Volodymyr Takhistov

Axion-like particles (ALPs) provide a compelling avenue for exploring physics beyond the Standard Model. In astrophysical magnetized plasmas, an ALP–photon coupling g _aγ induces energy-dependent oscillations in the photon survival probability that imprint modulations on emission spectra. X-ray observations of bright spectrally smooth sources can provide particularly sensitive probes of ultralight ALPs with masses m _a ≲ 10 ⁻¹¹ eV due to long propagation distances, strong magnetic fields, and high photon statistics. We present a comprehensive forecast of ALP–photon conversion in three representative systems: (i) background active galactic nuclei (AGNs) observed through foreground intracluster magnetic fields, (ii) central AGNs within their host cluster halos, and (iii) Galactic X-ray binaries viewed through the Milky Way field. Using detailed simulations, we assess the prospective sensitivity of high-resolution X-ray missions including XRISM, Athena, and Arcus. For typical magnetic field configurations, a 320 ks XRISM observation or an 8 ks Athena observation of the Perseus Cluster AGN NGC 1275 can reach down to g _aγ ∼ 5 × 10 ⁻¹³ GeV ⁻¹ at m _a ≲ 10 ⁻¹² eV, surpassing the current best limit. We quantify the impact of magnetic field modeling, photon statistics, and spectral binning strategies. Our results demonstrate the scientific potential of future X-ray observatories to probe photon–ALP coupling in previously inaccessible parameter space, offering a powerful window into physics beyond the Standard Model.

A bstract: Axions and axion-like particles generically appear in extensions of the Standard Model. While many searches assume only a single axion species, there may exist a whole spectrum of multiple such fields. We develop general formulas for axion-photon oscillations in the presence of multiple axions and analyze the implications for experimental searches, including light-shining-through-a-wall experiments, helioscopes and haloscopes. We demonstrate that axion multiplicity can qualitatively alter observational signatures, particularly through coherence and interference effects. Multiple axions can not only enhance signals compared to single axion scenarios, but also suppress them. We show that variations of experimental parameters and searches allow identifying contributions of multiple axions and obtaining information about their properties.

Extreme astrophysical environments provide unique laboratories for testing fundamental neutrino interactions. We present the first oscillation-independent astrophysical probe of nonstandard neutrino interactions (NSI), using coincident neutral-current signals across diverse detectors to break degeneracies that have long limited sensitivity reach. Using self-consistent NSI supernova simulations and flavor-independent neutral-current scattering we show that anticorrelated signatures between JUNO liquid scintillator and dark matter detectors such as DARWIN/XLZD, ARGO, or RES-NOVA enable clear discrimination between NSI and flavor-conversion effects. For a Galactic supernova at Betelgeuse distance our approach enables an independent probe of neutrino-quark NSI couplings in parameter space that can reach and extend beyond current terrestrial limits. This multidetector approach enables breaking degeneracies in terrestrial searches and is broadly applicable to a wide range of upcoming experiments, establishing a new principle for testing fundamental interactions with astrophysical data.

Sterile neutrinos produced in the early Universe that mix with active neutrinos of the Standard Model are typically considered to consist of a single population resulting from one dominant production mechanism. We show that the same sterile neutrino species can naturally emerge with multiple population components, yielding a multi-modal relic momentum spectrum. We consider four distinct production scenarios: active-sterile non-resonant oscillations following resonant oscillations in the presence of a primordial lepton asymmetry, gravitational production through sterile neutrinogenesis from populations of evaporating primordial black holes, and heavy singlet Higgs or inflaton decays combined with non-resonant active-sterile oscillations or neutrinogenesis. We identify sterile neutrino mass ranges where colder and warmer populations can be present and contribute non-negligibly to the dark matter relic abundance. We discuss some potential consequences of such a multi-population framework.

We present a comprehensive analysis of high-resolution transition-edge sensors (TESs) as a quantum sensing platform for detecting dark matter (DM). Operating near the thermodynamic noise limit with sub-eV energy resolution, TESs offer a powerful approach for probing light DM in the sub-GeV mass range. Optical TESs, realized on superconducting films with critical temperatures below 150 mK, achieve energy thresholds below 100 meV and enable precise calorimetric detection of individual energy depositions. We model TES response by incorporating fundamental noise sources and applying optimal filtering techniques, and we evaluate their sensitivity across a range of DM interaction channels, accounting for material responses in the target material. We show that even nanogram-month-scale exposures can reach previously unexplored DM-electron scattering cross sections below 10 − 27 cm 2 for sub-MeV masses and can probe the MeV-scale mass range for DM-nucleon couplings. Combining high-energy resolution, photon-number sensitivity, and scalability, optical TESs provide a compelling quantum sensing platform for rare-event searches at the intersection of particle physics and quantum metrology.

Ultralight bosonic (ULB) fields with mass m _ϕ ≪ 1 eV often arise in theories beyond the Standard Model (SM). If such fields exist, violent astrophysical events that result in emission of gravitational wave, photon, or neutrino signals could also produce bursts of high-density relativistic ULB fields. Detection of such ULB fields in terrestrial or space-based laboratories correlated with other signals from transient astrophysical events opens a novel avenue for multimessenger astronomy. We show that quantum sensors are particularly well-suited to observe emitted scalar and pseudoscalar axion-like ULB fields coupled to SM. We demonstrate that multimessenger astronomy with ULB fields is possible even when accounting for matter screening effects.