Dilaton Scalar Field Research Articles

Liouville Type Dilatonic Potential in Locally Rotationally Symmetric Bianchi I Model

Exact solutions are obtained for a special case of locally rotationally symmetric Bianchi I models consisting of a dilaton scalar field and a Liouville type dilatonic potential interacting with an electromagnetic field coupled with gravity, and the corresponding properties of the space-time are discussed.

P-Brane black holes as stability islands

In multidimensional gravity with an arbitrary number of internal Ricci-flat factor spaces, interacting with electric and magnetic p-branes, spherically symmetric configurations are considered. It is shown that all single-brane black hole solutions are stable under spherically symmetric perturbations, whereas similar solutions possessing naked singularities turn out to be catastrophically unstable. The black hole stability conclusion is extended to some classes of configurations with intersecting branes. These results do not depend on the particular composition of the D-dimensional space–time, on the number of dilatonic scalar fields ϕa and on the values of their coupling constants λsa. Some examples from 11-dimensional supergravity are considered.

D-dimensionalp-brane cosmological models associated with a Lie algebra of the typeA m

We study a D-dimensional cosmological model on the manifold M=R×M0×R×Mn describing an evolution of n+1 Einstein factor spaces Mi in a theory with several dilatonic scalar fields and differential forms admitting an interpretation in terms of intersecting p-branes. The equations of motion of the model are reduced to the Euler-Lagrange equations for the so-called pseudo-Euclidean Toda-like system. Assuming that the characteristic vectors related to the configuration of p-branes and their couplings to the dilatonic scalar fields can be interpreted as the root vectors of a Lie algebra of the type Am≡sl(m+1C), we reduce the model to an open Toda chain, which is integrable by the customary methods. The resulting metric has the form of the Kasner solution. We single out the particular model describing the Friedmanlike evolution of the three-dimensional external factor space M0 (in the Einsteinian conformal gauge) and the contraction of the internal factor spaces M1,...,Mn.

Consistent equations for massive spin-2 field coupled to gravity in string theory

We investigate the problem of derivation of consistent equations of motion for the massive spin 2 field interacting with gravity within both field theory and string theory. In field theory we derive the most general classical action with non-minimal couplings in arbitrary spacetime dimension, find the most general gravitational background on which this action describes a consistent theory and generalize the analysis for the coupling with background scalar dilaton field. We show also that massive spin 2 field allows in principle consistent description in arbitrary background if one builds its action in the form of an infinite series in the inverse mass square. Using sigma-model description of string theory in background fields we obtain in the lowest order in α′ the explicit form of effective equations of motion for the massive spin 2 field interacting with gravity from the requirement of quantum Weyl invariance and demonstrate that they coincide with the general form of consistent equations derived in field theory.

SCALE FACTOR DUALITY IN STRING BIANCHI COSMOLOGIES

We apply the scale factor duality transformations introduced in the context of the effective string theory to the anisotropic Bianchi-type models. We find dual models for all the Bianchi-types [except for types VIII and IX] and construct for each of them its explicit form starting from the exact original solution of the field equations. It is emphasized that the dual Bianchi class B models require the loss of the initial homogeneity symmetry of the dilatonic scalar field.

Sigma-model for generalized composite p-branes

A multidimensional gravitational model containing several dilatonic scalar fields and antisymmetric forms is considered. The manifold is chosen in the form , where are Einstein spaces . The block-diagonal metric is chosen and all fields and scale factors of the metric are functions of . For the forms composite (electromagnetic) p-brane ansatz is adopted. The model is reduced to a gravitating self-interacting sigma-model with certain constraints. In the pure electric and magnetic cases the number of these constraints is where is the number of one-dimensional manifolds among . In the `electromagnetic' case for additional constraints appear. A family of `Majumdar - Papapetrou-type' solutions governed by a set of harmonic functions is obtained, when all factor-spaces are Ricci-flat. These solutions are generalized to the case of non-Ricci-flat when some additional `internal' Einstein spaces of non-zero curvature are also added to M. As an example exact solutions for D = 11 supergravity and the related 12-dimensional theory are presented.

Intersecting Electric and Magnetic p-branes: Spherically Symmetric Solutions

We consider a D-dimensional self-gravitatingspherically symmetric configuration of a generalizedelectro-magnetic n-form F and a dilatonic scalar field,admitting an interpretation in terms of intersecting p-branes. For theories with additional(internal) times, selection rules are obtained, whichobstruct the existence of p-branes in certain subspaces.General static solutions are obtained under a specific restriction on the model parameters, whichcorresponds to certain orthogonality relations in thetarget-space of effective fields. More special familiesof solutions (with equal charges for some of the F-field components) are found with weakenedrestrictions on the input parameters. Black-holesolutions are determined, and it is shown that in theextreme limit the Hawking temperature may tend to zero, a finite value, or infinity, depending on thep-brane intersection dimension. A kind of no-hairtheorem is obtained, claiming that black holes cannotcoexist with a quasiscalar component of theF-field.

Euclidean Quantum Wormholes with Scalar Fields

We consider the quantum analogs of Euclidean wormholes obtained by Carlini and Mijić (CM), who analytically continued recollapsing closed universe models. Using a perfect fluid matter source, we obtain asymptotically Euclidean (AE) wormholes when the strong energy condition is satisfied. Such wormholes are found to be consistent with the Hawking–Page (HP) conjecture for quantum wormholes as solutions of the Wheeler–DeWitt (WDW) equation. By simulating the equation of state of a perfect fluid with a real scalar field, quantum wormholes are also found when the strong energy condition is violated, although generally not AE. The non-AE solutions are interpreted as excited states of the quantum wormhole spectrum. Our results give support to the claim of HP that quantum wormhole solutions are a fairly general property of the WDW equation for various matter sources. Matter sources giving quantum wormholes could now include those expected in low energy effective string theory: a dilaton scalar field with exponential potential. This is unlike the classical case where such matter sources do not allow wormhole solutions. We finally contrast quantum wormhole solutions with other boundary conditions of quantum cosmology describing an inflationary earlier behavior and a resulting large Lorentzian universe phase.

Generalized intersecting p-brane solutions from the σ-model approach

Multidimensional gravitational model on the manifold M = M 0 × ∏ i=1 n M i , where M i are Einstein spaces ( i ≥ 1), is considered. The action contains m = 2 n − 1 dilatonic scalar fields ϕ 1 and m (antisymmetric) forms A 1. When all fields and scale factors of the metric depend (essentially) on the point of M 0 and any A 1 is “proportional” to the volume form of submanifold M i 1 × … × M i k , 1 ≤ i 1 < … < i k ≤ n, the σ-model representation is obtained. A family of “Majumdar-Papapetrou type” solutions are obtained, when all M ν are Ricci-flat. Relation of our generalized p-branes to usual intersecting p-branes is discussed.

Multiscalar p-Brane Solitons

In a previous paper,10 supersymmetric p-brane solutions involving one dilatonic scalar field in maximal supergravity theories were classified. Although these solutions involve a number of participating field strengths, they are all equal and thus they carry equal electric or magnetic charges. In this paper, we generalize all these solutions to multiscalar solutions in which the charges become independent free parameters. The mass per unit p volume is equal to the sum of these Page charges. We find that for generic values of the Page charges, they preserve the same fraction of the supersymmetry as in their single scalar limits.

LIOUVILLE AND TODA SOLITONS IN M-THEORY

We study the general form of the equations for isotropic single-scalar, multi-scalar and dyonic p-branes in superstring theory and M-theory, and show that they can be cast into the form of Liouville, Toda (or Toda-like) equations. The general solutions describe non-extremal isotropic p-branes, reducing to the previously-known extremal solutions in limiting cases. In the non-extremal case, the dilatonic scalar fields are finite at the outer event horizon.

String effective gravitation and extended inflation

The low-energy string gravitation is investigated for the case of reduction with a variable (in string units) inner space. A flat cosmological model of the corresponding four-dimensional theory is constructed. The model equations are analyzed qualitatively for a potential-dominated scalar field as the source. It is demonstrated that an extended inflation stage with one purely scalar dilaton field is possible here, in contrast with the case of a constant inner space. The pattern of cosmological evolution in various conformal representations is discussed.

Jordan-Brans-Dicke stochastic inflation

We study stochastic inflation in the presence of a dynamical gravitational constant. We describe the Arnowitt-Deser-Misner formalism for Jordan-Brans-Dicke theory of gravity with an inflaton field. The inflaton and dilaton scalar fields can be separated into course-grained background fields and quantum fluctuations. We compute the amplitude of the perturbations generated by those quantum fluctuations in JBD theory with an arbitrary potential for the inflaton field. The effect of the quantum fluctuations on the background fields is equivalent to a Brownian motion of the scalar fields, which can be described with the use of a Fokker-Planck diffusion equation. The probability to find a given value of the fields in the comoving frame can be written as a Gaussian distribution centered on their classical trajectory, with decreasing dispersion along both field directions. We also calculate the condition for the Universe to enter a self-regenerating inflationary phase. The probability distribution in the physical frame, which takes into account the expansion of the proper volume of the inflationary domains, will be concentrated at the Planck boundary and will move along it towards large values of the fields.

DARK MATTER WITH VARIABLE MASSES

String effective theories contain a dilaton scalar field which couples to gravity, matter and radiation. In general, particle masses will have different dilaton couplings. We can always choose a conformal frame in which baryons have constant masses while (nonbaryonic) dark matter have variable masses, in the context of a scalar-tensor gravity theory. We are interested in the phenomenology of this scenario. Dark matter with variable masses could have a measurable effect on the dynamical motion of the halo of spiral galaxies, which may affect cold dark matter models of galaxy formation. As a consequence of variable masses, the energy-momentum tensor is not conserved; there is a dissipative effect, due to the dilaton coupling, associated with a “dark entropy” production. In particular, if axions had variable masses they could be diluted away, thus opening the “axion window.” Assuming that dark matter with variable masses dominates the cosmological evolution during the matter era, it will affect the primordial nucleosynthesis predictions on the abundances of light elements. Furthermore, the dilaton also couples to radiation in the form of a variable gauge coupling. Experimental bounds will constrain the parameters of this model.

Nonlinear constraint in scale-invariant theories.

We show the existence of a nonlinear constraint satisfied by fields in scale-invariant theories. Our model consists of a dilaton field and additional scalar fields in curved space-time. Using the constraint one of the fields becomes auxiliary, decreasing the number of physical degrees of freedom by 1. Implementation of the constraint in a Weyl-transformed scale-invariant model generates exponential interactions from polynomial potentials.