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1. 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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2. Sequence modeling of higher-order wave modes of quasi-circular, spinning, non-precessing binary black hole mergers

   https://doi.org/10.1088/1361-6382/ae2bd6  

   Tiki, Victoria; Pham, Kiet; Huerta, E A (December 2025, Classical and Quantum Gravity)

   Abstract Higher-order gravitational wave modes from quasi-circular, spinning, non-precessing binary-black-hole (BBH) mergers encode rich information about the nonlinear dynamics of strong-field gravity. We present a transformer-based sequence-completion surrogate that, given an early-inspiral segment, forecasts the subsequent late inspiral, merger, and ringdown. The intended applications are (i) patching or completing expensive or interrupted numerical-relativity (NR) simulations and (ii) providing late-time cross-checks and rapid hybridization studies. The training set is built from theNRHybSur3dq8surrogate, which provides spherical-harmonic modes up to $\ell \text{⩽}4$ (excluding (4, 0) and $(4,\pm 1)$ , and including (5, 5)) for mass ratios $q\text{⩽}8$ , dimensionless spin components $s_{1,2}^z\in [-0.8,0.8]$ , and inclination angles $\theta \in [0,\pi ]$ . Waveforms are supplied on the interval $t\in [-5000\mathrm{M},-100\mathrm{M})$ and the model autoregressively generates the plus and cross polarizations $(h_{+},h_{\times })$ on $t\in [-100\mathrm{M},130\mathrm{M}]$ . Training on the Delta supercomputer with 16 NVIDIA A100 GPUs required $\sim 15$  h on more than 14 million hybrid waveforms. Evaluation on a held-out test set of $\mathrm{840,000}$ samples yields mean and median overlaps of 0.996 and 0.997, respectively, with respect to the surrogate ground truth. The model generalises reasonably well to out-of-distribution NR simulations from the SXS catalogue: across 521 NR waveforms with mass ratios up toq = 15 and spin magnitudes $|s|\text{⩽}0.998$ , we obtain a median overlap of 0.969, rising to 0.998 for face-on/off orientations. Within the surrogate’s training domain, the transformer provides accurate, millisecond-scale sequence completion of BBH waveforms, including higher-order modes, from early inspiral to ringdown. The NR tests indicate promising performance on higher-fidelity, out-of-distribution data, particularly for detector-favourable orientations. 

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3. Observation of $\text{γ}\text{γ}\to \text{τ}\text{τ}$ in proton–proton collisions and limits on the anomalous electromagnetic moments of the τ lepton

   https://doi.org/10.1088/1361-6633/ad6fcb  

   CMS_Collaboration, The (September 2024, Reports on Progress in Physics)

   Abstract The production of a pair of τ leptons via photon–photon fusion, $\text{γ}\text{γ}\to \text{τ}\text{τ}$ , is observed for the first time in proton–proton collisions, with a significance of 5.3 standard deviations. This observation is based on a data set recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb⁻¹. Events with a pair of τ leptons produced via photon–photon fusion are selected by requiring them to be back-to-back in the azimuthal direction and to have a minimum number of charged hadrons associated with their production vertex. The τ leptons are reconstructed in their leptonic and hadronic decay modes. The measured fiducial cross section of $\text{γ}\text{γ}\to \text{τ}\text{τ}$ is ${\sigma }_{\text{obs}}^{\text{fid}}={12.4}_{-3.1}^{+3.8}\text{fb}$ . Constraints are set on the contributions to the anomalous magnetic moment ( $a_{\text{τ}}$ ) and electric dipole moments ( $d_{\text{τ}}$ ) of the τ lepton originating from potential effects of new physics on the $\text{γ}\text{τ}\text{τ}$ vertex: $a_{\text{τ}}={0.0009}_{-0.0031}^{+0.0032}$ and $|d_{\text{τ}}|<2.9\times {10}^{-17}e\text{cm}$ (95% confidence level), consistent with the standard model. 

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4. HSTPROMO Internal Proper-motion Kinematics of Dwarf Spheroidal Galaxies. I. Velocity Anisotropy and Dark Matter Cusp Slope of Draco

   https://doi.org/10.3847/1538-4357/ad571c  

   Vitral, Eduardo; van_der_Marel, Roeland P; Sohn, Sangmo Tony; Libralato, Mattia; del_Pino, Andrés; Watkins, Laura L; Bellini, Andrea; Walker, Matthew G; Besla, Gurtina; Pawlowski, Marcel S; et al (July 2024, The Astrophysical Journal)

   Abstract We analyze four epochs of Hubble Space Telescope imaging over 18 yr for the Draco dwarf spheroidal galaxy. We measure precise proper motions for hundreds of stars and combine these with existing line-of-sight (LOS) velocities. This provides the first radially resolved 3D velocity dispersion profiles for any dwarf galaxy. These constrain the intrinsic velocity anisotropy and resolve the mass–anisotropy degeneracy. We solve the Jeans equations in oblate axisymmetric geometry to infer the mass profile. We find the velocity dispersion to be radially anisotropic along the symmetry axis and tangentially anisotropic in the equatorial plane, with a globally averaged value $\overline{{\beta }_{\mathrm{B}}}=-{0.20}_{-0.53}^{+0.28}$ , (where 1 – ${\beta }_{\mathrm{B}}\equiv 〈v_{\tan }^2〉/〈v_{\mathrm{rad}}^2〉$ in 3D). The logarithmic dark matter (DM) density slope over the observed radial range, Γ_dark, is $-{0.83}_{-0.37}^{+0.32}$ , consistent with the inner cusp predicted in ΛCDM cosmology. As expected given Draco’s low mass and ancient star formation history, it does not appear to have been dissolved by baryonic processes. We rule out cores larger than 487, 717, and 942 pc at 1σ, 2σ, and 3σconfidence, respectively, thus imposing important constraints on the self-interacting DM cross section. Spherical models yield biased estimates for both the velocity anisotropy and the inferred slope. The circular velocity at our outermost data point (900 pc) is ${24.19}_{-2.97}^{+6.31}\mathrm{km}{\mathrm{s}}^{-1}$ . We infer a dynamical distance of ${75.37}_{-4.00}^{+4.73}$ kpc and show that Draco has a modest LOS rotation, with $\left(v/\sigma \right)=0.22\pm 0.09$ . Our results provide a new stringent test of the so-called “cusp–core” problem that can be readily extended to other dwarfs. 

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5. 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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