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1. CP violation in K → μ+μ− with and without time dependence through a tagged analysis

   https://doi.org/10.1007/JHEP09(2025)190  

   D’Ambrosio, Giancarlo; Dery, Avital; Grossman, Yuval; Kitahara, Teppei; Marchevski, Radoslav; Santos, Diego Martínez; Schacht, Stefan (September 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> We point out that using current knowledge of$$ \mathcal{B}\left({K}_L^0\to {\mu}^{+}{\mu}^{-}\right) $$ $B\left(K_L^0\to {\mu }^{+}{\mu }^{-}\right)$and$$ \mathcal{B}\left({K}_L^0\to \gamma \gamma \right) $$ $B\left(K_L^0\to \mathrm{\gamma \gamma }\right)$, one can extract short-distance information from the combined measurement of the time-integrated CP asymmetry,A_CP(K⁰→ μ⁺μ⁻), and of$$ \mathcal{B}\left({K}_S^0\to {\mu}^{+}{\mu}^{-}\right) $$ $B\left(K_S^0\to {\mu }^{+}{\mu }^{-}\right)$. We discuss the interplay between this set of observables, and demonstrate that determining sign[A_CP(K⁰→μ⁺μ⁻)] would eliminate the discrete ambiguity in the Standard Model prediction for$$ \mathcal{B}\left({K}_L^0\to {\mu}^{+}{\mu}^{-}\right) $$ $B\left(K_L^0\to {\mu }^{+}{\mu }^{-}\right)$. We then move on to feasibility studies within an LHCb-like setup, using both time-integrated and time-dependent information, employingK⁰and$$ {\overline{K}}^0 $$ ${\overline{K}}^0$tagging methods. We find that, within an optimistic scenario, the short-distance amplitude, proportional to the CKM parameter combination$$ \mid {A}^2{\lambda}^5\overline{\eta}\mid $$ $\mid A^2{\lambda }^5\overline{\eta }\mid$, could be constrained by LHCb at the level of about 35% of its Standard Model value, and the discrete ambiguity in$$ \mathcal{B}{\left({K}_L^0\to {\mu}^{+}{\mu}^{-}\right)}_{\textrm{SM}} $$ $B{\left(K_L^0\to {\mu }^{+}{\mu }^{-}\right)}_{\mathrm{SM}}$could be resolved at more than 3σby the end of the high luminosity LHC. 

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2. Search for the $$ {B}_s^0 $$ → μ+μ−γ decay

   https://doi.org/10.1007/JHEP07(2024)101  

   Aaij, R; Abdelmotteleb, A_S W; Abellan_Beteta, C; Abudinén, F; Ackernley, T; Adefisoye, A A; Adeva, B; Adinolfi, M; Adlarson, P; Agapopoulou, C; et al (July 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> A search for the fully reconstructed$$ {B}_s^0 $$ $B_s^0$→ μ⁺μ⁻γdecay is performed at the LHCb experiment using proton-proton collisions at$$ \sqrt{s} $$ $\sqrt{s}$= 13 TeV corresponding to an integrated luminosity of 5.4 fb⁻¹. No significant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are set$$ {\displaystyle \begin{array}{cc}\mathcal{B}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\gamma \right)<4.2\times {10}^{-8},& m\left({\mu}^{+}{\mu}^{-}\right)\in \left[2{m}_{\mu },1.70\right]\textrm{GeV}/{c}^2,\\ {}\mathcal{B}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\gamma \right)<7.7\times {10}^{-8},&\ m\left({\mu}^{+}{\mu}^{-}\right)\in \left[\textrm{1.70,2.88}\right]\textrm{GeV}/{c}^2,\\ {}\mathcal{B}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\gamma \right)<4.2\times {10}^{-8},& m\left({\mu}^{+}{\mu}^{-}\right)\in \left[3.92,{m}_{B_s^0}\right]\textrm{GeV}/{c}^2,\end{array}} $$ $\begin{array}{cc}B\left(B_s^0\to {\mu }^{+}{\mu }^{-}\gamma \right)<4.2\times {10}^{-8},& m\left({\mu }^{+}{\mu }^{-}\right)\in \left(2m_{\mu },1.70\right)\mathrm{GeV}/c^2,\\ B\left(B_s^0\to {\mu }^{+}{\mu }^{-}\gamma \right)<7.7\times {10}^{-8},& m\left({\mu }^{+}{\mu }^{-}\right)\in \left(\mathrm{1.70,\; 2.88}\right)\mathrm{GeV}/c^2,\\ B\left(B_s^0\to {\mu }^{+}{\mu }^{-}\gamma \right)<4.2\times {10}^{-8},& m\left({\mu }^{+}{\mu }^{-}\right)\in \left(3.92,m_{B_s^0}\right)\mathrm{GeV}/c^2,\end{array}$ at 95% confidence level. Additionally, upper limits are set on the branching fraction in the [2m_μ,1.70] GeV/c²dimuon mass region excluding the contribution from the intermediateϕ(1020) meson, and in the region combining all dimuon-mass intervals. 

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3. Bounds on eigenfunctions of quantum cat maps

   https://doi.org/10.1088/1402-4896/ad0331  

   Kim, Elena; Koirala, Robert (October 2023, Physica Scripta)

   Abstract We studyℓ^∞norms ofℓ²-normalized eigenfunctions of quantum cat maps. For maps with short quantum periods (constructed by Bonechi and de Biévre in F Bonechi and S De Bièvre (2000,Communications in Mathematical Physics,211, 659–686)) we show that there exists a sequence of eigenfunctionsuwith $\parallel u{\parallel }_{\infty }\gtrsim {\left(\log N\right)}^{-1/2}$. For general eigenfunctions we show the upper bound $\parallel u{\parallel }_{\infty }\lesssim {\left(\log N\right)}^{-1/2}$. Here the semiclassical parameter is $h={\left(2\pi N\right)}^{-1}$. Our upper bound is analogous to the one proved by Bérard in P Bérard (1977,Mathematische Zeitschrift,155, 249-276) for compact Riemannian manifolds without conjugate points. 

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4. Properties of Nuclear Star Clusters in Low Surface Brightness Galaxies

   https://doi.org/10.3847/1538-3881/ad4ed3  

   Khim, Donghyeon J; Zaritsky, Dennis; Lambert, Mika; Donnerstein, Richard (July 2024, The Astronomical Journal)

   Abstract Using the Systematically Measuring Ultra-Diffuse Galaxies and Sloan Digital Sky Survey catalogs and our own reprocessing of the Legacy Survey imaging, we investigate the properties of nuclear star clusters (NSCs) in galaxies having central surface brightnesses as low as 27 mag arcsec⁻². We identify 273 (123 with known redshift) and 32 NSC-bearing galaxies in the two samples, respectively, where we require candidate NSCs to have a separation of less than 0.10r_efrom the galaxy center. We find that galaxies with low central surface brightness (μ_0,g> 24 mag arcsec⁻²) are more likely to contain an NSC if they (1) have a higher stellar mass, (2) have a higher stellar-to-total mass ratio, (3) have a brighter central surface brightness, (4) have a larger axis ratio, or (5) lie in a denser environment. Because of the correlations among these various quantities, it is likely that only one or two are true physical drivers. We also find scaling relations for the NSC mass with stellar mass (M_NSC/ $M_{\odot }={10}^{6.02\pm 0.03}{(M_{*,\mathrm{gal}}/{10}^8{M}_{\odot })}^{0.77\pm 0.04}$) and halo mass (M_NSC/ $M_{\odot }={10}^{6.11\pm 0.05}{(M_{h,\mathrm{gal}}/{10}^{10}{M}_{\odot })}^{0.92\pm 0.05}$), although it is the scaling with halo mass that is consistent with a direct proportionality. In galaxies with an NSC,M_NSC≈ 10⁻⁴M_h,gal. This proportionality echoes the finding of a direct proportionality between the mass (or number) of globular clusters (GCs) in galaxies and the galaxy’s total mass. These findings favor a related origin for GCs and NSCs. 

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5. Distinguishing the XUV-induced Coulomb explosion dynamics of iodobenzene using covariance analysis

   https://doi.org/10.1088/1361-6455/ad8799  

   Walmsley, Tiffany; Allum, Felix; Harries, James R; Kumagai, Yoshiaki; Lim, Suzanne; McManus, Joseph; Nagaya, Kiyonobu; Britton, Mathew; Brouard, Mark; Bucksbaum, Philip; et al (October 2024, Journal of Physics B: Atomic, Molecular and Optical Physics)

   Abstract The primary and secondary fragmentation dynamics of iodobenzene following its ionization at 120 eV were determined using three-dimensional velocity map imaging and covariance analysis. Site-selective iodine 4d ionization was used to populate a range of excited polycationic parent states, which primarily broke apart at the carbon-iodine bond to produce I⁺with phenyl or phenyl-like cations (C_nH ${{}_x}^{+}$or C_nH ${{}_x}^{2+}$, withn  =  1 – 6 andx  =  1 – 5). The molecular products were produced with varying degrees of internal excitation and dehydrogenation, leading to stable and unstable outcomes. This further allowed the secondary dynamics of ${\mathrm{C}}_6{\mathrm{H}}_x{}^{2+}$intermediates to be distinguished using native-frame covariance analysis, which isolated these processes in their own centre-of-mass reference frames. The mass resolution of the imaging mass spectrometer used for these measurements enabled the primary and secondary reaction channels to be specified at the level of individual hydrogen atoms, demonstrating the ability of covariance analysis to comprehensively measure the competing fragmentation channels of aryl cations, including those involving intermediate steps. 

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