Modern Physics Letters A

We discuss possible D-brane configurations on SU(2) group manifolds in the sigma model approach. When we turn the boundary conditions of the space–time fields into the boundary gluing conditions of chiral currents, we find that for all D-branes except the spherical D2-branes, the gluing matrices R^a_b depend on the fields, so the chiral Kac–Moody symmetry is broken, but conformal symmetry is maintained. Matching the spherical D2-branes derived from the sigma model with those from the boundary state approach we obtain a U(1) field strength that is consistent with flux quantization.

A new local, covariant and nilpotent symmetry is shown to exist for the interacting BRST invariant U(1) gauge theory in two dimensions of space–time. Under this new symmetry, it is the gauge-fixing term that remains invariant and the corresponding transformations on the Dirac fields turn out to be the analogue of chiral transformations. The extended BRST algebra is derived for the generators of all the underlying symmetries, present in the theory. This algebra turns out to be the analogue of the algebra obeyed by the de Rham cohomology operators of differential geometry. Possible interpretations and implications of this symmetry are pointed out in the context of BRST cohomology and Hodge decomposition theorem.

We study the radiative leptonic D meson decays of , and D⁰→ l⁺l^-γ (l=e, μ) within the light front quark model. In the standard model, we find that the decay branching ratios of , and are 6.9×10^-6 (7.7×10^-5), 2.5×10^-5 (2.6×10^-4), and 6.0×10^-6 (3.2×10^-4), and that of D⁰→l⁺l^-γ (l=e, μ) and are 6.3×10^-11 and 2.7×10^-16, respectively.

It is shown that the 2×2 matrix Hamiltonian describing the dynamics of a charged spin-1/2 particle with g-factor 2 moving in an arbitrary, spatially dependent, magnetic field in two spatial dimensions can be written as the anticommutator of a nilpotent operator and its Hermitian conjugate. Consequently, the Hamiltonians for the two different spin projections form partners of a supersymmetric quantum mechanical system. The resulting supersymmetry algebra can then be exploited to explicitly construct the exact zero energy ground state wave function for the system. Modulo this ground state, the remainder of the eigenstates and eigenvalues of the two partner Hamiltonians form positive energy degenerate pairs. We also construct the spatially asymptotic form of the magnetic field which produces a finite magnetic flux and associated zero energy normalizable ground state wave function.

We discuss Weyl (conformal) transformations in two-dimensional matterless dilaton gravity. We argue that both classical and quantum dilaton gravity theories are invariant under Weyl transformations.

In recent work on experimental tests of quantum-gravity-motivated phenomenological models, a significant role has been played by the so-called "κ" deformations of Poincaré symmetries. Sensitivity to values of the relevant deformation length λ as small as 5×10^-33m has been achieved in recent analyses comparing the structure of κ-Poincaré symmetries with data on the gamma rays we detect from distant astrophysical sources. We investigate violations of CPT symmetry which may be associated with κ-Poincaré in the physics of the neutral-kaon system. A simple estimate indicates that experiments on the neutral kaons may actually be more λ-sensitive than the corresponding astrophysical experiments, and may already allow to probe values of λ of order the Planck length.

It is shown that the geometric constraint advocated in [R. S. Kaushal, Mod. Phys. Lett.A15, 1391 (2000)] is trivially satisfied. Therefore, such a constraint does not exist. We also point out another flaw in Kaushal's paper.