Prof. Stefano Profo proposes a mirror universe with black hole-like remnants—or gravitational creation from cosmic horizons—as possible sources of dark matter, based on established and testable physics.
Two new theories propose that dark matter was created either in a hidden “mirror” universe, or from quantum radiation from the cosmic horizon during the early universe.
One idea imagines a hidden “mirror universe” with its own particles and forces, in which the early cosmos forged tiny, very dense, black hole-like objects that may make up all the dark matter in the universe.
Another idea suggests that dark matter grew out of the rapid expansion of the universe, born from quantum radiation at the edge of the observable universe in a short but dramatic period after the Big Bang.
Both possibilities are based on established physics and offer testable explanations, continuing UCSC's tradition of connecting the smallest particles to the greatest cosmic mysteries.
What is the particle nature of dark matter?
Two new papers by Professor Stefano Profumo of the University of California, Santa Cruz, explore bold possibilities for solving one of the great mysteries of modern physics: the particle identity of dark matter.
A wealth of evidence suggests that this elusive entity, which makes up about 80% of all matter in the universe, is real. Its gravitational pull explains how galaxies hold together and why they rotate as they do. Clues from the super-arrangement of galaxies and precise measurements of the cosmic microwave background also point to the existence of something unknown filling the cosmic void.
What science still doesn’t know is how dark matter was created, or what particles it’s made of. These are questions that preoccupy theorists like Profumo. In his recent work, he approaches the problem from two different angles, both of which assume that dark matter grew “naturally” in the extreme conditions of the early universe, and not necessarily as a new particle interacting with ordinary matter in ways that we can now detect.
Shady Sources: Mirror Universe
In the more recent study, published July 8 in Physical Review D, Profumo examines whether dark matter was created in a “hidden sector”—in effect, a mirror universe with its own versions of particles and forces. This invisible shadow world would still obey many of the same physical principles that govern our cosmos.
The idea is based on quantum chromodynamics (QCD), the framework that describes how quarks bind together inside protons and neutrons using the strong nuclear force. UCSC has a long history in the field: Emeritus Professor Michael Dayne pioneered theoretical models of the QCD axion, one of the leading candidates for dark matter, while Research Professor Abe Seiden was a central figure in experiments that probed the structure of hadrons (particles made of quarks) in high-energy physics.
Black hole-like remnants as dark matter
In his new work, the strong force is replicated in the dark sector as a confining “dark QCD” theory, with its own particles—dark quarks and dark gluons—that bind together to form composite heavy particles called dark baryons. Under certain conditions in the early universe, these dark baryons can become so dense and heavy that they gravitationally collapse into tiny, stable objects that resemble—or behave like—black holes.
Such black hole-like remnants would be only a few times heavier than the fundamental mass scale of quantum gravity—the “Planck mass.” But if they were created in sufficient quantities, they could account for all of the dark matter known today. Because their interaction is purely gravitational, they are undetectable in particle detectors—but their presence shapes the universe on large scales.
This scenario offers a new and testable framework based on well-established physics, continuing UCSC's tradition of using deep theoretical principles to tackle one of the great open questions in cosmology.
Dark matter from the horizons of the universe
In another study, published in May, Profumo examines whether the production of dark matter could result from the expanding “cosmic horizon” of the universe—the cosmological equivalent of the event horizon of a black hole.
The article asks: If the universe underwent a brief period of accelerated expansion after inflation — less extreme than inflation, but still faster than radiation or matter would allow — could that phase have “radiated” particles into existence?
Using principles from quantum field theory in curved spacetime, the paper shows that a wide range of dark matter masses can be created in this mechanism, depending on the temperature and duration of the phase. Importantly, Profumo says, the idea requires no assumptions about dark matter interactions—only that it is stable and gravitationally created. The inspiration comes from the way observers near cosmic horizons, such as those of a black hole, “see” thermal radiation due to quantum effects.
Beyond accepted particle models
“Both mechanisms are highly speculative,” says Profumo, deputy director for theoretical physics at the Santa Cruz Institute for Particle Physics, “but they offer independent and calculable scenarios that do not rely on conventional particle models of dark matter, which are under increasing pressure due to the lack of experimental signals.”
Profumo could be said to have “written the book” on the search for the nature of dark matter. His 2017 textbook, An Introduction to Particle Dark Matter, presents current methods developed by researchers for building dark matter models and testing them in experiments, cosmological observations, and astrophysical phenomena at high energies.
The book describes the “dark matter paradigm” as one of the key developments at the interface between cosmology and particle physics, and is intended for anyone interested in the microscopic nature of dark matter as it is expressed in particle experiments, cosmological observations, and high-energy astrophysics in the early universe.
Profumo says the latest publications continue this tradition, exploring ideas that connect deep questions in particle physics with behavior on cosmic scales. “And they do so by drawing on familiar physics—from quantum field theory in curved spacetime to the familiar properties of SU(N) gauge theories—and extending them to new horizons,” he said.
Both studies appeared in Physical Review D, the leading journal of the American Society for Theoretical Particle Physics.
References:
“Dark baryon black holes” by Stefano Profumo, May 9, 2025, Physical Review D.
DOI: 10.1103/PhysRevD.111.095010
“Dark matter from quasi–de Sitter horizons” by Stefano Profumo, July 8, 2025, Physical Review D.
DOI: 10.1103/vmw2-4k77
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One response
The most amazing thing about the picture is the background on which the delusional theory is based.