Plasma and Dark Matter Modify Shadows of Bardeen Black Holes

A recent study has explored how the presence of a plasma medium and perfect fluid dark matter (PFDM) affects the optical appearance of a rotating Bardeen black hole. Researchers analyzed three plasma models: homogeneous, radially varying, and with both radial and angular dependence. The results indicate that both plasma and PFDM induce measurable modifications to the black hole's shadow morphology, suggesting that observing these shadows could offer valuable insights into the cosmic environment, in addition to the intrinsic properties of regular black holes. To assess the astrophysical viability of these effects, the plasma and PFDM parameters were constrained using observations from the Event Horizon Telescope (EHT). Specifically, the limits imposed by the EHT on shadow circularity and fractional diameter deviation were employed. These restrictions allowed for the determination of realistic ranges for the environmental parameters, ensuring that the predicted modifications were consistent with current observational data. This work highlights the importance of considering environmental effects when interpreting black hole images. The modifications in the shadow, induced by plasma and dark matter, not only complicate the determination of the black hole's properties itself but also open a new avenue for characterizing its surrounding medium. The ability to discern these environmental influences through the shadow image transforms black holes into natural probes for studying the distribution of matter and energy in their vicinity.

NASA to Preview Roman Space Telescope Before Launch

NASA has scheduled a virtual press conference for July 29 at 2 p.m. EDT to provide a preview of the Nancy Grace Roman Space Telescope mission. The event will be streamed live across various agency platforms and precedes the telescope's launch, which is set for August 30 from the Kennedy Space Center in Florida. The Roman Space Telescope, formerly known as WFIRST (Wide Field Infrared Survey Telescope), is a next-generation space observatory designed to address fundamental questions in astrophysics, including the nature of dark energy, the distribution of dark matter, and the search for exoplanets. Its key feature is a field of view 100 times larger than that of the Hubble Space Telescope in infrared wavelengths, enabling it to efficiently map vast areas of the sky and conduct large-scale surveys with unprecedented resolution.

Correlated Comagnetometry for Precision Measurements of Exotic Fields

Researchers have proposed a new correlated comagnetometry method that promises to significantly enhance sensitivity in detecting magnetic and exotic fields, even at high frequencies. Magnetometers are fundamental tools in science and technology, but their sensitivity is often limited by background magnetic noise. Traditional comagnetometry mitigates this noise through self-cancellation, although its effectiveness diminishes in the high-frequency range. The new proposal addresses this limitation by utilizing two species of alkali atoms within the same cell to cancel ambient magnetic noise across a broad frequency spectrum. The method relies on measuring the phase difference between the light-matter interaction responses of the two atomic species. This phase difference has been shown to be calibration-free and robust against common-mode intensity noise. As a test case, the researchers applied this technique to the detection of dark matter signals, achieving a background noise suppression of up to thirtyfold. This translates to an improvement in the signal-to-noise ratio by an order of magnitude or more, depending on the type of coupling to the hypothetical subatomic particles of dark matter. In addition to its increased sensitivity, correlated comagnetometry allows for differentiation between various theoretical models for exotic fields. This discrimination capability is crucial for precision physics, where identifying the exact nature of an interaction is as important as its detection. The enhanced sensitivity and model differentiation capability open new avenues for exploring subtle physical phenomena and searching for new fundamental interactions, such as those associated with dark matter or very low-mass fields.

Cosmological Models with Energy Exchange Refuted Due to Mathematical Inconsistencies

A new analysis has refuted cosmological models presented in a previous article published in the European Physical Journal C. The critique focuses on several mathematical inconsistencies detected in the original formulation, which invalidate the conclusions regarding nonlinear interactions and energy exchange in the cosmos. This work underscores the importance of mathematical precision in the construction of theoretical models in cosmology. This refuting study identifies key errors, including an incorrect simplification of a Liénard-type equation, the unjustified omission of integration constants, and an erroneous use of the variation-of-parameters method. By correcting these deficiencies and deriving the exact analytical solutions, the authors demonstrate that the revised mathematical framework fundamentally contradicts the claims of the original article. This implies that previous conclusions about cosmological dynamics under these interactions are not valid. The original research proposed scenarios where energy could be exchanged between different components of the universe in a nonlinear fashion, which could have implications for understanding dark matter, dark energy, and the evolution of the universe. However, the current re-evaluation suggests that such interactions, as modeled, cannot be mathematically sustained. This type of critical review is essential for the advancement of theoretical physics, ensuring the robustness of the foundations upon which new hypotheses and models are built.

New Model for Particle Production in Cosmic Bubble Collisions

Researchers have developed a new formalism to describe particle production during ultra-relativistic bubble collisions, a key phenomenon in cosmological phase transitions. This process can generate particles much heavier than the phase transition scale. The new approach addresses shortcomings of previous models, which parametrically overestimated hard particle production and showed dependence on gauge and field-space coordinate choices, thus compromising the robustness of their predictions. The proposed formalism offers a more precise and consistent description of these events. The new model is based on an analogy with the partonic description of high-energy collisions. In the ultra-relativistic limit, colliding bubbles undergo nearly free passage, and hard particle production arises from on-shell scatterings among the quanta constituting the Lorentz-contracted walls. This approach considers on-shell interactions, in contrast to previous models that relied on the off-shell decay of the scalar background. The application of this formalism has been extended to the study of heavy scalar, fermion, and vector particle production. This advancement has significant implications for various areas of physics, including dark matter generation, leptogenesis (a process that could explain the matter-antimatter asymmetry in the universe), graviton production, and the formation of primordial gravitational waves. The development of this more precise model is crucial for refining our understanding of the fundamental processes that occurred in the early universe.

LISA could detect low-mass dark matter halos via gravitational lensing

A new study proposes that the future space-based gravitational wave observatory LISA (Laser Interferometer Space Antenna) could detect low-mass dark matter halos, with masses between 10 and 10,000 solar masses (M☉). These halos, predicted by cold dark matter models, are sensitive to the fundamental nature of dark matter and the primordial power spectrum, but have remained undetected until now. The proposal is based on the wave-optics lensing effect that multiple dark matter halos would produce on gravitational waves. The method focuses on the statistical properties of stochastic diffraction, a phenomenon that would imprint correlated fluctuations on the amplitude and phase of the original gravitational waveforms. These stochastic distortions can be described by an orthogonal basis that captures the dominant "tones" associated with dark matter properties, a concept termed "dark timbre." This timbre is not degenerate with binary gravitational wave source parameters, allowing for their distinction. LISA would be particularly sensitive to dark matter halos in this mass range. Although the per-event signal would be very weak, on the order of 10⁻³ in the cold dark matter model, the study suggests that stacking the signals from 50 to 500 loud binaries (gravitational wave sources) could confirm the existence of these halos with a statistical significance of 2 to 5 standard deviations (σ). This would require major advances in waveform accuracy and data analysis techniques. Even without reaching this direct detection threshold, stochastic diffraction would allow for stringent bounds on models that enhance small-scale structure, such as axion miniclusters or primordial black holes.

Boson Stars Emit More Gravitational Waves Than Black Holes

A numerical relativity study has investigated head-on collisions of boson stars, employing an initial data method inspired by the Bowen-York approach, commonly used to model binary black hole systems. This method allows for the incorporation of information from the early, post-Newtonian inspiral phase in binary coalescences, simplifying the modeling of these cosmic events. The research included testing the method on a single boson star with linear momentum, as well as simulations of head-on collisions between two boson stars and encounters between boson stars and black holes. The results of this study are consistent with previous investigations, validating the effectiveness of the proposed initial data method. A key finding is that head-on collisions between boson stars emit a greater amount of energy in the form of gravitational waves compared to equivalent binary black hole collisions. This contrast suggests fundamental differences in the dynamics of gravitational wave emission between these compact objects. Conversely, head-on collisions between a boson star and a black hole showed less gravitational radiation emission than their binary black hole counterparts. These differences in gravitational wave emission provide valuable insights for gravitational wave astrophysics and the characterization of exotic compact objects such as boson stars, which are candidates for dark matter.

Constraints on dark matter in rotating black hole halos

Researchers have explored how the presence of a Hernquist-type dark matter halo affects the optical properties of a rotating Kerr black hole. The study focused on the spacetime geometry generated by this configuration, deriving the null geodesic equations and effective potentials. This approach allowed for the analysis of three-dimensional photon trajectories around the event horizon and ergoregion, as well as the calculation of critical impact parameters for unstable spherical photon orbits. The team constructed the black hole shadow contours for a distant observer, finding that the rotation parameter primarily shifts and distorts the shadow. However, the presence of the Hernquist dark matter halo significantly increases the photon capture region and, consequently, the apparent size of the shadow. By comparing the area-equivalent shadow diameter with Event Horizon Telescope (EHT) measurements for Sgr A* and M87*, they were able to establish constraints on the dimensionless halo parameter, $\hat{\rho}=M^2\rho$. The strongest restrictions come from Sgr A*, with values of $\hat{\rho}\sim(2.7-3.8)\times10^{-3}$ at $1\sigma$ and $\hat{\rho}\sim(4.1-5.2)\times10^{-3}$ at $2\sigma$. In addition to the shadow analysis, the study examined gravitational lensing in both the strong-field and weak-field regimes. In the strong-field regime, the halo shifts the unstable photon orbit and critical impact parameter, influencing the logarithmic deflection angle and the position of relativistic images. In the weak-field regime, the halo contributes to the leading bending angle and amplifies deviations from the Kerr metric as $\rho$ increases. Using the Einstein ring of ESO325-G004, further constraints were obtained for the parameter $\hat{\rho}$: $0\leq\hat{\rho}\lesssim0.00939$ at $1\sigma$ and $0\leq\hat{\rho}\lesssim0.01963$ at $2\sigma$.

Scotogenic Models Predict New Asymmetries in Lepton Decays

Researchers have re-evaluated a specific class of scotogenic models, known as "T1-2-A", which aim to simultaneously explain neutrino oscillation data and propose a viable dark matter candidate. The study focused on charged lepton flavor violating (cLFV) decays, particularly in rare muon transitions. The results suggest that these models can predict significant rates for cLFV observables, opening new avenues for experimental detection. The work explores in detail the model's parameter space, identifying regions where cLFV rates are appreciable. Furthermore, the scientists have considered the role of parity and time-reversal asymmetries in three-body lepton decays, specifically in processes like $\ell_\alpha^+ \to \ell_\beta^+ \ell_\gamma^+ \ell_\delta^-$. These asymmetries could be experimentally investigated in association with polarized muon and tau decays. The inclusion of these new observables offers complementary information on the "T1-2-A" scotogenic model, providing additional means to test its validity. If these asymmetries or the predicted cLFV rates were detected, it would strengthen the hypothesis that these models can describe phenomena beyond the Standard Model, such as the nature of dark matter and the origin of neutrino masses.

New R-axion model evades cosmological and astrophysical constraints

A recent theoretical study proposes a new model for the R-axion, a hypothetical particle associated with an R-symmetry, which allows for the relaxation of stringent constraints on its decay scale, $f_R$. Traditionally, the Dine-Festuccia-Komargodski (DFK) bound implies that $f_R$ must be comparable to the Planck scale, $M_{\rm Pl}$, for a nearly Minkowski vacuum. However, researchers demonstrate that this inference can be avoided in an effective field theory construction. The team achieves this relaxation by tuning the scalar potential near zero via a mixed F- and D-term uplift, leading to a metastable vacuum. In this scenario, the validity of the effective field theory and the metastability of the small $f_R$ vacuum generically imply a relaxed lower bound for $f_R$, approximately $f_R \gtrsim \sqrt{m_{3/2}M_{\rm Pl}}$. This approach allows the intermediate R-axion to circumvent previous objections. Furthermore, the study highlights that if the R-symmetry has a QCD anomaly, this R-axion could potentially play the role of the QCD axion. A crucial aspect is that with TeV-scale supersymmetry, a value of $f_R \sim 10^{11}$ GeV is obtained. This range not only evades certain astrophysical and cosmological axion constraints but notably lies in the window for which the observed dark matter abundance can be reproduced by the R-axion via the misalignment mechanism. This model offers a new avenue for exploring the nature of dark matter and extensions to the Standard Model.

Vector Dark Matter: Parametric Resonance Requires New Inflationary Conditions

A new study explores the viability of vector dark matter (VDM) production via parametric resonance in a Higgsed Abelian sector. This mechanism, which involves the amplification of a dark-Higgs field to generate VDM particles, critically depends on the initial displacement conditions of the dark-Higgs field. Researchers analyzed this problem using a calibrated nonlinear broad-resonance relic map and a stochastic inflationary analysis of the dark-Higgs condensate. The results show that a minimal light-spectator realization fails under standard inflationary duration. For broad resonance and isocurvature constraints to hold, an initial dark-Higgs field displacement of \( φ_0/H_I \gtrsim 3.3 imes10^4 \) is required, where \( H_I \) is the Hubble scale during inflation. However, stochastic equilibrium and finite-duration random walk only produce \( φ/H_I=\mathcal O(1) \). This large mismatch in initial displacement represents a robust, model-independent obstruction to the stochastic branch of VDM production. The study identifies a distinct, classically sourced branch where the condensate tracks a time-dependent minimum, \( φ_0=κH_*/\sqrt{λ_4} \), induced by a negative Hubble-induced mass. In this scenario, the radial fluctuation remains heavy during inflation. This sourced branch modifies the scaling relation of the dark matter particle mass, \( m_X \), from \( m_X\propto λ_4^{5/8}H_I^{-3/2} \) to \( m_X\propto κ^{-3/2}λ_4 H_*^{-3/2} \). The authors derived the simultaneous consistency conditions for this branch, including broad resonance, adiabatic tracking, perturbativity, sub-Planckian displacement, thermal non-erasure, spectator backreaction, and control of inflationary vector fluctuations. These findings suggest that Higgsed-vector resonance is not merely a dark matter production mechanism, but also a sensitive probe of the inflationary and reheating dynamics that determine its initial conditions. The work opens new avenues for exploring the connection between dark matter physics and early cosmological processes, potentially leading to tighter constraints on inflation models and the nature of dark matter.

Low-scale cosmological phase transitions and gravitational waves

A new study has investigated low-scale cosmological phase transitions within a dark Abelian Higgs sector, a gauge theory model describing spontaneous symmetry breaking. The work was motivated by recent evidence for a stochastic gravitational-wave (GW) background reported by pulsar timing array (PTA) collaborations. Researchers quantified the impact of thermal resummation, higher-order matching corrections, and higher-dimensional operators on the phase-transition thermodynamics and the resulting gravitational wave signal. Their analysis reveals that the parameter region favored by current PTA observations lies close to the boundary of validity of the effective field theory. In this regime, higher-dimensional operators become increasingly important. Despite substantial shifts induced by higher-order thermal corrections, the predicted signal from the model remains disfavored by PTA data, even within the controlled region of the theory. Furthermore, the study delineated parameter regions where the dark and visible sectors are thermally and hydrodynamically coupled or decoupled. It also revisited dark matter phenomenology, identifying asymmetric freeze-out as naturally compatible with both the observed relic abundance and the gauge couplings favored by strong phase transitions. These results underscore the importance of systematically controlled finite-temperature calculations for reliable GW predictions from low-scale cosmological phase transitions.

Chandra Reveals More Extended Spiral Arms in the Milky Way

New observations from NASA’s Chandra X-ray Observatory suggest that the outer spiral arms of the Milky Way extend further than previously thought. This finding could modify our current understanding of our galaxy's structure, challenging existing models of its morphology and size. A team of astronomers made this discovery by precisely measuring the distances to dust clouds, using Chandra data. The observatory's ability to detect X-ray emissions from these distant regions has been crucial for determining their location with unprecedented accuracy. These measurements have allowed for mapping the outermost regions of the spiral arms, revealing a greater extension than expected. The main implication of this research is that the Milky Way might be a larger barred spiral galaxy than previously believed. This not only affects theoretical models of galactic formation and evolution but could also influence the estimation of dark matter distribution and stellar dynamics in peripheral regions. Future research will focus on corroborating these results with other observational techniques and refining galactic structure models.

Euclid reveals millions of stars and thousands of hidden exoplanets in the Milky Way

The ESA's Euclid space telescope has captured an unprecedented view of the Milky Way's center, revealing a mosaic of tens of millions of stars in extraordinary detail. This observation, completed in just 26 hours, not only provides a detailed image of the region but also serves as a map of stellar evolution, from dark clouds where stars are born to ancient populations packed into the galactic bulge. Beyond the visible stars, this dense field of light conceals thousands of exoplanets that cannot be directly observed. Astronomers identify them through gravitational microlensing, a technique that measures tiny, temporary changes in light as one star passes in front of another. This method allows for the detection of planets and even the estimation of their masses based solely on their gravitational effects. Although Euclid was primarily designed to investigate dark matter and dark energy, its capabilities are opening a new window into exploring our own galaxy and the unseen worlds within it. This ability to detect exoplanets via gravitational microlensing in such a dense stellar region underscores the telescope's versatility and its potential to significantly contribute to exoplanetology, in addition to its primary cosmological objectives.

Dark Energy Model with Ghost Condensate and Dark Matter

Scientists have explored the cosmic evolution of a generalized dilatonic ghost condensate field as a dark energy candidate. This model is formulated from a Lagrangian density featuring two dominant kinetic terms—one linear and one of arbitrary integer order $n>2$—combined with an exponential potential. The novelty lies in the field's interaction with dark matter via a source term, allowing for the study of the present universe under different coupling scenarios. The study analyzed three situations: a non-interacting case ($Q=0$) and two specific interaction models ($Q\propto\rho_m\dot\varphi$ and $Q\propto\rho_m H$). For each model, a detailed phase-space analysis was performed to identify critical points and stability conditions. In all scenarios, the system reproduces standard cosmological dynamics, evolving towards late-time dark energy-dominated attractors, exhibiting quintessence or phantom features depending on the sign of the coupling parameter $\alpha$ associated with the standard kinetic term. A joint likelihood analysis was conducted using Cosmic Chronometers, PantheonPlus, and DESI observations for two values of $n$ ($n=3$ and $n=5$). This allowed for the determination of marginalized parameter constraints at 68% and 95% confidence levels for the different $Q$-models. For the interaction term $Q\propto\dot\varphi\rho_m$, the direction of energy flow depends on the sign of $\alpha$. However, for $Q\propto H\rho_m$, the energy flow is consistently negative, indicating an energy transfer from dark matter to dark energy, irrespective of the sign of $\alpha$.

Anadi Canepa, Spokesperson for the CMS Experiment at CERN

Italian physicist Anadi Canepa, a senior scientist at Fermilab, has been appointed spokesperson for the CMS (Compact Muon Solenoid) experiment at CERN. This appointment places her at the helm of one of the world's largest scientific collaborations, marking a significant milestone in high-energy particle physics. The CMS experiment is one of the two major detectors operating at the Large Hadron Collider (LHC) in Geneva, Switzerland. The CMS experiment is crucial for particle physics research, having played a fundamental role in the discovery of the Higgs boson in 2012, alongside the ATLAS experiment. Its primary objective is to explore the physics of the Standard Model and search for new physics beyond it, including the quest for supersymmetric particles, dark matter, and other fundamental interactions. The scale of the collaboration is reflected in the thousands of scientists and engineers from around the world who contribute to its design, construction, operation, and data analysis. The role of spokesperson involves coordinating the scientific and technical activities of the collaboration, as well as representing the experiment to the global scientific community and the public. This leadership is essential for maintaining the coherence and direction of such a large-scale project, ensuring that research objectives are met and that the results obtained are effectively communicated.

Cosmological Models Unite Decaying Dark Matter and Dynamic Dark Energy

Researchers have developed a new cosmological framework that integrates decaying dark matter (DDM) with a semi-cosmographic reconstruction of dark energy. This model allows the study of nonlinear structure formation in the universe, where a non-relativistic dark matter component decays into relativistic dark radiation with a decay rate Γ. In parallel, dark energy is modeled directly from the cosmic expansion history, rather than assuming a fixed cosmological constant. This unified approach connects a reconstructed dark energy sector and DDM to the nonlinear formation of cosmic structures, offering a more flexible perspective on the universe's evolution. To constrain this model, the team used data from the Baryon Acoustic Oscillation (BAO) measurements and compressed ShapeFit measurements from DESI DR1. These data were employed to determine the background cosmological evolution, propagating the resulting constraints into the nonlinear regime through spherical collapse and halo abundance calculations. The results indicate that the reconstructed dark energy equation of state can deviate from the standard ΛCDM value (w=-1), while the critical density threshold for structure collapse remains close to its standard prediction. The most significant signatures of this model emerge in the abundance of massive halos, reflecting modifications to the growth of structures driven by both dark matter decay and dynamic dark energy. By combining DESI DR1 clustering constraints with halo mass function measurements from the DESI Legacy Imaging Surveys DR9, joint constraints on the DDM lifetime and dark energy parameters were obtained. This demonstrates that halo abundances provide a powerful complementary probe for investigating non-standard dark sector physics, opening new avenues for understanding the nature of these fundamental components of the universe.

Dark Matter and Dark Energy Unified in a Solid Phase Model

Researchers have proposed a new model that unifies dark matter and dark energy into a single cosmic component. This component behaves as a pressureless fluid in the early universe, acting as dark matter. However, in late cosmological epochs, it undergoes a phase transition to become a solid, which can explain the observed accelerated expansion of the universe, attributed to dark energy. This approach simplifies the dark sector of the cosmos, which currently requires two distinct entities for its description. The model, based on a generalized Chaplygin-type solid, addresses a key problem of perfect-fluid unifications: the emergence of instabilities and strong acoustic oscillations. By postulating a solid nature for the dark medium in later stages, these instabilities are avoided, providing a more consistent description. This unification not only reproduces the transition from a dark matter-dominated universe to a dark energy-dominated one but also predicts observable signatures in cosmological perturbations. Among the distinctive predictions of the model are a suppression of large-scale structure growth, a nontrivial gravitational slip, and an effective mass for gravitational waves. These effects, which originate from the solid phase of the dark sector, primarily manifest at low redshifts, meaning that the cosmology of the early universe remains essentially unmodified. The potential detectability of these effects offers a pathway to test the validity of this unification and its implications for the evolution of the universe.

Radioactive Molecules: New Laboratories for Fundamental Physics

Radioactive molecules are emerging as promising tools to investigate fundamental physics, offering unique sensitivity to phenomena beyond the Standard Model. Unlike radioactive atoms, which have been used for decades, the molecular structure adds rotational and vibrational degrees of freedom that can amplify signals from fundamental interactions. This feature allows scientists to search for violations of fundamental symmetries, such as parity (P) and time-reversal (T), which are crucial for understanding the matter-antimatter asymmetry in the universe and the nature of dark matter. The interest in these molecules stems from their ability to host nuclei with large intrinsic electric dipole moments (EDMs) and to form quantum states that are highly sensitive to small interactions. The combination of molecular complexity with nuclear instability provides an experimental environment that can be more advantageous than stable atoms or ions for certain searches. Current experiments focus on developing techniques to create, cool, and manipulate these molecules, as well as on the precision measurement of their spectroscopic and decay properties. These investigations not only promise to refine our understanding of fundamental forces and elementary particles but could also offer new avenues for dark matter detection or the search for new short-range interactions. As molecular manipulation technology advances, radioactive molecules are expected to become quantum laboratories of unparalleled precision, opening a window to physics that lies beyond the current limits of our particle accelerators.

String Axions Enhance Superradiant Dark Matter Production

A recent study explores how the emission of string axions by light primordial black holes (PBHs) could boost dark matter production via superradiance. Researchers have shown that Hawking emission of a large number of light axion species, predicted in realistic string theory constructions (on the order of 100 to 10^5), can significantly increase the efficiency of superradiance. This enhancement is due to the associated increase in the PBH spin, suggesting a more effective mechanism for the formation of micro-boson stars, which are self-gravitating remnants of superradiant dark matter clouds. The concept of a "string axiverse" expands the parametric regions (dark matter mass, and PBH mass and spin) where a sizeable fraction of dark matter might exist in the form of these micro-boson stars. However, the study also points out a limitation: if the number of axion species is too large, PBHs evaporate too quickly, preventing superradiant clouds from attaining their maximum mass. This establishes a delicate balance in the contribution of axions to dark matter production. Assuming that all dark matter is produced by PBHs, through both superradiance and Hawking emission, the authors conclude that the axions emitted during PBH evaporation make an immeasurably small contribution to the relativistic degrees of freedom at recombination. This implies that while axions may play a crucial role in dark matter production, their direct impact on early cosmology, in terms of relativistic radiation, would be negligible and unobservable with current techniques.

Review of Evidence and Theories for Hypothetical X17 Particle

A recent study has reviewed the experimental evidence and theoretical frameworks supporting the existence of the hypothetical X17 particle. This particle, proposed to explain anomalies in nuclear decays, remains a subject of intense debate within the scientific community. The review aims to consolidate previous findings and theoretical interpretations, emphasizing the importance of further experimental verification. The X17 particle was initially postulated to explain an anomaly observed in the decay of a beryllium-8 nucleus, where an excess of electron-positron pairs with an energy of around 17 MeV was detected. Since then, similar observations have been reported in other decays, such as that of helium-4. If confirmed, the X17 could be a light boson that interacts weakly with ordinary matter, making it a candidate for dark matter or a mediator of a fifth fundamental force. Its mass and couplings to Standard Model particles are crucial for determining its nature. The review also addresses the implications of the X17's existence for the Standard Model of particle physics. A new particle with these characteristics would require an extension of the current model, opening the door to new theories about fundamental interactions and the composition of the universe. Various theoretical models that could accommodate the X17 are discussed, ranging from extensions of the dark sector to theories with new short-range forces. The definitive confirmation or refutation of the X17 is a key objective for particle physics in the coming years, with several experimental proposals underway to replicate and verify the observed anomalies.

Hubble Glimpses Merging Galaxy Clusters

The NASA Hubble Space Telescope has captured an image of the galaxy cluster CL0016+1609, also known as MACS J0018.5+1626. This cluster is notable for its intense emission at X-ray wavelengths and has been the subject of extensive studies in both X-ray and radio frequencies. Previous X-ray observations had already indicated that it was not a single cluster, but rather two distinct clusters in the process of merging, aligned along our line of sight from Earth. The Hubble image provides a detailed view of this cosmic event, where dark matter and hot gas interact in complex ways. The merging of galaxy clusters is one of the most energetic events in the universe, releasing colossal amounts of energy and affecting the distribution of matter on cosmological scales. These events are crucial for understanding the formation and evolution of the universe's large-scale structures.

Hubble Observes Galaxy Cluster Acting as Gravitational Lens

NASA’s Hubble Space Telescope has captured a detailed image of the galaxy cluster MACS0329-0211. This cluster, resembling a swarm of bees, is of great interest to astrophysicists, as galaxy clusters are crucial indicators in understanding the structural evolution of the universe. Their study allows researchers to trace how large cosmic structures formed and developed over cosmic time. One of the most notable properties of MACS0329-0211 is its ability to act as a natural gravitational lens. The immense mass concentrated within the cluster distorts spacetime around it, bending the path of light from much more distant galaxies located behind it. This gravitational lensing effect allows astronomers to observe galaxies that would otherwise be too faint or distant to detect, offering a unique window into the early stages of the universe. The observation of these clusters not only reveals the distribution of visible matter but also provides fundamental clues about dark matter, an invisible component that dominates the mass of clusters and is responsible for much of their lensing effect. By analyzing the distortion of background galaxies, scientists can map the distribution of total matter (visible and dark) within the cluster, refining our cosmological models and understanding the nature of dark matter.

High-Scale Mirror Dark Matter and Primordial Gravitational Waves

A recent study explores a dark matter model based on a "mirror sector" of the Standard Model, interacting with ordinary matter solely through gravity. This mirror sector would possess the same symmetries as the conventional Standard Model, but with significantly higher energy scales and different couplings. The research focuses on how these differences, including distinct Yukawa couplings for the mirror Higgs boson and mirror fermions, would influence the early evolution of the universe. The authors predict that in this model, a dark phase transition would occur at high temperatures of the baryonic universe, much earlier than the ordinary Standard Model's electroweak phase transition. This transition could be first or second order, depending on the universe's scale and the Yukawa couplings. The case of a second-order phase transition is particularly interesting, as it could leave a detectable imprint on the spectrum of stochastic gravitational waves, a phenomenon potentially observable by future gravitational wave detectors. The work also examines the ability of this high-scale mirror dark matter to form atoms, showing that in certain scenarios it could have both atomic and subatomic components. An approximation of the total equation of state for this mirror dark matter is provided, and the study discusses how this model could reconcile seemingly contradictory observations from galaxy clusters like the Bullet Cluster and Abell 520, which suggest different dark matter properties at various scales.

The Number of Elementary Particles: 17 or Nearly a Thousand?

The question of how many elementary particles truly exist in the universe is more complex than it appears, with answers varying drastically from the 17 particles of the Standard Model to nearly a thousand. This disparity arises from different definitions of "elementary" and the inclusion of hypothetical particles predicted by theories beyond the Standard Model, such as supersymmetry or string theories. The search for a definitive answer is central to particle physics and the fundamental understanding of matter and forces. The Standard Model of particle physics describes 17 fundamental particles: six quarks (up, down, charm, strange, top, bottom), six leptons (electron, muon, tau, and their respective neutrinos), four force bosons (photon, gluon, W and Z bosons), and the Higgs boson. These particles have been experimentally observed and form the basis of our current understanding of matter and fundamental interactions. However, this model does not explain phenomena such as dark matter, dark energy, or gravity, suggesting the existence of additional, yet undiscovered particles. Theories such as supersymmetry (SUSY) propose that each Standard Model particle has a more massive "superpartner," effectively doubling the number of elementary particles. Other extensions, like string theories or those postulating extra dimensions, could introduce an even larger number of particles, including gravitons, axions, or dark matter particles. The existence of these hypothetical particles is the subject of intense research at accelerators like the LHC and in dark matter detection experiments, with the hope of resolving the inconsistencies of the Standard Model and unifying the fundamental forces.

New Leptonic Interactions Proposed to Probe Flavour Symmetries

Researchers have proposed a new theoretical framework to explore non-abelian flavour symmetries within the lepton sector. These symmetries, potentially fundamental to a unified theory of flavour, manifest through flavour-transfer processes that, at low energies, partially mimic the Standard Model's charged current interactions. The systematic study of these theoretical constructions aims to identify specific experimental signatures detectable in particle accelerators, opening a new window for understanding the fundamental structure of leptons. The work examines various flavour structures and evaluates existing experimental constraints. It was found that, in the absence of flavour-breaking spurions, limitations derived from the lifetime of heavy leptons are the most restrictive across most of the parameter space. However, certain regions of this space remain open and could be explored in future electron-positron (ee-collider) searches. The methodology employed includes the use of the MARTY computational framework to obtain numerical predictions, allowing for consistent analysis of both light and heavy mediator regimes. Furthermore, the authors considered extensions of these models that could be compatible with dark matter relic density bounds, utilizing the DarkPack tool. This aspect suggests a possible connection between leptonic flavour interactions and the nature of dark matter, expanding the implications of this research beyond the lepton sector. The search for these new interactions could offer crucial clues about physics beyond the Standard Model and the unification of fundamental forces.

Weyl Semimetals Could Detect Axion Dark Matter

A new study proposes a method to detect sub-eV axion dark matter using the chiral magnetic effect in Weyl semimetals. Axions, hypothetical particles that could constitute dark matter, would behave as a coherent classical field capable of inducing a macroscopic current in certain quantum materials. This proposal opens a promising experimental avenue for the search for these elusive particles. The method relies on the chiral magnetic effect, a quantum phenomenon occurring in Weyl semimetals. Under a static external magnetic field, the presence of axions would induce a detectable electric current. Researchers demonstrate that, for a 1 cm² sample in a 10 T magnetic field, the expected signal would be in the femtoampere range, a magnitude that is observable with current technology. Implementing this experiment, using state-of-the-art SQUID-based current readout systems, would allow probing axion-electron couplings below existing stellar cooling bounds across a broad range of axion masses. This would offer unprecedented sensitivity in the search for axionic dark matter. This advance could provide direct evidence for the existence of axions and shed light on the composition of the universe's dark matter.

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.