# Black brane

In general relativity, a black brane is a solution of the equations that generalizes a black hole solution but it is also extended—and translationally symmetric—in p additional spatial dimensions. That type of solution would be called a black p-brane.[1]

In string theory, the term black brane describes a group of D1-branes that are surrounded by a horizon.[2] With the notion of a horizon in mind as well as identifying points as zero-branes, a generalization of a black hole is a black p-brane.[3] However, many physicists tend to define a black brane separate from a black hole, making the distinction that the singularity of a black brane is not a point like a black hole, but instead a higher dimensional object.

A BPS black brane is similar to a BPS black hole. They both have electric charges. Some BPS black branes have magnetic charges.[4]

The metric for a black p-brane in a n-dimensional spacetime is:

${\displaystyle {ds}^{2}=\left(\eta _{ab}+{\frac {r_{s}^{n-p-3}}{r^{n-p-3}}}u_{a}u_{b}\right)d\sigma ^{a}d\sigma ^{b}+\left(1-{\frac {r_{s}^{n-p-3}}{r^{n-p-3}}}\right)^{-1}dr^{2}+r^{2}d\Omega _{n-p-2}^{2}}$

where:

• η is the (p + 1)-Minkowski metric with signature (−, +, +, +, ...),
• σ are the coordinates for the worldsheet of the black p-brane,
• u is its four-velocity,
• r is the radial coordinate and,
• Ω is the metric for a (n − p − 2)-sphere, surrounding the brane.

## Curvatures

When ${\displaystyle ds^{2}=g_{\mu \nu }dx^{\mu }dx^{\nu }+d\Omega _{n+1}}$.

The Ricci Tensor becomes ${\displaystyle R_{\mu \nu }=R_{\mu \nu }^{(0)}+{\frac {n+1}{r}}\Gamma _{\mu \nu }^{r}}$, ${\displaystyle R_{ij}=\delta _{ij}g_{ii}({\frac {n}{r^{2}}}(1-g^{rr})-{\frac {1}{r}}(\partial _{\mu }+\Gamma _{\nu \mu }^{\nu })g^{\mu r})}$.

The Ricci Scalar becomes ${\displaystyle R=R^{(0)}+{\frac {n+1}{r}}g^{\mu \nu }\Gamma _{\mu \nu }^{r}+{\frac {n(n+1)}{r^{2}}}(1-g^{rr})-{\frac {n+1}{r}}(\partial _{\mu }g^{\mu r}+\Gamma _{\nu \mu }^{\nu }g^{\mu r})}$.

Where ${\displaystyle R_{\mu \nu }^{(0)}}$, ${\displaystyle R^{(0)}}$ are the Ricci Tensor and Ricci scalar of the metric ${\displaystyle ds^{2}=g_{\mu \nu }dx^{\mu }dx^{\nu }}$.

## Black string

A black string is a higher dimensional (D>4) generalization of a black hole in which the event horizon is topologically equivalent to S2 × S1 and spacetime is asymptotically Md−1 × S1.

Perturbations of black string solutions were found to be unstable for L (the length around S1) greater than some threshold L′. The full non-linear evolution of a black string beyond this threshold might result in a black string breaking up into separate black holes which would coalesce into a single black hole. This scenario seems unlikely because it was realized a black string could not pinch off in finite time, shrinking S2 to a point and then evolving to some Kaluza–Klein black hole. When perturbed, the black string would settle into a stable, static non-uniform black string state.

## Kaluza–Klein black hole

A Kaluza–Klein black hole is a black brane (generalisation of a black hole) in asymptotically flat Kaluza–Klein space, i.e. higher-dimensional spacetime with compact dimensions. They may also be called KK black holes.[5]

## References

1. ^ "black brane in nLab". ncatlab.org. Retrieved 2017-07-18.
2. ^ Gubser, Steven Scott (2010). The Little Book of String Theory. Princeton: Princeton University Press. pp. 93. ISBN 9780691142890. OCLC 647880066.
3. ^ "String theory answers". superstringtheory.com. Retrieved 2017-07-18.
4. ^ Koji., Hashimoto (2012). D-brane : superstrings and new perspective of our world. Berlin, Heidelberg: Springer-Verlag Berlin Heidelberg. ISBN 9783642235740. OCLC 773812736.
5. ^ Obers (2009), p. 212–213