Modern Physics Letters A

Stationary black holes in five-dimensional Einstein–Maxwell–Chern–Simons theory possess surprising properties. When considering the Chern–Simons coefficient λ as a parameter, two critical values of λ appear: the supergravity value λ_SG = 1, and the value λ = 2. At λ = 1, supersymmetric black holes with vanishing horizon angular velocity, but finite angular momentum exist. As λ increases beyond λ_SG a rotational instability arises, and counterrotating black holes appear, whose horizon rotates in the opposite sense to the angular momentum. Thus supersymmetry is associated with the borderline between stability and instability. At λ = 2, rotating black holes with vanishing angular momentum emerge. Beyond λ = 2, black holes may possess a negative horizon mass, while their total mass is positive. Charged rotating black holes with vanishing gyromagnetic ratio appear, and black holes are no longer uniquely characterized by their global charges.

We find a closed form for Seiberg–Witten (SW) map between ordinary and noncommutative (NC) Dirac–Born–Infeld actions. We show that NC Maxwell action after the exact SW map can be regarded as ordinary Maxwell action coupling to a metric deformed by gauge fields. We also show that reversed procedure by inverse SW map lead to a similar interpretation in terms of induced NC geometry. This implies that noncommutativity in field theory can be interpreted as field-dependent fluctuations of spacetime geometry, which genuinely realizes an interesting idea recently observed by Rivelles.

We develop a color bosonization approach to treat QCD gauge field ("gluons") at low energies in order to derive an effective color action of QCD taking into account the quark chiral anomaly in the case of SU(2) color. We have found that there exists such a region in the chiral sector of color space, where a gauge field coincides with chirally rotated vector field, while an induced axial vector field disappears. In this region, the unit color vector of chiral field plays a defining role, and a gauge field is parametrized in terms of chiral parameters, so that no additional degrees of freedom are introduced by the chiral field. A QCD gauge field decomposition in color bosonization is a sum of a chirally rotated gauge field and an induced axial-vector field expressed in terms of gluonic variables. An induced axial-vector field defines the chiral color anomaly and an effective color action of QCD. This action admits existence of a gauge invariant d = 2 condensate of induced axial-vector field and mass.

In the present work, an attempt has been made to explain the recent cosmic acceleration of the universe with two mutually interacting scalar fields, one being the Brans–Dicke scalar field and the other a quintessence scalar field. Conditions have been derived for which the quintessence scalar field has an early oscillation and it grows during a later time to govern the dynamics of the universe.

The quasinormal modes (QNMs) associated with the decay of massless arbitrary spin fields around a Schwarzschild black hole are investigated by using the continued fraction method in a united form and their universal properties are found. It is shown that these QNMs become evenly spaced for large angular quantum number l (for the boson perturbations) and j (for the fermion perturbations) and the spacing is given by which is independent of the spin number s and overtone number n, and in the complex plane they have an interesting trend which depends on n before they become the same value with the increasing l (or j). The distribution of the QNMs with arbitrary spin fields for large values l (or j) and small n can be expressed as . It is also shown that the angular quantum number has the surprising effect of increasing real part of the QNMs, but it almost does not affect the imaginary part, especially for the lowest lying mode. In addition, the spacing for imaginary part of the QNMs at high overtones is equidistant and equals to -i/4M, which is independent of l (or j) and s.

A class of proper and novel generalizations of the (anti) de Sitter solutions (parametrized by a family of radial functions R(r)) are presented that could provide a very plausible resolution of the cosmological constant problem along with a natural explanation of the ultraviolet/infrared (uv/ir) entanglement required to solve this problem. A nonvanishing value of the vacuum energy density of the order of is derived in agreement with the experimental observations. The presence of the radial function R(r) is instrumental to understand why the cosmological constant is not zero and why it is so tiny. The correct lower estimate of the mass of the observable universe related to the Dirac–Eddington's large number N = 10⁸⁰ is also obtained. Finally we present our most recent findings of how Weyl Geometry via a Brans–Dicke scalar field solves the riddle of dark energy in addition to providing another derivation of the vacuum energy density.