New Limits on Ultralight Axion Dark Matter with Gravitational Lensing

Researchers have used gravitational lensing data from the cosmic microwave background (CMB) to set the tightest limits to date on the abundance of ultralight axions (ULAs) within a specific mass range. ULAs are promising dark matter candidates that arise in various extensions of the Standard Model of particle physics. This study combines recent measurements from the Planck, Atacama Cosmology Telescope (ACT), and South Pole Telescope (SPT-3G) with a nonlinear clustering model calibrated by state-of-the-art simulations for ULAs. Ultralight axions with masses $m_\mathrm{a} \lesssim 10^{-27}$ eV were already strongly constrained by previous CMB temperature and polarization observations. This new analysis focuses on the mass range $10^{-26}\,\mathrm{eV}\leq m_\mathrm{a}\leq 10^{-24.5}\,\mathrm{eV}$, where ULAs could alleviate observed tensions in matter clustering inference if they constituted a small percentage of the universe's total dark matter. The results show that ULAs with a mass of $10^{-26}$ eV account for less than 1.5% of dark matter, while those with $10^{-25}$ eV constitute less than 9%, both at a 95% confidence level. Although a slight preference for a non-zero axion density at $10^{-24.5}$ eV with a significance of $2.1\sigma$ was identified, the authors note that this signal is primarily driven by a few data points. Therefore, further investigation into the nonlinear physics of ULAs is required to definitively confirm or rule out this possible signal. These findings are crucial for refining dark matter models and guiding future searches for these elusive particles.

Modeling Cosmological Tracers in Modified Gravity with HEFT

Modern cosmology relies on the analysis of large galaxy surveys to understand the large-scale structure of the universe. A crucial aspect is the modeling of the power spectrum of biased tracers (galaxies), which do not perfectly reflect the distribution of dark matter. For decades, perturbative templates have been developed in Eulerian and Lagrangian frameworks for the standard cosmological model $\Lambda$CDM. However, to go beyond $\Lambda$CDM and explore modified gravity theories, more sophisticated tools are required that can accurately handle nonlinear regimes. This work addresses the implementation of the biased perturbative expansion, within the local Lagrangian bias scheme, in the framework of the Hybrid Effective Field Theory (HEFT). HEFT combines perturbation theory with dark matter simulations to model the nonlinear regime. The researchers focused on $f(R)$ gravity, a modified gravity theory that exhibits scale-dependent growth and a "chameleon screening" effect, making it a particularly challenging scenario for Lagrangian perturbation theory calculations and for generating accurate numerical simulations. The authors present a detailed description of the elements necessary to analytically calculate biased power spectra with loop corrections. These analytical predictions are compared with the results of fully non-perturbative simulations, validating the approach. Finally, they propose a strategy to extend existing HEFT-based emulators for $\Lambda$CDM, such as \texttt{bacco} and \texttt{Aemulus}, to cosmologies beyond the standard model, opening the door to a more robust analysis of data from future galaxy surveys in the context of modified gravity theories.

Jessica Dempsey takes the helm at SKA Observatory

Jessica Dempsey has been appointed as the new Director-General of the Square Kilometre Array Observatory (SKAO), the world's largest and most sensitive radio telescope project. This appointment marks a milestone in the construction and future operation of a global scientific infrastructure that promises to revolutionize our understanding of the universe. The SKAO is designed to explore the cosmos with unprecedented sensitivity and resolution, allowing astronomers to study phenomena such as the formation of the first stars and galaxies, the nature of dark matter and dark energy, and the search for extraterrestrial life. With sites in Australia and South Africa, the observatory will combine thousands of antennas to create a collecting area equivalent to one square kilometer. Dempsey's experience in large astronomical projects will be crucial in guiding the SKAO through its construction and commissioning phases, ensuring that the observatory reaches its full scientific potential. The SKAO is expected to begin its initial scientific operations later this decade, opening a new window to the radio-frequency universe.

Roman Space Telescope's main mirror passes final inspection

Engineers at NASA's Goddard Space Flight Center in Greenbelt, Maryland, have completed the final inspection of the Nancy Grace Roman Space Telescope's primary mirror. This crucial component, with a diameter of 2.4 meters, will be responsible for collecting and focusing light from cosmic objects, allowing Roman to capture wide panoramas of the universe. This milestone represents a fundamental step in the assembly of the observatory, which is expected to revolutionize our understanding of dark energy, dark matter, and exoplanet formation. Roman's primary mirror is a high-precision optical element, designed to operate in a vacuum and at cryogenic temperatures. Its manufacturing and polishing have required advanced techniques to ensure a nearly perfect surface, essential for obtaining sharp and detailed images. The completion of this inspection confirms that the mirror meets the strict performance specifications required for the mission's ambitious scientific goals. The quality of this mirror is comparable to that of the Hubble Space Telescope, but with a field of view 100 times larger, which will allow for much more efficient mapping of vast regions of the sky. The successful completion of this inspection paves the way for the integration of the mirror into the rest of the telescope's structure. Once assembled and launched, the Roman Telescope will conduct large-scale surveys to study the expansion of the universe, search for exoplanets using gravitational microlensing, and characterize the atmospheres of distant worlds. Data collected by Roman is expected to complement and expand on findings from other missions such as the James Webb Space Telescope, providing an unprecedented view of the structure and evolution of the cosmos.

Journey to the Heart of a Galaxy Cluster

The European Space Agency (ESA) has released an image simulating a fly-through to the center of a galaxy cluster. This visualization, based on real data from telescopes such as Hubble and Chandra, offers a unique perspective on the distribution of dark matter and hot gas in these massive cosmic structures. Although the image is an artistic representation, it draws on astronomical observations to illustrate the complexity and scale of galaxy clusters, which are the largest structures in the universe held together by gravity. Galaxy clusters are characterized by containing hundreds or even thousands of galaxies, vast quantities of extremely hot intergalactic gas that emits X-rays, and a dominant fraction of dark matter. Dark matter, which does not interact with light, is only detected through its gravitational effects and constitutes most of a cluster's mass. The hot gas, meanwhile, can reach temperatures of millions of Kelvin and is a crucial component for understanding the dynamics and evolution of these structures. This visual simulation not only serves as an outreach tool but also underscores the importance of combining data from different wavelengths (optical, X-ray) to reconstruct a complete picture of the cosmos. The ability to virtually "travel" through these structures allows scientists and the public to better appreciate the intricate interaction between visible and invisible matter, and how gravity shapes the universe on its largest scales. These visualizations are fundamental for astrophysics research and education, offering new ways to explore the complex data obtained by space observatories.

Gravitational waves from binary black holes could reveal dark matter

Scientists have proposed a new model that would allow for the detection of dark matter from gravitational waves emitted by merging black holes. This approach suggests that the characteristics of these waves, detectable by observatories such as LIGO and Virgo, could contain distinctive "fingerprints" of the interaction between black holes and the surrounding dark matter. Dark matter, which constitutes approximately 27% of the universe, does not interact with light or other forms of electromagnetic radiation, making it extremely difficult to detect directly. Therefore, its study relies primarily on its gravitational effects. The model focuses on how dark matter could alter the orbital dynamics of black holes before their merger. If black holes are immersed in a dense halo of dark matter, it could exert a frictional force on them, subtly modifying the phase and amplitude of the emitted gravitational waves. These modifications would be small but, in principle, detectable with current and future detector sensitivity. The proposal opens a new window for the search for dark matter, complementing traditional methods based on direct particle detection or the observation of large-scale gravitational effects in galaxies and clusters. The ability to discern these small perturbations in gravitational wave signals will require very precise data analysis and comparison with detailed theoretical models of black hole mergers in the absence of dark matter. If such signatures were detected, it would not only confirm the existence of dark matter but also provide crucial information about its properties, such as its local density and its interaction with gravity in extreme environments. This method could offer a unique perspective on the nature of one of the greatest unknowns in modern physics.

Superconducting Bolometer Achieves Sub-zeptojoule Resolution

Researchers have developed a new superconducting bolometer capable of detecting energies with a resolution below one zeptojoule (10^-21 J). This breakthrough represents a significant improvement in the sensitivity of energy detectors, surpassing the limits of current devices. The ability to measure such minuscule amounts of energy opens new possibilities in the field of quantum physics and other areas where the detection of low-energy events is crucial. The development of this bolometer is part of the continuous search for more sensitive instruments for fundamental and applied research. Bolometers, which measure absorbed energy by a change in temperature, are fundamental in various applications, from astronomy to particle physics. The sub-zeptojoule resolution achieved by this new device positions it as a promising tool for experiments requiring extreme energy precision, such as the detection of single photons or the characterization of quantum states. The technology employed in this bolometer is based on superconductivity properties, which allow for highly efficient energy detection with minimal noise. The ability to operate at these sensitivities could have important implications for the development of quantum computing, where precise detection of energy states is essential. Furthermore, it could find applications in high-resolution spectroscopy and in the search for dark matter particles, where interactions are extremely weak and produce very low energy signals.

Emergent Neutrino Geometry in the Scotogenic Dark Matter Model

Researchers have explored the emergence of approximate structures in the neutrino mass matrix within the minimal scotogenic model. The study, based on extensive Casas-Ibarra parameter explorations, demonstrates that approximate suppressions in the neutrino texture can arise dynamically from phenomenological consistency conditions, rather than requiring externally imposed flavor symmetries. This finding suggests that the complex interactions between dark matter and lepton flavor violation are crucial for understanding the nature of neutrino masses. The scotogenic model is a theoretical framework that explains neutrino mass and the existence of dark matter through a dark sector that minimally interacts with the Standard Model. The radiative generation of neutrino mass, along with dark matter relic density requirements and lepton flavor violation (LFV) observations, induces a non-trivial flavor geometry in the parameter space. Specifically, particular suppressions in the (eμ) and (eτ) sectors have been observed to naturally emerge, while the diagonal entries of the mass matrix strongly resist any cancellation. The analysis also compared normal and inverted mass hierarchies for neutrinos, and examined reduced versus complete Casas-Ibarra geometries. Approximate scaling relations linking dark matter and flavor observables were identified, providing a unified framework for understanding these seemingly disparate phenomena. The results suggest that emergent flavor structures could be a dynamic consequence of radiative neutrino mass generation, opening new avenues for research in particle physics and cosmology.

Photon rings in black holes could reveal axions

Researchers have explored the conversion of photons into axions in the vicinity of rotating Kerr black holes, a phenomenon that could manifest as a dimming of the spectral luminosity of the photon ring. This process is favored by the intense gravity of these objects, which traps photons in nearly circular trajectories, significantly increasing their effective path length. Photon-axion conversion, driven by ambient magnetic fields, is predicted to be particularly efficient around supermassive black holes like M87*, where photon luminosity scales with the black hole's mass. The study analyzes how various parameters influence the conversion probability and the consequent dimming of spectral luminosity. These include photon frequency, axion mass, photon-axion coupling, magnetic field strength, plasma density, and black hole spin. The results indicate that conversion is more efficient at high frequencies, such as X-rays and gamma rays. Furthermore, the frequency window for efficient conversion broadens with stronger photon-axion coupling and narrows with lower electron density and lower axion mass. The magnitude of the spectral luminosity dimming primarily depends on the magnetic field, photon-axion coupling, and black hole spin; rotating black holes show amplified dimming compared to static ones. This work suggests that future observations with high-resolution telescopes, approximately 10⁻⁵ arcseconds in the X-ray/gamma-ray band, could detect this dimming. If confirmed, such measurements would provide valuable constraints on the axion mass and its coupling to photons. Axions are hypothetical particles that could solve the strong CP problem in quantum chromodynamics and are candidates for dark matter. Detecting this effect in photon rings would offer a unique experimental avenue to search for these elusive particles in extreme astrophysical environments.

Solving a Dark Matter Detector Mystery for Quantum Computing

Researchers at Lawrence Berkeley National Laboratory have unraveled an enigma in dark matter detectors that could have significant implications for the development of quantum computers. The study focuses on the interaction of light with superconducting materials, a crucial phenomenon for both the detection of dark matter particles and the stability of superconducting qubits. Understanding how visible and infrared light generates quasiparticles in these materials is fundamental to mitigating noise and improving coherence in quantum systems. The problem addressed stems from the observation that superconducting dark matter detectors, designed to be extremely sensitive to small amounts of energy, are susceptible to noise generated by low-energy photons, such as ambient light. These photons, even at very low levels, can break Cooper pairs in the superconductor, creating quasiparticles that mimic dark matter signals or introduce errors in qubits. Previous research had identified this problem, but the precise magnitude and mechanism of quasiparticle generation by low-energy photons were not entirely clear, limiting the ability to design more robust systems. The Berkeley Lab team has developed a detailed model and conducted experiments to characterize how visible and infrared light interacts with superconductors. They have quantified the efficiency with which low-energy photons can generate quasiparticles, revealing that even a small amount of light can have a disproportionate impact. This knowledge is not only vital for designing more sensitive and noise-free dark matter detectors but also offers a pathway to protect superconducting qubits, which are extremely sensitive to external disturbances, from light-induced decoherence. The ability to control and mitigate this effect is a crucial step towards building more stable and scalable quantum computers.