# Holographic self-tuning of the cosmological constant

## TL;DR

This paper introduces a holographic brane-world model where the four-dimensional cosmological constant is dynamically tuned to zero, ensuring a flat universe with stable gravity behavior and no ghost instabilities.

## Contribution

It presents a novel self-tuning mechanism for the cosmological constant within a holographic setup, including analysis of stability, fluctuations, and effective gravity regimes.

## Key findings

- Flat-brane solutions are stable and ghost-free.
- A regime of 4D gravity is viable at large distances.
- The model can avoid the vDVZ discontinuity.

## Abstract

We propose a brane-world setup based on gauge/gravity duality in which the four-dimensional cosmological constant is set to zero by a dynamical self-adjustment mechanism. The bulk contains Einstein gravity and a scalar field. We study holographic RG flow solutions, with the standard model brane separating an infinite volume UV region and an IR region of finite volume. For generic values of the brane vacuum energy, regular solutions exist such that the four-dimensional brane is flat. Its position in the bulk is determined dynamically by the junction conditions. Analysis of linear fluctuations shows that a regime of 4-dimensional gravity is possible at large distances, due to the presence of an induced gravity term. The graviton acquires an effective mass, and a five-dimensional regime may exist at large and/or small scales. We show that, for a broad choice of potentials, flat-brane solutions are manifestly stable and free of ghosts. We compute the scalar contribution to the force between brane-localized sources and show that, in certain models, the vDVZ discontinuity is absent and the effective interaction at short distances is mediated by two transverse graviton helicities.