arXiv subjects

C. P. Constantinidis

Publications and source records attributed to C. P. Constantinidis.

30 records · Page 2Linked to original sources

arXiv1999

Electrically Charged Cold Black Holes in Scalar-Tensor Theories

We study the possible existence of charged and neutral black holes in the Bergmann-Wagoner class of scalar-tensor theories (STT) of gravity in four dimensions. The existence of black holes is shown for anomalous versions of these theories, with a negative kinetic term in the Lagrangian. The Hawking temperature of these holes is zero, while the horizon area is (in most cases) infinite. As a special case, the Brans-Dicke theory is studied in more detail, and two kinds of infinite-area black holes are revealed, with finite and infinite proper time needed for an infalling particle to reach the horizon; among them, analyticity properties select a discrete subfamily of solutions, parametrized by two integers, which admit an extension beyond the horizon. The causal structure and stability of these solutions with respect to small radial perturbations is discussed. As a by-product, the stability properties of all spherically symmetric electrovacuum STT solutions are outlined.

gr-qc↗

arXiv1998

Two-dimensional N=1,2 Supersymmetric Chiral and Dual Models

Two-dimensional N=1,2 supersymmetric chiral models and their dual extensions are introduced and canonically quantized. Working within a superspace formalism, the non-manifest invariance under 2D-superPoincare' transformations is proven. The N=1,2 superVirasoro algebras are recovered as current algebras. The non-anomalous quantum invariances under 1D-superdiffeomorphisms (for chiral models) and N=1,2 superconformal transformations (for dual models) are shown to be a consequence of an N=1,2 super-Coulomb gas representation.

hep-th↗

arXiv1998

Cold Scalar-Tensor Black Holes: Causal Structure, Geodesics, Stability

We study the structure and stability of spherically symmetric Brans-Dicke black-hole type solutions with an infinite horizon area and zero Hawking temperature, existing for negative values of the coupling constant $ω$. These solutions split into two classes, depending on finite (B1) or infinite (B2) proper time needed for an infalling particle to reach the horizon. Class B1 metrics can be extended through the horizon only for discrete values of mass and scalar charge, depending on two integers m and n. For even m-n, the space-time is globally regular; for odd m, the metric changes its signature on the horizon but remains Lorentzian. Geodesics are smoothly continued across the horizon, but for odd m timelike geodesics become spacelike and vice versa. Causality problems, arising in some cases, are discussed. Tidal forces are shown to grow infinitely near type B1 horizons. All vacuum static, spherically symmetric solutions of the Brans-Dicke theory with $ω<-3/2$ are found to be linearly stable against spherical perturbations. This result extends to the generic case of the Bergmann-Wagoner class of scalar-tensor theories with the coupling function $ω(ϕ) < -3/2$.

gr-qc↗

arXiv1998

Symmetries and degrees of freedom in 2-dimensional dual models

The 2-dimensional version of the Schwarz and Sen duality model (Tseytlin model) is analyzed at the classical and quantum levels. The solutions are obtained after removing the gauge dependent sector using the Dirac method. The Poincarè invariance is verified at both levels. An extension with global supersymmetry is also proposed.

hep-th↗

arXiv1998

Structure and stability of cold scalar-tensor black holes

We study the structure and stability of the recently discussed spherically symmetric Brans-Dicke black-hole type solutions with an infinite horizon area and zero Hawking temperature, existing for negative values of the coupling constant $ω$. These solutions split into two classes: B1, whose horizon is reached by an infalling particle in a finite proper time, and B2, for which this proper time is infinite. Class B1 metrics are shown to be extendable beyond the horizon only for discrete values of mass and scalar charge, depending on two integers $m$ and $n$. In the case of even $m-n$ the space-time is globally regular; for odd $m$ the metric changes its signature at the horizon. All spherically symmetric solutions of the Brans-Dicke theory with $ω<-3/2$ are shown to be linearly stable against spherically symmetric \pns. This result extends to the generic case of the Bergmann-Wagoner class of scalar-tensor theories of gravity with the coupling function $ω(ϕ) < -3/2$.

gr-qc↗

arXiv1997

Cold black holes in scalar-tensor theories

We study the possible existence of black holes in scalar-tensor theories of gravity in four dimensions. Their existence is verified for anomalous versions of these theories, with a negative kinetic term in the Lagrangian. The Hawking temperature T_H of these holes is zero, while the horizon area is (in most cases) infinite. It is shown that an infinite value of T_H can occur only at a curvature singularity rather than a horizon. As a special case, the Brans-Dicke theory is studied in more detail, and two kinds of infinite-area black holes are revealed, with finite and infinite proper time needed for an infalling particle to reach the horizon.

gr-qc↗

arXiv1996

Toda lattice field theories, discrete W algebras, Toda lattice hierarchies and quantum groups

In analogy with the Liouville case we study the $sl_3$ Toda theory on the lattice and define the relevant quadratic algebra and out of it we recover the discrete $W_3$ algebra. We define an integrable system with respect to the latter and establish the relation with the Toda lattice hierarchy. We compute the the relevant continuum limits. Finally we find the quantum version of the quadratic algebra.

hep-th↗

arXiv1996

Toda lattice realization of integrable hierarchies

We present a new realization of scalar integrable hierarchies in terms of the Toda lattice hierarchy. In other words, we show on a large number of examples that an integrable hierarchy, defined by a pseudodifferential Lax operator, can be embedded in the Toda lattice hierarchy. Such a realization in terms the Toda lattice hierarchy seems to be as general as the Drinfeld--Sokolov realization.

hep-th↗

arXiv1995

Exact Correlators of Two-Matrix Models

We compute exact solutions of two--matrix models, i.e. detailed genus by genus expressions for the correlation functions of these theories, calculated without any approximation. We distinguish between two types of models, the unconstrained and the constrained ones. Unconstrained two--matrix models represent perturbations of $c=1$ string theory, while the constrained ones correspond to topological field theories coupled to topological gravity. Among the latter we treat in particular detail the ones based on the KdV and on the Boussinesq hierarchies.

hep-th↗

arXiv1993

Construction of Affine and Conformal Affine Toda Solitons by Hirota's Method

In this talk we report some results about the construction of soliton solutions for the Affine and Conformal Affine Toda models using the Hirota's method. We obtain new classes of solitons connected to the degeneracies of the Cartan matrix eigenvalues as well as to some particular features of the recursive scheme developed here. We obtain an universal mass formula for all those solitons. The examples of $SU(6)$ and $Sp(3)$ are discussed in some detail. ( Talk presented at the VII J.A. Swieca Summer School, Section: Particles and Fields, Campos do Jordão - Brasil - January/93)

hep-th↗

arXiv1992

Hirota's Solitons in the Affine and the Conformal Affine Toda Models

We use Hirota's method formulated as a recursive scheme to construct complete set of soliton solutions for the affine Toda field theory based on an arbitrary Lie algebra. Our solutions include a new class of solitons connected with two different type of degeneracies encountered in the Hirota's perturbation approach. We also derive an universal mass formula for all Hirota's solutions to the Affine Toda model valid for all underlying Lie groups. Embedding of the Affine Toda model in the Conformal Affine Toda model plays a crucial role in this analysis.

hep-th↗

arXiv1992

Connection between the Affine and Conformal Affine Toda Models and their Hirota's Solution

It is shown that the Affine Toda models (AT) constitute a ``gauge fixed'' version of the Conformal Affine Toda model (CAT). This result enables one to map every solution of the AT models into an infinite number of solutions of the corresponding CAT models, each one associated to a point of the orbit of the conformal group. The Hirota's $τ$-function are introduced and soliton solutions for the AT and CAT models associated to $\hat {SL}(r+1)$ and $\hat {SP}(r)$ are constructed.

hep-th↗