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Siahmazgi, S. G., Anderson, P. R., & Fabbri, A. (2025). Late-time behavior of scalar field modes for a collapsing null shell spacetime and for the Unruh state in Schwarzschild spacetime. Phys. Rev. D, 112(4), 045013–8pp.
Abstract: The behaviors of the spherically symmetric modes for a massless minimally coupled scalar field are investigated for the Unruh state for Schwarzschild spacetime and the in vacuum state for a spacetime in which a null shell collapses to form a Schwarzschild black hole. In both cases, there are two different sets of solutions to the mode equation that make up the state. For both spacetimes, one set of modes oscillates forever with no damping of the oscillations and the other set approaches zero at late times. The difference between a mode that oscillates forever in the null-shell spacetime and the corresponding mode for the Unruh state at late times vanishes as a power law in time. The modes that approach zero at late times also vanish as a power law in time. In all cases, the power-law damping is preceded by a period of oscillations that appear to be due to quasinormal modes.
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Vidal, F. P. et al, & Albiol, F. (2025). X-ray simulations with gVXR in education, digital twining, experiment planning, and data analysis. Nucl. Instrum. Methods Phys. Res. B, 568, 165804–32pp.
Abstract: gVirtualXray (gVXR) is an open-source framework that relies on the Beer-Lambert law to simulate X-ray images in real time on a graphics processor unit (GPU) using triangular meshes. A wide range of programming languages is supported (C/C++, Python, R, Ruby, Tcl, C#, Java, and GNU Octave). Simulations generated with gVXR have been benchmarked with clinically realistic phantoms (i.e. complex structures and materials) using Monte Carlo (MC) simulations, real radiographs and real digitally reconstructed radiographs (DRRs), and X-ray computed tomography (CT). It has been used in a wide range of applications, including real-time medical simulators, proposing a new densitometric radiographic modality in clinical imaging, studying noise removal techniques in fluoroscopy, teaching particle physics and X-ray imaging to undergraduate students in engineering, and XCT to masters students, predicting image quality and artifacts in material science, etc. gVXR has also been used to produce a high number of realistic simulated images in optimisation problems and to train machine learning algorithms. This paper presents a comprehensive review of such applications of gVXR.
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NEXT Collaboration(Parmaksiz, I. et al), Ayet, A., Carcel, S., Kellerer, F., Lopez-March, N., Martin-Albo, J., et al. (2025). Performance of an optical TPC Geant4 simulation with opticks GPU-accelerated photon propagation. Eur. Phys. J. C, 85(8), 910–9pp.
Abstract: We investigate the performance of Opticks, a NVIDIA OptiX API 7.5 GPU-accelerated photon propagation tool compared with a single-threaded Geant4 simulation. We compare the simulations using an improved model of the NEXT-CRAB-0 gaseous time projection chamber. Performance results suggest that Opticks improves simulation speeds by between 58.47 +/- 0.02 and 181.39 +/- 0.28 times relative to a CPU-only Geant4 simulation and these results vary between different types of GPU and CPU. A detailed comparison shows that the number of detected photons, along with their times and wavelengths, are in good agreement between Opticks and Geant4.
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Castro, A. R., Mezrag, C., Morgado Chavez, J. M., & Pire, B. (2025). Backward DVCS in a Sullivan process. Phys. Rev. D, 112(3), 034009–18pp.
Abstract: Mesons' internal structure and dynamics may be accessed through hard exclusive electroproduction processes such as deeply virtual Compton scattering in both near forward and near backward kinematics. With the help of the Sullivan process, which allows us to use a nucleon target as a quasireal meson emitter, we study backward scattering in the framework of collinear QCD factorization where pion-to-photon transition distribution amplitudes describe the photon content of the meson. We present a model of these transition distribution amplitudes based on the overlap of light-front wave functions primarily developed for generalized parton distributions, using a previously computed pion light-front wave function and deriving a new model for the light-front wave functions of the photon. This leads us to an estimate of the cross sections for JLab energies. We conclude that deeply virtual ep-* e gamma Mn processes, in backward kinematics, may be experimentally discovered in the near future.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2025). Search for Higgs boson decays into a pair of pseudoscalar particles in the γγτhadτhad final state using pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 03(3), 190–39pp.
Abstract: A search for exotic decays of the 125 GeV Higgs boson into a pair of new spin-0 particles, H -> aa, where one decays into a photon pair and the other into a tau-lepton pair, is presented. Hadronic decays of the tau-leptons are considered and reconstructed using a dedicated tagger for collimated tau-lepton pairs. The search uses 140 fb(-1) of proton-proton collision data at a centre-of-mass energy of root s = 13TeV recorded between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider. The search is performed in the mass range of the a boson between 10 GeV and 60 GeV. No significant excess of events is observed above the Standard Model background expectation. Model-independent upper limits at 95% confidence level are set on the branching ratio of the Higgs boson to the gamma gamma tau tau final state, B(H -> aa -> gamma gamma tau tau), ranging from 0.2% to 2%, depending on the a-boson mass hypothesis.
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