Highly Charged Ion (HCI) Clocks: Frontier candidates for testing variation of fine-structure constant

Attempts are made to unify gravity with the other three fundamental forces of nature. As suggested by higher dimensional models, this unification may require space and time variation of some dimensionless fundamental constants. In this scenario, probing temporal variation of the electromagnetic fine structure constant ($\alpha= \frac{e^2} {\hbar c}$) in low energy regimes at the cosmological time scale is of immense interest. Atomic clocks are ideal candidates for probing $\alpha$ variation because their transition frequencies are measured to ultra-high precision accuracy. Since atomic transition frequencies are functions of $\alpha$, measurements of clock frequencies at different temporal and spatial locations can yield signatures to ascertain such conjecture. Electrons in highly charged ions (HCIs) experience unusually enhanced relativistic effects. Hence level-crossings can be observed often in these ions compared to their isoelectronic neutral or singly charged atomic systems. Such a process features by their more significant relativistic sensitive coefficients ($q$) of atomic transitions. For unambiguous detection of subtle changes in the transition frequencies due to $\alpha$ variation, it would be judicious to contemplate transitions for which $q$ values are enormous. HCIs are considered one of the most suitable candidates for making atomic clocks as they are the least sensitive to external electromagnetic fields owing to their exceptionally contracted orbitals. The first HCI clock has been realized, but its accuracy is much less than the counter optical clocks based on neutral atoms and singly charged ions. The realization of HCI clocks can add an extra dimension to investigating fundamental physics. In this work, we survey HCIs suitable for clock candidates on the grounds of general features, including their potential to probe temporal variation of $\alpha$.Comment: 35 pages, 12 table

Research on double-yield surface model with considering time effect and its application in vibration engineering

In order to accurately study the dynamic characteristics of soft clay under vibrating loads, the classical double-yield surface model is improved in this paper, and it is introduced time effect which is proposed by Borja to build a constitutive model. The constitutive model considers creep and is suitable for analysis on dynamic characteristics of soft clay. Next, GDS dynamic triaxial experiment is carried out in the indoor, and validation analysis is conducted by means of the experimental data. In order to verify its actual effect, the improved model is applied to settlement calculation of soft clay during subway operation under vibrating loads, and then the calculation result is compared with the experimental data. It shows that the improved double-yield surface model which considers time effect can describe the dynamic deformation characteristics of soft clay more reasonably. And the proposed model is suitable for analysis on settlement of soft clay under vibrating loads of subway

Perturbative corrections to B→DB \to D form factors in QCD

We compute perturbative QCD corrections to $B \to D$ form factors at leading power in $\Lambda/m_b$, at large hadronic recoil, from the light-cone sum rules (LCSR) with $B$-meson distribution amplitudes in HQET. QCD factorization for the vacuum-to-$B$-meson correlation function with an interpolating current for the $D$-meson is demonstrated explicitly at one loop with the power counting scheme $m_c \sim {\cal O} \left (\sqrt{\Lambda \, m_b} \right )$. The jet functions encoding information of the hard-collinear dynamics in the above-mentioned correlation function are complicated by the appearance of an additional hard-collinear scale $m_c$, compared to the counterparts entering the factorization formula of the vacuum-to-$B$-meson correction function for the construction of $B \to \pi$ from factors. Inspecting the next-to-leading-logarithmic sum rules for the form factors of $B \to D \ell \nu$ indicates that perturbative corrections to the hard-collinear functions are more profound than that for the hard functions, with the default theory inputs, in the physical kinematic region. We further compute the subleading power correction induced by the three-particle quark-gluon distribution amplitudes of the $B$-meson at tree level employing the background gluon field approach. The LCSR predictions for the semileptonic $B \to D \ell \nu$ form factors are then extrapolated to the entire kinematic region with the $z$-series parametrization. Phenomenological implications of our determinations for the form factors $f_{BD}^{+, 0}(q^2)$ are explored by investigating the (differential) branching fractions and the $R(D)$ ratio of $B \to D \ell \nu$ and by determining the CKM matrix element $|V_{cb}|$ from the total decay rate of $B \to D \mu \nu_{\mu}$.Comment: 49 pages, 8 figures, version accepted for publication in JHE

QCD calculations of B→π,KB \to \pi, K form factors with higher-twist corrections

We update QCD calculations of $B \to \pi, K$ form factors at large hadronic recoil by including the subleading-power corrections from the higher-twist $B$-meson light-cone distribution amplitudes (LCDAs) up to the twist-six accuracy and the strange-quark mass effects at leading-power in $\Lambda/m_b$ from the twist-two $B$-meson LCDA $\phi_B^{+}(\omega, \mu)$. The higher-twist corrections from both the two-particle and three-particle $B$-meson LCDAs are computed from the light-cone QCD sum rules (LCSR) at tree level. In particular, we construct the local duality model for the twist-five and -six $B$-meson LCDAs, in agreement with the corresponding asymptotic behaviours at small quark and gluon momenta, employing the QCD sum rules in heavy quark effective theory at leading order in $\alpha_s$. The strange quark mass effects in semileptonic $B \to K$ form factors yield the leading-power contribution in the heavy quark expansion, consistent with the power-counting analysis in soft-collinear effective theory, and they are also computed from the LCSR approach due to the appearance of the rapidity singularities. We further explore the phenomenological aspects of the semileptonic $B \to \pi \ell \nu$ decays and the rare exclusive processes $B \to K \nu \nu$, including the determination of the CKM matrix element $|V_{ub}|$, the normalized differential $q^2$ distributions and precision observables defined by the ratios of branching fractions for the above-mentioned two channels in the same intervals of $q^2$.Comment: 36 pages, 9 figure

A New Method for Fast Computation of Moments Based on 8-neighbor Chain CodeApplied to 2-D Objects Recognition

2D moment invariants have been successfully applied in pattern recognition tasks. The main difficulty of using moment invariants is the computational burden. To improve the algorithm of moments computation through an iterative method, an approach for fast computation of moments based on the 8-neighbor chain code is proposed in this paper. Then artificial neural networks are applied for 2D shape recognition with moment invariants. Compared with the method of polygonal approximation, this approach shows higher accuracy in shape representation and faster recognition speed in experiment