Event-by-event simulation of the Hanbury Brown-Twiss experiment with coherent light

We present a computer simulation model for the Hanbury Brown-Twiss experiment that is entirely particle-based and reproduces the results of wave theory. The model is solely based on experimental facts, satisfies Einstein's criterion of local causality and does not require knowledge of the solution of a wave equation. The simulation model is fully consistent with earlier work and provides another demonstration that it is possible to give a particle-only description of wave phenomena, rendering the concept of wave-particle duality superfluous.Comment: Submitted to Commmun. Comput. Phy

Nonclassical effects in two-photon interference experiments: event-by-event simulations

It is shown that both the visibility ${\cal V} = 1/2$ predicted for two-photon interference experiments with two independent sources\textcolor{black}{, like the Hanbury Brown-Twiss experiment,} and the visibility ${\cal V} = 1$ predicted for two-photon interference experiments with a parametric down-conversion source\textcolor{black}{, like the Ghosh-Mandel experiment,} can be explained \textcolor{black}{by a discrete event simulation. This simulation approach reproduces the statistical distributions of wave theory not by requiring the knowledge of the solution of the wave equation of the whole system but by generating detection events one-by-one according to an unknown distribution.} There is thus no need to invoke quantum theory to explain the so-called nonclassical effects in the interference of signal and idler photons in parametric down conversion. Hence, a revision of the commonly accepted criterion of the nonclassical nature of light\textcolor{black}{, ${\cal V} > 1/2$,} is called for.Comment: arXiv admin note: substantial text overlap with arXiv:1208.2368, arXiv:1006.172

Highly nonlinear contact interaction and dynamic energy dissipation by forest of carbon nanotubes

Mechanical response and energy dissipation of an array of carbon nanotubes under high-strain rate deformation was studied using a simple drop-ball test with the measurement of the dynamic force between the ball and forest of nanotubes. This convenient process allows extracting force–displacement curves and evaluating dissipated energy by the nanotubes. The contact force exhibits a strongly nonlinear dependence on displacement being fundamentally different than the Hertz law. The forest of vertically aligned nanotubes may be used as a strongly nonlinear spring in discrete systems for monitoring signal propagation speed, and as a microstructure for localized energy absorption

Data analysis of Einstein-Podolsky-Rosen-Bohm laboratory experiments

Data sets produced by three different Einstein-Podolsky-Rosen-Bohm (EPRB) experiments are tested against the hypothesis that the statistics of this data is described by quantum theory. Although these experiments generate data that violate Bell inequalities for suitable choices of the time-coincidence window, the analysis shows that it is highly unlikely that these data sets are compatible with the quantum theoretical description of the EPRB experiment, suggesting that the popular statements that EPRB experiments agree with quantum theory lack a solid scientific basis and that more precise experiments are called for.Comment: arXiv admin note: substantial text overlap with arXiv:1112.262

Accidental Peccei-Quinn Symmetry from Discrete Flavour Symmetry and Pati-Salam

We show how an accidental $U(1)$ Peccei-Quinn (PQ) symmetry can arise from a discrete $A_4$ family symmetry combined with a discrete flavour symmetry $\mathbb{Z}_3 \times \mathbb{Z}_5^2$, in a realistic Pati-Salam unified theory of flavour. Imposing only these discrete flavour symmetries, the axion solution to the strong $CP$ problem is protected from PQ-breaking operators to the required degree. A QCD axion arises from a linear combination of $A_4$ triplet flavons, which are also responsible for fermion flavour structures due to their vacuum alignments. We find that the requirement of an accidental PQ symmetry arising from a discrete flavour symmetry constrains the form of the Yukawa matrices, providing a link between flavour and the strong $CP$ problem. Our model predicts specific flavour-violating couplings of the flavourful axion and thus puts a strong limit on the axion scale from kaon decays.Comment: 14 pages, 2 figure

Finite-temperature charge transport in the one-dimensional Hubbard model

We study the charge conductivity of the one-dimensional repulsive Hubbard model at finite temperature using the method of dynamical quantum typicality, focusing at half filling. This numerical approach allows us to obtain current autocorrelation functions from systems with as many as 18 sites, way beyond the range of standard exact diagonalization. Our data clearly suggest that the charge Drude weight vanishes with a power law as a function of system size. The low-frequency dependence of the conductivity is consistent with a finite dc value and thus with diffusion, despite large finite-size effects. Furthermore, we consider the mass-imbalanced Hubbard model for which the charge Drude weight decays exponentially with system size, as expected for a non-integrable model. We analyze the conductivity and diffusion constant as a function of the mass imbalance and we observe that the conductivity of the lighter component decreases exponentially fast with the mass-imbalance ratio. While in the extreme limit of immobile heavy particles, the Falicov-Kimball model, there is an effective Anderson-localization mechanism leading to a vanishing conductivity of the lighter species, we resolve finite conductivities for an inverse mass ratio of $\eta \gtrsim 0.25$.Comment: 13 pages, 11 figure