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Bumblebee models are effective field theories describing a vector field with a vacuum expectation value that spontaneously breaks Lorentz symmetry. The development of bumblebee models was motivated primarily by the discovery that mechanisms in string theory (and subsequently other quantum theories of gravity) can lead to tensor-valued fields acquiring vacuum expectation values. Bumblebee models are different from local ''U''(1) gauge theories. Nevertheless, in some bumblebee models, massless modes that behave like photons can appear. A bumblebee model is the simplest case of a theory with spontaneous Lorentz symmetry breaking. ==Introduction== Alan Kostelecký and Stuart Samuel showed in 1989 that mechanisms arising in the context of string theory can lead to spontaneous breaking of Lorentz symmetry.〔 A set of models at the level of effective field theory were defined that contained gravitational fields and a vector field ''Bµ'' that has a nonzero vacuum expectation value, '' Typically in these models, spontaneous Lorentz violation is caused by the presence of a potential term in the action. The vacuum value ''bµ'', along with a background metric, give a solution that minimizes the bumblebee potential. The vacuum value ''bµ'' acts as a fixed background field that spontaneously breaks Lorentz symmetry. It is an example, for the case of a vector, of a coefficient for Lorentz violation as defined in the Standard-Model Extension. The name ''bumblebee model'', coined by Kostelecký,〔 is based on an insect whose ability to fly has sometimes been questioned on theoretical grounds, but which nonetheless is able to fly successfully. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bumblebee models」の詳細全文を読む スポンサード リンク
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