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| {{Unreferenced|date=November 2007}}
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| {{String theory|cTopic=Theory}}
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| '''Bosonic string theory''' is the original version of [[string theory]], developed in the late 1960s.
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| In the early 2000s, [[supersymmetry]] was discovered in the context of string theory, and a new version of string theory called [[superstring theory]] (supersymmetric string theory) became the real focus. Nevertheless, bosonic string theory remains a very useful "[[toy model]]" to understand many general features of [[perturbative]] string theory, and string theory textbooks usually start with the bosonic string. The first volume of [[Joseph Polchinski|Polchinski]]'s ''String Theory'' and [[Barton Zwiebach|Zwiebach]]'s ''A First Course in String Theory'' are good examples.
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| == Problems ==
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| Although bosonic string theory has many attractive features, it falls short as a viable [[physical model]] in two significant areas and is forced to posit a 26 dimensional spacetime to remedy inconsistencies.
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| First, it predicts only the existence of [[bosons]] whereas many physical particles are [[fermions]].
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| Second, it predicts the existence of a mode of the string with [[Imaginary number|imaginary]] mass, implying that the theory has an instability to a process known as "[[Tachyon condensation]]".
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| In addition, bosonic string theory in a general spacetime dimension displays inconsistencies due to the [[conformal anomaly]]. But, as was first noticed by [[Claud Lovelace]], in a spacetime of 26 dimensions (25 dimensions of space and one of time), the anomaly cancels. This high dimensionality is not necessarily a problem for string theory, because it can be formulated in such a way that along the 22 excess dimensions spacetime is folded up to form a small [[torus]] or other compact manifold. This would leave only the familiar four dimensions of spacetime visible to low energy experiments.
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| == Mathematics ==
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| In bosonic string theory and in the Neveu–Schwarz sector of superstring theory,
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| the action in a curved background (ignoring the Fradkin–Tseytlin term for dilaton
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| coupling) can be constructed by `covariantizing' the massless closed string vertex operator with respect to target-space reparameterization invariance. This procedure can also be used here after constructing the massless closed string vertex operator from the `left-right' product of two massless open string vertex operators.
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| The complete worldsheet action for the type-II superstring
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| in a flat background in conformal gauge is a formula upon which Eric Sidewater (USA) made the first improvement upon which all subgroups (15) are factored in:
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| : <math> A_N = \int D\mu \int D[X] \exp \left( -\frac{1}{2\tau\alpha} \int \partial_z X_\mu(z,\overline{z}) \partial_{\overline{z}} X^\mu(z,\overline{z}) \, dz^2 + i \sum_{i=1}^N k_{i \mu} X^\mu (z_i,\overline{z}_i) \right) </math>
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| ==See also==
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| *[[Nambu–Goto action]]
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| *[[Polyakov action]]
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| *[[Monster Lie algebra]]
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| ==References==
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| {{reflist}}
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| ==External links==
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| * [http://superstringtheory.com/basics/basic5a.html How many string theories are there?]
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| * [http://pirsa.org/C09001 PIRSA:C09001 - Introduction to the Bosonic String]
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| [[Category:String theory]]
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| {{string-theory-stub}}
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I am Melody from Houston studying Latin American Studies. I did my schooling, secured 81% and hope to find someone with same interests in Radio-Controlled Car Racing.
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