International Journal of Modern Physics A

I review recent applications of the open quantum system framework in the understanding of quarkonium suppression in heavy-ion collisions, which has been used as a probe of the quark–gluon plasma for decades. The derivation of the Lindblad equations for quarkonium in both the quantum Brownian motion and the quantum optical limits and their semiclassical counterparts is explained. The hierarchy of time scales assumed in the derivation is justified from the separation of energy scales in nonrelativistic effective field theories of QCD. Physical implications of the open quantum system approach are also discussed. Finally, I list some open questions for future studies.

In this paper, we study the relativistic scalar particle described by the Klein–Gordon equation that interacts with the uniform magnetic field in the context of the Som–Raychaudhuri space–time. Based on the property of the biconfluent Heun function equation, the corresponding Klein–Gordon oscillator and generalized Klein–Gordon oscillator under considering the Coulomb potential are separately investigated, and the analogue of the Aharonov–Bohm effect is analyzed in this scenario. On this basis, we also give the influence of different parameters including parameter $\alpha$ and oscillator frequency $\omega$, and the potential parameter ${\xi }_2$ on the energy eigenvalues of the considered systems.

In this paper, a Kerr-type solution in the Regge calculus is considered. It is assumed that the discrete general relativity, the Regge calculus, is quantized within the path integral approach. The only consequence of this approach used here is the existence of a length scale at which edge lengths are loosely fixed, as considered in our earlier paper. In addition, we previously considered the Regge action on a simplicial manifold on which the vertices are coordinatized and the corresponding piecewise constant metric is introduced, and found that for the simplest periodic simplicial structure and in the leading order over metric variations between four-simplices, this reduces to a finite-difference form of the Hilbert–Einstein action. The problem of solving the corresponding discrete Einstein equations (classical) with a length scale (having a quantum nature) arises as the problem of determining the optimal background metric for the perturbative expansion generated by the functional integral. Using a one-complex-function ansatz for the metric, which reduces to the Kerr–Schild metric in the continuum, we find a discrete metric that approximates the continuum one at large distances and is nonsingular on the (earlier) singularity ring. The effective curvature $R_{\lambda \nu \nu \rho }$, including where $R_{\lambda \mu }\ne 0$ (gravity sources), is analyzed with a focus on the vicinity of the singularity ring.

It is proved that coordinate transformations of the Schwarzschild metric to new static and stationary metrics do not eliminate the mode of a particle “fall” to the event horizon of a black hole. This mode is unacceptable for the quantum mechanics of stationary states.

Multiplicity dependencies of midrapidity $p_t$ spectra of identified charged particles in inelastic $p+p$ collisions at ${(s)}^{1/2}=13$ TeV at the Large Hadron Collider (LHC), measured by ALICE Collaboration, have been analyzed. The combined minimum ${\chi }^2$ fits with thermodynamically consistent Tsallis function as well as Hagedorn function with the embedded transverse flow describe quite satisfactorily the $p_t$ spectra of particles in the studied 10 different classes of charged-particle multiplicity in inelastic $p+p$ collisions at ${(s)}^{1/2}=13$ TeV. The obtained effective temperatures $T$ of thermodynamically consistent Tsallis function demonstrate a consistent growth with an increase in multiplicity of charged particles in inelastic $p+p$ collisions at ${(s)}^{1/2}=13$ TeV, and the corresponding $T$ versus the average charged-particle (pseudorapidity) multiplicity density $(〈d{N}_{\mathrm{\text{ch}}}/d\eta 〉)$ dependence is described very well by the simple power function with exponent parameter $\approx$ (1/3) in the whole analyzed range $〈d{N}_{\mathrm{\text{ch}}}/d\eta 〉>4$. It is found that the transverse (radial) flow becomes significant at higher multiplicity events in $p+p$ collisions at ${(s)}^{1/2}=13$ TeV, reaching the maximum value $〈{\beta }_t〉=0.28\pm 0.02$ at the largest studied multiplicity density $〈d{N}_{\mathrm{\text{ch}}}/d\eta 〉=26.02\pm 0.35$. It is estimated from analysis of $T_0$ and $〈{\beta }_t〉$ versus $〈d{N}_{\mathrm{\text{ch}}}/d\eta 〉$ dependencies, obtained using Hagedorn function with the embedded transverse flow, that the probable onset of deconfinement phase transition in inelastic $p+p$ collisions at ${(s)}^{1/2}=13$ TeV occurs at $〈d{N}_{\mathrm{\text{ch}}}/d\eta 〉\approx 7.1\pm 0.2$.

In this paper, we calculate the vacuum fluctuation of the stress tensor of a higher-derivative theory around a thin cosmic string. To this end, we adopt the method to obtain the stress tensor from the effective action developed by Gibbons et al. By their method, the quantum stress tensor of higher-derivative scalar theories without self-interaction is expressed as a simple sum of quantum stress tensors of free massive scalar fields. Unlike the vacuum expectation value of the scalar field squared obtained in the similar model, there appears no reduction of the values near the conical singularity.

In this paper, we confine the trajectory of geometrical particles to the de Sitter three-dimensional space–time, we model geometrical particles as spacelike tachyons. Using the Legendrian duality theory of pseudo-spheres and contact manifolds theory we establish the dual relationships between spacelike moving trajectory of geometrical particles and future nullcone hypersurfaces.

The dynamics of dissipative gravitational collapse of a source is explored in Rastall gravity. The field equations are derived for the geometry and collapsing matter. The dynamical equations are formulated for the heat flux and diffusion approximation. The heat transportation equation is derived by using Müller–Israel–Stewart approach to investigate the effects of heat flux on the collapsing source. Moreover, an equation is found by combining the dynamical and heat transport equation, the consequences of this equation are discussed in detail. Furthermore, the Rastall parameter $\lambda$ effect is analyzed for the collapse of sphere.

Classical and quantum Tsallis distributions have been widely used in many branches of natural and social sciences. But, the quantum field theory of the Tsallis distributions is relatively a less explored arena. In this paper, we derive the expression for the thermal two-point functions in the Tsallis statistics with the help of the corresponding statistical mechanical formulations. We show that the quantum Tsallis distributions used in the literature appear in the thermal part of the propagator much in the same way the Boltzmann–Gibbs distributions appear in the conventional thermal field theory. As an application of our findings, we calculate the thermal mass in the ${\varphi }^4$ scalar field theory within the realm of the Tsallis statistics.

In this work, I investigate the finite temperature Casimir effect due to a massive and charged scalar field that breaks Lorentz invariance in a CPT-even, aether-like way. I study the cases of Dirichlet and mixed (Dirichlet–Neumann) boundary conditions on a pair of parallel plates. I will not examine the case of Neumann boundary conditions since it produces the same results as Dirichlet boundary conditions. The main tool used in this investigation is the $\zeta$-function technique that allows me to obtain the Helmholtz free energy and Casimir pressure in the presence of a uniform magnetic field perpendicular to the plates. Three cases of Lorentz asymmetry are studied: timelike, spacelike and perpendicular to the magnetic field, spacelike and parallel to the magnetic field. Asymptotic cases of small plate distance, high temperature, strong magnetic field, and large mass will be considered for each of the three types of Lorentz asymmetry and each of the two types of boundary conditions examined. In all these cases, simple and very accurate analytic expressions of the thermal corrections to the Casimir energy and pressure are obtained and I discover that these corrections strongly depend on the direction of the unit vector that produces the breaking of the Lorentz symmetry.