Coherent XUV generation driven by sharp metal tips photoemission

It was already experimentally demonstrated that high-energy electrons can be generated using metal nanotips as active media. In addition, it has been theoretically proven that the high-energy tail of the photoemitted electrons is intrinsically linked to the recollision phenomenon. Through this recollision process it is also possible to convert the energy gained by the laser-emitted electron in the continuum in a coherent XUV photon. It means the emission of harmonic radiation appears to be feasible, although it has not been experimentally demonstrated hitherto till now. In this paper, we employ a quantum mechanical approach to model the electron dipole moment including both the laser experimental conditions and the bulk matter properties and predict is possible to generate coherent UV and XUV radiation using metal nanotips as sources. Our quantum mechanical results are fully supported by their classical counterparts.Comment: arXiv admin note: substantial text overlap with arXiv:1309.034

N-Delta(1232) axial form factors from weak pion production

The N-Delta axial form factors are determined from neutrino induced pion production ANL & BNL data by using a state of the art theoretical model, which accounts both for background mechanisms and deuteron effects. We find violations of the off diagonal Goldberger-Treiman relation at the level of 2 sigma which might have an impact in background calculations for T2K and MiniBooNE low energy neutrino oscillation precision experiments.Comment: 4 pages, 1 figur

Periodic forcing in viscous fingering of a nematic liquid crystal

We study viscous fingering of an air-nematic interface in a radial Hele-Shaw cell when periodically switching on and off an electric field, which reorients the nematic and thus changes its viscosity, as well as the surface tension and its anisotropy (mainly enforced by a single groove in the cell). We observe undulations at the sides of the fingers which correlate with the switching frequency and with tip oscillations which give maximal velocity to smallest curvatures. These lateral undulations appear to be decoupled from spontaneous (noise-induced) side branching. We conclude that the lateral undulations are generated by successive relaxations between two limiting finger widths. The change between these two selected pattern scales is mainly due to the change in the anisotropy. This scenario is confirmed by numerical simulations in the channel geometry, using a phase-field model for anisotropic viscous fingering.Comment: completely rewritten version, more clear exposition of results (14 pages in Revtex + 7 eps figures

Weak Pion Production off the Nucleon

We develop a model for the weak pion production off the nucleon, which besides the Delta pole mechanism (weak excitation of the $\Delta(1232)$ resonance and its subsequent decay into $N\pi$), includes also some background terms required by chiral symmetry. We re-fit the $C_5^A(q^2)$ form factor to the flux averaged $\nu_\mu p \to \mu^-p\pi^+$ ANL $q^2-$differential cross section data, finding a substantially smaller contribution of the Delta pole mechanism than traditionally assumed in the literature. Within this scheme, we calculate several differential and integrated cross sections, including pion angular distributions, induced by neutrinos and antineutrinos and driven both by charged and neutral currents. In all cases we find that the background terms produce quite significant effects and that they lead to an overall improved description of the data, as compared to the case where only the Delta pole mechanism is considered. We also show that the interference between the Delta pole and the background terms produces parity-violating contributions to the pion angular differential cross section, which are intimately linked to $T-$odd correlations in the contraction between the leptonic and hadronic tensors. However, these latter correlations do not imply a genuine violation of time reversal invariance because of the existence of strong final state interaction effects.Comment: Typos corrected; comments adde

Influence of Disorder Strength on Phase Field Models of Interfacial Growth

We study the influence of disorder strength on the interface roughening process in a phase-field model with locally conserved dynamics. We consider two cases where the mobility coefficient multiplying the locally conserved current is either constant throughout the system (the two-sided model) or becomes zero in the phase into which the interface advances (one-sided model). In the limit of weak disorder, both models are completely equivalent and can reproduce the physical process of a fluid diffusively invading a porous media, where super-rough scaling of the interface fluctuations occurs. On the other hand, increasing disorder causes the scaling properties to change to intrinsic anomalous scaling. In the limit of strong disorder this behavior prevails for the one-sided model, whereas for the two-sided case, nucleation of domains in front of the invading front are observed.Comment: Accepted for publication in PR

Intruder States and their Local Effect on Spectral Statistics

The effect on spectral statistics and on the revival probability of intruder states in a random background is analysed numerically and with perturbative methods. For random coupling the intruder does not affect the GOE spectral statistics of the background significantly, while a constant coupling causes very strong correlations at short range with a fourth power dependence of the spectral two-point function at the origin.The revival probability is significantly depressed for constant coupling as compared to random coupling.Comment: 18 pages, 10 Postscript figure