Modern Physics Letters A

In this paper we review the properties of supertubes in type IIA superstring theory. The supertube is a tubular D2-brane which carries D0-brane charge N₀, fundamental string charge N₁ and angular momentum J. Even if we fix two charges N₀, N₁ and angular momentum J, a generic supertube has degrees of freedom to deform its shape of the cross-section. We explicitly count this degeneracy and evaluate the entropy of supertubes from the field theoretical viewpoint.

The Dirac equation is formulated in the background of three types of physically relevant potentials: scalar, vector and "Dirac-oscillator" potentials. Assuming these potentials to be spherically-symmetric and with generic polynomial forms in the radial variable, we construct the corresponding radial Dirac equation. Cases where this linear spectral equation is exactly solvable or quasi-exactly solvable are worked out in details. When available, relations between the radial Dirac operator and some super-algebra are pointed out.

The masses of the S-wave mesons consisting of the light (u, d, s) quarks are calculated within the constituent quark model. The relativistic Schrödinger-like equation with a confining potential is numerically solved for the complete relativistic potential including both spin-independent and spin-dependent terms. The obtained masses of the ground state π, ρ, K, K* and ϕ mesons and their first radial excitations are in a reasonably good overall agreement with experimental data.

The canonical structure of the Einstein–Hilbert Lagrange density is examined in two spacetime dimensions, using the metric density and symmetric affine connection as dynamical variables. The Hamiltonian reduces to a linear combination of three first-class constraints with a local SO(2, 1) algebra. The first-class constraints are used to find a generator of gauge transformations that has a closed off-shell algebra and which leaves the Lagrangian and det(h^μν) invariant. These transformations are distinct from diffeomorphism invariance, and are gauge transformations characterized by a symmetric matrix ζ_μν.

The Coulomb sum rule (CSR) and structure factor are calculated for inelastic electron scattering from nuclear matter at zero and finite temperature in the nonrelativistic limit. The effect of short-range correlation (SRC) is presented by using lowest order constrained variational (LOCV) method and the Argonne Av₁₈ and Δ-Reid soft-core potentials. The effects of different potentials as well as temperature are investigated. It is found that the nonrelativistic version of Bjorken scaling approximately sets in at the momentum transfer of about 1.1 to 1.2 GeV/c and the increase of temperature makes it to decrease. While different potentials do not significantly change CSR, the SRC improves the Coulomb sum rule and we get reasonably close results to both experimental data and others theoretical predictions.

In this paper, we show a dual gauge structure in the (2+1)D fermionic-σ model. For this model, there exists a confinement–deconfinement transition between ordered state and quantum disordered state. At the quantum critical point the effective Lagrangian is reduced to the massless, non-interacting Wess–Zumino model with an N = 1 supersymmetry.

Motivated by the recent interest in quantization of black hole area spectrum, we consider the area spectrum of Kerr and extremal Kerr black holes. Based on the proposal by Bekenstein and others that the black hole area spectrum is discrete and equally spaced, we implement Kunstatter's method to derive the area spectrum for the Kerr and extremal Kerr black holes. The real part of the quasinormal frequencies of Kerr black hole used for this computation is of the form mΩ where Ω is the angular velocity of the black hole horizon. The resulting spectrum is discrete but not as expected uniformly spaced. Thus, we infer that the function describing the real part of quasinormal frequencies of Kerr black hole is not the correct one. This conclusion is in agreement with the numerical results for the highly damped quasinormal modes of Kerr black hole recently presented by Berti, Cardoso and Yoshida. On the contrary, extremal Kerr black hole is shown to have a discrete area spectrum which in addition is evenly spaced. The area spacing derived in our analysis for the extremal Kerr black hole area spectrum is not proportional to ln 3. Therefore, it does not give support to Hod's statement that the area spectrum should be valid for a generic Kerr–Newman black hole.

We study the regularization ambiguities in an exact renormalized (1 +1)-dimensional field theory. We show a relation between the regularization ambiguities and the coupling parameters of the theory as well as their role in the implementation of a local gauge symmetry at quantum level.