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1. The Stellar Mass–Black Hole Mass Relation at z ∼ 2 down to ${}_{\mathrm{BH}}\sim {10}^7{M}_{\odot }$ Determined by HETDEX

   https://doi.org/10.3847/1538-4357/acc2c2  

   Zhang, Yechi; Ouchi, Masami; Gebhardt, Karl; Liu, Chenxu; Harikane, Yuichi; Cooper, Erin_Mentuch; Davis, Dustin; Farrow, Daniel_J; Gawiser, Eric; Hill, Gary_J; et al (May 2023, The Astrophysical Journal)

   Abstract We investigate the stellar mass–black hole mass ( ${\mathit{}}_{*}–{\mathit{}}_{\mathrm{BH}}$) relation with type 1 active galactic nuclei (AGNs) down to ${\mathit{}}_{\mathrm{BH}}={10}^7{M}_{\odot }$, corresponding to a ≃ −21 absolute magnitude in rest-frame ultraviolet, atz= 2–2.5. Exploiting the deep and large-area spectroscopic survey of the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX), we identify 66 type 1 AGNs with ${\mathit{}}_{\mathrm{BH}}$ranging from 10⁷–10¹⁰M_⊙that are measured with single-epoch virial method using Civemission lines detected in the HETDEX spectra. ${\mathit{}}_{*}$of the host galaxies are estimated from optical to near-infrared photometric data taken with Spitzer, the Wide-field Infrared Survey Explorer, and ground-based 4–8 m class telescopes byCIGALEspectral energy distribution (SED) fitting. We further assess the validity of SED fitting in two cases by host-nuclear decomposition performed through surface brightness profile fitting on spatially resolved host galaxies with the James Webb Space Telescope/NIRCam CEERS data. We obtain the ${\mathit{}}_{*}–{\mathit{}}_{\mathrm{BH}}$relation covering the unexplored low-mass ranges of ${\mathit{}}_{\mathrm{BH}}\sim {10}^7–{10}^8{M}_{\odot }$, and conduct forward modeling to fully account for the selection biases and observational uncertainties. The intrinsic ${\mathit{}}_{*}–{\mathit{}}_{\mathrm{BH}}$relation atz∼ 2 has a moderate positive offset of 0.52 ± 0.14 dex from the local relation, suggestive of more efficient black hole growth at higher redshift even in the low-mass regime of ${\mathit{}}_{\mathrm{BH}}\sim {10}^7–{10}^8{M}_{\odot }$. Our ${\mathit{}}_{*}–{\mathit{}}_{\mathrm{BH}}$relation is inconsistent with the ${\mathit{}}_{\mathrm{BH}}$suppression at the low- ${\mathit{}}_{*}$regime predicted by recent hydrodynamic simulations at a 98% confidence level, suggesting that feedback in the low-mass systems may be weaker than those produced in hydrodynamic simulations. 

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2. Observation of quantum entanglement in top quark pair production in proton–proton collisions at $\sqrt{s}=13$  TeV

   https://doi.org/10.1088/1361-6633/ad7e4d  

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

   Abstract Entanglement is an intrinsic property of quantum mechanics and is predicted to be exhibited in the particles produced at the Large Hadron Collider. A measurement of the extent of entanglement in top quark-antiquark ( $\mathrm{t}\overline{\mathrm{t}}$) events produced in proton–proton collisions at a center-of-mass energy of 13 TeV is performed with the data recorded by the CMS experiment at the CERN LHC in 2016, and corresponding to an integrated luminosity of 36.3 fb⁻¹. The events are selected based on the presence of two leptons with opposite charges and high transverse momentum. An entanglement-sensitive observableDis derived from the top quark spin-dependent parts of the $\mathrm{t}\overline{\mathrm{t}}$production density matrix and measured in the region of the $\mathrm{t}\overline{\mathrm{t}}$production threshold. Values of $D<-1/3$are evidence of entanglement andDis observed (expected) to be $-{0.480}_{-0.029}^{+0.026}$( $-{0.467}_{-0.029}^{+0.026}$) at the parton level. With an observed significance of 5.1 standard deviations with respect to the non-entangled hypothesis, this provides observation of quantum mechanical entanglement within $\mathrm{t}\overline{\mathrm{t}}$pairs in this phase space. This measurement provides a new probe of quantum mechanics at the highest energies ever produced. 

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3. Instantons and the large $N=4$ algebra

   https://doi.org/10.1088/1751-8121/ada64d  

   Witten, Edward (January 2025, Journal of Physics A: Mathematical and Theoretical)

   Abstract We investigate the differential geometry of the moduli space of instantons on ${\mathrm{S}}^3\times {\mathrm{S}}^1$. Extending previous results, we show that a sigma-model with this target space can be expected to possess a large $N=4$superconformal symmetry, supporting speculations that this sigma-model may be dual to Type IIB superstring theory on ${\mathrm{AdS}}_3\times {\mathrm{S}}^3\times {\mathrm{S}}^3\times {\mathrm{S}}^1$. The sigma-model is parametrized by three integers—the rank of the gauge group, the instanton number, and a ‘level’ (the integer coefficient of a topologically nontrivialB-field, analogous to a WZW level). These integers are expected to correspond to two five-brane charges and a one-brane charge. The sigma-model is weakly coupled when the level, conjecturally corresponding to one of the five-brane changes, becomes very large, keeping the other parameters fixed. The central charges of the large $N=4$algebra agree, at least semiclassically, with expectations from the duality. 

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4. Robust superconductivity and the suppression of charge-density wave in the quasi-skutterudites ${\text{Ca}}_3({\text{Ir}}_{1-x}{\text{Rh}}_x{)}_4{\text{Sn}}_{13}$ single crystals at ambient pressure

   https://doi.org/10.1088/1361-648X/ad5485  

   Krenkel, Elizabeth_H; Tanatar, Makariy_A; Ghimire, Sunil; Joshi, Kamal_R; Chen, Shuzhang; Petrovic, Cedomir; Prozorov, Ruslan (June 2024, Journal of Physics: Condensed Matter)

   Abstract Single crystals of the quasi-skutterudite compounds Ca₃(Ir_1-xRh_x)₄Sn₁₃(3–4–13) were synthesized by flux growth and characterized by x-ray diffraction, energy dispersive x-ray spectroscopy, magnetization, resistivity, and radio frequency magnetic susceptibility techniques. The coexistence and competition between the charge density wave (CDW) and superconductivity was studied by varying the Rh/Ir ratio. The superconducting transition temperature, $T_{\mathrm{c}}$, varies from 7 K in pure Ir (x = 0) to 8.3 K in pure Rh (x = 1). Temperature-dependent electrical resistivity reveals monotonic suppression of the CDW transition temperature,T_CDW(x). The CDW starts in pure Ir,x = 0, atT_CDW≈ 40 K and extrapolates roughly linearly to zero at $x_c\approx$0.53–0.58 under the superconducting dome. Magnetization and transport measurements show a significant influence of CDW on superconducting and normal states. Meissner expulsion is substantially reduced in the CDW region, indicating competition between the CDW and superconductivity. The low-temperature resistivity is higher in the CDW part of the phase diagram, consistent with the reduced density of states due to CDW gapping. Its temperature dependence just above $T_{\mathrm{c}}$shows signs of non-Fermi liquid behavior in a cone-like composition pattern. We conclude that the Ca₃(Ir_1-xRh_x)₄Sn₁₃alloy is a good candidate for a composition-driven quantum critical point at ambient pressure. 

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5. An optical atomic clock using $4D_J$ states of rubidium

   https://doi.org/10.1088/2058-9565/ad77ef  

   Duspayev, A.; Owens, C.; Dash, B.; Raithel, G. (September 2024, Quantum Science and Technology)

   Abstract We analyze an optical atomic clock using two-photon $5S_{1/2}\to 4D_J$transitions in rubidium. Four one- and two-color excitation schemes to probe the $4D_{3/2}$and $4D_{5/2}$fine-structure states are considered in detail. We compare key characteristics of Rb $4D_J$and $5D_{5/2}$two-photon clocks. The $4D_J$clock features a high signal-to-noise ratio due to two-photon decay at favorable wavelengths, low dc electric and magnetic susceptibilities, and minimal black-body shifts. Ac Stark shifts from the clock interrogation lasers are compensated by two-color Rabi-frequency matching. We identify a ‘magic’ wavelength near 1060 nm, which allows for in-trap, Doppler-free clock-transition interrogation with lattice-trapped cold atoms. From our analysis of clock statistics and systematics, we project a quantum-noise-limited relative clock stability at the ${10}^{-13}/\sqrt{\tau \left(s\right)}$-level, with integration timeτin seconds, and a relative accuracy of $\sim {10}^{-13}$. We describe a potential architecture for implementing the proposed clock using a single telecom clock laser at 1550 nm, which is conducive to optical communication and long-distance clock comparisons. Our work could be of interest in efforts to realize small and portable Rb clocks and in high-precision measurements of atomic properties of Rb $4D_J$-states. 

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