Modern Physics Letters A

Scalar mesons are a key expression of the infrared regime of QCD. The lightest of these is the σ. Now that its pole in the complex energy plane has been precisely located, we can ask whether this state is transiently or or a multi-meson molecule or largely glue? The two-photon decay of the σ can, in principle, discriminate between these possibilities. We review here how the γγ → π⁺π^-, π⁰π⁰ cross-sections can be accurately computed. The result not only agrees with experiment, but definitively fixes the radiative coupling of the σ. This equates to a two-photon width of (4.1 ± 0.3) keV, which accords with the simple nonrelativistic quark model expectation for a , scalar. Nevertheless, robust predictions from relativistic strong coupling QCD are required for each of the possible compositions before we can be sure which one really delivers the determined γγ coupling.

In this paper we obtain the exact mass-eigenstates of the Majorana physical neutrinos. We start by taking into account a general 3 × 3 mass matrix (ignoring any CP-phase violation). It is then diagonalized by exactly solving an appropriate set of equations. The solution provides straightforwardly the mass eigenvalues depending on the diagonal entries and mixing angles. Finally, the consequences of these analytical expressions are discussed assuming certain restrictions such as the global lepton number L = L_e - L_μ - L_τ (rigorously conserved or softly broken) and the μ - τ interchange symmetry. The minimal absolute mass in the neutrino sector is also obtained since the two plausible scenarios invoked above are employed.

Three-body systems are studied in the framework of the Boundary Condition Model, in which the relevant interactions are expressed in terms of the scattering lengths of the two-body subsystems. We demonstrate explicitly the role of resonant states in the two-body subsystems and of multiple scattering between the constituents in producing a weakly bound three-body system, i.e. a Borromean nucleus. We obtain qualitative relations between the spatial extension of the three-body bound state, its energy, and the scattering lengths in the subsystems. The results are compared with experimental data for the Borromean nucleus ¹¹Li and ¹⁴Be.

We study the supersymmetric quantum mechanics of an isospin particle in the background of spherically symmetric Yang–Mills gauge field. We show that on S² the number of supersymmetries can be made arbitrarily large for a specific choice of the spherically symmetric SU(2) gauge field. However, the symmetry algebra containing the supercharges becomes nonlinear if the number of fermions is greater than two. We present the exact energy spectra and eigenfunctions, which can be written as the product of monopole harmonics and a certain isospin state. We also find that the supersymmetry is spontaneously broken if the number of supersymmetries is even.

In this paper, the effect of a positive cosmological constant on spherically symmetric collapse with perfect fluid has been investigated. The matching conditions between static exterior and non-static interior spacetimes are given in the presence of a cosmological constant. We also study the apparent horizons and their physical significance. It is concluded that the cosmological constant slows down the collapse of matter and hence limit the size of the black hole. This analysis gives the generalization of the dust case to the perfect fluid. We recover the results of the dust case for p = 0.

In this work we obtain topological and equivalent theories on brane-worlds in several dimensions. Our brane is a solitonic-like hypersurface embedded in a spacetime with a specific dimensionality and it appears due to the breaking of a Peccei–Quinn-like symmetry. In the first part of this work, the obtained topological theories are related to a generalization of the axion–photon anomalous interaction in D = 4 (in the Abelian case) and to the Wess–Zumino term (in the non-Abelian case). In the second part, we construct equivalent models on the brane through a mechanism of explicit Lorentz symmetry breaking. The gauge symmetries of such models are discussed within the Stuckelberg formalism.

We estimate the charged lepton electric dipole moments and the branching ratios of radiative lepton flavor violating decays in the framework of the two Higgs doublet model with the inclusion of two extra dimensions. Here, we consider that the new Higgs doublet is accessible to one of the extra dimensions with a Gaussian profile and the fermions are accessible to the other extra dimension with uniform zero-mode profile. We observe that the numerical values of the physical quantities studied enhance with the additional effects due to the extra dimensions and they are sensitive to the new Higgs localization.