D-brane

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In string theories (certain hypothetical physical models that go beyond quantum field theory ), D-branes (English D-branes [ ˈdibɹeɪns ]) are a special class of p-branes at which the ends of open strings are attached. The concept comes from Joseph Polchinski (1989).

definition

D3 brane with bound strings

D-branes (or D p -branes) are p -dimensional objects to which open strings couple, which in p + 1 dimensions Neumann boundary conditions (i.e. the derivative vanishes at the end points) and in the 9-p other dimensions Dirichlet -Boundary conditions (i.e. the field disappears at the end points) suffice. The dimension number p indicates the number of spatial dimensions ; each D-brane also has an extension in time.

D-branes can also be interpreted as special cases of certain classical configurations (“ solitons ”). They can be infinitely extended, but also have a finite and even vanishing volume.

D-branes are BPS states; that is, they disappear when half of the supersymmetry operators are used.

origin

Two D-branes connected by an open string

D-branes are imagined as low-dimensional, dynamic objects embedded in a bulk , i.e. H. into a higher dimensional spacetime or into a hyperspace . They are part of string theory (see also M-branes in M-theory ). Since this describes a 10 + 1-dimensional space, the question arises why we can only perceive 3 + 1 dimensions (with time). These branes can be used as an explanation.

According to string theory, there are one-dimensional strings with open ends, as well as closed, ring-shaped strings. Open ended strings tend to "attach" to a bran; They can then no longer change dimensions at will, but are “trapped” on their branch. Interactions with particles in the bulk then only take place to a very limited extent. If the universe we know consists of such particles that are trapped in a bran, then humans cannot leave this universe either and are restricted to the low-dimensional space. These properties lead to the idea that our universe could consist of one or more D3 branes (corresponding to "our" perceptible three spatial dimensions). The bound strings therefore form almost all elementary particles , e.g. B. photons , electrons , quarks .

Ring-shaped strings, on the other hand, are not tied to a bran, but exist in bulk. They only interact to a limited extent with the particles in the bran; instead, their force is distributed over several dimensions. Today the graviton , the gauge boson of gravity , is considered a candidate for such a particle. This would explain why the Great Unified Theory so far only includes three of the four basic physical forces and why gravity is so weak in relation to the other basic forces. At the same time, there is an elegant solution for dark energy and dark matter . Due to the possibility of the graviton to move between the branes and thus interact with different branes, another universe could gravitationally interact with ours, which we would understand as dark energy or dark matter. On the other hand, it would also mean deviations from the current law of gravitation .

Through quantum effects and gravitational interactions, D-branes can be deformed and excited to vibrate . A satisfactory mathematical treatment of this phenomenon does not yet exist. There is evidence that D-branes can become unstable and decay. Some strongly deformed (e.g. spherical) D-branes are also known that can occur in curved spaces. The classification of all possible D-branes is an open problem of great importance for understanding string theory, especially its vacuum structure.

Other considerations lead to the fact that several of these branes exist and represent parallel universes . Since branes can move freely in space, two branes could collide. This would release as much energy as can only be imagined during the Big Bang . The ekpyrotic universe is derived from this, i.e. the idea that our universe was also created by such a collision.

See also

literature

Notes and individual references

  1. ↑ See e.g. B. Clifford V. Johnson - D-brane primer , arxiv : hep-th / 0007170 , page 127: the instability of a tachyon in the D-brane spectrum is concluded. Among other things, a D0 brane can change into a D2 brane.