Cosmic eggs to relax the cosmological constant

Abstract

In theories with extra dimensions, the cosmological hierarchy problem can be thought of as the unnaturally large radius of the observable universe in Kaluza-Klein units. We sketch a dynamical mechanism that relaxes this. In the early universe scenario we propose, three large spatial dimensions arise through tunneling from a 'cosmic egg', an effectively one-dimensional configuration with all spatial dimensions compact and of comparable, small size. If the string landscape is dominated by low-dimensional compactifications, cosmic eggs would be natural initial conditions for cosmology.A quantum cosmological treatment of a toy model egg predicts that, in a variant of the Hartle-Hawking state, cosmic eggs break to form higher dimensional universes with a small, but positive cosmological constant or quintessence energy. Hence cosmic egg cosmology yields a scenario in which the seemingly unnaturally small observed value of the vacuum energy can arise from natural initial conditions.

Towards an “AdS1/CFT0” correspondence from the D(−1)/D7 system?

“…Lastly we want to speculate about a broader use of these vacua. Outside the holographic context, the existence of 1d "vacua" have been suggested in a cosmological setting [29,30] as seed universes that lead to 3 observably large dimensions after decay. Interestingly the IKKT matrix model [31], which has been suggested as a non-perturbative definition of IIB string theory, seems to allow for dynamical solutions in which 3 large JHEP09(2022)249 classical dimensions emerge [32].…”

Complex saddles and Euclidean wormholes in the Lorentzian path integral

“…Because of this subtlety, previous analyses have not held the flux (a.k.a. axion charge) fixed as a boundary condition, although an appropriately rescaled scalar perturbation can amend the analysis in the axion frame (see [26]). We have also seen the importance of keeping all boundary terms for the gaugeinvariant modes Q j , namely in ruling out the even-parity perturbations for which the total derivative terms G j are not integrable.…”

“…The nature of the GS critical point can be analyzed by considering JHEP08(2022)064 fluctuations around the background geometry and looking for tachyonic directions in which the Euclidean action is decreased. There has been previous work in analyzing this saddle point in the axion picture [22] (see also [23][24][25][26]); here we approach the question of perturbative stability in the 3-form picture, which we argue provides a more transparent application of the correct boundary conditions. We find that no negative modes are present and the GS wormhole represents a true minimum of the Euclidean path integral.…”

Complex Saddles and Euclidean Wormholes in the Lorentzian Path Integral

“…The nature of the GS critical point can be analyzed by considering fluctuations around the background geometry and looking for tachyonic directions in which the Euclidean action is decreased. There has been previous work in analyzing this saddle point in the axion picture [22] (see also [23][24][25][26]); here we approach the question of perturbative stability in the 3-form picture, which we argue provides a more transparent application of the correct boundary conditions. We find that no negative modes are present and the GS wormhole represents a true minimum of the Euclidean path integral.…”