Open research questions in Dark Matter and Cosmic Phenomena

What the literature leaves open

• Even in the simplest topologies—or perhaps precisely in those—a full simulation is required to obtain a realistic result. For in these cases, accuracy is the most important factor. However, even if the correctly evaluated range is significantly lower than the theoretical estimate, the e+e− colliders allow the investigation of weaker dark photon couplings than at the HL-LHC, at least for masses greater than MZ . 2 This calculation is not trivial, and will be the topic of a future publication. 123 Eur. Phys. J. Plus (2026) 141:812 Page 7 of 8 812 Fig. 8 a Expected limits at LCF250, LCF550 and LCF1000, after doing the recast explained in the text. The current limits from CMS and Belle II, as well as a scaling of the CMS limits to HL-LHC are also shown; b a zoom to the masses up to 250 GeV, also showing the ILC250 full-sim result, used as an input to the LCF recasts It would be interesting to have a serious evaluation of the prospects for FCC-ee, up to its limited maximum reach of 365 GeV. Since full detector simulation, with full SM background is lacking for FCC-ee, firm conclusions will have to wait. At lower masses, the huge luminosity at FCC-ee, in particular at the Z-pole, will certainly out-perform LCF, and might even compete with Belle II. However, it is probable that the results at FCC-ee at the higher masses will not be better than LCF: FCC-ee will collect more luminosity, but the detectors will necessarily be less performant, since the FCC-ee conditions require lower detector B-field, and more material due to the need of cooling. Hence, the mass-resolution, crucial for this analysis, will be worse. This is an ongoing study. There is still room for improvement in the analysis. We have considered only the muon channel. This is because the muon channel is expected to exhibit the best mass resolution. It would also be possible to include A D → e+e−; however, to achieve sufficient mass resolution, it would be necessary to develop a method to compensate for bremsstrahlung. Furthermore, by utilising the properties of the detected ISR, it should be possible to reduce background noise when m A D is small. To make the most of the insights gained regarding errors at the event level, one could also consider an approach based on the unbinned maximum likelihood method. Finally, it is clear that the sensitivity is greatest when the collider operates at or near the dark photon mass. One might therefore consider devoting part of the operating time to a scan of EC M , provided that this does not pose any difficulties from the point of view of the facility’s operation. Among the proposed Higgs factories, only the LCF, ILC and C3 offers this possibility. Acknowledgements We would like to thank the LCC generator working group and the ILD software working group for providing the simulation and reconstruction tools and producing the Monte Carlo samples used in this study. This work has benefited from computing services provided by the ILC Virtual Organisation, supported by the national resource providers of the EGI Federation and the Open Science GRID. Funding Open Access funding enabled and organized by Projekt DEAL. Data availability The manuscript has no associated data. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

  Search for dark photons at future e$$^+$$e$$^-$$ colliders · 2026 · DOI

• Although several decades of indirect observations and direct experimental searches for mCPs at particle accelerators have led to severe constraints, a substantial window of the mCP mass–mixing parameter space remains unexplored at the energy frontier accessible to current state-of-the-art accelerators, such as the Large Hadron Collider (LHC).

  Minicharged particles at accelerators: progress and prospects · 2026 · DOI

• The following six research directions are explicitly identified as beyond the scope of the present paper. Each represents a self-contained calculation or simulation whose completion will either validate or constrain the R5+ framework at a quantitative level. (i) Rigorous derivation of 𝑛class = 4 from the disk Klein-Gordon equation The argument in Section 5 that 𝑛class = 4 rests on a dimensional power-counting in 𝐷 = 4 spacetime dimensions. A complete derivation requires: (a) solving the 2D radial Klein- Gordon equation for 𝜙1(𝑟) in the thin-disk limit with an exponential profile Σ(𝑟) = Σ0 exp(−𝑟/𝑅𝑑); (b) computing the density-weighted coupling integral 𝛽eff(Σ0) = ∫ 0 and (c) demonstrating analytically that 𝛽eff ∝ Σ4 0 in the weakly screened regime. This calculation is tractable analytically in the WKB approximation near the screening radius and numerically for the full profile. It is the highest-priority calculation for the theory companion paper. 𝛽1(𝑟)Σ(𝑟)𝑟 𝑑𝑟/ ∫ 0 Σ(𝑟)𝑟 𝑑𝑟; ∞ ∞ (ii) 1-loop heat kernel on the Schwarzschild conical defect = 𝛾BH = 0.0931 is the central hypothesis connecting the galactic and The identification 𝛾𝜙1 black hole sectors of R5+.

  UNIFIED SPACETIME DYNAMICS IN THE R5+ FRAMEWORK: GALACTIC ROTATION CURVES, BULLET CLUSTER OFFSETS, AND BLACK HOLE REMNANTS FROM A SYMMETRON-PROCA SECTOR · 2026 · DOI

• (i) Quantitative CMB fit. Section 10 demonstrates qualitative compatibility. A quantitative fit to the Planck power spectrum requires modifying a Boltzmann code (CAMB/CLASS) with the impedance Poisson equation following the recipe in §10.5 — computational work, not a conceptual gap. (ii) The interpolation function. μ(x) = x/(1+x) is chosen for simplicity. A derivation from the vacuum’s microscopic impedance structure would eliminate this remaining freedom. (iii) First-principles derivation of α. The impedance-memory amplification factor α ≈ 15 is currently extracted from the Bullet Cluster lensing fit, with a heuristic order-of-magnitude estimate from the MOND boost × occupation ratio × trace-reversal enhancement (§5.4) showing that the value is consistent with the microscopic picture. A genuine derivation would tie α to the dense-matter trace-reversal prediction of UTI v2.6 §6 via a calculation of the effective coupling enhancement in long-occupied vacuum regions. (iv) Cluster lensing maps. Detailed comparison with Bullet Cluster, Abell 1689, MACS J0025, and CLASHsurvey lensing maps requires numerical solutions of the covariant field equation (15) for realistic mass distributions, including the dynamical impedance-memory evolution. A coupled grid-based lensing + impedance-memory code is the natural follow-up. (v) Large-scale structure. The matter power spectrum P(k) in the impedance framework, particularly the BAO feature and the transition from linear to nonlinear clustering, requires the same Boltzmann-code work as the CMB fit plus N-body integration of the modified Poisson equation. (vi) Lattice links to UTI v2.6. A lattice computation of fσ = 0|T|σ and the canonical-normalization factor Z (UTI v2.6 open question (i)) would supply the first-principles value of the nuclear coupling g η = fσ/ZT 1/2 that anchors the trace-channel interpretation of the impedance scalar η, and constrains how much of the galactic μ can be inherited from the microscopic theory versus supplied as new phenomenology. The gradient-flow EMT approach of Suzuki (UTI v2.6 §14.4) is the natural calculational route.

  Impedance Contrast Theory: Galaxy Rotation Curves and Gravitational Lensing from Vacuum Impedance Susceptibility · 2026 · DOI

• 1Max-Planck-Institut für Physik, Garching bei München, Germany. 2Institut für Hochenergiephysik der Österreichischen Akademie der Wissenschaften, Wien, Austria. 3Atominstitut, Technische Universität Wien, Wien, Austria. 4Kirchhoff-Institute for Physics, Heidelberg University, Heidelberg, Germany. 5Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia. 6INFN, Laboratori Nazionali del Gran Sasso, Assergi, Italy. 7Eberhard-Karls-Universität Tübingen, Tübingen, Germany. 8Physik-Department, TUM School of Natural Sciences, Technische Universität München, Garching, Germany. 9Department of Physics, University of Oxford, Oxford, UK. 10Institute for Astroparticle Physics, Karlsruhe Institute of Technology, Karlsruhe, Germany. 11Present address: LIBPhys, Departamento de Fisica, Universidade de Coimbra, Coimbra, Portugal. 12Present address: Dipartimento di Fisica, Università di Milano Bicocca, Milano, Italy. 13Present address: School of Physics, The University of Melbourne, Melbourne, VIC, Australia. 14Present address: ARC Centre of Excellence for Dark Matter Particle Physics, Melbourne, VIC, Australia. 15Present address: Walther-Meißner-Institut für Tieftemperaturforschung, Garching, Germany. 16Present address: Instituto de Física da Universidade de São Paulo, São Paulo, Brazil. 17Present address: Dipartimento di Ingegneria Civile e Meccanica, Università degli Studi di Cassino e del Lazio Meridionale, Cassino, Italy.

  The CRESST experiment towards the next generation of sub GeV direct dark matter detection · 2026 · DOI

• 35. Abdelhameed, A. H. et al. Geant4-based electromagnetic 62. Amole, C. et al. Dark matter search results from the complete exposure of background model for the CRESST dark matter experiment. Eur. Phys. J. C. 79, 881 (2019). [Erratum: Eur. Phys. J. C 79, 987 (2019)]. 36. Wulandari, H. et al. Neutron flux at the Gran Sasso underground laboratory revisited. Astropart. Phys. 22, 313–322 (2004). 37. Strauss, R. et al. A detector module with highly efficient surface-alpha event rejection operated in CRESST-II Phase 2. Eur. Phys. J. C. 75, 352 (2015). 38. Zema, V. Excess workshop 2022/2023. Presented at the EXCESS Workshop (2023). Workshop presentation “The low energy excess in CRESST-III” https://indico.cern.ch/event/1213348/contributions/ 5411385/. 39. Anthony-Petersen, R. et al. A stress-induced source of phonon bursts and quasiparticle poisoning. Nat. Commun. 15, 6444 (2024). 40. Stahlberg, M. Probing Low-Mass DarkMatter with CRESST-III—Data Analysis and First Results. Ph.D. thesis, TU Wien (2021). 41. Adams, D. Q. et al. Search for Majorana neutrinos exploiting millikelvin cryogenics with CUORE. Nature 604, 53–58 (2022). 42. Einfalt, L. Light Quenching in Scintillator-Based Cryogenic Detectors for Dark Matter Searches. Ph.D. thesis, TU Wien (2024). 43. Kinast, A. et al. Improving the quality of CaWO4 target crystals for CRESST. J. Low. Temp. Phys. 209, 1128–1134 (2022). 44. Strauss, R. et al. Beta/gamma and alpha backgrounds in CRESST-II Phase 2. J. Cosmol. Astropart. Phys. 06, 030 (2015). 45. An, H., Pospelov, M., Pradler, J. & Ritz, A. Direct detection constraints on dark photon dark matter. Phys. Lett. B 747, 331–338 (2015). 46. Hochberg, Y., Lin, T. & Zurek, K. M. Absorption of light dark matter in semiconductors. Phys. Rev. D. 95, 023013 (2017). 47. Zema, V. et al. Dark matter-electron scattering search using cryogenic light detectors. Phys. Rev. D. 110, 123012 (2024). 48. Bento, A. et al. Solar neutrinos in cryogenic detectors. Eur. Phys. J. C. 84, 1118 (2024). 49. Liu, Z. Z. et al. Constraints on spin-independent nucleus scattering with sub-GeV weakly interacting massive particle dark matter from the CDEX-1B experiment at the China Jinping Underground Laboratory. Phys. Rev. Lett. 123, 161301 (2019). 50. Agnese, R. et al. Search for low-mass dark matter with CDMSlite using a profile likelihood fit. Phys. Rev. D. 99, 062001 (2019). the PICO-60 C3F8 bubble chamber. Phys. Rev. D. 100, 022001 (2019).

  The CRESST experiment towards the next generation of sub GeV direct dark matter detection · 2026 · DOI

• detectors, each with a threshold between about 5 eV and 30 eV, and plans an exposure of at least 500 kg ⋅ day. This configuration is expected to enable sensitivity to cross sections as low as Oð10(cid:2)43Þ cm2 and to DM masses below 100 MeV/c2. While great progress has been achieved in elucidating the origin and pursuing the reduction of the LEE, these efforts are still ongoing, and further notable improvements are anticipated. But even in case the LEE cannot be fully eliminated, the CRESST experiment can deliver leading results. Clas- sification of events occurring exclusively at the interface between the target and a sensor has been demonstrated already with new detector module designs. This enables the rejection of excess events that are localized at such interfaces, in contrast to DM events which are expected to interact uni- formly throughout the target bulk. By employing a time-dependent LEE model in a likelihood-based framework, the impact of the LEE on the experiment’s sensitivity can be even further reduced. Moreover, as the LEE decays over time, after 1.5 years of operation a tenfold reduction in the LEE is anticipated, providing a cross section sensitivity that improves over CRESST-III results by more than two orders of magnitude after at most an additional year of data-taking. After 3 years of operation, a reduction factor of 100 is expected, further enhancing the sensitivity significantly. The CRESST upgrade phase will thus be highly sensitive to light DM with masses below 100 MeV/c2 and will additionally have sensitivity to spin-dependent DM interactions, solar axions, dark photons and ALPs. If DM is not dis- covered during this program, the CRESST Collaboration plans to pursue additional upgrades to further improve the sensitivity to light DM, facilitate solar axion and relic dark boson studies, and enable precision measurements of solar neutrinos.

  The CRESST experiment towards the next generation of sub GeV direct dark matter detection · 2026 · DOI

• Spin-dependent dark matter interaction. The CRESST experiment has previously demonstrated the sensitivity of lithium-based targets to spin- dependent interactions. Lithium, with its two isotopes, 6Li and 7Li, is particularly well-suited for these studies. It features unpaired protons and unpaired neutrons, making it sensitive to spin-dependent interactions with both protons and neutrons, and the model uncertainties on the nuclear structure with only few nucleons are comparatively small. In an earlier run, CRESST successfully operated two LiAlO2 detector modules9. This configuration achieved leading limits on spin-dependent proton- only interactions for DM particle masses in the range of 0.25–2.5 GeV/c2 showcasing the potential of lithium-based targets in the search for light DM. In the range of 0.074 to 0.25 GeV/c2, CRESST SOS detectors11 obtained leading limits, using 27Al as a probe to neutron-only interactions. Building on this success, the upgraded CRESST setup will allow for the operation of a significantly larger number of LiAlO2 detectors, substantially improving the sensitivity to spin-dependent interactions. The main back- ground source for these detectors is the decay of tritium, which is produced through neutron capture on 6Li. Reducing this background will require significant efforts to prevent the lithium from exposure to neutrons from mining extraction to crystal production and detector operation. This background, however, is well understood9 and can be incorporated into a likelihood analysis. Consequently, similar improvements as in the case of searches for spin-independent interactions in CaWO4 are expected. Additional science potential with CRESST detectors Bosonic dark matter: dark photons and ALPs. Relic dark photons and ALPs, collectively referred to as dark bosons, are expected to be absorbed in cryogenic calorimeters followed by the emission of an electron car- rying the incoming energy16,45,46. The expected signature of dark bosons is thus a mono-energetic electron recoil peak centered on the rest mass of the dark boson, with a width determined by the resolution of the detector. This spectral shape is distinct from the monotonically decaying energy spectrum of a potential LEE background. CRESST-III achieved energy thresholds down to 6.7 eV with a SOS detector11 and down to 10 eV with a silicon detector8 which correspond directly to the dark boson mass sensitivity. Preliminary studies based on the methods developed in ref. 47 demonstrate the feasibility of these searches in CRESST. The future CRESST experiment has the potential to probe a new region of the bosonic DM mass range, specifically for dark photons and ALPs. To have a statistically significant observation of a peak above background, the larger exposure accessible with the upgraded setup will be required. Solar axions. The potential of cryogenic bolometers for axion detection is demonstrated in ref. 14, which presents an experiment utilizing a Tm3Al5O12 crystal to search for solar axions. This crystal contains 169Tm nuclei, which serve as targets for axion detection via resonant absorption. Given the demonstrated sensitivity of this method and its scalability, it is worth exploring the feasibility of incorporating solar axion searches as a new research avenue within the CRESST program. The upcoming upgrade of the CRESST experiment is expected to increase the number of simultaneously operating detectors, offering a promising platform for such investigations. The Tm3Al5O12 crystals would allow to simultaneously search for light DM and solar axions interactions opening the possibility of different DM- model studies inside CRESST. By utilizing the CRESST facility at LNGS, the extensive shielding that protects against environmental and cosmic radia- tion is likely to reduce background noise, thereby enhancing the sensitivity to solar axions.

  The CRESST experiment towards the next generation of sub GeV direct dark matter detection · 2026 · DOI

• Fig. 6 | Projected sensitivities at 90% confidence level (two-sided) on the elastic, spin-independent DM-nucleon scattering cross section. The simulations are based on the Detector A performance exploring 26 CaWO4 detectors with a threshold of 5 eV and an exposure of 15 kg ⋅ day (double dash double dotted) and 70 CaWO4 detectors with a threshold of 30.1 eV and an exposure of 500 kg ⋅ day (dashed) for two reduction scenarios of the existing Detector A LEE (Excess): 10 times less LEE (in light burgundy color) and 100 times less LEE (in light orange color). For comparison, the limit for Detector A10 (CRESST-III 2019, solid red line), the same limit but with 10% LEE (dashed red line), and the limit for the SOS detector11 (CRESST-III 2024, solid red line) are shown. The bands represent the 1σ region around the median. The gray area highlights the so-called neutrino fog, calculated for CaWO4 in ref. 48. factor applied to the exponential function describing the LEE. For masses up to about 1 GeV/c2, the low-threshold 2 g modules with an exposure of 15 kg ⋅ day provide the strongest exclusion sensitivity. These specialized detectors extend the experiment’s sensitivity range to cover DM masses down to 60 MeV/c2, significantly broadening the experimental reach. At higher masses, the large combined exposure of the 24 g modules yields superior exclusion power. To ensure the readability of the plot, the projections for the two sets of modules are shown only in the mass range where they exhibit leading sensitivity.

  The CRESST experiment towards the next generation of sub GeV direct dark matter detection · 2026 · DOI

• Fig. 3 | CRESST-III detector module. Schematic view (a) and photo (b) of a CRESST-III detector module. Parts in blue are CaWO4, in red are the TESs. The block-shaped target crystal (20 × 20 × 10 mm3) has a mass of 23.6 g. It is held by three CaWO4 sticks. Three additional CaWO4 sticks keep the light detector (20 × 20 × 0.4 mm3) in place. Performance studies with upgraded setup and with LEE The presence of the LEE has significantly limited the experiment’s sensitivity to light DM, which is the primary focus of CRESST-III. To mitigate this excess and to increase the potential discovery to light DM, the collaboration is taking the two aforementioned approaches: The LEE background is being reduced by implementing improved module designs, and advanced analysis strategies are being developed to mitigate the remaining background. Based on recent advancements in detector development, an LEE reduction of a factor of 10–100 is deemed achievable. If none of the mitigation efforts fully eliminate the LEE, or at least significantly reduce it, the reduction factors of 10 and 100 are projected to be reached after ~1.5 and 3 years of continuous operation at base temperature, respectively. These two reduction factors are considered as benchmark values for CRESST upgrade sensitivity studies. A limit projection with the reduction factor of 10 for the LEE, while keeping the background level of Detector A10 constant, was calculated using a likelihood framework34,42. The projection inherits the same 5.594 kg ⋅ day exposure as Detector A. In order to keep the spectral shape of the simulated data close to the observed spectrum, a simultaneous fit of the background and LEE is performed based on the method described in refs. 34,42. The LEE is modeled with an exponential function. The reduction is simulated by scaling the amplitude of the LEE, while all other backgrounds remain unchanged. A thousand Monte-Carlo simulations were performed from which the median and 1σ band were extracted. The result is shown in Fig. 5 in comparison with the current experimental status of world-wide elastic, spin-independent DM-nucleon scattering searches. The implementation of a likelihood analysis framework34 has already demonstrated enhanced sensitivity even in the presence of the LEE and without including its time dependence. In the case of a LEE reduction by a factor of ten for Detector A, the likelihood analysis is expected to improve by a factor of five compared to the Yellin method. Currently the likelihood results in weaker limits than the Yellin method because the latter is designed to deal with unknown backgrounds while likelihood methods rely on an accurate model of all signal and background components present in the data. Thus, a more accurate description of the excess could lead to significantly improved limits.

  The CRESST experiment towards the next generation of sub GeV direct dark matter detection · 2026 · DOI

• allows to efficiently veto recoil events from alpha decays on surfaces or surface-near layers of materials surrounding the crystal31,37. The detector and its schematic view are presented in Fig. 3. Currently, the CRESST experiment tests in different runs a variety of detector modules, each exhibiting distinct configurations22,26. These varia- tions include the use of target materials other than CaWO4 in certain modules, as well as differing crystal holding mechanisms, applying either bronze clamps or copper sticks and gravity-based approaches. These modifications are systematically implemented to investigate potential sources of the LEE.

  The CRESST experiment towards the next generation of sub GeV direct dark matter detection · 2026 · DOI

• detectors. The PE shields against environmental neutrons. The muon veto, covering 98.7% of the experiment’s outer surface, identifies muons, allowing for the rejection of muon-induced events. The experiment is shielded from gamma radiation by 20 cm of lead, weighing 24 t, which effectively absorbs gamma rays due to its high atomic number and density. Within the lead shielding, there is a 14 cm thick layer consisting of 10 t of radiopure copper layer. An additional PE layer inside the experimental volume shields the detectors from neutrons produced by interactions in the lead and copper. To minimize the radioactive background, all materials used around and within the detectors are carefully selected based on their radiopurity. The cooling to the operational temperature of Oð15Þ mK is achieved using a commercial 3He/4He dilution refrigerator. The cryostat and the dewars containing cryogenic liquids do not extend into the low background experimental volume (cold box), ensuring that there is no direct line of sight between the non-radiopure dilution refrigerator and the detectors. The low temperature of the dilution refrigerator is brought into the cold box via a 1.5 m long cold finger. The cold box consists of five concentric radiation shields that surround the experimental volume and the cold finger. The cold finger and the shields are made of radiopure copper.

  The CRESST experiment towards the next generation of sub GeV direct dark matter detection · 2026 · DOI

• both in terms of technological advancements and particle physics include single-photon detection capabilities using a silicon-on-sapphire (SOS) cryogenic detector11, and the first measurement of the 180W α-decay, with a half-life of 1.8(2) × 1018 years13. In addition to the achievable thresholds, another notable advantage of the CRESST technology is its flexibility in the target material, allowing the use of nuclei sensitive to both SI and SD couplings9–11. With well-established technology, CRESST is ready to embark on a comprehensive upgrade. This new phase will feature 288 readout channels, significantly increasing the achievable exposure, with the aim of unprece- dented sensitivity in sub-GeV DM searches reaching a scattering cross section of Oð10(cid:2)42Þ cm2 at 1 GeV/c2. Although the primary goal of CRESST is to probe new DM parameter space for elastic DM-nucleus scattering in the sub-GeV range, it will also enable investigations into other intriguing physics cases, including searches for solar axions14, axion-like particles (ALPs)15, dark photons16 and constraints on self-interaction cross-sections of dark matter in universal bound states17. However, this upgrade presents several challenges. The large number of low-temperature detectors with TESs and Direct Current Superconducting Quantum Interference Devices (DC-SQUIDs) readout introduces additional complexity in the setup. A reformulation of the data processing pipeline is underway to handle the increased data rate and to automate the optimization of detector operational conditions including bias current using reinforcement learning18. First-level quality and live-time cuts, with substantial machine learning efforts are foreseen19 along with the adaptation of existing simulation techniques to efficiently model the entire setup. The new approach will use the likelihood normalization method20 from the current background model while mini- mizing the time required for simulations, analysis, and model development. The original plans for this upgrade have been delayed by the discovery of an increased background event rate below ~200 eV, which was first reported by CRESST-III in 2019. This phenomenon is now known as the Low-Energy Excess (LEE)10. A comparable LEE was soon also reported by other low-threshold experiments employing different detection techniques and/or target materials21–23. The scientific community is making consider- able efforts to understand and mitigate this excess, which hampers sensi- tivity to light DM. To address the LEE, the collaboration has developed new detector layouts24–26, launching dedicated measurement campaigns, the most recent of which began in 2024.

  The CRESST experiment towards the next generation of sub GeV direct dark matter detection · 2026 · DOI

• The paper presents conversion factor calculations only for discrete frequency scans at 25° latitude with integration times of a few hours, and notes that longer time intervals between scans create conversion factor peaks (e.g., at 4.787 GHz). The effect of varying observation latitude, different integration time distributions, and seasonal variations in dark matter halo velocity dispersion on dark photon sensitivity has not been explored.

  Dark photon dark matter constraints at the Taiwan Axion Search Experiment with Haloscope · 2026 · DOI

• The rescanning procedure successfully eliminated 20 out of 22 SNR>3.355 candidates, but the two candidates that persisted (at 4.74730–4.74738 GHz attributed to laboratory instrumentation and 4.71017–4.71019 GHz remaining after magnetic field shutdown) were identified only through external antenna measurements and magnetic field tests. A more systematic characterization of instrumental backgrounds and environmental contamination sources specific to the TASEH haloscope geometry would enable automated candidate rejection.

  Dark photon dark matter constraints at the Taiwan Axion Search Experiment with Haloscope · 2026 · DOI

• The conversion factor calculation assumes isotropic sampling of dark photon polarization directions (θX, ϕX) averaged over discrete scan intervals, but the sensitivity to dark photon polarization states that occur during time gaps between scans (particularly those exceeding 40 minutes) is not quantitatively assessed. Investigation of temporal sampling bias in polarization-dependent detection efficiency would clarify systematic uncertainties.

  Dark photon dark matter constraints at the Taiwan Axion Search Experiment with Haloscope · 2026 · DOI

• The merging procedure for combining five consecutive bins relies on weighted standard deviations of the combined spectrum, but the effects of bin merging on the conversion factor are only evaluated by taking average or minimal values among five adjacent bins. A rigorous statistical treatment accounting for covariance between bins during the merging operation and its impact on signal lineshape reconstruction for dark photon dark matter would strengthen the analysis.

  Dark photon dark matter constraints at the Taiwan Axion Search Experiment with Haloscope · 2026 · DOI

• The TASEH experiment uses averaged Lorentzian cavity response factors (¯Lk values) across the 90 MHz frequency range at 5 GHz, assuming constant lineshape behavior. However, the validity of this approximation and potential systematic biases from frequency-dependent variations in the cavity response function for polarized dark photon detection across broader frequency ranges (beyond the operational range) has not been characterized.

  Dark photon dark matter constraints at the Taiwan Axion Search Experiment with Haloscope · 2026 · DOI

• The dependence on the ordinary matter equation of state for mass-radius measurements in dark matter admixed neutron stars is noted but not systematically characterized; controlled variations across different ordinary matter EoS models (beyond the three employed) are needed to quantify this sensitivity.

  Strongly interacting dark matter admixed neutron stars · 2026 · DOI

• For large dark matter candidate masses where dark matter forms compact cores, the light and heavy ensemble equations of state produce divergent dark matter radii; the specific physical conditions and equation of state parameters that cause this bifurcation require detailed investigation.

  Strongly interacting dark matter admixed neutron stars · 2026 · DOI

• The paper identifies solutions with light dark matter (mC = 0.5 GeV) that form massive dark matter halos (>4 M⊙) at ordinary matter radii similar to neutron stars, but does not specify the formation mechanisms, stability criteria, or observational distinguishability of these non-standard compact stellar objects from conventional neutron stars.

  Strongly interacting dark matter admixed neutron stars · 2026 · DOI

• The study shows that tidal deformability of dark matter admixed neutron stars does not depend on the dark matter equation of state but mostly on the dark matter candidate mass; however, the mechanisms underlying this independence and how it translates to observational signatures in gravitational wave events remain uncharacterized.

  Strongly interacting dark matter admixed neutron stars · 2026 · DOI

• Neutrino oscillations in DM-dense regions such as sub-halos and DM stars may provide indirect tests to the DM density, representing an unexplored application area.

  Neutrino oscillation in dark matter with <i>L</i> _<i>μ</i> − <i>L</i> _<i>τ</i> · 2026 · DOI

• The results can be applied to evaluate the DM density distribution indirectly by analyzing neutrino oscillation data of known astrophysical sourced neutrino beams, suggesting future work in indirect DM detection.

  Neutrino oscillation in dark matter with <i>L</i> _<i>μ</i> − <i>L</i> _<i>τ</i> · 2026 · DOI

• Neutrino oscillation may decouple for an ultra-large Aχ, and it is unlikely to get a large Aχ except for a super high energy neutrino beam given typical DM densities on Earth (~0.4 GeV/cm³).

  Neutrino oscillation in dark matter with <i>L</i> _<i>μ</i> − <i>L</i> _<i>τ</i> · 2026 · DOI

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• Sealed forward prediction: the dark-energy equation of state is exactly w = −1 (UCT program) · Zenodo (CERN European Organization for Nuclear Research) · 2026
• Minicharged particles at accelerators: progress and prospects · The European Physical Journal Special Topics · 2026
• Improved Dark Photon Sensitivity from a Superconducting-Radio-Frequency-Cavity Experiment · Physical Review Letters · 2026
• How Dark is Dark? A Reflectance and Scattering Analysis of Black Materials · Journal of the Optical Society of America A · 2026
• Highest-energy neutrino event constrains dark matter-neutrino interactions · Physical Review D · 2026
• Model-independent searches of new physics in DARWIN with deep learning · The European Physical Journal C · 2026
• Rare event searches using cryogenic detectors via direct detection methods · Modern Physics Letters A · 2026
• Neutrino oscillation in dark matter with <i>L</i> _<i>μ</i> − <i>L</i> _<i>τ</i> · Communications in Theoretical Physics · 2026
• Dark photon dark matter constraints at the Taiwan Axion Search Experiment with Haloscope · Physical Review D · 2026
• Strongly interacting dark matter admixed neutron stars · SciPost Physics Core · 2026

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