Physics Skip to main content Search Submit Donate Log in Search arXiv Press Enter to search · Advanced search Physics New submissions Cross-lists Replacements See recent articles Showing new listings for Monday, 17 August 2026 Total of 122 entries Showing up to 2000 entries per page: fewer | more | all New submissions (showing 61 of 61 entries) [1] arXiv:2608.13633 [pdf, html, other] Title: Unknown Unknowns: Model Misspecification in Machine Learning for Physics Juan Cruz-Martinez, Carolina Cuesta-Lazaro, Alexander Held, Michael Kagan Comments: 25 pages, 2 figures, part of the VERaiPHY initiative Subjects: Data Analysis, Statistics and Probability (physics.data-an); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); Machine Learning (cs.LG); High Energy Physics - Experiment (hep-ex); High Energy Physics - Phenomenology (hep-ph) Machine learning is now a central tool for solving inverse problems in particle physics and astronomy. Models are trained on simulation and deployed on real data, raising the question not just of whether they fit, but of whether they are wrong in ways we did not anticipate: the unknown unknowns. This challenge of model misspecification is not unique to machine learning. In physics, misspecification is sometimes exactly what we want to find: new discoveries appear as failures of existing models. At other times, we want such effects absorbed into the analysis without biasing the measurement. A robust analysis is one that absorbs the misspecifications we are not interested in, while preserving sensitivity to the ones we are. Machine learning can both amplify misspecification and provide new tools to address it. We discuss the challenges of model misspecification, diagnostics for detecting it, and strategies for mitigation. No single diagnostic can confirm that a model is correctly specified: detection and mitigation are two halves of an iterative loop, in which a battery of complementary diagnostics is applied, the model is updated, and the process repeated. Robustness against unknown unknowns is ultimately less about any single technique than about a disposition: a willingness to suspect one's own model, and to design analyses that can survive being wrong in ways one did not anticipate. [2] arXiv:2608.13635 [pdf, other] Title: From the Earth to the Sun Dieynaba Young Subjects: History and Philosophy of Physics (physics.hist-ph); Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR) This year marks 360 years since the founding of the French Academy of Sciences. This is the story of the academy's daring 17th century expedition to measure the Earth-sun distance. A truncated version first appeared in National Geographic Magazine; the following is closer to the original draft, with updated information and references. [3] arXiv:2608.13646 [pdf, html, other] Title: Dual-species alkali and alkaline-earth-like optical tweezer arrays via interferometrically aligned high-NA objectives K. Weber, M. McMaster, M. Anderson, J. Tu, S. E. Eustice, N. A. Schine, I. B. Spielman, J. V. Porto, S. L. Rolston, S. Subhankar Subjects: Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph) We have developed a dual-species optical tweezer array apparatus combining $^{87}\text{Rb}$ and $^{174}\text{Yb}$ atoms with a permanent hybrid Twyman-Green--Fizeau interferometer, which provides precision co-alignment of two opposing 0.6-numerical aperture (NA) objectives and the high NA beams that pass through the system. This technique is extensible to other tweezer platforms operating at high numerical aperture across widely-separated wavelengths. Here we present simultaneous trapping and single-site resolved imaging of both species in co-aligned tweezer arrays with $^{87}\text{Rb}$ confined at $840\ \rm{nm}$ and $^{174}\text{Yb}$ at $532\ \rm{nm}$. The platform provides a foundation for hybrid quantum register operation, including mid-circuit measurements and asymmetric intra- and inter-species interactions, greatly expanding the capabilities of neutral atom arrays. [4] arXiv:2608.13683 [pdf, html, other] Title: Generalized space-charge solver for three-dimensional converging or diverging beams Ji Qiang Subjects: Accelerator Physics (physics.acc-ph) Nonlinear space-charge effects play a critical role in the dynamics of high-intensity, high-brightness beams. While conventional space-charge forces scale inversely with the square of the relativistic Lorentz factor ($\gamma$) as beam energy increases, this suppression may not apply to all components of the electromagnetic force. In this paper, we present a generalized space-charge solver that accounts for contributions from transverse currents in three-dimensional (3D) converging or diverging beams. We demonstrate that these additional forces from transverse currents lack an explicit dependence on $\gamma$, potentially rendering them significant in specific high-energy applications. We provide a semi-analytical solution for a 3D converging or diverging beam with the Gaussian density distribution and identify the regimes in which these transverse current forces become comparable to conventional space-charge forces. Furthermore, we present a numerical solution for the generalized model applicable to arbitrary density distributions. Finally, we evaluate the impact of these forces on strongly converging electron beams within the interaction regions of the FCC-ee and ILC, as well as the second bunch compressor of LCLS-II-HE; our results indicate that these extra forces do not significantly alter the final electron beam quality in these specific cases. [5] arXiv:2608.13686 [pdf, html, other] Title: Strong-field Herman-Kluk propagator method for high-harmonic generation in molecules Phi-Hung Tran, Hao Quan Truong, R. Esteban Goetz, Anh-Thu Le Comments: 12 pages, 9 figures Subjects: Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph) We extend our recently developed semiclassical strong-field Herman-Kluk (SFHK) propagator method to calculate high-order harmonic generation (HHG) in diatomic molecules driven by few-cycle intense laser fields. On the example of applications to H2 and N2, we show that our method, based on a combination of the Herman-Kluk propagator and the strong-field approximation, can provide very accurate results for both HHG yield and phase, nearly identical to those from the exact numerical solutions of the time-dependent Schrodinger equation. To compare with experimental measurements, averaging over molecular orientations must be performed. Here we demonstrate a distinct and powerful advantage of the SFHK, as its Monte Carlo sampling for the integration over the alignment distribution can be efficiently combined with the integration over the initial momentum distributions of electron wave-packet right after the tunnel exit. Therefore, the total number of trajectories used for the alignment-averaged HHG spectrum does not increase much compared to that for a single fixed alignment. Similar to atomic targets, the main computational task in the SFHK is to solve the classical Hamiltonian equations for the active electron in the combined electron-target ion potential and electron-laser interaction. The motion of the center of each electron wave packet in the continuum, represented by a coherent state, is governed by an independent classical trajectory so that the computation can be parallelized very efficiently. [6] arXiv:2608.13700 [pdf, html, other] Title: Precision calculations of the hyperfine constants and isotope and isomer shifts in low-lying states of 229Th3+ S.G. Porsev, M.S. Safronova Comments: 6 pages Subjects: Atomic Physics (physics.atom-ph) We present high-precision calculations of the hyperfine constants, isotope shift, and isomer shift in low-lying states of Th3+ relevant to spectroscopy of the 229Th nuclear isomer. The removal energy and hyperfine constants are calculated using a relativistic coupled-cluster method including single, double, and triple excitations, demonstrating the importance of higher-order correlation effects. The isotope shift of the 5f_5/2 -7s transition is evaluated using both the CI+MBPT and CI+all-order methods, providing an estimate of the theoretical uncertainty. We find that the isotope shift is dominated by the field shift, with the mass shift contributing negligibly. Combining the calculated field-shift coefficient with the measured difference in the nuclear mean-square charge radii of the ground and isomeric states, we predict the 7s isomer shift to be (Delta E^(m,g))= 0.9(1) GHz. These results provide benchmark atomic data for Th3+ and support ongoing precision spectroscopy of 229Th and the development of a nuclear clock. [7] arXiv:2608.13710 [pdf, html, other] Title: Optical Characterization Measurements of Commercial Polyvinyltoluene Scintillators for Accurate Geant4 Detector Modeling Fergus Martin Huggins, Micah S. Johnson, Matthew Quinn Buckner Comments: 8 pages, 7 figures, 5 tables Subjects: Instrumentation and Detectors (physics.ins-det); High Energy Physics - Experiment (hep-ex); Nuclear Experiment (nucl-ex); Optics (physics.optics) Accurate Monte Carlo simulation of plastic scintillator detectors requires precise wavelength-dependent optical properties. We present the first comprehensive measurements of wavelength-dependent refractive index $n(\lambda)$ and bulk absorption length $L_{\mathrm{abs}}(\lambda)$ for six commercial polyvinyltoluene (PVT)-based scintillators (Saint Gobain BC-400, BC-404, BC-408, BC-418, BC-422, and BC-430) across the 370-660 nm range. Using a precision refraction apparatus and variable-thickness transmission measurements, we characterize material-specific dispersion that deviates substantially from both the manufacturer specification and literature values for pure PVT. Validation simulations of a BC-422 detector demonstrate a 7.2% reduction in detected photon counts when using our measured $n(\lambda)$ compared to the constant manufacturer value, highlighting the practical importance of accurate optical property data for detector design and calibration. We successfully measure absorption lengths for BC-430 across most of the visible spectrum (2.2-12.4 mm) and for all materials at 372 nm (21-38 mm), while establishing lower bounds exceeding 750 mm for weakly absorbing formulations at longer wavelengths. [8] arXiv:2608.13740 [pdf, html, other] Title: Development of the RIOT 2 for use in LA-supported classrooms Gina M. Quan, Cassandra Paul, Nithin Keshavamurthy, Owen Knight, Aarav Ghai, Kamalbabu Rupanagudi Comments: 6 pages, 4 figures Subjects: Physics Education (physics.ed-ph) This paper describes the development of the RIOT 2, an observational tool that can be used to study classrooms in which there are multiple members of an instructional team. The RIOT 2 is based on the Real-time Instructor Observational Tool (RIOT), which characterizes the behavior of an instructor over time. While the RIOT was previously developed for classrooms with only one instructor, our team has developed a version to observe classrooms supported by Learning Assistants (LAs). LA are undergraduate peer educators who facilitate discussions in active-learning classrooms. Unlike the RIOT, the RIOT 2 allows for the categorization of LA-instructor interactions. In this paper, we describe the development of RIOT 2 and present some initial data collected using the RIOT 2. While our data are preliminary, they illustrate how the RIOT 2 may be useful for future research and practice. This work is part of a broader research effort to understand how LA-faculty partnerships impact what LAs and instructors do in the classroom. [9] arXiv:2608.13743 [pdf, html, other] Title: Nonlinear wave dynamics in photonic time crystals Fabio Biancalana Subjects: Optics (physics.optics); Pattern Formation and Solitons (nlin.PS) Maxwell's wave equation in the presence of a cubic nonlinearity and a perio…