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1. Magnetogram-matching Biot–Savart Law and Decomposition of Vector Magnetograms

   https://doi.org/10.3847/1538-4357/add895  

   Titov, Viacheslav S; Downs, Cooper; Török, Tibor; Linker, Jon A; Prazak, Michael; Qiu, Jiong A (July 2025, The Astrophysical Journal)

   Abstract We generalize a magnetogram-matching Biot–Savart law (BSl) from planar to spherical geometry. For a given coronal current densityJ, this law determines the magnetic field $\tilde{\mathit{B}}$ whose radial component vanishes at the surface. The superposition of $\tilde{\mathit{B}}$ with a potential field defined by a given surface radial field,B_r, provides the entire configuration whereB_rremains unchanged by the currents. Using this approach, we (1) upgrade our regularized BSls for constructing coronal magnetic flux ropes (MFRs) and (2) propose a new method for decomposing a measured photospheric magnetic field as $\mathit{B}={\mathit{B}}_{\mathrm{pot}}+{\mathit{B}}_T+{\mathit{B}}_{\tilde{S}}$ , where the potential,B_pot, toroidal,B_T, and poloidal, ${\mathit{B}}_{\tilde{S}}$ , fields are determined byB_r,J_r, and the surface divergence ofB–B_pot, respectively, all derived from magnetic data. OurB_Tis identical to the one in the alternative Gaussian decomposition by P. W. Schuck et al., whileB_potand ${\mathit{B}}_{\tilde{S}}$ are different from their poloidal fields ${\mathit{B}}_{\mathrm{P}}^{<}$ and ${\mathit{B}}_{\mathrm{P}}^{>}$ , which arepotentialin the infinitesimal proximity to the upper and lower side of the surface, respectively. In contrast, our ${\mathit{B}}_{\tilde{S}}$ has no such constraints and, asB_potandB_T, refers to thesameupper side of the surface. In spite of these differences, for a continuousJdistribution across the surface,B_potand ${\mathit{B}}_{\tilde{S}}$ are linear combinations of ${\mathit{B}}_{\mathrm{P}}^{<}$ and ${\mathit{B}}_{\mathrm{P}}^{>}$ . We demonstrate that, similar to the Gaussian method, our decomposition allows one to identify the footprints and projected surface-location of MFRs in the solar corona, as well as the direction and connectivity of their currents. 

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2. Search for heavy pseudoscalar and scalar bosons decaying to a top quark pair in proton–proton collisions at $\sqrt{s}=13\text{TeV}$

   https://doi.org/10.1088/1361-6633/ae2207  

   Collaboration, The CMS (December 2025, Reports on Progress in Physics)

   Abstract A search for pseudoscalar or scalar bosons decaying to a top quark pair ( $\text{t}\overline{\text{t}}$ ) in final states with one or two charged leptons is presented. The analyzed proton–proton collision data was recorded at $\sqrt{s}=13\text{TeV}$ by the CMS experiment at the CERN LHC and corresponds to an integrated luminosity of 138  ${\text{fb}}^{-1}$ . The invariant mass $m_{\mathrm{t}\overline{\mathrm{t}}}$ of the reconstructed $\text{t}\overline{\text{t}}$ system and variables sensitive to its spin and parity are used to discriminate against the standard model $\text{t}\overline{\text{t}}$ background. Interference between pseudoscalar or scalar boson production and the standard model $\text{t}\overline{\text{t}}$ continuum is included, leading to peak-dip structures in the $m_{\mathrm{t}\overline{\mathrm{t}}}$ distribution. An excess of the data above the background prediction, based on perturbative quantum chromodynamics (QCD) calculations, is observed near the kinematic $\text{t}\overline{\text{t}}$ production threshold, while good agreement is found for high $m_{\mathrm{t}\overline{\mathrm{t}}}$ . The data are consistent with the background prediction if the contribution from a simplified model of a color-singlet ${}^1{\text{S}}_0^{\left[1\right]}$ $\text{t}\overline{\text{t}}$ quasi-bound state ${\eta }_{\mathrm{t}}$ , inspired by nonrelativistic QCD, is added. Upper limits at 95% confidence level are set on the coupling between the pseudoscalar or scalar bosons and the top quark for boson masses in the range 365–1000 GeV, relative widths between 0.5% and 25%, and two background scenarios with or without ${\eta }_{\mathrm{t}}$ contribution. 

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3. Observation of a pseudoscalar excess at the top quark pair production threshold

   https://doi.org/10.1088/1361-6633/adf7d3  

   Collaboration, The CMS (August 2025, Reports on Progress in Physics)

   Abstract A search for resonances in top quark pair ( $\mathrm{t}\bar{\mathrm{t}}$ ) production in final states with two charged leptons and multiple jets is presented, based on proton–proton collision data collected by the CMS experiment at the CERN LHC at $\sqrt{s}=13\text{TeV}$ , corresponding to 138 fb⁻¹. The analysis explores the invariant mass of the $\mathrm{t}\bar{\mathrm{t}}$ system and two angular observables that provide direct access to the correlation of top quark and antiquark spins. A significant excess of events is observed near the kinematic $\mathrm{t}\bar{\mathrm{t}}$ threshold compared to the non-resonant production predicted by fixed-order perturbative quantum chromodynamics (pQCD). The observed enhancement is consistent with the production of a color-singlet pseudoscalar ( ${}^1{\text{S}}_0^{\left[1\right]}$ ) quasi-bound toponium state, as predicted by non-relativistic quantum chromodynamics. Using a simplified model for ${}^1{\text{S}}_0^{\left[1\right]}$ toponium, the cross section of the excess above the pQCD prediction is measured to be $8.8{}_{-1.4}^{+1.2}\text{pb}$ . 

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4. (Nearly) Model-independent Constraints on the Neutral Hydrogen Fraction in the Intergalactic Medium at z ∼ 5–7 Using Dark Pixel Fractions in Lyα and Lyβ Forests

   https://doi.org/10.3847/1538-4357/aca678  

   Jin, Xiangyu; Yang, Jinyi; Fan, Xiaohui; Wang, Feige; Bañados, Eduardo; Bian, Fuyan; Davies, Frederick B.; Eilers, Anna-Christina; Farina, Emanuele Paolo; Hennawi, Joseph F.; et al (January 2023, The Astrophysical Journal)

   Abstract Cosmic reionization was the last major phase transition of hydrogen from neutral to highly ionized in the intergalactic medium (IGM). Current observations show that the IGM is significantly neutral atz> 7 and largely ionized byz∼ 5.5. However, most methods to measure the IGM neutral fraction are highly model dependent and are limited to when the volume-averaged neutral fraction of the IGM is either relatively low ( ${\overline{x}}_{\mathrm{H}\mathrm{I}}\lesssim {10}^{-3}$ ) or close to unity ( ${\overline{x}}_{\mathrm{H}\mathrm{I}}\sim 1$ ). In particular, the neutral fraction evolution of the IGM at the critical redshift range ofz= 6–7 is poorly constrained. We present new constraints on ${\overline{x}}_{\mathrm{H}\mathrm{I}}$ atz∼ 5.1–6.8 by analyzing deep optical spectra of 53 quasars at 5.73 <z< 7.09. We derive model-independent upper limits on the neutral hydrogen fraction based on the fraction of “dark” pixels identified in the Lyαand Lyβforests, without any assumptions on the IGM model or the intrinsic shape of the quasar continuum. They are the first model-independent constraints on the IGM neutral hydrogen fraction atz∼ 6.2–6.8 using quasar absorption measurements. Our results give upper limits of ${\overline{x}}_{\mathrm{H}\mathrm{I}}(z=6.3)<0.79\pm 0.04$ (1σ), ${\overline{x}}_{\mathrm{H}\mathrm{I}}(z=6.5)<0.87\pm 0.03$ (1σ), and ${\overline{x}}_{\mathrm{H}\mathrm{I}}(z=6.7)<{0.94}_{-0.09}^{+0.06}$ (1σ). The dark pixel fractions atz> 6.1 are consistent with the redshift evolution of the neutral fraction of the IGM derived from Planck 2018. 

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5. Metallicity Dependence of Pressure-regulated Feedback-modulated Star Formation in the TIGRESS-NCR Simulation Suite

   https://doi.org/10.3847/1538-4357/ad59ab  

   Kim, Chang-Goo; Ostriker, Eve C; Kim, Jeong-Gyu; Gong, Munan; Bryan, Greg L; Fielding, Drummond B; Hassan, Sultan; Ho, Matthew; Jeffreson, Sarah_M R; Somerville, Rachel S; et al (August 2024, The Astrophysical Journal)

   Abstract We present a new suite of numerical simulations of the star-forming interstellar medium (ISM) in galactic disks using the TIGRESS-NCR framework. Distinctive aspects of our simulation suite are (1) sophisticated and comprehensive numerical treatments of essential physical processes including magnetohydrodynamics, self-gravity, and galactic differential rotation, as well as photochemistry, cooling, and heating coupled with direct ray-tracing UV radiation transfer and resolved supernova feedback and (2) wide parameter coverage including the variation in metallicity over $Z\prime \equiv Z/Z_{\odot }\sim 0.1-3$ , gas surface density Σ_gas∼ 5–150M_⊙pc⁻², and stellar surface density Σ_star∼ 1–50M_⊙pc⁻². The range of emergent star formation rate surface density is Σ_SFR∼ 10⁻⁴–0.5M_⊙kpc⁻²yr⁻¹, and ISM total midplane pressure isP_tot/k_B= 10³–10⁶cm⁻³K, withP_totequal to the ISM weight $\mathcal{W}$ . For given Σ_gasand Σ_star, we find ${\mathrm{\Sigma }}_{\mathrm{SFR}}\propto Z{\prime }^{0.3}$ . We provide an interpretation based on the pressure-regulated feedback-modulated (PRFM) star formation theory. The total midplane pressure consists of thermal, turbulent, and magnetic stresses. We characterize feedback modulation in terms of the yield ϒ, defined as the ratio of each stress to Σ_SFR. The thermal feedback yield varies sensitively with both weight and metallicity as ${\mathrm{\Upsilon }}_{\mathrm{th}}\propto {\mathcal{W}}^{-0.46}Z{\prime }^{-0.53}$ , while the combined turbulent and magnetic feedback yield shows weaker dependence ${\mathrm{\Upsilon }}_{\mathrm{turb}+\mathrm{mag}}\propto {\mathcal{W}}^{-0.22}Z{\prime }^{-0.18}$ . The reduction in Σ_SFRat low metallicity is due mainly to enhanced thermal feedback yield, resulting from reduced attenuation of UV radiation. With the metallicity-dependent calibrations we provide, PRFM theory can be used for a new subgrid star formation prescription in cosmological simulations where the ISM is unresolved. 

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