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Thompson (Romps), Descent relations in Type 0A/0B, Phys Rev D, 2002
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Intro to String Theory

Prior to the 1980's, physicists had assumed that all fundamental pieces of matter -- such as electrons (in electricity), quarks (in the nucleus), and photons (constituents of light) -- were zero-dimensional point particles. In other words, particles were believed to have no volume, no area, and no length. This assumption met with considerable success, allowing physicists to predict the behavior of particles with astonishing accuracy.

Despite this success, some very important problems remained. When the masses of particles were calculated using the point-particle theories, the equations became infinite and meaningless. In addition, the theory of gravity could not be made to fit within the point-particle paradigm.

In 1984, physicists showed that both of these problems were resolved by treating particles as one-dimensional ``strings'' rather than zero-dimensional points. This pivotal year in the history of physics has been called the ``first string revolution'' and has transformed the field of theoretical particle physics. Among its many achievements, string theory has fulfilled Einstein's dream of unifying the four forces (weak, strong, electromagnetic, and gravitational) into a single force, it has revealed seven other spatial dimensions in addition to the usual x, y, and z, and it has led to the discovery of branes, which are higher-dimensional cousins of the particle strings.

Description

By the early 1990's, physicists had discovered several different string theories. This was a disappointment to many string theorists who had hoped that there would be one unique theory that would explain the workings of the Universe. In 1995, participants in the ``second string revolution'' discovered that all of these different theories were really manifestations of the same theory, called M-theory. Although this is known in principle, M-theory is poorly understood and some of its manifestations -- such as the Type 0 theories -- remain mysterious.

In the paper ``Descent relations in Type 0A/0B,'' I detail how the various branes in the Type 0 theories are related to each other by various physical and mathematical transformations. Whereas a particle string can be pictured as a wiggling rubber band, a two-dimensional brane can be pictured as an oscillating piece of paper. In fact, string theory has many types of branes, from zero-dimensional branes to nine-dimensional branes. As I show in this paper, the various branes in Type 0 theories are all related to each other. In an example using the analogy of paper and rubber bands, two sheets of paper (D2+$\bar{\text{D}}$2+), when brought together, will collapse into a single rubber band ($\hat{\text{D}}$1+), which then shrinks to a point (D0+).

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Strominger and Thompson (Romps), Quantum Bousso Bound, Phys Rev D, 2004