Abstract
We identify a class of Randall–Sundrum type models with a successful first order cosmological phase transition during which a 5D dual of approximate conformal symmetry is spontaneously broken. Our focus is on soft-wall models that naturally realize a light radion/dilaton and suppressed dynamical contribution to the cosmological constant. We discuss phenomenology of the phase transition after developing a theoretical and numerical analysis of these models both at zero and finite temperature. We demonstrate a model with a TeV-Planck hierarchy and with a successful cosmological phase transition where the UV value of the curvature corresponds, via AdS/CFT, to an N of 20, where 5D gravity is expected to be firmly in the perturbative regime.
Highlights
Randall–Sundrum (RS) models [1] offer an attractive solution to the hierarchy problem, and they put the cosmological constant problem [2] into a new perspective [3,4]
The effective 4D value of the cosmological constant is a sum of terms involving the bulk 5D cosmological constant, and two brane tensions associated with the UV and IR branes
The tiny observed value of the cosmological constant is obtained by separately tuning the UV brane tension against the bulk cosmological constant, and the IR brane tension against the same bulk cosmological constant
Summary
Randall–Sundrum (RS) models [1] offer an attractive solution to the hierarchy problem, and they put the cosmological constant problem [2] into a new perspective [3,4]. The tiny observed value of the cosmological constant is obtained by separately tuning the UV brane tension against the bulk cosmological constant, and the IR brane tension against the same bulk cosmological constant In addition to this naturalness issue, a more phenomenological and pressing problem plagues these models: The phase transition during which the vacuum expectation value for the radion develops is first order, and estimates of bubble nucleation rates in early-universe cosmology strongly suggested that a RS phase transition would not proceed to completion due to Hubble expansion out-pacing true-vacuum bubble creation. We address the question whether a recently studied class of geometries which contain a light dilaton/radion and suppressed cosmological constant while deviating very far from AdS in the infrared region of the geometry achieve a better transition rate while retaining a perturbative 5D gravity description.
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