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In particle physics, the ADD model, also known as the model with large extra dimensions (LED), is a model framework that attempts to explain the weakness of gravity relative to the other forces. This theory requires that the fields of the Standard Model are confined to a four-dimensional membrane, while gravity propagates in several additional spatial dimensions that are large compared to the Planck scale.〔For a pedagogical introduction, see 〕 The model was proposed by Nima Arkani-Hamed, Savas Dimopoulos, and Gia Dvali in 1998.〔 〕〔 〕 Results from the Large Hadron Collider do not appear to support the model thus far.〔CMS Collaboration, 2010, "Search for Microscopic Black Hole Signatures at the Large Hadron Collider", http://arxiv.org/abs/1012.3375〕〔CMS Collaboration, 2011, "Search for microscopic black holes in pp collisions at sqrt(s) = 7 TeV", http://arxiv.org/abs/1202.6396〕〔ATLAS Collaboration, 2013, "Search for microscopic black holes in a like-sign dimuon final state using large track multiplicity with the ATLAS detector", http://arxiv.org/abs/1308.4075〕〔ATLAS Collaboration, 2013, "Search for Quantum Black-Hole Production in High-Invariant-Mass Lepton+Jet Final States Using Proton-Proton Collisions at sqrt(s) = 8 TeV and the ATLAS Detector", http://arxiv.org/abs/1311.2006〕〔ATLAS Collaboration, 2014, "Search for microscopic black holes and string balls in final states with leptons and jets with the ATLAS detector at sqrt(s) = 8 TeV", http://arxiv.org/abs/1405.4254〕 However the operation range of the LHC (4 TeV) covers only a small part of the predicted range in which evidence for LED would be recorded (a few TeV to 1016TeV).〔http://physicsworld.com/cws/article/indepth/2011/jan/18/reality-check-at-the-lhc〕 ==Proponents' views== Traditionally in theoretical physics the Planck scale is the highest energy scale and all dimensionful parameters are measured in terms of the Planck scale. There is a great hierarchy between the weak scale and the Planck scale and explaining the ratio of strength of weak force and gravity is the focus of much of beyond-Standard-Model physics. In models of large extra dimensions the fundamental scale is much lower than the Planck. This occurs because the power law of gravity changes. For example, when there are two extra dimensions of size , the power law of gravity is for objects with and for objects with . If we want the Planck scale to be equal to the next accelerator energy (1 TeV), we should take to be approximately 1 mm. For larger numbers of dimensions, fixing the Planck scale at 1 TeV, the size of the extra-dimensions become smaller and as small as 1 femtometer for six extra dimensions. By reducing the fundamental scale to the weak scale, the fundamental theory of quantum gravity, such as string theory, might be accessible at colliders such as the Tevatron or the LHC.〔 〕 There has been recent progress in generating large volumes in the context of string theory.〔 〕 Having the fundamental scale accessible allows the production of black holes at the LHC,〔 〕〔 〕 though there are constraints on the viability of this possibility at the energies at the LHC.〔 〕 There are other signatures of large extra dimensions at high energy colliders.〔 〕〔 〕〔 〕〔 〕〔 〕 Many of the mechanisms that were used to explain the problems in the Standard Model used very high energies. In the years after the publication of ADD, much of the work of the beyond the Standard Model physics community went to explore how these problems could be solved with a low scale of quantum gravity. Almost immediately there was an alternate explanation to the see-saw mechanism for the neutrino mass.〔 〕〔 〕 Using extra dimensions as a new source of small numbers allowed for new mechanisms for understanding the masses and mixings of the neutrinos.〔 〕〔 〕 Another huge problem with having a low scale of quantum gravity was the existence of possibly TeV-suppressed proton decay, flavor violating, and CP violating operators. These would be disastrous phenomenologically. It was quickly realized that there were novel mechanisms for getting small numbers necessary for explaining these very rare processes.〔 〕〔 〕〔 〕〔 〕〔 〕 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「large extra dimension」の詳細全文を読む スポンサード リンク
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