Mixed quantum-classical dynamics from the exact decomposition of electron-nuclear motion

We present a novel mixed quantum-classical approach to the coupled electron-nuclear dynamics based on the exact factorization of the electron-nuclear wave function, recently proposed in [A. Abedi, N. T. Maitra, and E. K. U. Gross, Phys. Rev. Lett. 105, 123002 (2010)]. In this framework, classical nuclear dynamics is derived as the lowest order approximation of the time dependent Schr\"odinger equation that describes the evolution of the nuclei. The effect of the time dependent scalar and vector potentials, representing the exact electronic back-reaction on the nuclear subsystem, is consistently derived within the classical approximation. We examine with an example the performance of the proposed mixed quantum-classical scheme in comparison with exact calculations

Signal modeling of high-purity Ge detectors with a small read-out electrode and application to neutrinoless double beta decay search in Ge-76

The GERDA experiment searches for the neutrinoless double beta decay of Ge-76 using high-purity germanium detectors enriched in Ge-76. The analysis of the signal time structure provides a powerful tool to identify neutrinoless double beta decay events and to discriminate them from gamma-ray induced backgrounds. Enhanced pulse shape discrimination capabilities of "Broad Energy Germanium" detectors with a small read-out electrode have been recently reported. This paper describes the full simulation of the response of such a detector, including the Monte Carlo modeling of radiation interaction and subsequent signal shape calculation. A pulse shape discrimination method based on the ratio between the maximum current signal amplitude and the event energy applied to the simulated data shows quantitative agreement with the experimental data acquired with calibration sources. The simulation has been used to study the survival probabilities of the decays which occur inside the detector volume and are difficult to assess experimentally. Such internal decay events are produced by the cosmogenic radio-isotopes Ge-68 and Co-60 and the neutrinoless double beta decay of Ge-76. Fixing the experimental acceptance of the double escape peak of the 2.614 MeV photon to 90%, the estimated survival probabilities at Qbb = 2.039 MeV are (86+-3)% for Ge-76 neutrinoless double beta decays, (4.5+-0.3)% for the Ge-68 daughter Ga-68, and (0.9+0.4-0.2)% for Co-60 decays.Comment: 27 pages, 17 figures. v2: fixed typos and references. Submitted to JINS

Ultrafast dynamics with the exact factorization

The exact factorization of the time-dependent electron-nuclear wavefunction has been employed successfully in the field of quantum molecular dynamics simulations for interpreting and simulating light-induced ultrafast processes. In this work, we summarize the major developments leading to the formulation of a trajectory-based approach, derived from the exact factorization equations, capable of dealing with nonadiabatic electronic processes, and including spin-orbit coupling and the non-perturbative effect of an external time-dependent field. This trajectory-based quantum-classical approach has been dubbed coupled-trajectory mixed quantum-classical (CT-MQC) algorithm, whose performance is tested here to study the photo-dissociation dynamics of IBr

Gait parameters of elderly subjects in single-task and dual-task with three different MIMU set-ups

The increasing average age of the population emphasizes the strong correlation between cognitive decline and gait disorders of elderly people. Wearable technologies such as magnetic inertial measurement units (MIMUs) have been ascertained as a suitable solution for gait analysis. However, the relationship between human motion and cognitive impairments should still be investigated, considering outcomes of different MIMU set-ups. Accordingly, the aim of the present study was to compare single-task and dual-task walking of an elderly population by using three different MIMU set-ups and correlated algorithms (trunk, shanks, and ankles). Gait sessions of sixteen healthy elderly subjects were registered and spatio-temporal parameters were selected as outcomes of interest. The analysis focused both on the comparison of walking conditions and on the evaluation of differences among MIMU set-ups. Results pointed out the significant effect of cognition on walking speed (p = 0.03) and temporal parameters (p ≤ 0.05), but not on the symmetry of gait. In addition, the comparison among MIMU configurations highlighted a significant difference in the detection of gait stance and swing phases (for shanks-ankles comparison p < 0.001 in both single and dual tasks, for trunk-ankles comparison p < 0.001 in single task and p < 0.01 in dual task). Overall, cognitive impact and MIMU set-ups revealed to be fundamental aspects in the analysis of gait spatio-temporal parameters in a healthy elderly population

Search for Light Exotic Fermions in Double-Beta Decays

The Standard Model of Particle Physics predicts the double-β decay of certain nuclei with the emission of two active neutrinos. In this letter, we argue that double-β decay experiments could be used to probe models with light exotic fermions through the search for spectral distortions in the electron spectrum with respect to the Standard Model expectations. We consider two concrete examples: models with light sterile neutrinos, singly produced in the double-β decay, and models with a light -odd fermion, pair produced due to a symmetry. We estimate the discovery potential of a selection of double-β decay experiments and find that future searches will test for the first time a new part of the parameter space of interest at the MeV-mass scale

Does Perceptual Belongingness Affect Lightness Constancy?

Scientists have shown that two equal grey patches may differ in lightness when belonging to different reflecting surfaces. We extend this investigation to the constancy domain. In a CRT simulation of a bipartite field of illumination, we manipulated the arrangement of twelve patches: six squares and six diamonds. Patches of the same shape could be placed: (i) all within the same illumination field; or (ii) forming a row across the illumination fields. Furthermore, we manipulated proximity between the innermost patches and the illumination edge. The patches could be (i) touching (forming an X-junction); or (ii) not touching (not forming an X-junction). Observers were asked to perform a lightness match between two additional patches, one illuminated and the other in shadow. We found better lightness constancy when the patches of the same shape formed a row across the fields, with no effect of X-junctions