kTk_T factorization of exclusive processes

We prove $k_T$ factorization theorem in perturbative QCD (PQCD) for exclusive processes by considering $\pi\gamma^*\to \gamma(\pi)$ and $B\to\gamma(\pi) l\bar\nu$. The relevant form factors are expressed as the convolution of hard amplitudes with two-parton meson wave functions in the impact parameter $b$ space, $b$ being conjugate to the parton transverse momenta $k_T$. The point is that on-shell valence partons carry longitudinal momenta initially, and acquire $k_T$ through collinear gluon exchanges. The $b$-dependent two-parton wave functions with an appropriate path for the Wilson links are gauge-invariant. The hard amplitudes, defined as the difference between the parton-level diagrams of on-shell external particles and their collinear approximation, are also gauge-invariant. We compare the predictions for two-body nonleptonic $B$ meson decays derived from $k_T$ factorization (the PQCD approach) and from collinear factorization (the QCD factorization approach).Comment: 11 pages, REVTEX, 5 figure

Fluorine Abundances of Galactic Low-Metallicity Giants

With abundances and 2{\sigma} upper limits of fluorine (F) in seven metal-poor field giants, nucleosynthesis of stellar F at low metallicity is discussed. The measurements are derived from the HF(1-0) R9 line at 23358{\AA} using nearinfrared K-band high-resolution spectra obtained with CRIRES at the Very Large Telescope. The sample reaches lower metallicities than previous studies on F of field giants, ranging from [Fe/H] = -1.56 down to -2.13. Effects of three-dimensional model atmospheres on the derived F and O abundances are quantitatively estimated and shown to be insignificant for the program stars. The observed F yield in the form of [F/O] is compared with two sets of Galactic chemical evolution models, which quantitatively demonstrate the contribution of Type II supernova (SN II) {\nu}-process and asymptotic giant branch/Wolf-Rayet stars. It is found that at this low-metallicity region, models cannot well predict the observed distribution of [F/O], while the observations are better fit by models considering an SN II {\nu}-process with a neutrino energy of E_{\nu} = 3 x 10^53 erg. Our sample contains HD 110281, a retrograde orbiting low-{\alpha} halo star, showing a similar F evolution as globular clusters. This supports the theory that such halo stars are possibly accreted from dwarf galaxy progenitors of globular clusters in the halo.Comment: 8 pages, 8 figures, 2 tables, published in The Astrophysical Journa

Factorization theorems, effective field theory, and nonleptonic heavy meson decays

The nonleptonic heavy meson decays $B\to D^{(*)}\pi(\rho), J/\psi K^{(*)}$ and $D\to K^{(*)}\pi$ are studied based on the three-scale perturbative QCD factorization theorem developed recently. In this formalism the Bauer-Stech-Wirbel parameters a_1 and a_2 are treated as the Wilson coefficients, whose evolution from the W boson mass down to the characteristic scale of the decay processes is determined by effective field theory. The evolution from the characteristic scale to a lower hadronic scale is formulated by the Sudakov resummation. The scale-setting ambiguity, which exists in the conventional approach to nonleptonic heavy meson decays, is moderated. Nonfactorizable and nonspectator contributions are taken into account as part of the hard decay subamplitudes. Our formalism is applicable to both bottom and charm decays, and predictions, including those for the ratios R and R_L associated with the $B\to J/\psi K^{(*)}$ decays, are consistent with experimental data.Comment: 39 pages, latex, 5 figures, revised version with some correction

Determination of a set of constitutive equations for an al-li alloy at SPF conditions

© 2015 The Authors.Uniaxial tensile tests of aluminium-lithium alloy AA1420wereconducted at superplastic forming conditions. The mechanical properties of this Al-Li alloy were then modelled by a set of physicallybased constitutive equations. The constitutive equations describe the isotropic work hardening,recovery and damage by dislocation density changes and grain size evolution. Based on a recent upgraded optimisation technique, the material constants for these constitutive equations were determined

Threshold resummation for exclusive B meson decays

We argue that double logarithmic corrections $\alpha_s\ln^2 x$ need to be resumed in perturbative QCD factorization theorem for exclusive $B$ meson decays, when the end-point region with a momentum fraction $x\to 0$ is important. These double logarithms, being of the collinear origin, are absorbed into a quark jet function, which is defined by a matrix element of a quark field attached by a Wilson line. The factorization of the jet function from the decay $B\to\gamma l\bar\nu$ is proved to all orders. Threshold resummation for the jet function leads to a universal, {\it i.e.}, process-independent, Sudakov factor, whose qualitative behavior is analyzed and found to smear the end-point singularities in heavy-to-light transition form factors.Comment: 10 pages, more details are include

Probabilistic teleportation and entanglement matching

Teleportation may be taken as sending and extracting quantum information through quantum channels. In this report, it is shown that to get the maximal probability of exact teleportation through partially entangled quantum channels, the sender (Alice) need only to operate a measurement which satisfy an ``entanglement matching'' to this channel. An optimal strategy is also provided for the receiver (Bob) to extract the quantum information by adopting general evolutions.Comment: 3.5 pages, No figure

Study of 0-π\pi phase transition in hybrid superconductor-InSb nanowire quantum dot devices

Hybrid superconductor-semiconducting nanowire devices provide an ideal platform to investigating novel intragap bound states, such as the Andreev bound states (ABSs), Yu-Shiba-Rusinov (YSR) states, and the Majorana bound states. The competition between Kondo correlations and superconductivity in Josephson quantum dot (QD) devices results in two different ground states and the occurrence of a 0-$\pi$ quantum phase transition. Here we report on transport measurements on hybrid superconductor-InSb nanowire QD devices with different device geometries. We demonstrate a realization of continuous gate-tunable ABSs with both 0-type levels and $\pi$-type levels. This allow us to manipulate the transition between 0 and $\pi$ junction and explore charge transport and spectrum in the vicinity of the quantum phase transition regime. Furthermore, we find a coexistence of 0-type ABS and $\pi$-type ABS in the same charge state. By measuring temperature and magnetic field evolution of the ABSs, the different natures of the two sets of ABSs are verified, being consistent with the scenario of phase transition between the singlet and doublet ground state. Our study provides insights into Andreev transport properties of hybrid superconductor-QD devices and sheds light on the crossover behavior of the subgap spectrum in the vicinity of 0-$\pi$ transition

Applicability of perturbative QCD to Λb→Λc\Lambda_b \to \Lambda_c decays

We develop perturbative QCD factorization theorem for the semileptonic heavy baryon decay $\Lambda_b \to \Lambda_c l\bar{\nu}$, whose form factors are expressed as the convolutions of hard $b$ quark decay amplitudes with universal $\Lambda_b$ and $\Lambda_c$ baryon wave functions. Large logarithmic corrections are organized to all orders by the Sudakov resummation, which renders perturbative expansions more reliable. It is observed that perturbative QCD is applicable to $\Lambda_b \to \Lambda_c$ decays for velocity transfer greater than 1.2. Under requirement of heavy quark symmetry, we predict the branching ratio $B(\Lambda_b \to \Lambda_c l{\bar\nu})\sim 2$, and determine the $\Lambda_b$ and $\Lambda_c$ baryon wave functions.Comment: 12 pages in Latex file, 3 figures in postscript files, some results are changed, but the conclusion is the sam