Spacelike Branes Research Articles

Dimensional reductions of M-theory S-branes to string theory S-branes

We study both the direct and the double-dimensional reduction of space-like branes of M-theory and point out some peculiarities in the process unlike their time-like counterpart. In particular, we show how starting from SM2 and SM5-brane solutions we can obtain SD2 and SNS5-brane as well as SNS1 and SD4-brane solutions of string theory by direct and double-dimensional reductions, respectively. In the former case we need to use delocalized SM-brane solutions, whereas in the latter case we need to use anisotropic SM-brane solutions in the directions which are compactified.

Brane classical and quantum cosmology from an effective action

Motivated by the Randall-Sundrum braneworld scenario, we discuss the classical and quantum dynamics of a $(d+1)$-dimensional boundary wall between a pair of $(d+2)$-dimensional topological Schwarzschild-AdS black holes. We assume there are quite general---but not completely arbitrary---matter fields living on the boundary ``brane universe,'' and that its geometry is that of a Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) model. The effective action governing the model in the minisuperspace approximation is derived. We find that the presence of black hole horizons in the bulk gives rise to a complex action for certain classically allowed brane configurations, but that the imaginary contribution plays no role in the equations of motion. Classical and instanton brane trajectories are examined in general and for special cases, and we find a subset of configuration space that is not allowed at the classical or semiclassical level; this subset corresponds to spacelike branes carrying tachyonic matter. The Hamiltonization and Dirac quantization of the model is then performed for the general case; the latter involves the manipulation of the Hamiltonian constraint before it is transformed into an operator that annihilates physical state vectors. The ensuing covariant Wheeler-DeWitt equation is examined at the semiclassical level, and we consider the possible localization of the brane universe's wave function away from the cosmological singularity. This is easier to achieve for branes with low density and/or spherical spatial sections.

Accelerating cosmologies from spacelike branes.

We point out that the recently proposed model of a flat four-dimensional universe with accelerated expansion in string or M theory is a special case of time-dependent solutions that the author found under the name of spacelike (S) branes. We also show that similar accelerating models can be obtained from S branes if the internal space is chosen to be hyperbolic or flat spaces.

Spacelike brane actions.

We derive effective actions for "spacelike branes" (S-branes) and find a solution describing the formation of fundamental strings in the rolling tachyon background. The S-brane action is a Dirac-Born-Infeld action for Euclidean world volumes defined in the context of time-dependent tachyon condensation of non-BPS (Bogomol'nyi-Prasad-Sommerfield) branes. It includes gauge fields and, in particular, a scalar field associated with translation along the time direction. We show that the BIon spike solutions constructed in this system correspond to the production of a confined electric flux tube (a fundamental string) at late time of the rolling tachyon.

Intersection rules for S-branes

We give a model-independent derivation of general intersecting rules for spacelike branes (S-branes) in arbitrary dimensions d. This is achieved by directly solving bosonic field equations for supergravity coupled to a dilaton and antisymmetric tensor fields with minimal ansätze. We compare the results with those in eleven-dimensional supergravity and other solutions.

Does the Tachyon Matter?

We study time-dependent solutions of Einstein–Maxwell gravity in four dimensions coupled to tachyon matter—the Dirac–Born–Infeld Lagrangian that provides an effective description of a decaying tachyon on an unstable D-brane in string theory. Asymptotically, the solutions are similar to the recently studied space-like brane solutions and carry S-brane charge. They do not break the Lorentzian R-symmetry. We study tachyon matter as a probe in such a background and analyze its backreaction. For early/late times, the tachyon field has a constant energy density and vanishing pressure as in flat space. On the other hand, at intermediate times, the energy density of the tachyon diverges and produces a space-like curvature singularity.

The Atick–Witten free energy, closed tachyon condensation and deformed Poincaré symmetry

The dependence of the free energy of string theory on the temperature at T⪢ T Hag was found long ago by Atick and Witten and is F( T)∼ ΛT 2, where Λ diverges because of a tachyonic instability. We show that this result can be understood assuming that, above the Hagedorn transition, Poincaré symmetry is deformed into a quantum algebra. Physically this quantum algebra describes a non-commutative spatial geometry and a discrete Euclidean time. We then show that in string theory this deformed Poincaré symmetry indeed emerges above the Hagedorn temperature from the condensation of vortices on the world-sheet. This result indicates that the endpoint of the condensation of closed string tachyons with non-zero winding is an infinite stack of space-like branes with a given non-commutative world-volume geometry. On a more technical side, we also point out that T-duality along a circle with antiperiodic boundary conditions for space–time fermions is broken by world-sheet vortices, and the would-be T-dual variable becomes non-compact.

Spacelike and Time Dependent Branes from DBI

Spacelike branes are new time-dependent systems to explore and it has been observed that related supergravity solutions can be obtained by analytically continuing known D-brane solutions. Here we show that analytic continuation of known solutions of the Dirac-Born-Infeld equations also lead to interesting analogs of time dependent gravity solutions. Properties of these new solutions, which are similar to the Witten bubble of nothing and S-branes, are discussed. We comment on how these new bubble solutions seem relevant to the tachyon condensation process of non-BPS branes, and remark on their application to cosmological scenarios. Unstable brane configurations which resemble S-brane type solutions are also discussed.

S-brane solutions in supergravity theories

In this paper time dependent solutions of supergravities with dilaton and arbitrary rank antisymmetric tensor field are found. Although the solutions are nonsupersymmetric the equations of motions can be integrated in a simple form. Such supergravity solutions are related to Euclidean or spacelike branes (S-branes).

Supergravity S-Branes

We construct supergravity solutions corresponding to space-like branes in string theory. Our approach is to apply the usual solution generating techniques to an appropriate time-dependent solution of the eleven dimensional vacuum Einstein equations. In this way all SDp-brane solutions are obtained, as well as the NS and M-theory space branes. Bound states of SDp/SD(p-2)- and SDp/SD(p-4)-branes are also constructed. Finally, we begin an investigation of the near-brane regions and singularity structure of these solutions.