A Large Mass Hierarchy from a Small Extra Dimension

A Large Mass Hierarchy from a Small Extra Dimension

4 May 1999 | Lisa Randall, Raman Sundrum
This paper proposes a new mechanism for solving the hierarchy problem by introducing a small extra dimension. The weak scale is generated from a large scale of order the Planck scale through an exponential hierarchy, which arises from the background metric rather than gauge interactions. This mechanism relies on a single additional dimension and involves two three-branes, one containing the Standard Model fields. The experimental consequences are distinctive, with fundamental spin-2 excitations of weak scale mass, coupled with weak scale strength to standard model particles. These models differ from large extra dimension scenarios, as current constraints on large extra dimensions do not apply. The paper introduces a non-factorizable metric, which leads to a dramatic solution for the hierarchy problem. The metric is a solution to Einstein's equations with two three-branes and appropriate cosmological terms. Four-dimensional mass scales are related to five-dimensional input mass parameters and the warp factor. The hierarchy is generated through an exponential function of the compactification radius, not requiring extremely large radii. The solution is distinct from previous proposals, with a hierarchy between the fundamental five-dimensional Planck scale and the compactification scale of order 50, and only one additional dimension. The solution involves a compactification radius, r_c, which is independent of x due to four-dimensional Poincaré invariance. The classical solution to the five-dimensional Einstein equations is derived, leading to a metric with a warp factor. The solution requires that the boundary and bulk cosmological terms are related in terms of a single scale k. The resulting metric is a slice of an AdS_5 geometry. The physical implications of this solution include a four-dimensional effective field theory description, with the Planck scale determined by the five-dimensional scales, M, k, and r_c. The mass parameters of the four-dimensional fields are determined by the five-dimensional scales. The physical mass scales are set by a symmetry-breaking scale, leading to a hierarchy between the weak scale and the Planck scale. The gravitational modes have masses and couplings determined by the TeV scale, with couplings to matter set by the weak scale rather than the Planck scale. The phenomenological implications of this scenario are distinctive, with gravitational resonances of order a TeV and couplings to matter set by the weak scale. The solution is subject to experimental verification and has important implications for the consistency of the scenario beyond tree level. The results contrast with large extra dimension scenarios, where Kaluza-Klein modes are much lighter. The solution offers a potential resolution to the hierarchy problem, with the weak scale generated through an exponential factor, and the apparent scale where the theory becomes strongly coupled is of order the weak scale. The solution is subject to experimental verification and has important implications for future collider searches.This paper proposes a new mechanism for solving the hierarchy problem by introducing a small extra dimension. The weak scale is generated from a large scale of order the Planck scale through an exponential hierarchy, which arises from the background metric rather than gauge interactions. This mechanism relies on a single additional dimension and involves two three-branes, one containing the Standard Model fields. The experimental consequences are distinctive, with fundamental spin-2 excitations of weak scale mass, coupled with weak scale strength to standard model particles. These models differ from large extra dimension scenarios, as current constraints on large extra dimensions do not apply. The paper introduces a non-factorizable metric, which leads to a dramatic solution for the hierarchy problem. The metric is a solution to Einstein's equations with two three-branes and appropriate cosmological terms. Four-dimensional mass scales are related to five-dimensional input mass parameters and the warp factor. The hierarchy is generated through an exponential function of the compactification radius, not requiring extremely large radii. The solution is distinct from previous proposals, with a hierarchy between the fundamental five-dimensional Planck scale and the compactification scale of order 50, and only one additional dimension. The solution involves a compactification radius, r_c, which is independent of x due to four-dimensional Poincaré invariance. The classical solution to the five-dimensional Einstein equations is derived, leading to a metric with a warp factor. The solution requires that the boundary and bulk cosmological terms are related in terms of a single scale k. The resulting metric is a slice of an AdS_5 geometry. The physical implications of this solution include a four-dimensional effective field theory description, with the Planck scale determined by the five-dimensional scales, M, k, and r_c. The mass parameters of the four-dimensional fields are determined by the five-dimensional scales. The physical mass scales are set by a symmetry-breaking scale, leading to a hierarchy between the weak scale and the Planck scale. The gravitational modes have masses and couplings determined by the TeV scale, with couplings to matter set by the weak scale rather than the Planck scale. The phenomenological implications of this scenario are distinctive, with gravitational resonances of order a TeV and couplings to matter set by the weak scale. The solution is subject to experimental verification and has important implications for the consistency of the scenario beyond tree level. The results contrast with large extra dimension scenarios, where Kaluza-Klein modes are much lighter. The solution offers a potential resolution to the hierarchy problem, with the weak scale generated through an exponential factor, and the apparent scale where the theory becomes strongly coupled is of order the weak scale. The solution is subject to experimental verification and has important implications for future collider searches.
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