Transverse single spin asymmetry in the Drell-Yan process

We revisit the transverse single spin asymmetry in the angular distribution of a Drell-Yan dilepton pair. We study this asymmetry by using twist-3 collinear factorization, and we obtain the same result both in covariant gauge and in the light-cone gauge. Moreover, we have checked the electromagnetic gauge invariance of our calculation. Our final expression for the asymmetry differs from all the previous results given in the literature. The overall sign of this asymmetry is as important as the sign of the Sivers asymmetry in Drell-Yan.Comment: 9 page

Domain walls in gapped graphene

The electronic properties of a particular class of domain walls in gapped graphene are investigated. We show that they can support mid-gap states which are localized in the vicinity of the domain wall and propagate along its length. With a finite density of domain walls, these states can alter the electronic properties of gapped graphene significantly. If the mid-gap band is partially filled,the domain wall can behave like a one-dimensional metal embedded in a semi-conductor, and could potentially be used as a single-channel quantum wire.Comment: 4 pgs. revte

Collins Fragmentation and the Single Transverse Spin Asymmetry

We study the Collins mechanism for the single transverse spin asymmetry in the collinear factorization approach. The correspondent twist-three fragmentation function is identified. We show that the Collins function calculated in this approach is universal. We further examine its contribution to the single transverse spin asymmetry of semi-inclusive hadron production in deep inelastic scattering and demonstrate that the transverse momentum dependent and twist-three collinear approaches are consistent in the intermediate transverse momentum region where both apply.Comment: 10 pages, 2 figure

Obtaining correct orbital ground states in ff electron systems using a nonspherical self-interaction corrected LDA+UU method

The electronic structure of lanthanide and actinide compounds is often characterized by orbital ordering of localized $f$-electrons. Density-functional theory (DFT) studies of such systems using the currently available LDA+$U$ method are plagued by significant orbital-dependent self-interaction, leading to erroneous orbital ground states. An alternative scheme that modifies the exchange, not Hartree, energy is proposed as a remedy. We show that our LDA+$U$ approach reproduces the expected degeneracy of $f^1$ and $f^2$ states in free ions and the correct ground states in solid PrO$_2$. We expect our method to be useful in studying compounds of $f$- and heavy-$d$ elements.Comment: 11 pages, 4 figure

Quantum computation with un-tunable couplings

Most quantum computer realizations require the ability to apply local fields and tune the couplings between qubits, in order to realize single bit and two bit gates which are necessary for universal quantum computation. We present a scheme to remove the necessity of switching the couplings between qubits for two bit gates, which are more costly in many cases. Our strategy is to compute in and out of carefully designed interaction free subspaces analogous to decoherence free subspaces, which allows us to effectively turn off and turn on the interactions between the encoded qubits. We give two examples to show how universal quantum computation is realized in our scheme with local manipulations to physical qubits only, for both diagonal and off diagonal interactions.Comment: 5 pages, 2 figure

Towards the assignment for the 41S04 ^1S_0 meson nonet

The strong decays of the $\pi(2070)$, $\eta(2010)$, $\eta(2100)$, $\eta(2190)$, and $\eta(2225)$ as the $4 ^1S_0$ quark-antiquark states are investigated in the framework of the $^3P_0$ meson decay model. It is found that the $\pi(2070)$, $\eta(2100)$, and $\eta(2225)$ appear to be the convincing $4 ^1S_0$ $q\bar{q}$ states while the assignment of the $\eta(2010)$ and $\eta(2190)$ as the $4 ^1S_0$ isoscalar states is not favored by their widths. In the presence of the $\pi(2070)$, $\eta(2100)$, and $\eta(2225)$ being the members of the $4 ^1S_0$ meson nonet, the $4 ^1S_0$ kaon is phenomenologically determined to has a mass of about 2153 MeV. The width of this unobserved kaon is expected to be about 197 MeV in the $^3P_0$ decay model.Comment: 15 pages, 5 figures, version accepted for publication in Physical Review