A Two-Form Formulation of the Vector-Tensor Multiplet in Central Charge Superspace

A two-form formulation for the N=2 vector-tensor multiplet is constructed using superfield methods in central charge superspace. The N=2 non-Abelian standard supergauge multiplet in central charge superspace is also discussed, as is with the associated Chern-Simons form. We give the constraints, solve the Bianchi identities and present the action for a theory of the vector-tensor multiplet coupled to the non-Abelian supergauge multiplet via the Chern-Simons form.Comment: 16 pages, LaTeX2e with AMS-LaTe

Quantum N = 2 Supersymmetric Black Holes in the S-T Model

We consider axion-free quantum corrected black hole solutions in the context of the heterotic S-T model with half the N=2, D=4 supersymmetries unbroken. We express the perturbatively corrected entropy in terms of the electric and magnetic charges in such a way, that target-space duality invariance is manifest. We also discuss the microscopic origin of particular quantum black hole configurations. We propose a microscopic interpretation in terms of a gas of closed membranes for the instanton corrections to the entropy

Classical and Quantum Analysis of Repulsive Singularities in Four Dimensional Extended Supergravity

Non--minimal repulsive singularities (``repulsons'') in extended supergravity theories are investigated. The short distance antigravity properties of the repulsons are tested at the classical and the quantum level by a scalar test--particle. Using a partial wave expansion it is shown that the particle gets totally reflected at the origin. A high frequency incoming particle undergoes a phase shift of $\frac{\pi}{2}$. However, the phase shift for a low--frequency particle depends upon the physical data of the repulson. The curvature singularity at a finite distance $r_h$ turns out to be transparent for the scalar test--particle and the coordinate singularity at the origin serves as a repulsive barrier at which particles bounce off.Comment: 20 pages, 14 figure

Induced mass in N=2 super Yang-Mills theories

The masses of the matter fields of N=2 Super-Yang-Mills theories can be defined as parameters of deformed supersymmetry transformations. The formulation used involves central charges for the matter fields. The explicit form of the deformed supersymmetry transformations and of the invariant Lagrangian in presence of the gauge supermultiplet are constructed. This works generalizes a former one, due to the same authors, which presented the free matter case.Comment: 15 pages, Late

Heuristic Models of Two-Fermion Relativistic Systems with Field-Type Interaction

We use the chain of simple heuristic expedients to obtain perturbative and exactly solvable relativistic spectra for a family of two-fermionic bound systems with Coulomb-like interaction. In the case of electromagnetic interaction the spectrum coincides up to the second order in a coupling constant with that following from the quantum electrodynamics. Discrepancy occurs only for S-states which is the well-known difficulty in the bound-state problem. The confinement interaction is considered too. PACS number(s): 03.65.Pm, 03.65.Ge, 12.39.PnComment: 16 pages, LaTeX 2.0

N=2 central charge superspace and a minimal supergravity multiplet

We extend the notion of central charge superspace to the case of local supersymmetry. Gauged central charge transformations are identified as diffeomorphisms at the same footing as space-time diffeomorphisms and local supersymmetry transformations. Given the general structure we then proceed to the description of a particular vector-tensor supergravity multiplet of 24+24 components, identified by means of rather radical constraints

Reissner-Nordstrom Expansion

We propose a classical mechanism for the cosmic expansion during the radiation-dominated era. This mechanism assumes that the Universe is a two-component gas. The first component is a gas of ultra-relativistic "normal" particles described by an equation of state of an ideal quantum gas of massless particles. The second component consist of "unusual" charged particles (namely, either with ultra-high charge or with ultra-high mass) that provide the important mechanism of expansion due to their interaction with the "normal" component of the gas. This interaction is described by the Reissner--Nordstr\"om metric purely geometrically -- the ``unusual'' particles are modeled as zero-dimensional naked singularities inside spheres of gravitational repulsion. The radius of a repulsive sphere is inversely proportional to the energy of an incoming particle or the temperature. The expansion mechanism is based on the inflating of the "unusual" particles (of charge $Q$) with the drop of the temperature -- this drives apart all neutral particles and particles of specific charge $q/m$ such that ${sign}(Q) q/m \ge - 1$. The Reissner--Nordstr\"om expansion naturally ends at recombination. We discuss the range of model parameters within which the proposed expansion mechanism is consistent with the restrictions regarding quantum effects.Comment: 9 pages, LaTe

Black Holes and Flop Transitions in M-Theory on Calabi-Yau Threefolds

We present fivedimensional extreme black hole solutions of M-theory compactified on Calabi-Yau threefolds and study these solutions in the context of flop transitions in the extended Kahler cone. In particular we consider a specific model and present black hole solutions, breaking half of N=2 supersymmetry, in two regions of the extended Kahler cone, which are connected by a flop transition. The conditions necessary to match both solutions at the flop transition are analysed. Finally we also discuss the conditions to obtain massless black holes at the flop transition.Comment: 19 pp, LaTe

AdS and stabilized extra dimensions in multidimensional gravitational models with nonlinear scalar curvature terms 1/R and R^4

We study multidimensional gravitational models with scalar curvature nonlinearities of the type 1/R and R^4. It is assumed that the corresponding higher dimensional spacetime manifolds undergo a spontaneous compactification to manifolds with warped product structure. Special attention is paid to the stability of the extra-dimensional factor spaces. It is shown that for certain parameter regions the systems allow for a freezing stabilization of these spaces. In particular, we find for the 1/R model that configurations with stabilized extra dimensions do not provide a late-time acceleration (they are AdS), whereas the solution branch which allows for accelerated expansion (the dS branch) is incompatible with stabilized factor spaces. In the case of the R^4 model, we obtain that the stability region in parameter space depends on the total dimension D=dim(M) of the higher dimensional spacetime M. For D>8 the stability region consists of a single (absolutely stable) sector which is shielded from a conformal singularity (and an antigravity sector beyond it) by a potential barrier of infinite height and width. This sector is smoothly connected with the stability region of a curvature-linear model. For D<8 an additional (metastable) sector exists which is separated from the conformal singularity by a potential barrier of finite height and width so that systems in this sector are prone to collapse into the conformal singularity. This second sector is not smoothly connected with the first (absolutely stable) one. Several limiting cases and the possibility for inflation are discussed for the R^4 model.Comment: 28 pages, minor cosmetic improvements, Refs. added; to appear in Class. Quantum Gra

Black holes and black strings of N=2, d=5 supergravity in the H-FGK formalism

We study general classes and properties of extremal and non-extremal static black-hole solutions of N=2, d=5 supergravity coupled to vector multiplets using the recently proposed H-FGK formalism, which we also extend to static black strings. We explain how to determine the integration constants and physical parameters of the black-hole and black-string solutions. We derive some model-independent statements, including the transformation of non-extremal flow equations to the form of those for the extremal flow. We apply our methods to the construction of example solutions (among others a new extremal string solution of heterotic string theory on K_3 \times S^1). In the cases where we have calculated it explicitly, the product of areas of the inner and outer horizon of a non-extremal solution coincides with the square of the moduli-independent area of the horizon of the extremal solution with the same charges.Comment: 33 pages. Revised version: references added. No other change