An example of exceptional points in the continuous spectrum of a real, pseudo-Hermitian Hamiltonian of von Neumann-Wigner type is presented and discussed. Remarkably, these exceptional points are associated with a double pole in the normalization fac
tor of the Jost eigenfunctions normalized to unit flux at infinity. At the exceptional points, the two unnormalized Jost eigenfunctions are no longer linearly independent but coalesce to give rise to two Jordan cycles of generalized bound state eigenfunctions embedded in the continuum and a Jordan block representation of the Hamiltonian. The regular scattering eigenfunction vanishes at the exceptional point and the irregular scattering eigenfunction has a double pole at that point. In consequence, the time evolution of the regular scattering eigenfunction is unitary, while the time evolution of the irregular scattering eigenfunction is pseudounitary. The scattering matrix is a regular analytical function of the wave number $k$ for all $k$ including the exceptional points.
An investigation on the additive manufacturing and the experimental testing of 3D models of tensegrity prisms and columns is presented. An electron beam melting facility (Arcam EBM S12) is employed to 3D print structures composed of tensegrity prisms
endowed with rigid bases and temporary supports, which are made out of the titanium alloy Ti6Al4V. The temporary supports are removed after the additive manufacturing phase, when Spectra cross-strings are added to the 3D printed models, and a suitable state of internal prestress is applied to the structure. The experimental part of the study shows that the examined structures feature sitffening-type elastic response under large or moderately large axial strains induced by compressive loading. Such a geometrically nonlinear behavior confirms previous theoretical results available in the literature, and paves the way to the use of tensegrity prisms and columns as innovative mechanical metamaterials and smart devices.
In this contribution we compute some nonleptonic and semileptonic decay widths of $B_s$ mesons, working in the context of constituent quark models cite{Albertus:2014gba, Albertus:2014bfa}. For the case of semileptonic decays we consider reactions lea
ding to kaons or different $J^pi$ $D_s$ mesons. The study of nonleptonic decays has been done in the factorisation approximation and includes the final states enclosed in Table 2.
We study the $f^+$ form factor for the $bar B_sto K^+ell^-bar u_ell$ semileptonic decay in a nonrelativistic quark model. The valence quark contribution is supplemented with a $bar B^*$-pole term that dominates the high $q^2$ region. To extend the qu
ark model predictions from its region of applicability near $q^2_{rm max}=(M_{B_s}-M_K)^2$, we use a multiply-subtracted Omn`es dispersion relation. We fit the subtraction constants to a combined input from previous light cone sum rule results in the low $q^2$ region and the quark model results (valence plus $bar B^*$-pole) in the high $q^2$ region. From this analysis, we obtain $Gamma(bar B_sto K^+ell^-bar u_ell)=(5.47^{+0.54}_{-0.46})|V_{ub}|^2times 10^{-9},{rm MeV}$, which is about 10% and 20% higher than predictions based on Lattice QCD and QCD light cone sum rules respectively.
We study the $f^+$ form factor for the semileptonic $bar B_sto K^+ell^-bar u_ell$ decay in a constituent quark model. The valence quark estimate is supplemented with the contribution from the $bar B^*$ pole that dominates the high $q^2$ region. We us
e a multiply-subtracted Omn`es dispersion relation to extend the quark model predictions from its region of applicability near $q^2_{rm max}=(M_{B_s}-M_K)^2sim 23.75$ GeV$^2$ to all $q^2$ values accessible in the physical decay. To better constrain the dependence of $f^+$ on $q^2$, we fit the subtraction constants to a combined input from previous light cone sum rule [Phys. Rev. D 78 (2008) 054015] and the present quark model results. From this analysis, we obtain $Gamma(bar B_sto K^+ell^-bar u_ell)=(5.45^{+0.83}_{-0.80})|V_{ub}|^2times 10^{-9},{rm MeV}$, which is about 20% higher than the prediction based only on QCD light cone sum rule estimates. Differences are much larger for the $f^+$ form factor in the region above $q^2=15$ GeV$^2$.
We compare our pion production results with recent MiniBooNE data measured in mineral oil. Our total cross sections lie below experimental data for neutrino energies above 1 GeV. Differential cross sections show our model produces too few high energy
pions in the forward direction as compared to data. The agreement with experiment improves by artificially removing pion final state interaction.
We study one pion production in both charged and neutral current neutrino nucleus scattering for neutrino energies below 2 GeV. We use a theoretical model for one pion production at the nucleon level that we correct for medium effects. The results ar
e incorporated into a cascade program that apart from production also includes the pion final state interaction inside the nucleus. Besides, in some specific channels coherent pion production is also possible and we evaluate its contribution as well. Our results for total and differential cross sections are compared with recent data from the MiniBooNE Collaboration. The model provides an overall acceptable description of data, better for NC than for CC channels, although theory is systematically below data. Differential cross sections, folded with the full neutrino flux, show that most of the missing pions lie on the forward direction and at high energies.
We describe a model for pion production off nucleons and coherent pions from nuclei induced by neutrinos in the 1 GeV energy regime. Besides the dominant Delta pole contribution, it takes into account the effect of background terms required by chiral
symmetry. Moreover, the model uses a reduced nucleon-to-Delta resonance axial coupling, which leads to coherent pion production cross sections around a factor two smaller than most of the previous theoretical estimates. Nuclear effects like medium corrections on the Delta propagator and final pion distortion are included.
We propose a free energy expression accounting for the formation of spherical vesicles from planar lipidic membranes and derive a Fokker-Planck equation for the probability distribution describing the dynamics of vesicle formation. We found that form
ation may occur as an activated process for small membranes and as a transport process for sufficiently large membranes. We give explicit expressions for the transition rates and the characteristic time of vesicle formation in terms of the relevant physical parameters.
We examine structural and dynamical properties of quantum resonances associated with an avoided crossing and identify the parameter shifts where these properties attain maximal or extreme values, first at a general level, and then for a two-level sys
tem coupled to a harmonic oscillator, of the type commonly found in quantum optics. Finally the results obtained are exemplified and applied to optimize the fidelity and speed of quantum gates in trapped ions.
