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To discover new physics, AI may need to ‘unlearn’ the old one

A study in the Journal of Cosmology and Astroparticle Physics explores how a machine-learning strategy known as transfer learning could dramatically reduce the computational cost of searching for new physics beyond the standard cosmological model—while also revealing an unexpected risk: Sometimes AI systems can become too reliant on what they already know.

Artificial intelligence is widely used in cosmology to analyze the universe. But testing theories beyond the standard cosmological model, known as ΛCDM, remains extremely computationally demanding.

Although ΛCDM successfully describes many properties of the universe—from its expansion to the distribution of galaxies—physicists know it is probably incomplete. Recent observations hint that phenomena such as massive neutrinos, modified gravity or evolving dark energy could point toward new physics beyond the current model.

Physicists observe synchronized quantum dance of excitons and phonons

An international team of researchers has reported a major advance in understanding quantum dynamics in semiconductor materials. They directly observed how excitons and phonons evolve together in perovskite nanocrystals, revealing a fully coherent quantum dance between light-induced electronic excitations and crystal lattice vibrations. They published their findings in Nature Communications.

An exciton is created when light excites an electron inside a semiconductor. The electron absorbs energy and leaves behind a positively charged “hole”; the two bind together and move through the crystal as a single quantum object. A phonon is a different kind of quantum object, as it is a quantum of crystal lattice vibration. Though fundamentally different objects, in perovskites they are strongly linked and evolve together as a coupled quantum system.

Perovskite nanocrystals are miniature crystals only a few nanometers in size, a thousand times smaller than the thickness of a hair. Each crystal forms a nanoscale “box” that traps both excitons and phonons. This confinement makes the interaction between them especially strong: An exciton inside the nanocrystal is tightly coupled to vibrations of the surrounding crystal lattice.

How a single mutation rewired a 23-species bacterial community over four years

The time-development of species communities cannot be understood solely through ecological interactions or environmental factors, as evolution can also alter community dynamics. This observation helps to understand, among other things, the consequences of antibiotic resistance.

Evolution can alter the composition of communities, but its effects are difficult to investigate in nature, as they begin to manifest only after long periods of time. However, the rapid pace of microbial reproduction makes it possible to observe evolution in the laboratory “in real time,” from one generation to the next.

“In studies focusing on the microbiome, using synthetic microbial communities, as we did in this study, has opened up new avenues for investigating key questions related to complex communities,” says Professor Teppo Hiltunen from the University of Turku.

Possible dark matter-deficient twins discovered in the Fornax Cluster

Astronomers have identified a possible new example of one of the universe’s strangest galaxy types: galaxies that appear to contain little or no dark matter. The newly studied pair, FCC 224 and FCC 240, on the outskirts of the Fornax Cluster, share several unusual traits with the only known pair of controversial dark-matter-deficient galaxies. The findings were uploaded to the arXiv preprint server on May 22.

Ultra-diffuse galaxies are faint systems that are roughly the size of the Milky Way but have much less mass, containing far fewer stars. They have sparked debate for more than 10 years, mainly because they have been observed with two contrasting levels of dark matter content.

On one end, the dark-matter-rich ultra-diffuse galaxies are reasonably well understood: These are thought to be “failed galaxies” quenched early, never building much stellar mass but holding on to many globular clusters. The opposite extreme is far stranger. A small number of ultra-diffuse galaxies appear to contain little or no dark matter at all, and the globular clusters they host are unusually bright.

Monolayer WSe₂ unlocks high-performance p-type transistors that could change how future chips balance speed and power

Transistors, small devices that can amplify or switch electrical signals, are central components of all modern computer chips and digital devices. There are two main types of transistors, known as n-type and p-type transistors.

N-type transistors conduct current using electrons (i.e., negatively charged particles), while p-type transistors utilize electron holes (i.e., positively charged spaces in a crystal lattice without electrons).

Electronics engineers worldwide have been exploring different solutions that could help reduce the size of existing transistors without compromising their performance, which could enable the further miniaturization of electronic devices. One promising route is to fabricate transistors using two-dimensional (2D) semiconductors, semiconducting materials that are just a single atom or a few atoms thick.

Hardy ice plant’s optical innovation inspires reflective design possibilities

Nature is filled with remarkable visual phenomena created by microscopic surface structures that interact with light in fascinating ways. The iridescent wings of butterflies, the shimmering feathers of birds and the glossy surfaces of flower petals are all examples of how living organisms control the reflection, absorption and scattering of light. These optical effects are not only visually striking but also serve important biological functions, including attracting pollinators, communication, camouflage and protection from environmental stress. Understanding these naturally occurring photonic structures has become an important area of research, as they provide inspiration for the development of advanced biomimetic materials and optical technologies.

One such example is the hardy ice plant, Delosperma cooperi, a perennial succulent native to South Africa and widely cultivated in Japan. The flower’s petals display a striking glossy appearance, prompting researchers to investigate the mechanism responsible for this effect.

Researchers from Shinshu University, led by professor Hiroshi Moriwaki, conducted this study to understand how the petals generate gloss and whether their surface structure could inspire the design of novel reflective materials. Kazuma Tanabe also was part of the research team. The findings are published in the journal Optical Materials.

Water locked in 1-nanometer channels could enable safer energy storage

Can pure water store electrical energy? A research team led by Dr. Vasily Artemov within the Cluster of Excellence “BlueMat—Water-Driven Materials” at Hamburg University of Technology has now shown that it can. By confining water within nanometer-sized channels in clay minerals, the researchers created a supercapacitor capable of efficiently storing and transporting electrical charge.

What makes the finding unusual is that it uses pure water as its electrolyte—the medium that transports electrical charge. Today’s batteries and supercapacitors typically rely on added salts, acids, or other chemical electrolytes. In contrast, the new system works without such additives and is based solely on abundant, naturally occurring materials: water, clay, and carbon.

“Our goal is to develop safer and more sustainable energy-storage technologies based on abundant materials rather than complex chemical compounds,” says Artemov, lead author of the paper published in Nature Communications. “The device stores and releases energy efficiently, operates at a comparatively high voltage for a water-based system, and remains stable over tens of thousands of charging cycles.”

Mapping brain network changes linked to bipolar disorder severity and treatment

New research from the Mark and Mary Stevens Neuroimaging and Informatics Institute (Stevens INI) at the Keck School of Medicine of USC has discovered subtle but widespread differences in the brain’s communication networks in people with bipolar disorder, offering new insight into how illness severity and treatment may relate to brain wiring.

Published in Biological Psychiatry, the study was led by Leila Nabulsi, Ph.D., a senior research associate at the Stevens INI, together with Dara M. Cannon, Ph.D., professor at the University of Galway, Ireland. The team analyzed brain scans from 449 people with bipolar disorder and 510 healthy controls across 16 international research sites through the ENIGMA Bipolar Disorder Working Group.

This work was made possible by ENIGMA, an international consortium founded and led in part by Paul M. Thompson, Ph.D., associate director of the Stevens INI. ENIGMA brings together researchers worldwide to pool their brain imaging and clinical data, allowing them to detect subtle patterns that would be difficult to identify in smaller studies.

Physicists harness potential of quantum phase transitions

Researchers at University College Dublin and international collaborators have just published a detailed and accessible guide that aims to translate theoretical ideas into practical devices for quantum enhanced sensing technologies.

Conventional sensors have enabled technologies from global positioning systems to satellite imaging. Quantum systems, however, provide the absolute best precision allowable by the laws of physics.

The challenge, however, is that quantum devices are often fragile. A promising theoretical avenue for designing quantum sensors not hindered by this fragility is called “critical quantum sensing.”

Neutron-rich nuclei yield beta-decay clues that could refine heavy-element origin models

How are heavy elements formed in the universe? Extremely neutron-rich atomic nuclei and their beta-decay rates play an important role in this process. Until now, it has been very difficult to determine these rates experimentally. Researchers at TU Darmstadt have developed theoretical predictions for such processes and successfully compared them with experimental data, where they exist. The results were published in Physical Review Letters.

The study focuses on beta-decay rates of neutron-rich nuclei, which are of great importance for element synthesis in the universe. To better understand and predict these decay rates, the team developed modern “ab initio” methods in nuclear physics for these systems. These methods calculate the properties of atomic nuclei directly from the fundamental interactions between their constituents, without making empirical adjustments to known measured values.

The researchers combined modern nuclear forces and decay operators with many-particle methods to precisely determine the structure of nuclei and, from this, the decay rates. A key finding of the work is that the theoretical predictions agree very well with experimental data—in the range where such extremely neutron-rich nuclei can currently be studied at accelerator facilities. The latest experiments on these nuclei took place at the RIKEN research center in Japan.

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