Nonrelativistic treatment of fully-heavy tetraquarks as diquark-antidiquark states

The goal of the present work is to obtain a reliable estimate of the masses of the ground and radially excited states of fully-heavy tetraquark systems. In order to do this, we use a nonrelativistic model of tetraquarks which are assumed to be compact and consist of diquark-antidiquark pairs. This nonrelativistic model is composed of Hulthen potential, a linear confining potential and spin-spin interaction. We computed ground, first, and second radially excited $$cc{\bar{c}}{\bar{c}}$$ c c c ¯ c ¯ and $$bb{\bar{b}}{\bar{b}}$$ b b b ¯ b ¯ tetraquark masses. It was found that predicted masses of ground states of $$cc{\bar{c}}{\bar{c}}$$ c c c ¯ c ¯ and $$bb{\bar{b}}{\bar{b}}$$ b b b ¯ b ¯ tetraquarks are significantly higher than the thresholds of the fall-apart decays to the lowest allowed two-meson states. These states should be broad and are thus difficult to observe experimentally. First radially excited states are considerably lower than their corresponding (2S-2S) two-meson thresholds. We hope that our study may be helpful to the experimental search for ground and excited $$cc{\bar{c}}{\bar{c}}$$ c c c ¯ c ¯ and $$bb{\bar{b}}{\bar{b}}$$ b b b ¯ b ¯ tetraquark states.

POLARIZATION OBSERVABLES OF THE γd→πNN REACTION IN THE Δ(1232)-RESONANCE REGION

Polarization observables of the three charge states of the pion for the γd→π NN reaction with polarized photon beam and/or oriented deuteron target are evaluated over the whole Δ(1232)-resonance region adopting a nonrelativistic model based on time-ordered perturbation theory. Results for the π-meson spectra, linear photon asymmetry, vector and tensor target asymmetries are presented. Particular attention is given, for the first time, to double polarization asymmetries for which we present results for [Formula: see text] and [Formula: see text]. We find that all other double polarization asymmetries of photon and deuteron targets vanish.

TWO PHOTON DECAYS OF SCALAR MESONS IN A COVARIANT QUARK MODEL

Two photon decay widths of the JP = O+ scalar mesons a0(980), f0(980), f0(1370) and χc0 are calculated in a covariant model which is characterized by the quark–antiquark structure. Previously such models were used to calculate current form factors. Here a different application is tried. A simple version of the model uses adjusted nonrelativistic model parameters with small quark masses. The results seem to prefer nonideal mixing of f0(980) and f0(1370). The calculated decay rate of χc0 agrees with the experimental results.

DEVIATIONS FROM SPONTANEOUS LYMAN-α EXPONENTIAL DECAY REVISITED: A RIGOROUS TREATMENT WITHIN A TWO-LEVEL NONRELATIVISTIC MODEL

A recent paper by Facchi and Pascazio, in which the advantage of numerical evaluations of deviations from exponential decay was pointed out, makes a revisitation of the subject necessary. All the more, since the above-mentioned authors have not estimated the error bounds (being absolutely necessary in any calculation) for their results. On the contrary, the accuracy of all results presented in this paper is proved by error estimates. Moreover, for the first time, the power of the simple iteration method in calculating both the exponential and non-exponential time evolution of an unstable atomic state is demonstrated.

SYSTEMATIC THEORETICAL SEARCH FOR DIBARYONS IN A RELATIVISTIC MODEL

A relativistic quark potential model is used to do a systematic search for quasi-stable dibaryon states in the u, d and s three-flavor world. Flavor symmetry breaking and channel coupling effects are included and an adiabatic method and fractional parentage expansion technique are used in the calculations. The relativistic model predicts dibaryon candidates completely consistent with the nonrelativistic model.

TIME MACHINES AND THE PRINCIPLE OF SELF-CONSISTENCY AS A CONSEQUENCE OF THE PRINCIPLE OF STATIONARY ACTION (II): THE CAUCHY PROBLEM FOR A SELF-INTERACTING RELATIVISTIC PARTICLE

We consider the action principle to derive the classical, relativistic motion of a selfinteracting particle in a 4D Lorentzian spacetime containing a wormhole and which allows the existence of closed time-like curves. In particular, we study the case of a pointlike particle subject to a “hard-sphere” self-interaction potential and which can traverse the wormhole an arbitrary number of times, and show that the only possible trajectories for which the classical action is stationary are those which are globally self-consistent. Generically, the multiplicity of these trajectories (defined as the number of self-consistent solutions to the equations of motion beginning with given Cauchy data) is finite, and it becomes infinite if certain constraints on the same initial data are satisfied. This confirms the previous conclusions (for a nonrelativistic model) by Echeverria, Klinkhammer and Thorne that the Cauchy initial value problem in the presence of a wormhole “time machine” is classically “ill-posed” (far too many solutions). Our results further extend the recent claim by Novikov et al. that the “principle of self-consistency” is a natural consequence of the “principle of minimal action.”