Modern Physics Letters A

In this paper, we briefly survey open questions in cosmology that either have been or could potentially be addressed with the help of the causal set theory approach to quantum gravity. Our discussion includes topics ranging from dark matter and dark energy to primordial quantum fluctuations and horizon entropy. By putting together all in one place, these cosmologically relevant directions of work within causal set theory, we hope to impart a bird’s-eye view of this important research theme.

In this paper, $F(\nu )$ cosmology is proposed for the accelerating universe with asymptotic de Sitter expansion in terms of Hankel function index $\nu$. To some extent, both the initial expansion during early inflation and the current accelerated expansion can be studied with a vacuum cosmic fluid, i.e. $\mathrm{\Lambda }$ in the pure de Sitter phase. Observational data further support the notion of a quasi-vacuum fluid, rather than a pure vacuum, contributing to the quasi-de Sitter acceleration in both the early and late universe. By examining the asymptotic expansion of the Henkel function as an approximate solution of the Mukhanov–Sasaki equation, we seek a more detailed study of quasi-de Sitter solutions in cosmology containing vacuum-like fluid.

In this paper, we introduce a novel model for collective-dephasing noise in $d$-dimensional space. After that, we construct a multi-particle entangled state to resist the given collective-dephasing noise. Based on the measurement laws of multi-particle entangled state under two different bases, we propose a multipartite quantum key agreement protocol. In this protocol, multiple participants would obtain $d$-dimensional secret key even if the quantum channel is influenced by collective-dephasing noise. The security analysis indicates that this protocol can resist both dishonest participant attack and the outsider attacks which include intercept-resend attack and entangle-measure attack. By comparing with the existing QKA protocols, it is clear that our protocol has greater universality from the perspective of dimensionality and number of participants.

In this work, a Liouville–Caputo fractional order (FO) derivative for the mathematical system based on the accelerating universe in the modified gravity (AUMG), i.e. FO-AUMG is proposed to get more accurate solutions. The nonlinear dynamics of the FO-AUMG is classified into five dynamics. The performances of the designed nonlinear FO-AUMG are numerically stimulated with the stochastic procedures of Levenberg–Marquardt backpropagated (LMB) scheme-based neural networks. The statics for FO-AUMS is used for the nonlinear FO-AUMG as 72%, 16% and 12% for training, authorization, and testing. Twenty neurons in hidden layers have been used to approximate the solution of the nonlinear FO-AUMS. The comparison of three different cases of the nonlinear FO-AUMS is performed with dataset generated by Adams method. To validate the uniformity, legitimacy, precision, and competence of LMB-based adaptive neural networks, the outcomes of the state transitions parameters, regression, correlation, error-histogram plots have been exploited.

In this paper, we introduce the black brane solutions in anti-de Sitter (AdS) space in four-dimensional (4D) Einstein–Gauss–Bonnet–Yang–Mills theory in the presence of string cloud and quintessence. Shear viscosity to entropy density ratio is computed via fluid–gravity duality, as a transport coefficient for this model.

In this work, we try to find the volume inside the power-Maxwell charged black hole in Rastall gravity based on the definition and method proposed by Christodoulou and Rovelli. We find the interior volume as well as CR volume for this black hole. We also analyze our work numerically and show that our result is compatible with previous results obtained by various authors.

We know that space and time are treated almost equally in classical physics, but we also know that this is not the case for quantum mechanics. A quantum description of both space and time is important to really understand the quantum nature of reality. The Page–Wootters mechanism of quantum time is a promising starting point, according to which the evolution of the quantum system is described by the entanglement between it and quantum temporal degrees of freedom. In this paper, we consider a qubit clock that is entangled with a quantum system due to the Wigner rotation induced by Lorentz transformation. We study how this time-system entanglement depends on the rapidity of the Lorentz boost. We consider the case of a spin-1/2 particle with Gaussian momentum distribution as a concrete example. We also compare the time-system entanglement entropy with the spin-momentum entanglement entropy and find that the former is smaller than the latter.