this shadow sector would obey many of the same physical laws as the known universe.<\/p>\n The idea draws inspiration from quantum chromodynamics<\/a> (QCD), the theory that describes how quarks are bound together inside protons and neutrons by the strong nuclear force. UC Santa Cruz has deep roots in this area: Emeritus physics professor Michael Dine helped pioneer theoretical models<\/a> involving the QCD axion, a leading dark matter candidate, while research professor Abe Seiden contributed to major experimental efforts probing the structure of hadrons\u2014particles made of quarks\u2014in high-energy physics experiments.<\/p>\n In Profumo’s new work, the strong force is replicated in the dark sector as a confining “dark QCD” theory, with its own particles\u2014dark quarks and dark gluons\u2014binding together to form heavy composite particles known as dark baryons. Under certain conditions in the early universe, these dark baryons could become dense and massive enough to collapse under their own gravity into extremely small, stable black holes\u2014or objects that behave much like black holes<\/a>.<\/p>\n These black hole\u2013like remnants would be just a few times heavier than the Planck mass\u2014the fundamental mass scale of quantum gravity\u2014but if produced in the right quantity, they could account for all the dark matter observed today. Because they would interact only through gravity, they would be completely invisible to particle detectors\u2014yet their presence would shape the universe on the largest scales.<\/p>\n This scenario offers a new, testable framework grounded in well-established physics, while extending UC Santa Cruz’s long-standing exploration of how deep theoretical principles might help explain one of the biggest open questions in cosmology.<\/p>\n On the horizon<\/p>\n Profumo’s other recent study<\/a>, published in May in the same journal, explores whether dark matter might be produced by the universe’s expanding “cosmic horizon”\u2014essentially, the cosmological equivalent of a black hole’s event horizon.<\/p>\n \n Discover the latest in science, tech, and space with over 100,000 subscribers who rely on Phys.org for daily insights. This paper asks, if the universe underwent a brief period of accelerated expansion after inflation\u2014something less extreme than inflation, but still expanding faster than radiation or matter would allow\u2014could that phase itself have “radiated” particles into existence?<\/p>\n Using principles from quantum field theory<\/a> in curved spacetime, the paper shows that a wide range of dark matter masses could result from this mechanism, depending on the temperature and duration of this phase.<\/p>\n Importantly, Profumo said this doesn’t require any assumptions about how the dark matter interacts\u2014only that it is stable and produced gravitationally. The idea is inspired by the way observers near cosmic horizons, like those of a black hole, perceive thermal radiation due to quantum effects.<\/p>\n “Both mechanisms are highly speculative, but they offer self-contained and calculable scenarios that don’t rely on conventional particle dark matter models, which are increasingly under pressure from null experimental results,” said Profumo, who is also deputy director for theory at the Santa Cruz Institute for Particle Physics.<\/p>\n One could say Profumo wrote the book on the quest to understand the nature of dark matter. His 2017 textbook<\/a> “An Introduction to Particle Dark Matter” presents lessons that he personally learned and used in his research work from state-of-the-art techniques that scientists have developed over the years to build and test particle models for dark matter.<\/p>\n The book describes the “paradigm of dark matter” as “one of the key developments at the interface of cosmology and elementary particle physics,” and is intended for anyone interested in the microscopic nature of dark matter<\/a> as it manifests itself in particle physics experiments, cosmological observations, and high-energy astrophysical phenomena.<\/p>\n Researchers here have played a key role in cosmology for decades, contributing to the development of the standard Lambda-Cold Dark Matter model\u2014still the best fit to all cosmological data\u2014and to the theoretical and observational study of how structure forms in the universe. In addition, UC Santa Cruz has long supported a close interplay between theory and observation, with strengths in particle physics, astrophysics, and early universe cosmology.<\/p>\n Profumo said these recent publications continue in that tradition, exploring ideas that connect the deepest questions in particle physics with the large-scale behavior of the cosmos. “And they do so in a way that remains rooted in known physics\u2014whether quantum field theory in curved spacetime, or the well-studied properties of SU(N) gauge theories\u2014while extending them to new frontiers,” he said.<\/p>\n More information: Stefano Profumo, Dark baryon black holes, Physical Review D (2025). DOI: 10.1103\/PhysRevD.111.095010<\/a><\/p>\n \n\t\t\t\t\t\t\t\t\t\t\t\t\tProvided by \t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/a>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/p>\n \n\t\t\t\t\t\t\t\t\t\t\t\tCitation: \n\t\t\t\t\t\t\t\t\t\t\t This document is subject to copyright. 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\n\t\t\t\t\t\t\t\t\t\t\t\tStefano Profumo, Dark matter from quasi\u2013de Sitter horizons, Physical Review D (2025). DOI: 10.1103\/vmw2-4k77<\/a>\n<\/p>\n
\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\tUniversity of California – Santa Cruz<\/a>
\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/p>\n
\n\t\t\t\t\t\t\t\t\t\t\t\tTheories on dark matter’s origins point to ‘mirror world’ and universe’s edge (2025, August 4)
\n\t\t\t\t\t\t\t\t\t\t\t\tretrieved 5 August 2025
\n\t\t\t\t\t\t\t\t\t\t\t\tfrom https:\/\/phys.org\/news\/2025-08-theories-dark-mirror-world-universe.html\n\t\t\t\t\t\t\t\t\t\t\t <\/p>\n
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