Curvature squared terms and string theories

Zwiebach, Barton

doi:10.1016/0370-2693(85)91616-8

Cited by 1,329 publications

(1,395 citation statements)

References 10 publications

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“…In particular, as was shown in [46] by Gross and Sloan, in the low-energy effective action the dilaton is coupled to a Gauss-Bonnet term. It is well known that such a term, expanded about a Minkowski vacuum, ensures that the theory is ghost-free (see [47]). …”

Section: The Physical Degrees Of Freedommentioning

confidence: 99%

Ghosts, instabilities, and superluminal propagation in modified gravity models

Felice

Hindmarsh

Trodden

2006

J. Cosmol. Astropart. Phys.

162

167

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We consider Modified Gravity models involving inverse powers of fourth-order curvature invariants.Using these models' equivalence to the theory of a scalar field coupled to a linear combination of the invariants, we investigate the properties of the propagating modes. Even in the case for which the fourth derivative terms in the field equations vanish, we find that the second derivative terms can give rise to ghosts, instabilities, and superluminal propagation speeds. We establish the conditions which the theories must satisfy in order to avoid these problems in Friedmann backgrounds, and show that the late-time attractor solutions generically exhibit superluminally propagating tensor or scalar modes. * a. de-felice@sussex.ac.uk

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Section: The Physical Degrees Of Freedommentioning

confidence: 99%

Ghosts, instabilities, and superluminal propagation in modified gravity models

Felice

Hindmarsh

Trodden

2006

J. Cosmol. Astropart. Phys.

162

167

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“…This will inevitably lead to perturbative ghosts, which are known to be absent in the full non perturbative version of string theory. One can avoid this apparent inconsistency (to leading order) if the slope expansion takes the form of the Lovelock action [5]. Indeed, the second order curvature terms are known to take the form of the Gauss-Bonnet combination [6].…”

Section: Introductionmentioning

confidence: 99%

“…Given the higher order nature of the theory (1.1), the vacuum field equations generically admit multiple solutions with maximally symmetry (up to the order n in number). For EGB, we therfore have up to two distinct maximally symmetric vacuum solutions, with two possible effective cosmological constants, 5) where…”

Section: Introductionmentioning

confidence: 99%

The instability of vacua in Gauss-Bonnet gravity

Charmousis

Padilla

2008

J. High Energy Phys.

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Owing to the quadratic nature of the theory, Einstein-Gauss-Bonnet gravity generically permits two distinct vacuum solutions. One solution (the "Einstein" vacuum) has a well defined limit as the Gauss-Bonnet coupling goes to zero, whereas the other solution (the "stringy" vacuum) does not. There has been some debate regarding the stability of these vacua, most recently from Deser & Tekin who have argued that the corresponding black hole solutions have positive mass and as such both vacua are stable. Whilst the statement about the mass is correct, we argue that the stringy vacuum is still perturbatively unstable. Simply put, the stringy vacuum suffers from a ghost-like instability that is not excited by the spherically symmetric black hole, but would be excited by any source likely to emit gravitational waves, such as a binary system. This result is reliable except in the strongly coupled regime close to the Chern-Simons limit, when the two vacua are almost degenerate. In this regime, we study instanton transitions between branches via bubble nucleation, and calculate the nucleation probability. This demonstrates that there is large mixing between the vacua, so that neither of them can accurately describe the true quantum vacuum. We also present a new gravitational instanton describing black hole pair production in de Sitter space on the Einstein branch, which is preferred to the usual Nariai instantons and is not present in pure Einstein gravity.

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“…Since the Lovelock tensor contains metric derivatives no higher than second order, the quantization of the linearized Lovelock theory is ghost-free [4] The gravitational action satisfying the assumption of Einstein is precisely of the form proposed by Lovelock [3]:…”

Section: Introductionmentioning

confidence: 99%

Spacetimes with longitudinal and angular magnetic fields in third order Lovelock gravity

Dehghani

Bostani

2007

Phys. Rev. D

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We obtain two new classes of magnetic brane solutions in third order Lovelock gravity. The first class of solutions yields an (n + 1)-dimensional spacetime with a longitudinal magnetic field generated by a static source. We generalize this class of solutions to the case of spinning magnetic branes with one or more rotation parameters. These solutions have no curvature singularity and no horizons, but have a conic geometry. For the spinning brane, when one or more rotation parameters are nonzero, the brane has a net electric charge which is proportional to the magnitude of the rotation parameters, while the static brane has no net electric charge. The second class of solutions yields a spacetime with an angular magnetic field. These solutions have no curvature singularity, no horizon, and no conical singularity. Although the second class of solutions may be made electrically charged by a boost transformation, the transformed solutions do not present new spacetimes. Finally, we use the counterterm method in third order Lovelock gravity and compute the conserved quantities of these spacetimes. * email address: mhd@shirazu.ac.ir

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Curvature squared terms and string theories

Cited by 1,329 publications

References 10 publications

Ghosts, instabilities, and superluminal propagation in modified gravity models

Ghosts, instabilities, and superluminal propagation in modified gravity models

The instability of vacua in Gauss-Bonnet gravity

Spacetimes with longitudinal and angular magnetic fields in third order Lovelock gravity

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