Super-precise optical clocks in four nations tick in harmony

Four of the world's most precise optical clocks, located in Japan, Germany, France, and the United Kingdom, have synchronized their ticks with unprecedented accuracy. This milestone represents a significant advance in time metrology, demonstrating the ability of these devices to maintain coherence over long distances and laying the groundwork for a future redefinition of the second. Optical clocks use atomic transitions in the optical range of the electromagnetic spectrum, allowing them to achieve much higher stability and precision than current cesium atomic clocks, which define the second. Synchronization was achieved using fiber optic networks that transmit time signals with extreme fidelity, compensating for environmental fluctuations and signal losses over thousands of kilometers. This experiment validates the robustness of optical clock technology for practical time distribution applications. This achievement has profound implications for fundamental science and technology. A global network of optical clocks could enable the detection of low-frequency gravitational waves, the search for dark matter, the improvement of global positioning systems (GPS), and the exploration of variations in fundamental physical constants. Furthermore, the ability to compare and synchronize these clocks internationally is a crucial step towards the eventual redefinition of the second, which is expected to be based on an optical clock in the near future, improving the precision of the unit of time by several orders of magnitude.

TeV Higgsino Interpretation of LUX-ZEPLIN High-Recoil Event

A recent high-recoil event reported by the LUX-ZEPLIN (LZ) experiment has motivated a new theoretical interpretation within the framework of supersymmetry. This event, featuring a significant recoil, could be explained by the interaction of a Higgsino with a mass on the order of a TeV, characterized by a sub-MeV energy splitting between its neutral states. In the Minimal Supersymmetric Standard Model (MSSM), such a small gap in the Higgsino's neutral states, absent specific cancellations, typically implies electroweak gaugino masses on the order of $10^7$ GeV, a value much higher than the Higgsino's own mass. Researchers have proposed that a non-universal boundary condition for gaugino masses ($M_1^G/M_2^G = -3/5$) at the SU(5) Grand Unified Theory (GUT) scale could resolve this discrepancy. This condition would allow for the cancellation of leading bino and wino contributions and would be preserved under homogeneous one-loop evolution down to the Higgsino scale. This opens the possibility for a controlled tree-level solution with a wino mass near 120 TeV for a 350 keV gap, a 1.091 TeV Higgsino, and $\tan\beta = 10$. Mixed SU(5) representations that realize the required gaugino ratio have been identified. It is crucial to note that, despite this new interpretation, a full-density thermal Higgsino remains subject to published solar-capture bounds. This is because the inelastic Z coupling remains essentially unsuppressed, implying that the astrophysical and transport assumptions used in solar-capture limits are still valid for this scenario. The radiative sensitivity and spectrum consistency of this theoretical construction have been examined to ensure its viability.

Inelastic Electroweak Dark Matter Proposed for LZ Events

A new study proposes an electroweak dark matter model that could explain the high-energy inelastic nuclear recoil events recently reported by the LUX-ZEPLIN (LZ) Collaboration. This model extends minimal electroweak dark matter with a Majorana and a Dirac multiplet, coupled through Higgs interactions, providing a predictive framework for high-energy inelastic nuclear recoils. In this scheme, electroweak symmetry breaking induces a neutral-state splitting, δ, and an off-diagonal Z interaction. For a series of coupled multiplets (such as 3M2D, 5M4D, etc.), both the splitting and the leading inelastic interaction are universal for a fixed (mχ, y), independent of the electroweak representation. The high recoil energy observed by LZ points to splittings of a few hundred keV. The fixed Z-mediated rate allows for the determination of a mass-dependent δLZ(mχ) by requiring one expected inelastic event in the LZ exposure, with a two-sided 90% Poisson band. This defines a universal region in the (mχ, y) plane. Intersecting this region with the representation-dependent thermal relic trajectories selects a benchmark for each multiplet. The corresponding electroweak representation then predicts a correlated loop-induced elastic spin-independent signal at lower recoil energies, which could be sought in future experiments.

LUX-ZEPLIN detects high-energy event consistent with inelastic dark matter

The LUX-ZEPLIN (LZ) experiment has reported the detection of a single nuclear recoil event with an energy of $248\pm23({\rm stat})\pm23({\rm sys})\keV$. This event, observed within an extended search window, is significantly more energetic than expected for conventional dark matter interactions. Researchers propose that this occurrence could be a signal of inelastic dark matter, a model in which the scattering between dark matter particles and detector nuclei is an endothermic process, requiring energy to excite the dark matter particle to a higher mass state. This type of interaction naturally explains the high recoil energy observed.

1.1 TeV Higgsino Explains Dark Matter Anomalies in LZ and Fermi-LAT

A new study proposes that the Higgsino, a supersymmetric particle, could be responsible for anomalies observed in the LZ and Fermi-LAT experiments, which search for dark matter signals. This interpretation suggests that the Higgsino, a WIMP (Weakly Interacting Massive Particle) candidate from the Minimal Supersymmetric Standard Model, would have a mass of approximately 1.1 TeV. This mass value is derived from the relic abundance of dark matter in the universe, while the nuclear recoil spectrum observed by LZ points to a mass splitting of a few hundred keV. The LZ experiment, an underground liquid xenon detector, has reported an excess of nuclear recoil events that cannot be explained by known backgrounds. Simultaneously, 14 years of data from the Fermi-LAT space telescope show a mild preference for a gamma-ray signal in the Galactic center, consistent with the annihilation of dark matter particles. The 1.1 TeV Higgsino hypothesis successfully reconciles both results, providing a unified explanation for these seemingly disparate observations. In addition to explaining the LZ and Fermi-LAT anomalies, this Higgsino interpretation is also consistent with solar neutrino constraints imposed by the IceCube experiment over 10 years. The model predicts the existence of a gamma-ray line and an endpoint signal in the Galactic center, which are near the current sensitivity of the H.E.S.S. observatory and within the projected reach of the future Cherenkov Telescope Array Observatory (CTAO). This means that this classic dark matter hypothesis could be experimentally tested in the near future, opening a window for the direct detection of these elusive particles.

High-Energy Event in LUX-ZEPLIN Could Be Fermionic Dark Matter

The LUX-ZEPLIN (LZ) experiment has reported an anomalous single candidate event in the high-energy nuclear recoil window of $248\pm32.5\ \mathrm{keV}_{\mathrm{nr}}$, with an exposure of $2.80\ \mathrm{ton}\cdot\mathrm{yr}$. This event is notable as the low-energy spectrum measured by LZ remains consistent with background expectations. Researchers propose that this excess could be naturally explained by the neutral-current absorption of fermionic dark matter on xenon nuclei. Under this hypothesis, a dark matter particle with a mass of $m_\chi \simeq 247\ \mathrm{MeV}$ could produce a monoenergetic nuclear recoil at approximately $248\ \mathrm{keV}_{\mathrm{nr}}$ through coherent absorption. At this momentum transfer, the absorption process would enter an incoherent regime, where scattering off individual nucleons produces a broad recoil spectrum extending from about $200\ \mathrm{keV}$ to $100.2\ \mathrm{MeV}$. A single effective field theory (EFT) coupling could simultaneously produce this one event in the specified window while remaining consistent with the non-observation of events in neighboring energy regions. The required single-nucleon absorption cross section for this scenario is $ \sigma_{\chi N}^{\mathrm{NC}} = 1.07\times10^{-46}\ \mathrm{cm}^2$, corresponding to an effective field theory scale of $ \Lambda \simeq 11.5\ \mathrm{TeV}$. However, a recasting analysis of KamLAND data on the neutron-emission channel $ \chi+{}^{12}\mathrm{C} \to \nu+ n + {}^{11}\mathrm{C}^*$ excludes this benchmark parameter space. This establishes a significant tension between the LZ excess interpretation and existing constraints from large-volume scintillator detectors, highlighting the need for future dedicated high-energy analyses to resolve this discrepancy.

NASA’s Nancy Grace Roman Space Telescope Successfully Launched

NASA’s Nancy Grace Roman Space Telescope has successfully launched aboard a SpaceX Falcon Heavy rocket from Kennedy Space Center in Florida on August 30, 2026. This space observatory, named after NASA’s first chief astronomer, is designed to conduct a comprehensive survey of billions of stars and galaxies, promising an unprecedented view of the universe. The Roman telescope's distinguishing feature is its field of view, significantly larger than that of the Hubble Space Telescope. This capability will allow it to map vast regions of the sky much more efficiently, which is crucial for its primary objectives: investigating dark energy, dark matter, and the search for exoplanets. Its wide field of view will facilitate the detection of transient phenomena and the statistical study of stellar and galactic populations on a large scale. The launch of Roman represents a significant milestone in space astronomy, as it is expected to complement and expand upon discoveries made by previous missions. Its data will be fundamental to understanding the accelerated expansion of the universe and the nature of the dark components that dominate its mass and energy. Furthermore, its capability for gravitational microlensing will open new avenues in the detection and characterization of exoplanets, including those that could be Earth analogs.

NASA's Nancy Grace Roman Space Telescope: Wide-Field View Mission

NASA's Nancy Grace Roman Space Telescope, formerly known as WFIRST (Wide Field Infrared Survey Telescope), is a next-generation mission designed to address fundamental questions in astrophysics, including the nature of dark energy and dark matter, the search for exoplanets, and the study of galaxy formation and evolution. Its most distinctive feature is a field of view 100 times larger than that of the Hubble Space Telescope, which will allow it to map large areas of the sky much more efficiently. Roman is equipped with a 2.4-meter primary mirror, the same size as Hubble's, but its instrumentation is optimized for near-infrared observations. This is crucial for observing distant, faint objects, as the expansion of the universe shifts the light from these objects to longer wavelengths. The mission includes two key instruments: the Wide Field Instrument (WFI), which will provide high-resolution imaging and wide-field spectroscopy, and the Coronagraph Instrument (CGI), a technology demonstration that will block starlight to enable direct observation of exoplanets. Roman's primary scientific objectives focus on cosmology and exoplanet astrophysics. In cosmology, it will conduct weak gravitational lensing and Type Ia supernova surveys to measure the universe's expansion history and understand dark energy. In exoplanets, it will use the gravitational microlensing technique to discover thousands of exoplanets, including those in wide orbits and of low mass, and the CGI will attempt to directly characterize the atmospheres of nearby exoplanets.

Composite Higgs Models Predict Dark Matter with Magnetic Moment

Researchers have explored the interaction of dark matter (DM) with nucleons and nuclei within the framework of Composite Higgs Models (CHMs). In these models, the lightest Dirac composite particle (LDCP) can be stable and constitute a significant fraction of the observed relic dark matter abundance. The study focuses on the elastic scattering of the LDCP on nucleons, as well as on xenon (Xe) and argon (Ar) nuclei, considering a non-zero magnetic dipole moment for the LDCP. The peculiarity of this scenario is that the LDCP's magnetic moment, its mass, and its coupling to the Higgs doublet are suppressed by an approximate U(1) symmetry. A non-zero magnetic dipole moment for the LDCP can lead to a substantial enhancement in the differential event rate in direct detection (DD) experiments, especially at low nuclear recoil energies. This effect could be key to its detection. Assuming the LDCP constitutes at least 10% (ξ ≥ 0.1) of the relic dark matter, the authors have identified a region of the parameter space where this enhancement in the event rate could be potentially observable. Furthermore, they have specified some observables that could be useful in discriminating between dark matter fermions with a magnetic moment and other types of dark matter particles that do not possess similar electromagnetic properties. This opens a path to identify the nature of dark matter if a signal with these characteristics is detected.

NASA's Roman Space Telescope Prepares for Launch

NASA's Nancy Grace Roman Space Telescope, set to launch on August 30, is poised to become a pivotal instrument for exploring vast regions of the cosmos. This space observatory is designed to address key questions in areas such as dark energy, dark matter, the detection and characterization of exoplanets, and the formation and evolution of galaxies over cosmic time. The Roman mission will focus on conducting wide-field surveys, enabling it to map large swathes of the sky with unprecedented efficiency. This will be crucial for understanding the large-scale distribution of matter in the universe and for investigating the nature of dark energy, the mysterious force driving the accelerated expansion of the cosmos. Furthermore, its ability to observe billions of galaxies will provide valuable data on how these structures evolved from the early universe to the present day.

Neutron Stars with Dark Matter Cores: An Analytical Model

Researchers have developed an analytical relativistic model for neutron stars that incorporates a mixed core of ordinary matter and dark matter. In this model, both types of matter coexist as independent, incompressible perfect fluids, interacting solely through the spacetime geometry. Ordinary matter extends throughout the star, while dark matter is confined exclusively to the core, forming an envelope of pure ordinary matter around this mixed core. The main novelty of this work is the ability to keep the system analytically tractable, despite the complexity of a two-fluid core structure and an internal interface. This has allowed for explicit expressions for pressures and metric functions, facilitating the direct study of how the dark matter fraction and relative core size affect the star's properties. The model also determined the physically admissible parameter space and derived a Buchdahl-like critical compactness, linked to the divergence of central pressure, whose value depends on the relative dark matter density and the size of the mixed core. The mass-radius analysis reveals that configurations with the same global compactness can exhibit very different internal matter distributions. In the one-fluid limit, the model recovers the Schwarzschild constant-density star and its standard critical value of 2M/R = 8/9. This construction not only provides an analytically controlled description of a core-confined second component but also serves as a valuable benchmark for identifying qualitative trends that can be explored in more realistic dark matter admixed neutron star models, whose detailed treatment is beyond the scope of this work.

Centuries-old precision experiment could detect millicharged particles

Researchers at Fermilab, Stanford University, and the University of Delaware have proposed that one of the oldest precision experiments in physics could be adapted to search for millicharged particles. This approach represents a new avenue for detecting these hypothetical particles, which possess an extremely small fractional electric charge compared to the elementary charge of the electron (e). Millicharged particles are candidates for dark matter or for mediators of interactions between the dark sector and ordinary matter. Their detection is challenging due to their extremely weak interaction with conventional detectors. The proposal focuses on reinterpreting and optimizing a classic experiment, which could offer complementary sensitivity to current search methods, such as collider experiments or large-volume dark matter detectors. The suggested method leverages the inherent sensitivity of these historical experiments to extremely weak forces, which could manifest as subtle deviations in measurements. Although the original article does not detail the specific experiment, the reference to a "centuries-old precision experiment" suggests a well-established technique now being re-evaluated under a new theoretical light. This type of approach, which reuses existing instrumentation or experimental principles, is often a cost-effective and efficient way to explore new frontiers in particle physics.

APOD Features Three Interacting Galaxy Pairs

The Astronomy Picture of the Day (APOD) program today highlighted an image showcasing three pairs of interacting galaxies. These cosmic formations offer a window into the dynamic processes that shape galaxy evolution in the universe. Gravitational interactions between galaxies are common phenomena that can trigger bursts of star formation, alter galactic morphology, and ultimately lead to the merger of the involved galaxies. Each galaxy pair illustrates different stages of interaction, from initial close encounters to advanced mergers. These observations are crucial for understanding how large-scale structures in the universe develop over billions of years. Astronomers use these images not only to study the physics of galactic collisions but also to infer the distribution of dark matter, which plays a fundamental role in the gravitational dynamics of these systems. Numerical simulations of these interactions are compared with observations to refine our models of galaxy formation and evolution.

Neutron Stars Could Exist Hidden Inside Black Holes

Researchers have explored a theoretical scenario where a neutron star could persist as a regular configuration within the event horizon of a black hole. This study considers neutron stars with an anisotropic dark matter halo, described by an Einasto density profile. This dark matter model has previously been shown to generate regular, singularity-free black hole solutions, providing a framework for this new hypothesis. To reach this conclusion, the team solved the modified Tolman-Oppenheimer-Volkoff (TOV) equations, which describe the structure of neutron stars in hydrostatic equilibrium. They used two different equations of state for nuclear matter (BSk19 and SLy4), allowing them to verify the robustness of their findings. The results indicate that the presence of the dark matter halo significantly alters the internal structure of the neutron star. Most notably, for a specific range of dark matter halo parameters, the $g_{rr}^{-1}$ component of the metric tensor changes sign outside the stellar surface. This change is the indicator of the formation of an event horizon, implying that the neutron star becomes enveloped by a black hole. This configuration, termed "neutron stars in black holes," appears with both equations of state, suggesting it does not depend on the specifics of nuclear matter. This finding opens a new perspective on the nature of what might reside inside black holes, offering a concrete and computable instance for future theoretical investigations.

Excited Boson Stars: Radial Modes and Critical Points

A recent study has investigated the radial modes of spherically symmetric boson stars, including both mini boson stars and models with quartic self-interaction. The researchers reformulated the pulsation equations using additive variables that remain regular even at points where the background scalar field vanishes. This allowed for direct integration of the eigenvalue problem through the nodes of excited configurations, providing a regular perturbative framework for these exotic structures. The analysis revealed a notable coincidence: for all branches examined, the first zero of the constrained fundamental radial eigenvalue coincides, within numerical resolution, with the first simultaneous critical point of the Arnowitt-Deser-Misner (ADM) mass, Noether charge, and binding energy. This correlation is crucial for understanding the stability of boson stars. Furthermore, the radial eigenvalue was evaluated for the threshold models identified in nonlinear spherical evolutions of excited boson stars, finding a simple empirical correlation with the node number and self-interaction strength. These results clarify the relationship between constrained radial modes, equilibrium critical points, and nonlinear stability diagnostics. Boson stars are hypothetical compact objects formed by bosons, which could be candidates for dark matter or compact objects other than black holes. Understanding their dynamics and stability is fundamental for theoretical astrophysics and the search for new particles. This work lays the groundwork for future research into the stability and evolution of these fascinating configurations.

Neural Networks Identify Two-Component Dark Matter at LHC

Researchers have demonstrated that a convolutional neural network (CNN) can identify and characterize signals of two-component dark matter at the Large Hadron Collider (LHC). Using mono-jet and mono-Z probes, the CNN not only detects the presence of two dark matter particles but is also capable of inferring their masses and spins (0 or 1/2), based on detector-level analysis. This work represents a conceptual proof-of-concept, laying the groundwork for future research. Dark matter, which constitutes approximately 27% of the universe, remains one of the biggest mysteries in physics. Although the Standard Model of particle physics successfully describes the interactions of ordinary matter, it does not include any candidate particles for dark matter. The hypothesis that dark matter could be composed of multiple particle types is a natural extension of existing models, offering solutions to certain anomalies and providing a more complete picture of the universe's composition. The ability to distinguish between different dark matter components is crucial for validating these theories. The method employed relies on machine learning, specifically a CNN, to analyze collision data generated at the LHC. Mono-jet and mono-Z probes refer to events where a jet or a Z boson is produced along with a large amount of missing transverse energy, which could indicate the production of dark matter particles that do not interact with detectors. The CNN processes these complex patterns, learning to identify the distinctive features associated with the production of two types of dark matter particles. Although this study did not include a signal-to-background analysis, its success in characterizing particle properties (mass and spin) from simulated detector-level data is a promising step. This advancement suggests a new path for dark matter searches in high-energy experiments. The ability of neural networks to extract detailed information about dark matter particle properties could accelerate the discovery and characterization of more complex models. The critical next step will be to integrate signal-to-background analysis to evaluate the viability of this technique in a real experimental environment, where dark matter signals must be distinguished from a much more abundant background of Standard Model processes.

't Hooft-Polyakov Monopoles as Dark Matter with Cosmological Signature

A new model proposes that dark matter could consist of 't Hooft-Polyakov magnetic monopoles, formed during a thermal phase transition in the early universe. Unlike stable elementary particles, the abundance of these monopoles is usually negligible. However, the study demonstrates that a relevant abundance is achievable if the lightest stable particle in the dark sector, a dark fermion, is sufficiently light for its abundance to be suppressed, yet heavy enough to satisfy constraints on dark radiation. This scenario opens a parameter window where magnetic monopoles could constitute dark matter. In this model, the mass of the magnetic monopoles is estimated to be approximately 10^8 GeV or larger, depending on the characteristics of the phase transition that generated them. This high mass places these dark matter candidates beyond the reach of current conventional detection experiments. Nevertheless, the model necessarily predicts the existence of dark radiation, with a ΔN_eff value (the effective contribution to the number of neutrino degrees of freedom) close to current cosmological observational bounds. Furthermore, if the dark phase transition was strongly first-order, the model predicts a gravitational wave spectrum that lies in a region potentially accessible to future interferometers. This offers a prospective avenue for the indirect detection of these monopoles through their cosmological imprints, opening new perspectives for the search for dark matter beyond elementary particles and current direct detection methods.

Small-Scale Cosmic Structure Constrains Dark Matter Nature

A recent analysis highlights how small-scale cosmic structure has become a fundamental tool for investigating the fundamental nature of dark matter (DM). Alternative models to the standard cold dark matter (CDM) paradigm, such as warm, fuzzy, or self-interacting dark matter, predict distinct effects on matter distribution at small scales. These models modify the abundance and internal structure of dark matter halos through phenomena like free-streaming, wave interference, or interactions with the Standard Model, leaving observable imprints in the universe. Cosmological and astrophysical probes of nonlinear structure are particularly sensitive to these effects. These include dwarf galaxies, strong gravitational lensing, the Lyman-α forest, stellar streams, and high-redshift galaxies. The study focuses on the constraints these observations impose on dark matter, paying special attention to scales smaller than approximately 1 Mpc, which represent the current frontier of measurements. It details how these constraints have been translated into limits for microphysical dark matter models, as well as key modeling uncertainties and observational systematics. The work emphasizes the growing importance of combining different probes and simulation-based inference to advance this field. Furthermore, it anticipates future observational facilities that will allow for further refinement of dark matter physics tests through small-scale structure. These advances are crucial for distinguishing between proposed models and, ultimately, for understanding the true nature of dark matter, one of the greatest mysteries in modern physics.

Q-ball dark matter could flatten galactic density cusps

A new theoretical model proposes that Q-balls of dark matter, non-topological solitons stabilized by a conserved charge, could resolve the "cusp-core" problem in galaxies. This problem refers to the discrepancy between cosmological predictions of a sharp dark matter density profile in the center of galaxies and observations, which suggest flatter profiles or "cores." The mechanism proposed by Q-balls offers a dynamic explanation for this flattening, without requiring drastic modifications to the standard cosmological model. Q-balls would form in the early universe within the dark sector and grow in the dense regions of galactic halos. Their interaction cross-section would decrease as their soliton mass increases. This process preferentially operates in halo centers, converting part of the rest-mass energy stored in massive Q-balls into relativistic dark-sector particles. This energy flow modifies the inner mass-density profile, flattening the cusp. The key to the mechanism lies in a self-regulating, density-dependent energy loss. This dynamic process allows the dark matter halo density cusps to be flattened in their central regions, leaving the outer parts of the halo largely unaffected. This model could explain the observed diversity in inner rotation curves and central densities of galaxies for a fixed halo mass, offering an elegant solution to one of the persistent tensions in the standard cold, collisionless dark matter model at galactic scales.

String Theory Predicts Quadratic Axion Couplings

Researchers have explored the emergence of quadratic couplings between axions and the electromagnetic kinetic term (θ²F²) within the framework of string theory. This type of interaction, which differs from the more commonly studied linear coupling (θF F̃), opens new avenues for detecting axion-like particles (ALPs). Axions are compelling candidates for physics beyond the Standard Model, including dark matter and dark energy, and their study is crucial for understanding unexplained cosmological phenomena. The work categorizes the generation mechanisms for these quadratic couplings in string theory into three types: classical, perturbative, and non-perturbative. It has been found that quantum contributions, both perturbative and non-perturbative (such as instantons), lead to suppressed couplings (g ≪ 1 in units of 1/f², where f is the axion decay constant). Despite this suppression, these couplings can be significantly larger than analogous ones for the QCD axion, which are generated through loops of charged pions. These analyses suggest that quadratic axion couplings to gauge fields are a ubiquitous feature in string theory. Their study not only provides a new probe for the string theory "axiverse" —the collection of axions and ALPs predicted by this theory— but also offers opportunities for the spectroscopy of these particles. Detecting such couplings could validate dynamic axion models and provide crucial insights into the fundamental structure of the universe.

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.