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1. Statistical Analysis of the Differential Deep Penetration of Energetic Electrons and Protons into the Low L Region ( L  < 4)

   https://doi.org/10.1029/2022JA031125  

   Zhao, H.; Califf, S. T.; Goyal, R.; Li, X.; Gkioulidou, M.; Manweiler, J. W.; Krantz, S. (April 2023, Journal of Geophysical Research: Space Physics)

   Abstract Deep penetration of energetic electrons (10s–100s of keV) to lowL‐shells (L < 4), as an important source of inner belt electrons, is commonly observed during geomagnetically active times. However, such deep penetration is not observed as frequently for similar energy protons, for which underlying mechanisms are not fully understood. To study their differential deep penetration, we conducted a statistical analysis using phase space densities (PSDs) ofµ = 10–50 MeV/G,K = 0.14 G^1/2Re electrons and protons from multiyear Van Allen Probes observations. The results suggest systematic differences in electron and proton deep penetration: electron PSD enhancements at lowL‐shells occur more frequently, deeply, and faster than protons. Forµ = 10–50 MeV/G electrons, the occurrence rate of deep penetration events (defined as daily‐averaged PSD enhanced by at least a factor of 2 within a day atL < 4) is ∼2–3 events/month. For protons, only ∼1 event/month was observed forµ = 10 MeV/G, and much fewer events were identified forµ > 20 MeV/G. Leveraging dual‐Probe configurations, fast electron deep penetrations atL < 4 are revealed: ∼70% of electron deep penetration events occurred within ∼9 hr; ∼8%–13% occurred even within 3 hr, with lower‐µelectrons penetrating faster than higher‐µelectrons. These results suggest nondiffusive radial transport as the main mechanism of electron deep penetrations. In comparison, proton deep penetration happens at a slower pace. Statistics also show that the electron PSD radial gradient is much steeper than protons prior to deep penetration events, which can be responsible for these differential behaviors of electron and proton deep penetrations. 

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2. Limits on Kaluza-Klein portal dark matter models

   https://doi.org/10.1103/PhysRevD.111.075030  

   Chivukula, R Sekhar; Gill, Joshua A; Mohan, Kirtimaan A; Sanamyan, George; Sengupta, Dipan; Simmons, Elizabeth H; Wang, Xing (April 2025, Physical Review D)

   We revisit the phenomenology of dark matter (DM) scenarios within radius-stabilized Randall-Sundrum models. Specifically, we consider models where the dark matter candidates are Standard Model (SM) singlets confined to the TeV-brane and interact with the SM via spin-2 and spin-0 gravitational Kaluza-Klein (KK) modes. We compute the thermal relic density of DM particles in these models by applying recent work showing that scattering amplitudes of massive spin-2 KK states involve an intricate cancellation between various diagrams. Considering the resulting DM abundance, collider searches, and the absence of a signal in direct DM detection experiments, we show that spin-2 KK portal DM models are highly constrained. In particular, we confirm that within the usual thermal freeze-out scenario, scalar dark matter models are essentially ruled out. In contrast, we show that fermion and vector dark matter models are viable in a region of parameter space in which dark matter annihilation through a KK graviton is resonant. Specifically, vector models are viable for dark matter masses ranging from 1.1 to 5.5 TeV for theories in which the scale of couplings of the KK modes is of order 40 TeV or lower. Fermion dark matter models are viable for a similar mass region, but only for KK coupling scales of order 20 TeV. In this work, we provide a complete description of the calculations needed to arrive at these results and, provide a discussion of new KK-graviton couplings needed for the computations, which have not previously been discussed in the literature. Here, we focus on models in which the radion is light, and the backreaction of the radion stabilization dynamics on the gravitational background can be neglected. The phenomenology of a model with a heavy radion and the consideration of the effects of the radion stabilization dynamics on the DM abundance will be addressed in forthcoming work. Published by the American Physical Society2025 

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3. Machine Learning Approach for Estimating Magnetic Field Strength in Galaxy Clusters from Synchrotron Emission

   https://doi.org/10.3847/1538-4357/adeb7a  

   Zhang, Jiyao; Hu, Yue; Lazarian, Alex (August 2025, The Astrophysical Journal)

   Abstract Magnetic fields play a crucial role in various astrophysical processes within the intracluster medium, including heat conduction, cosmic-ray acceleration, and the generation of synchrotron radiation. However, measuring magnetic field strength is typically challenging due to the limited availability of Faraday rotation measure sources. To address the challenge, we propose a novel method that employs Convolutional Neural Networks (CNNs) alongside synchrotron emission observations to estimate magnetic field strengths in galaxy clusters. Our CNN model is trained on either magnetohydrodynamic (MHD) turbulence simulations or MHD galaxy cluster simulations, which incorporate complex dynamics such as cluster mergers and sloshing motions. The results demonstrate that CNNs can effectively estimate magnetic field strengths with mean-squared error of approximately 0.135µG², 0.044µG², and 0.02µG²forβ = 100, 200, and 500 conditions, respectively. Additionally, we have confirmed that our CNN model remains robust against noise and variations in viewing angles with sufficient training, ensuring reliable performance under a wide range of observational conditions. We compare the CNN approach with the traditional magnetic field strength estimate method that assumes equipartition between cosmic-ray electron energy and magnetic field energy. In contrast to the equipartition method, this CNN approach relies on the morphological feature of synchrotron images, offering a new perspective for complementing traditional estimates and enhancing our understanding of cosmic-ray acceleration mechanisms. 

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4. Band alignments, conduction band edges and intralayer bandgap renormalisation in MoSe ₂ /WSe ₂ heterobilayers

   https://doi.org/10.1088/2053-1583/ad7b51  

   Graham, A_J; Nguyen, P_V; Park, H.; Nunn, J.; Kandyba, V.; Cattelan, M.; Giampietri, A.; Barinov, A.; Xu, X.; Cobden, D_H; et al (September 2024, 2D Materials)

   Abstract Stacking two semiconducting transition metal dichalcogenide (MX₂) monolayers to form a heterobilayer creates a new variety of semiconductor junction with unique optoelectronic features, such as hosting long-lived dipolar interlayer excitons. Despite many optical, transport, and theoretical studies, there have been few direct electronic structure measurements of these junctions. Here, we apply angle-resolved photoemission spectroscopy with micron-scale spatial resolution (µARPES) to determine the band alignments in MoSe₂/WSe₂heterobilayers, usingin-situelectrostatic gating to electron-dope and thus probe the conduction band edges. By comparing spectra from heterobilayers with opposite stacking orders, that is, with either MoSe₂or WSe₂on top, we confirm that the band alignment is type II, with the valence band maximum in the WSe₂and the conduction band minimum in the MoSe₂. The overall band gap isE_G= 1.43 ± 0.03 eV, and to within experimental uncertainty it is unaffected by electron doping. However, the offset between the WSe₂and MoSe₂valence bands clearly decreases with increasing electron doping, implying band renormalisation only in the MoSe₂, the layer in which the electrons accumulate. In contrast,µARPES spectra from a WS₂/MoSe₂heterobilayer indicate type I band alignment, with both band edges in the MoSe₂. These insights into the doping-dependent band alignments and gaps of MX₂heterobilayers will be useful for properly understanding and ultimately utilizing their optoelectronic properties. 

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5. Manganese catalysed dehydrocoupling of silanes and siloxanes with ammonia to prepare oligosilazanes and polysiloxazanes

   https://doi.org/10.1039/d4dt01982b  

   Mehta, Gautam K; Nguyen, Thao T; Flores, Marco; Trovitch, Ryan J (August 2024, Dalton Transactions)

   The halogen-free synthesis of oligosilazanes has been observed upon dehydrocoupling silanes with ammonia at 25 °C using [(2,6-iPr2PhBDI)Mn(µ-H)]2. Extending this methodology to polymethyl-hydrosiloxanes afforded thermally robust polysiloxazane solids, and the dehydrocoupling of 1,3,5,7-tetramethylcyclotetrasiloxane with ammonia afforded a polysiloxazane having a weight-average molecular weight of 4300 g/mol. A representative oligosilazane has been applied to a copper surface and found to afford a 20 μm thick coating that resists corrosion after 24 h under water. Addition of ammonia to [(2,6-iPr2PhBDI)Mn(µ-H)]2 allowed for characterization of the catalyst resting state, [(2,6-iPr2PhBDI)Mn(µ-NH2)]2, which has been found to mediate Si‒N dehydrocoupling. 

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