Naked singularities in low-energy, effective string theory

Abstract

Solutions to the equations of motion of the low energy, effective field theory emerging out of compactified heterotic string theory are constructed by making use of the well-known duality symmetries. Beginning with fourdimensional solutions of the Einstein-massless scalar field theory in the canonical frame we first rewrite the corresponding solutions in the string frame.Thereafter, using the T and S duality symmetries of the low energy string effective action we arrive at the corresponding uncharged, electrically charged and magnetically charged solutions. Brief comments on the construction of dual versions of the Kerr-Sen type using the dilatonic Kerr solution as the seed are also included. Thereafter, we verify the status of the energy conditions for the solutions in the string frame. Several of the metrics found here are shown to possess naked singularities although the energy conditions are obeyed. Dual solutions exhibit a duality in the conservation/violation of the Null and Averaged Null Energy Conditions (NEC/ANEC), a fact demonstrated earlier in the context of black holes (hep-th/9604047) and cosmologies (hep-th/9611122). Additionally, those backgrounds which conserve the * Electronic Address : sayan@iucaa.ernet.in NEC/ANEC in spite of possesing naked singularities serve as counterexamples to cosmic censorship in the context of low energy, effective string theory.

Traversable Lorentzian wormholes in the vacuum low energy effective string theory in Einstein and Jordan frames

“…They can be grouped as string class I [Eqs. (26), (27) [15], but the rest of the three sets of solutions given here are essentially new to our knowledge. Note that it is not possible to recover the seed EMS solutions by any choice of the free parameters.…”

“…Under a suitable re-identification of constants and coordinates, the above solution reduces to that discussed by Kar [15]. To first order in (1/r), we have the strength of the dilatonic sourceσ given byΦ…”

The Momentum Four-Vector in Brans–Dicke Wormholes

“…Note that the zero values of other matter fields do not impose any additional constraints either on the metric or on the dilaton (Kar, 1999). Under the substitution e −2 = ψ, the above action reduces to the Brans-Dicke action…”

New features of extended wormhole solutions in the scalar field gravity theories

“…where g µν is the string metric and Φ is the dilaton field. Note that the zero values of other matter fields do not impose any additional constraints either on the metric or on the dilation [12]. Under the substitution e −2 e Φ = φ, the above action reduces to the BD action…”