Domain wall (string theory)
In physics, a domain wall is any of several similar things in string theory, magnetism, or optics. These phenomena can all be generically described as topological solitons that occur whenever a discrete symmetry is spontaneously broken.
In string theory, a domain wall is a theoretical 2-dimensional singularity. A domain wall is meant to represent an object of codimension one embedded into space (a defect in space localized in one spatial dimension). For example, D8-branes are domain walls in type II string theory. In M-theory, the existence of Horava–Witten domain walls, "ends of the world" that carry an E8 gauge theory, is important for various relations between superstring theory and M-theory.
If domain walls exist, it seems plausible that they will violently emit gravitational waves if two such walls would collide. As the Laser Interferometer Gravitational-Wave Observatory and future observatories of its kind will search for direct evidence of gravitational waves, this phenomenon would be included as well in such searches.
- S. Weinberg, The Quantum Theory of Fields, Vol. 2. Chap 23, Cambridge University Press (1995).
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