Abstract The interest in the Klein–Gordon equation with different potentials has increased in recent years due to its possible applications in Cosmology, Hadron Physics and High-Energy Physics. In this work, we investigate the solutions of the Klein–Gordon equation for bosons under the influence of an external potential by using the Feshbach–Villars method. We present detailed results for two cases: the Coulombic potential and the harmonic potential. For the latter case, we studied the effects of self-interacting particles by adopting a mean-field approach. We show that our results converge smoothly to the solution of the Schrödinger equation for the same systems as the relativistic effects diminish.
Abstract The interest in the Klein–Gordon equation with different potentials has increased in recent years due to its possible applications in Cosmology, Hadron Physics and High-Energy Physics. In this work, we investigate the solutions of the Klein–Gordon equation for bosons under the influence of an external potential by using the Feshbach–Villars method. We present detailed results for two cases: the Coulombic potential and the harmonic potential. For the latter case, we studied the effects of self-interacting particles by adopting a mean-field approach. We show that our results converge smoothly to the solution of the Schrödinger equation for the same systems as the relativistic effects diminish.
Quantum relativistic solutions for a particle in a one-dimensional Morse potential are presented using methods previously proposed and applied to a particle in a harmonic oscillator. The methods lead to both numerical and analytical solutions, with the latter allowing smooth variation of the system parameters from non-relativistic to ultrarelativistic limits. Analytical expressions for the energy levels and wavefunctions are obtained, as solutions to a Schrödinger-type equation, including relativistic effects through a state dependent rescaled mass. The eigenstates of the Morse potential exhibit suitable and smooth behavior, and approach the corresponding harmonic oscillator solutions as the depth of the Morse potential well increases, as expected. A comparison is also presented between the relativistic harmonic oscillator obtained with this method, and the so-called Klein-Gordon oscillator.
We analyze the the remarkable analogy between the classical Klein–Gordon equation for a test scalar field in a flat and also in a curved background, and the Gross–Pitaevskii equation for a Bose–Einstein condensate trapped by an external potential. We stress here that the solution associated with the Klein–Gordon equation (KG) in a flat space time has the same mathematical structure, under certain circumstances, to those obtained for the Gross–Pitaevskii equation, that is, a static soliton solution. Additionally, Thomas–Fermi approximation is applied to the 3–dimensional version of this equation, in order to calculate some thermodynamical properties of the system in curved a space–time back ground. Finally, we stress the fact that a gravitational background provides, in some cases, a kind of confining potential for the scalar field, allowing us to remarks even more the possible connection between scalar fields and the phenomenon of Bose–Einstein condensation.
We review our recent theoretical advances in the dynamics of Bose-Einstein condensates with tunable interactions using Feshbach resonance and external potential. A set of analytic and numerical methods for Gross-Pitaevskii equations are developed to study the nonlinear dynamics of Bose-Einstein condensates. Analytically, we present the integrable conditions for the Gross-Pitaevskii equations with tunable interactions and external potential, and obtain a family of exact analytical solutions for one- and two-component Bose-Einstein condensates in one and two-dimensional cases. Then we apply these models to investigate the dynamics of solitons and collisions between two solitons. Numerically, the stability of the analytic exact solutions are checked and the phenomena, such as the dynamics and modulation of the ring dark soliton and vector-soliton, soliton conversion via Feshbach resonance, quantized soliton and vortex in quasi-two-dimensional are also investigated. Both the exact and numerical solutions show that the dynamics of Bose-Einstein condensates can be effectively controlled by the Feshbach resonance and external potential, which offer a good opportunity for manipulation of atomic matter waves and nonlinear excitations in Bose-Einstein condensates.
We examine the occurrence of Bose-Einstein condensation in both nonrelativistic and relativistic systems with no self-interactions in a general setting. A simple condition for the occurrence of Bose-Einstein condensation can be given if we adopt generalized ζ-functions to define the quantum theory. We show that the crucial feature governing Bose-Einstein condensation is the dimension q associated with the continuous part of the eigenvalue spectrum of the Hamiltonian for nonrelativistic systems or the spatial part of the Klein-Gordon operator for relativistic systems. In either case Bose-Einstein condensation can only occur if q ≥ 3 [1]. Several examples, some of them not completely solved before, may be treated very easily using our simple criterion [2]. These examples are charged free gases confined in finite volumes as torus, boxes, spheres, cylinders (see also [3, 4, 5, 6]) and in the presence of general constant external magnetic fields ([7, 8, 9, 10]).
The aim of this work is to investigate how energy depends on the two-body interaction potential in Bose-Einstein condensation (BEC) phenomena. An equation of state is obtained which is valid both for low and high energy BEC, through the application of a revised form of quantum statistics. An extension of the singularity conditions describing the state of BEC is given, in order to consider interactions between particles due to a central interatomic potential. From the singularity conditions of the corresponding system of hard-sphere bosons and the equation for the energy of the system in its ground state, the equation of state connecting temperature, density and energy in BEC is deduced, with upper and lower limits for the energy depending on the form of the central interaction potential. It is shown that high energy mode is allowed in the case of Coulomb type interaction only, low energy mode in the case of non-Coulomb type interaction. Numerical results are then derived for low energy BEC, occurring in neutral matter, with application to He-4 and alkali-metal atoms, and in the case of high energy BEC occurring in systems of charged bosons, with application to atomic nuclei.
This study examined the relativistic Klein–Gordon equation and highlighted the characteristics of positive and negative energies. Positive energies correspond to real particles, as they exhibit stable motion forward in time, while negative energies correspond to non-real systems due to antiparticles, highlighting the understanding of particles in relativistic quantum theory. The system’s stability is more pronounced at small screening parameters as the creation of particles (indicated by negative energies) also enlarged. The study further explores the contributions of component potentials in an interacting potential, with a focus on the Pöschl–Teller and symmetric trigonometric Rosen–Morse potentials. The duality of positive and negative energy solutions exemplifies the symmetry between matter and antimatter. The solution of the Schrödinger equation with the same potential is also studied and applied to diatomic models, specifically Cl2, Br2, I2, K2, N2 and F2, comparing analytic results with tested data for various quantum states. The analytic results demonstrate excellent agreement with experimental results, with deviations attributed to experimental methods or theoretical model limitations. The study underscores the reliability of the proposed analytic methods for predicting molecular properties.