Modern Physics Letters A

The KLOE experiment at DAΦNE has collected data for an integrated luminosity of ~ 1.3 fb^-1 from e⁺e^- collisions at center-of-mass energy around the ϕ-meson peak, W ~1.02 GeV. A selection of results obtained from a sample of 450 pb^-1 of data acquired during year 2001 and 2002 is presented. Studying tagged K_S and K_L-mesons produced in the reaction e⁺e^-→ϕ→K_S K_L we measured the branching ratio of the decay K_S→πeν, the upper limit on the decay K_S→π⁰π⁰π⁰, and the main K_L decay branching ratios. Exploiting the initial state radiation in the reaction e⁺e^-→π⁺π^-γ, we extracted the hadronic cross-section as a function of the squared center-of-mass energy s_π of the π π system, in the range 0.35 < s_π < 0.95 GeV².

Quarks come in three colors and have electric charges in multiples of one-third. There are also three families of quarks and leptons. Though the first two properties can be understood in terms of unification symmetries such as SU(5), SO(10), or E₆, why should there only be three families remains a mystery. We propose how all three properties involving the number three are connected in a fivefold application of the gauge symmetry SU(3).

The peculiarities of doing a canonical analysis of the first-order formulation of the Einstein–Hilbert action in terms of either the metric tensor g^αβ or the metric density along with the affine connection are discussed. It is shown that the difference between using g^αβ as opposed to h^αβ appears only in two spacetime dimensions. Despite there being a different number of constraints in these two approaches, both formulations result in there being a local Poisson brackets algebra of constraints with field independent structure constants, closed off-shell generators of gauge transformations and off-shell invariance of the action. The formulation in terms of the metric tensor is analyzed in detail and compared with earlier results obtained using the metric density. The gauge transformations, obtained from the full set of first-class constraints, are different from a diffeomorphism transformation in both cases.

In Spacetime–Matter theory we assume that the 4D induced matter of the 5D Ricci-flat bouncing cosmological solutions contains a perfect fluid as well as an induced scalar field. Then we show that the conventional 4D quintessence and phantom models of dark energy could be recovered from the 5D cosmological solutions. By using the phase-plane analysis to study the stability of evolution of the 5D models, we find that the conventional 4D late-time attractor solution is also recovered. This attractor solution shows that the scale factors of the phantom dominated universes in both the 4D and 5D theories will reach infinity in a finite time and the universes will be ended at a new kind of spacetime singularity at which everything will be annihilated. We also find that the repulsive force of the phantom may provide us with a mechanics to explain the bounce.

Recently developed time-independent bound-state perturbation theory is extended to treat the scattering domain. The changes in the partial wave phase shifts are derived explicitly and the results are compared with those of other methods.

In this work we investigate the quantum dynamics of an electric dipole in a (2+1)-dimensional conical spacetime. For specific conditions, the Schrödinger equation is solved and bound states are found with the energy spectrum and eigenfunctions determined. We find that the bound states spectrum extends from minus infinity to zero with a point of accumulation at zero. This unphysical result is fixed when a finite radius for the defect is introduced.

In this paper, we investigate the influence of gravity and noncommutativity on Dirac particles. By adopting the tetrad formalism, we show that the modified Dirac equation keeps the same form. The only modification is in the expression of the covariant derivative. The new form of this derivative is the product of its counterpart given in curved spacetime with an operator which depends on the noncommutative θ-parameter. As an application, we have computed the density number of the created particles in the presence of constant strong electric field in an anisotropic Bianchi universe.