Winding Modes and Large Extra-Dimensions


We review briefly the main features of the Large Extra Dimensions scenario in the framework of weakly coupled Type I string theory. Kaluza-Klein (KK) excitations of the graviton are expected, whereas no KK modes for the gauge bosons arise if the gauge group is tied to a D3-brane. In this scenario, typical signatures such as direct production of KKmodes of the graviton at high-energy colliders could test the size of the compactified dimensions. We point out that contrary to what considered in the literature on the subject, in the general case of anisotropic compactification Winding Modes of the Standard Model gauge bosons could also be directly observable, thus further constraining the model. Talk given at the XXXIVth Rencontres de Moriond by A. Donini. Large Extra Dimensions The Newton law is tested at present from very large scale down to Rexp ≥ 1 cm. However, the typical length scale where gravity is expected to become strongly interacting, thus requiring the inclusion of quantum effects, is RP lanck ≃ 10−33cm. It is possible that deviations from the Einstein-Newton theory could be observed at the planned gravitational experiments [1] testing 4-dimensional gravity down to R ∼ 10 μm. In [2] a scenario was proposed where extra dimensions open at the sub-millimeter scale, thus modifying the 4-dimensional gravity. The relation between the fundamental (4+n)-dimensional Planck scale and the 4-dimensional one is M P lanck 8π = RM (4+n) (1) where R is the size of the compactified dimensions. If the compactified volume (V ∼ R) is large enough the fundamental Planck scale M(4+n) could be well below the 4-dimensional one, MP lanck ∼ 10 GeV. If the fundamental Planck mass is at the TeV-scale, the long-standing hierarchy problem is solved in a natural way: in this framework, there is no hierarchy at all (or a very small one) between the electroweak scale and the fundamental Planck scale. New physics at the TeV-scale would be quantum gravity itself. Since the only consistent theory of quantum gravity at present implies an underlying (10dimensional) superstring theory and the string scale is related to the fundamental Planck scale, the scenario proposed in [2] naturally involves string theory at the TeV-scale, such as was soon noticed in [3]. The string scale is directly fixed to the 4-dimensional Planck scale in weakly coupled heterotic string theory, Ms = √ α 2 MP lanck (where α is the GUT gauge coupling), and thus it is not possible to lower it to the TeV-scale. In weakly coupled Type I string theory, however, the string scale is not uniquely fixed by the 4-dimensional Planck scale and the gauge coupling, the relation involving also the compactified volume V . It is then possible to achieve a low-energy string scale (see [4] for details on heterotic and Type I strings). The scenario proposed in [2, 3], then, implies the exciting possibility of direct experimental observation of stringy effects at the planned high energy colliders, such as LHC. D-branes and String Modes Due to the compactification of extra dimensions, gravitons and Standard Model particles acquire massive replicas, the Kaluza-Klein (KK) excitations, with mass mKK ∝ 1/R. If the radius is large enough to bring down the string scale to 1 TeV, these massive excitations are extremely light. If the compactification radius is ∼ 1 mm, mKK ∼ 10−12 GeV. Clearly, such a low mass for SM particles replicas is forbidden by the experiments. A possible solution to this

2 Figures and Tables

Cite this paper

@inproceedings{Donini1999WindingMA, title={Winding Modes and Large Extra-Dimensions}, author={Andrea Donini and Stefano Rigolin}, year={1999} }