Modern Physics Letters A

We illustrate the powerfulness of Padé approximants (PAs) as a summation method and explore one of their extensions, the so-called quadratic approximant (QAs), to access both space- and (low-energy) time-like (TL) regions. As an introductory and pedagogical exercise, the function $\frac{1}{z}\mathrm{\text{ln}}(1+z)$ is approximated by both kind of approximants. Then, PAs are applied to predict pseudoscalar meson Dalitz decays and to extract $V_{ub}$ from the semileptonic $B\to \pi \ell {\nu }_{\ell }$ decays. Finally, the $\pi$ vector form factor in the TL region is explored using QAs.

In this paper, we review the precision determination of the bottom and top quark masses from the total pair-production cross-section near threshold. The theory prediction of the cross-section includes QCD corrections up to third-order. We further discuss the combined impact of Higgs corrections, the QED Coulomb potential, non-resonant production, and P-wave production on the extraction of top quark properties.

Two methods for determining $\left|V_{us}\right|$ employing inclusive hadronic $\tau$ decay data are discussed. The first is the conventional flavor-breaking sum rule determination whose usual implementation produces results $\sim 3\sigma$ low compared to three-family unitary expectations. The second is a novel approach combining experimental strange hadronic $\tau$ distributions with lattice light-strange current–current two-point function data. Preliminary explorations of the latter show the method promises $\left|V_{us}\right|$ determinations competitive with those from $K_{\ell 3}$ and $\mathrm{\Gamma }[K_{\mu 2}]/\mathrm{\Gamma }[{\pi }_{\mu 2}]$. For the former, systematic issues in the conventional implementation are investigated. Unphysical dependences of $\left|V_{us}\right|$ on the choice of sum rule weight, $w$, and upper limit, $s_0$, of the weighted experimental spectral integrals are observed, the source of these problems identified and a new implementation which overcomes these problems developed. Lattice results are shown to provide a tool for quantitatively assessing truncation uncertainties for the slowly converging $D=2$ OPE series. The results for $\left|V_{us}\right|$ from this new implementation are shown to be free of unphysical $w$- and $s_0$-dependences, and $\sim 0.0020$ higher than those produced by the conventional implementation. With preliminary new $K\pi$ branching fraction results as input, we find $\left|V_{us}\right|$ in excellent agreement with that obtained from $K_{\ell 3}$, and compatible within errors with expectations from three-family unitarity.

Assuming that the corrections to relevant Wilson coefficients from new physics (NP) contain the possible CP phases, we analyze the constraints on the NP corrections from the updated experimental data on rare B decays from LHCb, BABAR, and BELLE, etc. systematically. Through global fit among the theoretical evaluations and corresponding experimental observations, we find that the possible CP phases of the corrections to relevant Wilson coefficients from NP affect the allowed parameter space obviously.

This paper addresses a problem of Casimir apparatus in dense medium, put in weak gravitational field. The falling of the apparatus has to be governed by the equivalence principle with proper account for contributions to the weight of the apparatus from its material part and from distorted quantum fields. We discuss general expression for the corresponding force in metric with cylindrical symmetry. By way of example, we compute explicit expression for Archimedes force, acting on the Casimir apparatus of finite size, immersed into thermal bath of free scalar field. It is shown that besides universal term, proportional to the volume of the apparatus, there are non-universal quantum corrections, depending on the boundary conditions.

In this paper, we present an approximate analytic solution to the Dirac equation in the Schwarzschild geometry to investigate the Zitterbewegung (ZB) effect. The analytical expression for the current density, which is induced by the motion of a wave packet of electrons, is obtained. In addition, the intensity of dipole radiation near the black hole is calculated. The proposed approach is based on the Schrödinger representation, thereby allowing to consider the ZB effect in the case of a curved space. The considered example demonstrates a possibility for applying this approach to astrophysical applications, in particular to problems of the electron radiation in the vicinity of real black holes.

In a recent work, authors prove a yet another no-go theorem that forbids the existence of a universal probabilistic quantum protocol producing a superposition of two unknown quantum states. In this short note, we show that in the presence of closed time-like curves (CTCs), one can indeed create superposition of unknown quantum states and evade the no-go result.