A self-tuning mechanism in 6d gravity-scalar theory


We present a new type of self-tuning mechanism for 6d brane world models in the framework of gravity-scalar theory. This new type of self-tuning mechanism exhibits a remarkable feature. In the weak coupling limit gs0g_s \to 0, the geometry of bulk spacetime remains virtually unchanged by an introduction of the Standard Model(SM)-brane, and consequently it is virtually unaffected by quantum corrections to the brane tension due to the dynamics of SM degrees of freedom. Such a feature can be obtained by introducing Neveu-Schwarz(NS)-brane as a background brane on which our SM-brane is to be set. Indeed, field equations naturally require the existence of the background NS-brane. Among the given such models, of the most interest is the case with Λ=0\Lambda=0, where Λ\Lambda represents the bulk cosmological constant. This model contains two coincident branes (of the SM- and the NS-branes), one of which is a codimension-2 brane placed at the origin of 2d transverse space (Σ2\equiv \Sigma_2), another a codimension-1 brane placed at the edge of Σ2\Sigma_2. These two branes are T-duals of each other, and one of them is identified as our SM-brane (plus the background NS-brane). In the presence of the background NS-brane (and in the absence of Λ\Lambda), the 2d transverse space Σ2\Sigma_2 becomes R2R_2 (or an orbifold R2/ZnR_2 /Z_n) with an appropriate deficit angle. But this is possible only if the 6d Planck scale M6M_6 and the string scale MsM_s(1/α\equiv 1/\sqrt{\alpha^{\prime}}) are of the same order, which accords with an assumption \cite{1,2,3} that the electroweak scale mEWm_{EW} is the only short distance scale in nature

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This paper was published in CERN Document Server.

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