Measuring ∣Vub∣|V_{ub}| at future B-Factories

We calculate the so--called Fermi motion parameter $p_{_F}$ of ACCMM model using the variational method in a potential model approach. We also propose hadronic invariant mass distribution as an alternative experimental observable to measure $V_{ub}$ at future asymmetric $B$ factories.Comment: 9 pages (1 fugure not included

Exchange and correlation effects on drag in low density electron bilayers: Coulomb and virtual-optical-phonon-mediated electron-electron interaction

We investigate the effect of exchange and correlation (xc) in low-density electron bilayers. Along with the direct Coulomb interaction, the effective electron-electron interaction mediated by the exchange of virtual polar optical (PO) phonons is considered. We find that the introduction of xc corrections results in a significant enhancement of the transresistivity and qualitative changes in its temperature dependence. The virtual PO-phonon contribution behaves similarly to the Coulomb drag and reduces noticeably the total drag thereby resulting in a better agreement with the recent experimental findings.Comment: 5 pages, 4 figures, Int. Conf. EP2DS-1

Measuring of ∣Vub∣|V_{ub}| in the forthcoming decade

I first introduce the importance of measuring V_ub precisely. Then, from a theoretician's point of view, I review (a) past history, (b) present trials, and (c) possible future alternatives on measuring |V_ub| and/or |V_ub/V_cb|. As of my main topic, I introduce a model-independent method, which predicts \Gamma(B -> X_u l \nu) / \Gamma(B -> X_c l \nu) \equiv (\gamma_u / \gamma_c) \times | V_{ub} / V_{cb}|^2 \simeq (1.83 \pm 0.28) \times |V_ub / V_cb|^2 and |V_ub/V_cb| \equiv (\gamma_c / \gamma_u)^{1/2} \times [{\cal{B}}(B -> X_u l \nu)/{\cal{B}}(B -> X_c l \nu)]^{1/2} \simeq (0.74 \pm 0.06) \times [{\cal{B}}(B -> X_u l \nu)/ {\cal{B}}(B -> X_c l \nu)]^{1/2}, based on the heavy quark effective theory. I also explore the possible experimental options to separate B -> X_u l \nu from the dominant B -> X_c l \nu: the measurement of inclusive hadronic invariant mass distributions, and the `D - \pi' (and `K - \pi') separation conditions. I also clarify the relevant experimental backgrounds.Comment: 9 pages(LaTeX), 1 Postscript figur

Average Kinetic Energy of Heavy Quark and Virial Theorem

We derive the virial theorem of the relativistic two-body system for the study of the B-meson physics. It is also shown that the solution of the variational equation always satisfies the virial theorem. From the virial theorem we also obtained $\mu_\pi^2 \equiv -\lambda_1 \equiv = 0.40\sim 0.58$ GeV$^2$, which is consistent with the result of the QCD sum rule calculations of Ball $et$ $al.$Comment: 13 pages. A lot of parts of the manuscript have been revised. To appear in Physics Letters

Determination of HQET parameter \lambda_1 from Inclusive Semileptonic B Meson Decay Spectrum

We estimate the heavy quark effective theory parameter \lambda_1 from inclusive semileptonic B-meson decay spectrum. By using recent CLEO double lepton tagging data of B -> X e nu, which shows the lepton momentum as low as 0.6 GeV, we extracted \lambda_1 \sim -0.58 GeV^2. We also derived \bar\Lambda \sim 0.46 GeV and |V_{cb}| = 0.041 \pm 0.002.Comment: 13 pages, 3 figures, LaTeX. Typos are corrected, and added one commen

Depth-Resolved Composition and Electronic Structure of Buried Layers and Interfaces in a LaNiO3_3/SrTiO3_3 Superlattice from Soft- and Hard- X-ray Standing-Wave Angle-Resolved Photoemission

LaNiO$_3$ (LNO) is an intriguing member of the rare-earth nickelates in exhibiting a metal-insulator transition for a critical film thickness of about 4 unit cells [Son et al., Appl. Phys. Lett. 96, 062114 (2010)]; however, such thin films also show a transition to a metallic state in superlattices with SrTiO$_3$ (STO) [Son et al., Appl. Phys. Lett. 97, 202109 (2010)]. In order to better understand this transition, we have studied a strained LNO/STO superlattice with 10 repeats of [4 unit-cell LNO/3 unit-cell STO] grown on an (LaAlO$_3$)$_{0.3}$(Sr$_2$AlTaO$_6$)$_{0.7}$ substrate using soft x-ray standing-wave-excited angle-resolved photoemission (SWARPES), together with soft- and hard- x-ray photoemission measurements of core levels and densities-of-states valence spectra. The experimental results are compared with state-of-the-art density functional theory (DFT) calculations of band structures and densities of states. Using core-level rocking curves and x-ray optical modeling to assess the position of the standing wave, SWARPES measurements are carried out for various incidence angles and used to determine interface-specific changes in momentum-resolved electronic structure. We further show that the momentum-resolved behavior of the Ni 3d eg and t2g states near the Fermi level, as well as those at the bottom of the valence bands, is very similar to recently published SWARPES results for a related La$_{0.7}$Sr$_{0.3}$MnO$_3$/SrTiO$_3$ superlattice that was studied using the same technique (Gray et al., Europhysics Letters 104, 17004 (2013)), which further validates this experimental approach and our conclusions. Our conclusions are also supported in several ways by comparison to DFT calculations for the parent materials and the superlattice, including layer-resolved density-of-states results

A New Model-independent Method of Determining |V_{ub}/V_{cb}|

In order to determine the ratio of CKM matrix elements |V_{ub}/V_{cb}| (and |V_{ub}|), we propose a new model-independent method based on the heavy quark effective theory, which is theoretically described by the phase space factor and the well-known perturbative QCD correction only. In the forthcoming asymmetric B-experiments with microvertex detectors, BABAR and BELLE, the total separation of b --> u semileptonic decays from the dominant b --> c semileptonic decays would be experimentally viable. We explore the possible experimental option: the measurement of inclusive hadronic invariant mass distributions. We also clarify the relevant experimental backgrounds.Comment: 13 pages, no figures, ordinary LaTeX. Many improvements. To be published at Phys. Lett.

Topological doping and the stability of stripe phases

We analyze the properties of a general Ginzburg-Landau free energy with competing order parameters, long-range interactions, and global constraints (e.g., a fixed value of a total ``charge'') to address the physics of stripe phases in underdoped high-Tc and related materials. For a local free energy limited to quadratic terms of the gradient expansion, only uniform or phase-separated configurations are thermodynamically stable. ``Stripe'' or other non-uniform phases can be stabilized by long-range forces, but can only have non-topological (in-phase) domain walls where the components of the antiferromagnetic order parameter never change sign, and the periods of charge and spin density waves coincide. The antiphase domain walls observed experimentally require physics on an intermediate lengthscale, and they are absent from a model that involves only long-distance physics. Dense stripe phases can be stable even in the absence of long-range forces, but domain walls always attract at large distances, i.e., there is a ubiquitous tendency to phase separation at small doping. The implications for the phase diagram of underdoped cuprates are discussed.Comment: 18 two-column pages, 2 figures, revtex+eps

Initial-State Interactions in the Unpolarized Drell-Yan Process

We show that initial-state interactions contribute to the $\cos 2 \phi$ distribution in unpolarized Drell-Yan lepton pair production $p p$ and $p \bar p \to \ell^+ \ell^- X$, without suppression. The asymmetry is expressed as a product of chiral-odd distributions $h_1^\perp(x_1,\bm{p}_\perp^2)\times \bar h_1^\perp(x_2,\bm{k}_\perp^2)$, where the quark-transversity function $h_1^\perp(x,\bm{p}_\perp^2)$ is the transverse momentum dependent, light-cone momentum distribution of transversely polarized quarks in an {\it unpolarized} proton. We compute this (naive) $T$-odd and chiral-odd distribution function and the resulting $\cos 2 \phi$ asymmetry explicitly in a quark-scalar diquark model for the proton with initial-state gluon interaction. In this model the function $h_1^\perp(x,\bm{p}_\perp^2)$ equals the $T$-odd (chiral-even) Sivers effect function $f^\perp_{1T}(x,\bm{p}_\perp^2)$. This suggests that the single-spin asymmetries in the SIDIS and the Drell-Yan process are closely related to the $\cos 2 \phi$ asymmetry of the unpolarized Drell-Yan process, since all can arise from the same underlying mechanism. This provides new insight regarding the role of quark and gluon orbital angular momentum as well as that of initial- and final-state gluon exchange interactions in hard QCD processes.Comment: 22 pages, 6 figure

Linear and non-linear perturbations in dark energy models

I review the linear and second-order perturbation theory in dark energy models with explicit interaction to matter in view of applications to N-body simulations and non-linear phenomena. Several new or generalized results are obtained: the general equations for the linear perturbation growth; an analytical expression for the bias induced by a species-dependent interaction; the Yukawa correction to the gravitational potential due to dark energy interaction; the second-order perturbation equations in coupled dark energy and their Newtonian limit. I also show that a density-dependent effective dark energy mass arises if the dark energy coupling is varying.Comment: 12 pages, submitted to Phys. Rev; v2: added a ref. and corrected a typ