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¹²C isotope composing 3$\alpha$ cluster was investigated in this study. Therefore, ¹²C can be considered as a 3-body system. For studying the interactions in 3$\alpha$ clusters, a central potential was applied. Jacobi relative coordinates were also employed and center of mass motion was removed. In this paper, the Klein–Gordon (K–G) equation was solved using Nikiforov–Uvarov potential. At the end, the energy spectrum and wave function of isotope ¹²C were determined and the results were compared with the experimental data which showed good coincidence reflecting the success of our model in prediction.

A relativistic plane wave formalism for quasifree eta meson photoproduction is presented. The sensitivity of the unpolarized differential cross section, the recoil nucleon polarization, and the photon asymmetry is investigated. The results indicate that the S₁₁ resonance dominates the unpolarized differential cross section, but that its contribution to the spin observables are very small, for which the D₁₃ resonance plays the primary role.

We make a critical comparison of relativistic and nonrelativistic classical and quantum mechanics of particles in inertial frames as well of the open problems in particle localization at both levels. The solution of the problems of the relativistic center-of-mass, of the clock synchronization convention needed to define relativistic 3-spaces and of the elimination of the relative times in the relativistic bound states leads to a description with a decoupled nonlocal (nonmeasurable) relativistic center-of-mass and with only relative variables for the particles (single particle subsystems do not exist). We analyze the implications for entanglement of this relativistic spatial nonseparability not existing in nonrelativistic entanglement. Then, we try to reconcile the two visions showing that also at the nonrelativistic level in real experiments only relative variables are measured with their directions determined by the effective mean classical trajectories of particle beams present in the experiment. The existing results about the nonrelativistic and relativistic localization of particles and atoms support the view that detectors only identify effective particles following this type of trajectories: these objects are the phenomenological emergent aspect of the notion of particle defined by means of the Fock spaces of quantum field theory.

Presented are the conclusions drawn from experimental investigations of the Landau–Pomeranchuk–Migdal (LPM) effect in amorphous and crystalline targets as well as the preceding and ensuing theoretical activities. In amorphous targets the phenomenon is by now well studied both experimentally and theoretically and is at a mature stage where extrapolations to other energies or materials are well founded. In crystalline targets, the effect is not as well studied as it is harder to deconvolute from other effects like e.g. multiple photon emission. Even in this case, though, a seemingly consistent picture of the suppression mechanism that alters the effective radiation length emerges. Due to the increased scattering, crystals might be used to explore hitherto untested regimes of the LPM effect.

The zeroth principle of thermodynamics in the form "temperature is uniform at equilibrium" is notoriously violated in relativistic gravity. Temperature uniformity is often derived from the maximization of the total number of microstates of two interacting systems under energy exchanges. Here we discuss a generalized version of this derivation, based on informational notions, which remains valid in the general context. The result is based on the observation that the time taken by any system to move to a distinguishable (nearly orthogonal) quantum state is a universal quantity that depends solely on the temperature. At equilibrium the net information flow between two systems must vanish, and this happens when two systems transit the same number of distinguishable states in the course of their interaction.

Possibility of occurrence of chaotic behavior in multiparticle production in relativistic nuclear collisions is examined. Erraticity spectrum and entropy index are determined and compared with those of FRITIOF-generated events. The results obtained in the present study reveal existence of erraticity in multiparticle production in relativistic nuclear collisions.

The variational method in a reformulated Hamiltonian formalism of quantum electrodynamics (QED) is used to derive relativistic wave equations for systems consisting of n fermions and antifermions of various masses. The derived interaction kernels of these equations include one-photon exchange interactions. The equations have the expected Schrödinger non-relativistic limit. Application to some exotic few lepton systems is discussed briefly.

Using the LAMP model for nuclear quark structure, we calculate the binding energy and quark structure of a B meson merging with a D meson. Our variational calculation shows that a molecular, deuteron-like state structure changes rather abruptly, as the separation between the two mesons decreases, and at a separation of about 0.14 fm, the hadronic system transforms into a four-quark bound state, although one maintaining an internal structure rather than that of a four-quark "bag." Unlike the deuteron, pion exchange does not provide any contribution to the ≈ 150 MeV binding.

An area metric is a -tensor with certain symmetries on a 4-manifold that represents a non-dissipative linear electromagnetic medium. A recent result by Schuller, Witte and Wohlfarth gives a pointwise algebraic classification for such area metrics. This result is similar to the Jordan normal form theorem for -tensors, and the result shows that pointwise area metrics divide into 23 metaclasses and each metaclass requires two coordinate representations. For the first 7 metaclasses, we show that only one coordinate representation is needed. For the remaining 16 metaclasses we find an additional third coordinate representation.

I discuss the progress in the numerical modeling of accretion flows made possible after solving the general relativistic radiation-hydrodynamics equations through the moment formalism and with Godunov-type methods. I first present the necessary numerical tools for coping with the stiffness of the source terms in the equations and for treating the intermediate regime between the optically thick and the optically thin. Then, I show some applications to spherical accretion and to supersonic Bondi-Hoyle accretion onto a black hole, discussing its astrophysical relevance.