Modern Physics Letters A

In this paper, we investigate the cosmological dynamics in a spatially flat Friedmann–Lemaître–Robertson–Walker geometry in scalar-tensor and scalar-torsion theories where the nonminimally coupled scalar field is a complex field. We derive the cosmological field equations and we make use of dimensionless variables in order to determine the stationary points and determine their stability properties. The physical properties of the stationary points are discussed while we find that the two-different theories, scalar-tensor and scalar-torsion theories, share many common features in terms of the evolution of the physical variables in the background space.

We introduce a time-delay function in bulk viscosity cosmology. Even for bulk viscosity functions where closed-form solutions are known, because of the time-delay term, the exact solutions are lost. Therefore in order to study the cosmological evolution of the resulting models we perform a detailed analysis of the stability of the critical points, which describe de Sitter solutions, by using Lindstedt’s method. We find that for the stability of the critical points it depends also on the time-delay parameter, where a critical time-delay value is found which plays the role of a bifurcation point. For time-delay values near the critical value, the cosmological evolution has a periodic evolution, this oscillating behavior is because of the time-delay function. We find a new behavior near the exponential expansion point, which can be seen also as an alternative way to exit the exponential inflation.

In this work, we consider a modern form of single-field inflationary models (known as power-law plateau inflation and preheating phase for a class of plateau inflationary model) and ASPIC models by considering the Dirac–Born–Infeld (DBI) non-canonical scalar field in the light of warm inflationary scenario. For these models, we assume constant sound speed $(c_s)$ and compute different slow-roll $(𝜖$, $\eta$ and $\kappa )$ as well as inflationary parameters (number of $e$-folds $(N)$, spectral index $(n_s)$, scalar spectral index $({\alpha }_s)$ and tensor-to-scalar ratio $(r)$) for specific anti-de Sitter warp factor of the DBI inflation. Next, we plot the trajectories of $n_s-N$, ${\alpha }_s-N$ and $r-N$ with different choices of $c_s$ and found the ranges $0.969_{-0.007}^{+0.007}$, $-0.0012_{-0.0002}^{+0.0002}$, $0.0009_{-0.0003}^{+0.0003}$ (for minimal inflation model), $0.962_{-0.006}^{+0.006}$, $-0.0009_{-0.0003}^{+0.0003}$, $-1.4_{-0.9}^{+0.9}$ (for modified minimal inflation model) and $0.98_{-0.02}^{+0.02}$, $-0.000157_{-0.000008}^{+0.000008}$, $0.00043_{-0.00012}^{+0.00012}$ (mixed large field inflation), respectively. Moreover, the ranges of these parametric plots for power-law plateau inflationary model are $0.961_{-0.005}^{+0.005}(n_s-N)$, $-0.009_{-0.005}^{+0.005}({\alpha }_s-N)$, $-1.15_{-0.85}^{+0.85}(r-N)$. Finally, we find that the results of all these parametric plots are consistent with 68% and 95% with current observational data except scalar-to-tensor ratio $r$ for modified minimal and power-law Plateau inflation models.

This work analyzes the dynamical variables and information transfer of a collapsing string fluid in the theory of Rainbow gravity (RG). Modifications are made to the field equations for the anisotropic string fluid in spherical geometry with the necessary rainbow functions. We have calculated the radius and time when effective horizons formed. This calculation helps to estimate the time of the observer reaching the apparent horizon. Moreover, we have computed the dynamical variables concerning the string fluid including mass density, pressure and the string tension. The behavior of the dynamical quantities is presented graphically. It is found that the rainbow parameter $\eta$ affects the dynamical variables. The results enable us to understand the physics of a collapsing fluid and the information transfer in the collapsing scenario.

Power Maxwell nonlinear electrodynamics has become one of the well-known nonlinear models. Initially, it was proposed to make Maxwell’s theory conformally invariant in higher dimensions. Therefore, it was not expected from the model to remove the electric field’s singularity at the point charges’ location. Such singularity removal was the core of the very early model known as the Born–Infeld model. In the literature, this point has been highlighted very recently in [B. E. Panah, EPL  134, 20005 (2021)] where a variable power Maxwell model has been introduced to remove the field’s singularity. Here, in this short study, we shed more light on the issue by giving a physically acceptable mechanism for removing the singularity of the point charge at its location by applying the power Maxwell’s nonlinear electrodynamics.

For the quantum quartic anharmonic oscillator with the Hamiltonian $H=\frac{1}{2}(p^2+x^2)+\lambda x^4$, which is one of the traditional quantum-mechanical and quantum-field-theory models, the summation of its factorially divergent perturbation series is studied on the basis of the proposed method of the averaging of the corresponding Padé approximants. Thus, applying proper averaging weight function, we are able for the first time to construct the Padé-type approximations that possess correct asymptotic behavior at infinity with a rise of the coupling constant $\lambda$. The approach gives very essential theoretical and applicatory-computational advantages in applications of the given method. The convergence of the utilized approximations is studied and the values for the ground state energy $E_0(\lambda )$ of the anharmonic oscillator are calculated by the proposed method for a wide range of variation of the coupling constant $\lambda$. In addition, we perform comparative analysis of the proposed method with the modern Weniger delta-transformation method and show insufficiency of the latter to sum the divergent perturbation series in the region of the superstrong coupling $\lambda \gtrsim 5$.

Hierarchical remote preparation of equatorial states has practical applications but has not been studied before. We first propose a deterministic protocol for two-dimensional equatorial states via a four-qubit cluster state. The sender can asymmetrically transmit the secret state to any one of the three agents who are ranked in terms of their authorities. A set of useful measurement bases is elaborately constructed which plays a key role in the protocol. Then the protocol is generalized to high-dimensional system. Further, taking advantage of cluster state’s symmetry, we give a universal protocol with multiple agents. The high-grade agent needs the assistance of the remaining high-grade agents as well as one of the low-grade agents. While the low-grade agent needs the cooperation of all the other agents. The agents’ recovery operators are expressed by a general formula which clearly reveals the relationship with the measurement results. Additionally, the impact of two kinds of noise is analyzed.