Navarro-Salas, J., & Pla, S. (2022). Particle Creation and the Schwinger Model. Symmetry-Basel, 14(11), 2435–9pp.
Abstract: We study the particle creation process in the Schwinger model coupled with an external classical source. One can approach the problem by taking advantage of the fact that the full quantized model is solvable and equivalent to a (massive) gauge field with a non-local effective action. Alternatively, one can also face the problem by following the standard semiclassical route. This means quantizing the massless Dirac field and considering the electromagnetic field as a classical background. We evaluate the energy created by a generic, homogeneous, and time-dependent source. The results match exactly in both approaches. This proves in a very direct and economical way the validity of the semiclassical approach for the (massless) Schwinger model, in agreement with a previous analysis based on the linear response equation. Our discussion suggests that a similar analysis for the massive Schwinger model could be used as a non-trivial laboratory to confront a fully quantized solvable model with its semiclassical approximation, therefore mimicking the long-standing confrontation of quantum gravity with quantum field theory in curved spacetime.
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Driencourt-Mangin, F., Rodrigo, G., Sborlini, G. F. R., & Torres Bobadilla, W. J. (2019). Universal four-dimensional representation of H -> gamma gamma at two loops through the Loop-Tree Duality. J. High Energy Phys., 02(2), 143–39pp.
Abstract: We extend useful properties of the H unintegrated dual amplitudes from one- to two-loop level, using the Loop-Tree Duality formalism. In particular, we show that the universality of the functional form regardless of the nature of the internal particle still holds at this order. We also present an algorithmic way to renormalise two-loop amplitudes, by locally cancelling the ultraviolet singularities at integrand level, thus allowing a full four-dimensional numerical implementation of the method. Our results are compared with analytic expressions already available in the literature, finding a perfect numerical agreement. The success of this computation plays a crucial role for the development of a fully local four-dimensional framework to compute physical observables at Next-to-Next-to Leading order and beyond.
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Faleiro, R., Pavao, R., Costa, H. A. S., Hiller, B., Blin, A. H., & Sampaio, M. (2020). Perturbative approach to entanglement generation in QFT using the S matrix. J. Phys. A, 53(36), 365301–19pp.
Abstract: We compute the variation of the von Neumann (VN) entropy Delta Sbetween the asymptoticinandoutmomenta modes of a real scalar field A, when elastically scattered against the modes of another scalar field B. This is done to see how the entanglement between the two fields' momenta changes under the scattering procedure. The calculation is separated into two case studies, one where the fields' asymptoticinstates are separable, and another where they are arbitrarily entangled. We perform a perturbative calculation to one loop order in the separable case, and verify that Delta Schanges in a non-trivial way when we vary the momentum of the incoming field modes and/or the coupling of the theory. Finally, also in the separable case, we show an explicit dependence between Delta Sand the cross-section of the collision, consistent with perturbation theory.
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Massimi, C., Cristallo, S., Domingo-Pardo, C., & Lederer-Woods, C. (2022). n_TOF: Measurements of Key Reactions of Interest to AGB Stars. Universe, 8(2), 100–19pp.
Abstract: In the last 20 years, the neutron time-of-flight facility nTOF at CERN has been providing relevant data for the astrophysical slow neutron capture process (s process). At nTOF, neutron-induced radiative capture (n,gamma) as well as (n,p) and (n,alpha) reaction cross sections are measured as a function of energy, using the time-of-flight method. Improved detection systems, innovative ideas and collaborations with other neutron facilities have lead to a considerable contribution of the n_TOF collaboration to studying the s process in asymptotic giant branch stars. Results have been reported for stable and radioactive samples, i.e.,Mg- 24,Mg-25,Mg-26, Al-26, S-33,Fe- 54,Fe-57, Ni-58,Ni-59,Ni-62,Ni-63, Ge-70,Ge-72,Ge-73, Zr-90,Zr-91,Zr-92,Zr-93,Zr-94,Zr-96, La-139, Ce-140, Pm-147, Sm-151,Gd- 154,Gd-155,Gd-157, Tm-171, Os-186,Os-187,Os-188, Au-197, Tl-203,Tl-204,Pb- 204,Pb-206,Pb-207 and Bi-209 isotopes, while others are being studied or planned to be studied in the near future. In this contribution, we present an overview of the most successful achievements, and an outlook of future challenging measurements, including ongoing detection system developments.
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n_TOF Collaboration(Mazzone, A. et al), Babiano-Suarez, V., Caballero, L., Domingo-Pardo, C., Ladarescu, I., & Tain, J. L. (2020). Measurement of the Gd-154(n, gamma) cross section and its astrophysical implications. Phys. Lett. B, 804, 135405–6pp.
Abstract: The neutron capture cross section of Gd-154 was measured from 1 eV to 300 keV in the experimental area located 185 m from the CERN n_TOF neutron spallation source, using a metallic sample of gadolinium, enriched to 67% in Gd-154. The capture measurement, performed with four C6D6 scintillation detectors, has been complemented by a transmission measurement performed at the GELINA time-of-flight facility (JRC-Geel), thus minimising the uncertainty related to sample composition. An accurate Maxwellian averaged capture cross section (MACS) was deduced over the temperature range of interest for s process nucleosynthesis modelling. We report a value of 880(50) mb for the MACS at kT = 30 keV, significantly lower compared to values available in literature. The new adopted Gd-154(n, gamma) cross section reduces the discrepancy between observed and calculated solar s-only isotopic abundances predicted by s-process nucleosynthesis models.
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