Deep Thermalization and Quantum Non-Locality

A new study explores the nature of locality in the phenomenon of deep thermalization, where universal quantum state ensembles emerge in subsystems due to projective measurements on their complement. Researchers examined a subsystem partitioned into two disjoint subregions that remain causally disconnected under unitary dynamics. The work reveals that the onset of deep thermalization in this configuration is fundamentally bounded by measurement-induced entanglement teleportation between the subregions. Although measurements on the environment generate entanglement across the disconnected partitions, suggesting apparent non-locality, the study demonstrates that generic locally interacting systems exhibit emergent locality. Specifically, the timescales for both deep thermalization and entanglement teleportation scale logarithmically with the distance separating the subregions. This implies that, despite the quantum connection, the influence of measurements propagates in a way that respects a form of locality. Exceptions to this rule exist, such as certain special circuits where the randomness of measurement outcomes is perfectly transmitted to the subsystem's state ensemble, conditioned on those outcomes. In these particular cases, the timescale for deep thermalization is finite, leading to genuine non-locality. This finding underscores the complexity of quantum interactions and how locality can manifest or be circumvented in different thermalization scenarios.

New Radiative-Recoil Correction to Lamb Shift in Muonium Calculated

Scientists have calculated a new radiative-recoil contribution of order $Z^2\alpha(Z\alpha)^5(m/M)^2m$ to the Lamb shift in muonium. This correction arises from the insertion of radiative photons in the heavy line within two-photon exchange diagrams. This advance is crucial for precision physics, as the Lamb shift is one of the most sensitive quantities for testing quantum electrodynamics (QED) in bound systems. Muonium, an exotic atom composed of a muon and an electron, is an ideal system for these tests due to the simplicity of its components and the absence of internal structure in the muon, unlike the proton in hydrogen. The precision in determining the Lamb shift in muonium allows for the refinement of fundamental constants and interaction theories, especially in the low-energy regime. The newly calculated correction is particularly relevant given that current experiments are aiming for unprecedented accuracy in the $1S-2S$ and $2S-2P$ transitions of muonium. This calculation is inspired by a new round of high-precision muonium experiments currently in progress. The inclusion of this theoretical correction is fundamental for correctly interpreting experimental results and for ensuring that comparisons between theory and experiment are made with the highest possible accuracy. Improvements in theoretical precision are as important as experimental ones for revealing potential deviations from the Standard Model or for refining its parameters.

NNLO QCD Corrections for Exclusive Drell-Yan Processes with Pions and Kaons

A new study has calculated the next-to-next-to-leading order (NNLO) quantum chromodynamics (QCD) corrections for exclusive Drell-Yan processes induced by pions and kaons. These processes, which correspond to inverse deeply virtual meson production, are crucial for future investigations at facilities like J-PARC. The calculations focus on the reactions $π^- p\to γ^*(\to l^+l^-) + n$ and $K^- p\to γ^*(\to l^+l^-) + Λ$, providing a more robust theoretical foundation for comparison with anticipated experimental data. The research was conducted within the generalized parton distribution (GPD) factorization framework, ensuring accuracy to leading twist in the generalized Bjorken limit ($Q^2\gg |t|,\,Λ_{\rm QCD}^2$). This approach is essential for describing the internal structure of hadrons, such as pions and kaons, in terms of their fundamental constituents (quarks and gluons). The ability to model these processes with high theoretical precision is fundamental for extracting detailed information about GPDs, which encode the three-dimensional distribution of partons within nucleons and mesons. The results indicate that the NNLO QCD corrections are substantial and positive. This means their inclusion is indispensable for obtaining reliable theoretical predictions that can be meaningfully confronted with experimental data generated in upcoming experiments. Omitting these corrections could lead to erroneous interpretations of data and an incomplete understanding of parton dynamics at high energies. This theoretical advancement sets the stage for a new era of precision in the study of hadronic structure.