Light-front model of the kaon electromagnetic current

The electromagnetic form factor is extracted from both components of the electromagnetic current: J(plus) and J(minus) with a pseudo-scalar coupling of the quarks to the kaon. In the case of J(plus) there is no pair term contribution in the Drell-Yan frame. However, J(minus) component of the electromagnetic current the pair term contribution is different from zero and is necessary include it to preserve the rotational symmetry of the current.Comment: 4 pages, 1 figure, uses World Scientific style file. To be published by World Scientific in the proceedings of the "VIII International Workshop on Hadron Physics,(HADRONS 2002)", Bento Goncalves, RS, Brazi

Solutions of the bound state Faddeev-Yakubovsky equations in three dimensions by using NN and 3N potential models

A recently developed three-dimensional approach (without partial-wave decomposition) is considered to investigate solutions of Faddeev-Yakubovsky integral equations in momentum space for three- and four-body bound states, with the inclusion of three-body forces. In the calculations of the binding energies, spin-dependent nucleon-nucleon (NN) potential models (named, S$_{3}$, MT-I/III, YS-type and P$_{5.5}$GL) are considered along with the scalar two-meson exchange three-body potential. Good agreement of the presently reported results with the ones obtained by other techniques are obtained, demonstrating the advantage of an approach in which the formalism is much more simplified and easy to manage for direct computation.Comment: 16 pages, 1 figure and 6 tables; to appear in Physical review

Quasi-bound states in continuum

We report the prediction of quasi-bound states (resonant states with very long lifetimes) that occur in the eigenvalue continuum of propagating states for a wide region of parameter space. These quasi-bound states are generated in a quantum wire with two channels and an adatom, when the energy bands of the two channels overlap. A would-be bound state that lays just below the upper energy band is slightly destabilized by the lower energy band and thereby becomes a resonant state with a very long lifetime (a second QBIC lays above the lower energy band).Comment: 4 pages, 4figures, 1 tabl

Ambegaokar-Baratoff relations of Josephson critical current in heterojunctions with multi-gap superconductors

An extension of the Ambegaokar-Baratoff relation to a superconductor-insulator-superconductor (SIS) Josephson junction with multiple tunneling channels is derived. Appling the resultant relation to a SIS Josephson junction formed by an iron-based (five-band) and a single-band Bardeen-Cooper-Schrieffer (BCS) type superconductors, a theoretical bound of the Josephson critical current ($I_{\rm c}$) multiplied by the resistance of the junction ($R_{\rm n}$) is given. We reveal that such a bound is useful for identifying the pairing symmetry of iron-pnictide superconductors. One finds that if a measured value of $I_{\rm c}R_{\rm n}$ is smaller than the bound then the symmetry is $\pm s$-wave, and otherwise $s$-wave without any sign changes. In addition, we stress that temperature dependence of $I_{\rm c}R_{\rm n}$ is sensitive to the difference of the gap functions from the BCS type gap formula in the above heterojunction.Comment: 7 pages, 6 figure

Effect of nearest- and next-nearest neighbor interactions on the spin-wave velocity of one-dimensional quarter-filled spin-density-wave conductors

We study spin fluctuations in quarter-filled one-dimensional spin-density-wave systems in presence of short-range Coulomb interactions. By applying a path integral method, the spin-wave velocity is calculated as a function of on-site (U), nearest (V) and next-nearest (V_2) neighbor-site interactions. With increasing V or V_2, the pure spin-density-wave state evolves into a state with coexisting spin- and charge-density waves. The spin-wave velocity is reduced when several density waves coexist in the ground state, and may even vanish at large V. The effect of dimerization along the chain is also considered.Comment: REVTeX, 11 pages, 9 figure

Role of Collective Mode for Optical Conductivity and Reflectivity in Quarter-Filled Spin-Density-Wave State

Taking account of a collective mode relevant to charge fluctuation, the optical conductivity of spin-density-wave state has been examined for an extended Hubbard model with one-dimensional quarter-filled band. We find that, within the random phase approximation, the conductivity exhibits several peaks at the frequency corresponding to the excitation energy of the commensurate collective mode. When charge ordering appears with increasing inter-site repulsive interactions, the main peak with the lowest frequency is reduced and the effective mass of the mode is enhanced indicating the suppression of the effect of the collective mode by charge ordering. It is also shown that the reflectivity becomes large in a wide range of frequency due to the huge dielectric constant induced by the collective mode.Comment: 11 pages, 16 figure

The asymptotic limits of zero modes of massless Dirac operators

Asymptotic behaviors of zero modes of the massless Dirac operator $H=\alpha\cdot D + Q(x)$ are discussed, where $\alpha= (\alpha_1, \alpha_2, \alpha_3)$ is the triple of $4 \times 4$ Dirac matrices, $D=\frac{1}{i} \nabla_x$, and $Q(x)=\big(q_{jk} (x) \big)$ is a $4\times 4$ Hermitian matrix-valued function with $| q_{jk}(x) | \le C ^{-\rho}$, $\rho >1$. We shall show that for every zero mode $f$, the asymptotic limit of $|x|^2f(x)$ as $|x| \to +\infty$ exists. The limit is expressed in terms of an integral of $Q(x)f(x)$.Comment: 9 page