Controlling and reversing the transition from classical diffusive to quantum ballistic transport in a quantum walk by driving the coin

We show that the standard quantum-walk quantum-to-classical transition, characterized by ballistic-to-diffusive spreading of the walker's position, can be controlled by externally modulating the coin state. We illustrate by showing an oscillation between classical diffusive and quantum ballistic spreading using numerical and asymptotically exact closed-form solutions, and we prove that the walker is in a controllable incoherent mixture of classical and quantum walks with a reversible quantum-to-classical transition.Comment: 7 pages, 6 figure

Large-x d/u Ratio in W-boson Production

Recent analysis of proton and deuteron deep-inelastic scattering data have suggested that the extracted d/u quark distribution ratio at large x may be significantly larger than previously believed, if the data are corrected for nuclear binding effects in the deuteron. We examine the sensitivity to the large-x d/u ratio of lepton asymmetries from W-boson production in p-pbar and p-p collisions at large rapidity, which do not suffer from nuclear contamination.Comment: 15 pages revtex, 5 postscript figures; new data on lepton asymmetry included, references added, version to be published in Phys. Lett.

π\pi-J/ψJ/\psi Correlation and Elliptic Flow Parameter v2v_2 of Charmed Mesons at RHIC Energy

We study the correlation between the trigger $\pi$ and the associated $J/\psi$ on near and away sides in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. In the region of trigger momentum $p_t>4$ GeV/$c$, the $\pi$ spectrum is composed of thermal-shower and shower-shower recombinations in the frame work of the recombination model. We consider the azimuthal anisotropy in the quenched hard parton distribution and then calculate the elliptic flow parameter $v_2$ of charmed mesons ($J/\psi$, $D^0$ and $D_s$) for different centralities.Comment: 17 pages, 6 figure

Tail Asymptotics of Deflated Risks

Random deflated risk models have been considered in recent literatures. In this paper, we investigate second-order tail behavior of the deflated risk X=RS under the assumptions of second-order regular variation on the survival functions of the risk R and the deflator S. Our findings are applied to approximation of Value at Risk, estimation of small tail probability under random deflation and tail asymptotics of aggregated deflated riskComment: 2