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1. Azimuthal single- and double-spin asymmetries in semi-inclusive deep-inelastic lepton scattering by transversely polarized protons

   https://doi.org/10.1007/JHEP12(2020)010  

   Airapetian, A.; Akopov, N.; Akopov, Z.; Aschenauer, E. C.; Augustyniak, W.; Avakian, R.; Bacchetta, A.; Belostotski, S.; Bryzgalov, V.; Capitani, G. P.; et al (December 2020, Journal of High Energy Physics)

   null (Ed.)

   A bstract A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi-inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized protons is presented. These asymmetries include the previously published HERMES results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining four single-spin and four double-spin asymmetries allowed in the one-photon-exchange approximation of the semi-inclusive deep-inelastic scattering process for target-polarization orientation perpendicular to the direction of the incoming lepton beam. Among those results, significant non-vanishing cos ( ϕ−ϕ S ) modulations provide evidence for a sizable worm-gear (II) distribution, $$ {g}_{1\mathrm{T}}^q\left(x,{\mathrm{p}}_T^2\right) $$ g 1 T q x p T 2 . Most of the other modulations are found to be consistent with zero with the notable exception of large sin ( ϕ S ) modulations for charged pions and K + . 

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2. Wavelet-based ULF pulsation indices and their application to geomagnetically conjugate ULF pulsation studies at high latitudes

   Xu, Z; Clauer, C; Hartinger, M; Kim, H; Weimer, D (March 2024, CHINESE JOURNAL OF POLAR RESEARCH)

   He, Jian_Jun (Ed.)

   Geomagnetic Ultra Low Frequency (ULF) are terrestrial manifestations of the propagation of very low frequency magnetic fluid waves in the magnetosphere, and it is critical to develop near real-time space weather products to monitor these geomagnetic disturbances. A wavelet-based index is described in this paper and applied to study geomagnetic ULF pulsations observed in Antarctica and their magnetically conjugate locations in West Greenland. Results showed that (1) the index is effective for identification of pulsation events in the Pc4–Pc5 frequency range, including transient events, and measures important characteristics of ULF pulsations in both the temporal and frequency domains. (2) Comparison between conjugate locations reveals the similarities and differences between ULF pulsations in northern and southern hemispheres during solstice conditions, when the largest asymmetries are expected. Results also showed that the geomagnetic pulsations at conjugate locations respond differently according to the Interplanetary Magnetic Field condition, magnetic field topology, magnetic latitude of the observation, and other conditions. The actual magnetospheric and ionospheric configurations and driving conditions in the case need to be further studied. 

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3. Constraints on primordial lepton asymmetries with full neutrino transport

   https://doi.org/10.1103/PhysRevD.110.103551  

   Froustey, Julien; Pitrou, Cyril (November 2024, Physical Review D)

   Primordial neutrino-antineutrino asymmetries can be constrained through big-bang nucleosynthesis (BBN) relic abundances and cosmic microwave background (CMB) anisotropies, both observables being sensitive to neutrino properties. The latter constraint, which is due to gravitational effects from all neutrino flavors, is very minute since it is at least quadratic in the asymmetries. On the contrary, the constraints from primordial abundances presently dominate, although these abundances are almost only sensitive to the electron flavor asymmetry. It is generally assumed that neutrino asymmetries are sufficiently averaged by flavor oscillations prior to BBN, which allows one to constrain a common primordial neutrino asymmetry at the epoch of BBN. This simplified approach suffers two caveats that we deal with in this article, combining a neutrino evolution code and BBN calculation throughout the MeV era. First, flavor “equilibration” is not true in general, therefore an accurate dynamical evolution of asymmetries is needed to connect experimental observables to the asymmetries. Second, the approximate averaging of asymmetries through flavor oscillations is associated to a reheating of the primordial plasma. It is therefore crucial to correctly describe the interplay between flavor equilibration and neutrino decoupling, as an energy redistribution prior to decoupling does not significantly alter the final effective number of neutrino species’ value. Overall, we find that the space of allowed initial asymmetries is generically unbound when using currently available primordial abundances and CMB measurements. We forecast constraints using future CMB experiment capabilities, which should reverse this experimental misfortune. Published by the American Physical Society2024 

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4. Quantifying Extreme Values in Geomagnetic Perturbations Using Ground Magnetic Records

   https://doi.org/10.1029/2024SW003991  

   Rodríguez‐Zuluaga, J.; Gjerloev, J.; Ohtani, S.; Zou, Y.; Anderson, B. (July 2024, Space Weather)

   Abstract We comprehensively analyzed geomagnetic perturbations using ground magnetic records from over 400 stations spanning four solar cycles, from 1976 to 2023. We assess the perturbations in the three magnetic components separately. Our study covers low, middle, and high magnetic latitudes in the northern magnetic hemisphere, with the primary objective of quantifying extreme values and evaluating their variability on magnetic latitude, local time, and solar cycle phases “minimum, ascending, maximum, and declining.” Our findings reveal spatial patterns to be less discernible as perturbations intensify, with distinct responses at middle and high latitudes. The extreme values, defined as percentiles 0 and 100, were observed to be localized and randomly distributed in local time, especially in the east magnetic component. Additionally, we observed dusk‐dawn asymmetries in the magnitude of perturbations related to the auroral electrojets, indicating complex interactions between the magnetosphere and ionosphere. Furthermore, the results reveal a preference for the most significant extreme values to occur in the declining phase of the solar cycle. These insights deepen our understanding of geomagnetic perturbations and their variability, contributing to space weather forecasting and mitigation strategies. 

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5. The Loss of Starlink Satellites in February 2022: How Moderate Geomagnetic Storms Can Adversely Affect Assets in Low‐Earth Orbit

   https://doi.org/10.1029/2023SW003716  

   Baruah, Yoshita; Roy, Souvik; Sinha, Suvadip; Palmerio, Erika; Pal, Sanchita; Oliveira, Denny M; Nandy, Dibyendu (April 2024, Space Weather)

   Abstract On 3 February 2022, SpaceX launched 49 Starlink satellites, 38 of which unexpectedly de‐orbited. Although this event was attributed to space weather, definitive causality remained elusive because space weather conditions were not extreme. In this study, we identify solar sources of the interplanetary coronal mass ejections that were responsible for the geomagnetic storms around the time of launch of the Starlink satellites and for the first time, investigate their impact on Earth's magnetosphere using magnetohydrodynamic modeling. The model results demonstrate that the satellites were launched into an already disturbed space environment that persisted over several days. However, on performing comparative satellite orbital decay analyses, we find that space weather alone was not responsible but conspired together with a low‐altitude insertion and low satellite mass‐to‐area ratio to precipitate this unusual loss. Our work bridges space weather causality across the Sun–Earth system—with relevance for space‐based human technologies. 

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