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Category: cosmology

In the new study, however, these shapes appeared in calculations describing the energy radiated as gravitational waves when two black holes cruised past one another. This marks the first time they’ve appeared in a context that could, in principle, be tested through real-world experiments.

Mogull likens their emergence to switching from a magnifying glass to a microscope, revealing features and patterns previously undetectable. “The appearance of such structures sheds new light on the sorts of mathematical objects that nature is built from,” he said.

These findings are expected to significantly enhance future theoretical models that aim to predict gravitational wave signatures. Such improvements will be crucial as next-generation gravitational wave detectors — including the planned Laser Interferometer Space Antenna (LISA) and the Einstein Telescope in Europe — come online in the years ahead.

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A team of researchers from TU Dortmund University, the University of Paderborn, and the University of Nottingham has developed a new optical method to detect ultra-weak atomic motion. Their experiment performed in Dortmund has demonstrated unprecedented sensitivity of the detection of atomic motion in crystals by exploiting light interference.

The findings, recently published in Nature Materials, open new ways for studying ultrafast processes in materials.

Precise optical measurements rely on interferometers, where the beam probing a distance of interest interferes with a reference beam traveling a fixed path. This allows for assessing the path length difference of the two beams with high precision. A striking example is gravitational interferometers, which detect induced by a distant event in the universe, such as the collision of black holes.

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High-energy particles or gamma rays are usually needed to kick an atomic nucleus up to a higher-energy state. But last year, scientists excited thorium-229 nuclei with just laser light (see Viewpoint: Shedding Light on the Thorium-229 Nuclear Clock Isomer). Laser-excited nuclei could be useful for making precise timekeepers and sensitive quantum sensors. And now, Wolfram Ratzinger at the Weizmann Institute of Science in Israel and his colleagues have shown how these nuclei also provide a way to detect certain speculative particles that may constitute dark matter [1].

Several models of dark matter involve axions or other extremely light bosons. Thanks to their lightness, these particles would have to be abundant—so much so that they would collectively behave like a classical field, oscillating at a frequency proportional to their mass. The particles’ interactions with the building blocks of nuclei—quarks and gluons—would cause various nuclear properties to oscillate at that same frequency. Among those properties is the energy of the photon emitted by an excited thorium-229 nucleus. Crucially, the oscillations in that energy are predicted to be much more pronounced, and therefore easier to detect, than those in other properties.

Ratzinger and his colleagues conducted the first-ever search for these oscillations in a previously reported spectrum of light emitted by excited thorium-229 nuclei. Finding no oscillations, the researchers set upper limits on the coupling strength of ultralight dark matter particles to quarks and gluons for particles ranging in mass from 10–20 to 10–13 eV. These limits are less stringent than those obtained through other means, but the team anticipates that ongoing and future experiments could set much stronger and possibly decisive constraints.

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In a new study published in Physical Review Letters, scientists have estimated a new lower bound on the mass of ultra-lightweight bosonic dark matter particles.

Purported to make up about 85% of the matter content in the universe, dark matter has eluded direct observation. Its existence is only inferred by its gravitational effects on cosmic structures.

Because of this, scientists have been unable to identify the nature of dark matter and, therefore, its mass. According to our current model of quantum mechanics, all fundamental particles must be either fermions or bosons.

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As searches for the leading dark matter candidates—weakly interacting massive particles, axions, and primordial black holes—continue to deliver null results, the door opens on the exploration of more exotic alternatives. Guanming Liang and Robert Caldwell of Dartmouth College in New Hampshire have now proposed a dark matter candidate that is analogous with a superconducting state [1]. Their proposal involves interacting fermions that could exist in a condensate similar to that formed by Cooper pairs in the Bardeen-Cooper-Schrieffer theory of superconductivity.

The novel fermions considered by Liang and Caldwell emerge in the Nambu–Jona-Lasinio model, which can be regarded as a low-energy approximation of the quantum chromodynamics theory that describes the strong interaction. The duo considers a scenario where, in the early Universe, the fermions behave like radiation, reaching thermal equilibrium with standard photons. As the Universe expands and the temperature drops below a certain threshold, however, the fermions undergo a phase transition that leads them to pair up and form a massive condensate.

The proposed scenario has several appealing features, say Liang and Caldwell. The fermions’ behavior would be consistent with that of the cold dark matter considered by the current standard model of cosmology. Further, the scenario implies a slight imbalance between fermions with different chiralities (left-and right-handed). Such an imbalance might be related to the yet-to-be-explained matter–antimatter asymmetry seen in the Universe. What’s more, the model predicts that the fermions obey a time-dependent equation of state that would produce unique, potentially observable signatures in the cosmic microwave background (CMB) radiation. The researchers suggest that next-generation CMB measurements—by the Simons Observatory and by so-called stage 4 CMB telescopes—might reach sufficient precision to vet their idea.

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A study by Dartmouth researchers proposes a new theory about the origin of dark matter, the mysterious and invisible substance thought to give the universe its shape and structure. They say the hypothetical force shaping the universe sprang from particles that rapidly condensed, like steam into water.

The researchers report in Physical Review Letters that could have formed in the early life of the universe from the collision of high-energy massless particles that lost their zip and took on an incredible amount of mass immediately after pairing up, according to their mathematical models.

Hypothetical dark matter is believed to exist based on observed gravitational effects that cannot be explained by visible matter. Scientists estimate that 85% of the universe’s total mass is dark matter.

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