Modern Physics Letters A

Entanglement and atomic coherence are investigated for a system that consists of a four-level atom (FLA) coupled with a nonlinear field. We explore the influence of field deformation and photon transition on the dynamical behavior of the quantum measures when the quantized field is initially in a coherent state or in a Schrödinger cat state with and without energy dissipation. The results indicate that the entanglement and coherence in the FLA–field system can be controlled and manipulated through the nature and initial state of the quantized field.

Role of gauge symmetry in the proton spin problem has intricate and unresolved aspects. One of the interesting approaches to gain physical insights is to explore the Landau problem in this context. A detailed study using the group theoretic method to understand the Landau problem establishes the significance of the gauge transformation intimately related with the space translation symmetry. An important implication of this result is that the E(2)-like Wigner’s little group for massless particles could throw more light on the question of gauge symmetry in QED and QCD. A generalized Landau-Zeeman Hamiltonian is proposed in which Dirac two-oscillator system and the symmetry of the group SO(3,2) become important. It is argued that nontrivial topology of pure gauge field holds promise to resolve the unsettled questions.

We present a classification and an explicit form of all constant solutions of the Yang–Mills equations with $\mathrm{\text{SU}}(2)$ gauge symmetry for an arbitrary constant non-Abelian current in pseudo-Euclidean space ${ℝ}^{p,q}$ of arbitrary finite dimension $n=p+q$. Using hyperbolic singular value decomposition and two-sheeted covering of orthogonal group by spin group, we solve the nontrivial system for constant solutions of the Yang–Mills equations of $3n$ cubic equations with $3n$ unknowns and $3n$ parameters in the general case. We present a new symmetry of this system of equations. All solutions in terms of the potential, strength and invariant of the Yang–Mills field are presented. Nonconstant solutions of the Yang–Mills equations can be considered in the form of series of perturbation theory using all constant solutions as a zeroth approximation.

In this paper, we perform a detailed group classification for a generalized convection-reaction-diffusion equation with three unknown functions. Specifically, we determine all the functional forms for the unknown functions where the given equation admits nontrivial Lie point symmetries. The classification problem provides us with eight families of equations summarized in four categories. The admitted Lie symmetries form the four Lie algebras $2A_1$, $A_{4,4}$, $A_{2,1}\oplus A_1$ and $A_{2,1}\oplus A_{2,1}$. For the four families of the classification problem we calculate the one-dimensional optimal system and we derive all the similarity transformations which reduce the partial differential equation into an ordinary differential equation. Applications of the similarity transformations are presented while exact solutions are derived.

In this paper, we consider Einstein–Hilbert gravity in the presence of cosmological constant and an electric field of Yang–Mills type, which is minimally coupled to gravity. We couple the Ricci scalar to the Yang–Mills invariant to obtain a modified theory of gravity. The black brane solution of this model is introduced up to the first order of the $R{F}_{\mu \alpha }^{(a)}{F}^{(a)\mu \alpha }$ term. Then, the color non-Abelian direct current (DC) conductivity and the ratio of shear viscosity to entropy density are calculated for this solution. Our results recover the Yang–Mills Schwarzschild AdS black brane in the limit of $q_2\to 0$.

In this paper, we study the late accelerating expansion of the universe by incorporating bulk viscous matter with the running vacuum. The running vacuum is assumed to be varied as the square of the Hubble parameter (${\rho }_{\mathrm{\Lambda }}\propto H^2$), while the coefficient of bulk viscosity of matter is taken to be proportional to the Hubble parameter ($\xi \propto H$). We have analytically solved for the Hubble parameter and estimated the model parameters using the combined data set $\mathrm{\text{SNIa}}+\mathrm{\text{CMB}}+\mathrm{\text{BAO}}+\mathrm{\text{OHD}}+\mathrm{\text{QSO}}$. The evolution of the cosmological parameters was analyzed, and the universe’s age is estimated to be 13.94Gyr. The evolution of the universe in the present model marked considerable improvement compared to bulk viscous matter-dominated models. The transition from matter-dominated decelerated phase to vacuum energy-dominated accelerating phase occurred at a transition redshift, $z_T=0.73$, and the evolution asymptotically approaches a de Sitter epoch. We have obtained the coefficient of bulk viscosity of the matter component as $9.94\times 10^4\mathrm{\text{kg}}{\mathrm{\text{m}}}^{-1}{\mathrm{\text{s}}}^{-1}$ which is two orders of magnitude less than the value predicted by most of the bulk viscous matter-dominated models. The statefinder analysis distinguishes our model from the $\mathrm{\Lambda }$CDM model at present, and the $r-s$ trajectory reveals the quintessence behavior of the vacuum energy. The model was found to satisfy the generalized second law of thermodynamics, and the entropy is maximized in the far future evolution.

In this study, Higgs production processes, Higgsstrahlung and vector boson ($W$ and $Z$) fusion processes, are investigated for four different future lepton colliders (CEPC, ILC, CLIC, and FCC-ee). The cross-sections for each production process and corresponding backgrounds are calculated considering the Initial State Radiation (ISR) and Beamstrahlung (BS) effects. Various cuts and the b-tagging method are used to reduce the background. Finally, the number of events for each collider is determined, and significance calculations are performed. In our calculations, high event numbers are obtained for all four colliders for the Higgsstrahlung, $W$, and $Z$ fusion process. This shows that electron–positron colliders will play an important role in future Higgs physics research.

New agegraphic dark energy (NADE) model with bulk viscosity is proposed by assuming that the universe is composed of the NADE and dark matter, and both the dark components have a bulk viscosity. At the matter-dominated epoch, the density parameter and the equation of state (EoS) of the viscous NADE are given by ${\mathrm{\Omega }}_q={(1-9{\tau }_m)}^2{n}^2{(1+z)}^{-2}∕4$ and $w_q=-2∕3+3({\tau }_q-{\tau }_m)$, respectively, where ${\tau }_q$ and ${\tau }_m$ are viscosity parameters. In the late time $z\to -1$, the NADE dominates ${\mathrm{\Omega }}_q\to 1$ and $w_q\to -1+3{\tau }_q$. Owing to the special analytic features at the matter-dominated epoch for the viscous NADE model, the initial condition ${\mathrm{\Omega }}_q(z_{\mathrm{\text{ini}}})={(1-9{\tau }_m)}^2{n}^2{(1+z_{\mathrm{\text{ini}}})}^{-2}∕4$ at $z_{\mathrm{\text{ini}}}=2000$ is used to solve the differential equation of ${\mathrm{\Omega }}_q$, and the other physical quantities can be obtained correspondingly. We also find that the viscosity of dark matter affects the current density and the start time of the cosmic acceleration. However, in the late time $w_q$ only depends on the viscosity of the dark energy. Furthermore, we investigate the viscous NADE model by means of statefinder diagnostic. The viscosity of dark matter significantly affects the evolution of the statefinder parameters. Therefore, the bulk viscosity plays a significant role in the cosmological evolution.