物理最新文献

The formalism of the horizon quantum mechanics is applied to electrically neutral and spherically symmetric black hole geometries emerging from coherent quantum states of gravity to compute the probability that the matter source is inside the horizon. We find that quantum corrections to the classical horizon radius become significant if the matter core has a size comparable to the Compton length of the constituents, and the system is indeed a black hole with probability very close to one unless the core radius is close to the (classical) gravitational radius.

The Rossby mode (r-mode) perturbation in pulsars as a steady gravitational wave source has been explored. The effect of a rigid crust on viscous damping and dissipation rate in the boundary layer between the fluid core and the crust has been studied. The intensity of the emitted GWs in terms of the strain tensor amplitude has been estimated with the approximation of slow rotation using equation of state derived from the APR and Skyrme effective interactions with Brussels–Montreal parameter sets. The core of the neutron star has been considered to be (beta )-equilibrated nuclear matter containing neutrons, protons, electrons and muons, surrounded by a solid crust. Calculations have been made for critical frequencies, time evolution and rate of change of the spin frequencies across a broad spectrum of pulsar masses.

We present a comprehensive analysis of weak transition form factors, semileptonic decays, and nonleptonic decays of (B_c) mesons involving pseudoscalar (P) and vector (V) mesons for bottom-conserving and bottom-changing decay modes. We employ the self-consistent covariant light-front quark model (CLFQM), termed type-II correspondence, to calculate the (B_c) to P(V) transition form factors. The type-II correspondence in the CLF approach gives self-consistent results associated with the (B^{(i)}_j) functions, which vanish numerically after the replacement (M^{prime (prime prime )} rightarrow M_0^{prime (prime prime )}) in traditional type-I correspondence, and the covariance of the matrix elements is also restored. We investigate these effects on bottom-conserving (B_c) to P(V) form factors that have not yet been studied in CLFQM type-II correspondence. In addition, we quantify the implications of self-consistency propagating to weak decays involving both bottom-conserving and bottom-changing (B_c) transition form factors. We use two different parameterizations, the usual three-parameter function of (q^{2}) and the model-independent z-series expansion, to establish a clear understanding of (q^{2}) dependence. Using the numerical values of the form factors, we predict the branching ratios other physical observables, including forward-backward asymmetries, polarization fractions, etc. of the semileptonic (B_c) decays. Subsequently, we predict the branching ratios of two-body nonleptonic weak decays using the factorization hypothesis in self-consistent CLFQM. We also compare our results with those of other theoretical studies.

A novel cross-polarized converter that receives line-polarized waves and converts them into cross-polarized ones is proposed with a 10 dB impedance bandwidth of 6.8%, based on which a 2-bit metasurface cell is constructed, which consists of only one dielectric substrate and has a cell size of only 0.14 times the electrical wavelength. The metasurface designed based on this unit can effectively beam the electromagnetic waves emitted by the horn feeder and increase the gain, which has the potential to be used in various wireless systems.

In this work, we obtain the Demkov–Fradkin tensor of symmetries for the quantum curved harmonic oscillator in a space with constant curvature given by a parameter (kappa). In order to construct this tensor, we have firstly found a set of basic operators which satisfy the following conditions: (i) Their products give symmetries of the problem; in fact, the Hamiltonian is a combination of such products; (ii) they generate the space of eigenfunctions as well as the eigenvalues in an algebraic way; (iii) in the limit of zero curvature, they come into the well-known creation/annihilation operators of the flat oscillator. The appropriate products of such basic operators will produce the curved Demkov–Fradkin tensor. However, these basic operators do not satisfy Heisenberg commutators but close another Lie algebra which depends on (kappa). As a by-product, the classical Demkov–Fradkin tensor for the classical curved harmonic oscillator has been obtained by the same method. The case of two dimensions has been worked out in detail: Here, the operators close a (so_kappa (4)) Lie algebra; the spectrum and eigenfunctions are explicitly solved in an algebraic way and in the classical case the trajectories have been computed.

The current analysis focusses on the three-dimensional viscous flow caused by an expanding or contracting porous slider under the impact of heat source(/)sink, magnetic field and waste discharge concentration. The amount of fluid injected to levitate the slider is not constant; rather, it varies over time based on the slider's location at any given moment. The fluid flow between the ground and the slider is represented by the unsteady nonlinear equations of motion, which are converted into ordinary differential equations by employing the apt similarity transformations. These simplified equations are solved by applying the hybrid residual power series method (HRPSM). Using graphical representations, the physical behaviour of significant parameters is investigated. Tabular data are used to compare the hybrid residual power series method and the numerical scheme to check the convergence and accuracy of the hybrid residual power series method. A rise in the magnetic parameter results in a very modest rise in the fluid's longitudinal velocity in the regions closest to the upper or lower plates and a clear drop in the liquid's longitudinal velocity in the centre region. An increase in pollutant external-source parameter increases the amount of pollutants introduced into the fluid system.

We present a coil system designed to generate a highly uniform magnetic field for the n2EDM experiment at the Paul Scherrer Institute. It consists of a main (B_0) coil and a set of auxiliary coils mounted on a cubic structure with a side length of (273~hbox {cm}), inside a large magnetically shielded room (MSR). We have assembled this system and characterized its performances with a mapping robot. The apparatus is able to generate a (1~upmu hbox {T}) vertical field with a relative root mean square deviation (sigma (B_z)/B_z = 3times 10^{-5}) over the volume of interest, a cylinder of radius (40~hbox {cm}) and height ({30}~hbox {cm}). This level of uniformity overcomes the n2EDM requirements, allowing a measurement of the neutron Electric Dipole Moment with a sensitivity better than (1times 10^{-27}e,hbox {cm}).

Motivated by the growing interest in the nonmetricity-matter couplings, we develop the scalar–tensor formulation of recently introduced f(Q, T) gravity, where Q is the nonmetricity and T is the trace of the energy–momentum tensor. The main properties of the scalar–tensor formalism for the Friedmann–Lemaître–Robertson–Walker (FLRW) Universe are discussed, and we introduce an appropriate set of dynamical variables to analyze the cosmic evolution of the scalar–tensor f(Q, T) cosmology as a dynamical system. By considering two distinct cosmic fluids, namely matter and radiation, we have demonstrated that the cosmological phase space exhibits the typical curvature-dominated, radiation-dominated, matter-dominated, and exponentially accelerated fixed points. Furthermore, under an appropriate set of initial conditions compatible with the current observations from the Planck satellite, our analysis shows that the scalar–tensor f(Q, T) successfully yields models indistinguishable from the (Lambda )CDM cosmology and compatible with the weak-field solar system dynamics, without the inclusion of a cosmological constant (Lambda ). Thus, the theory introduced herein may be regarded as a suitable candidate to describe the cosmological dynamics of the Universe.