A Symmetry for the Cosmological Constant

TL;DR

Addresses the cosmological constant naturalness problem by introducing a discrete energy-parity symmetry that pairs the Standard Model with a ghost copy to cancel vacuum contributions to the cosmological constant, leaving a bare term $\rho_0$. The framework enforces equal-and-opposite vacuum energies between the visible and ghost sectors, with gravity weakly breaking the symmetry at short distances and a graviton momentum cutoff $\mu$ setting the scale for quantum gravity corrections of order ${\cal O}(\mu^4)$, so that $\rho_0 \sim {\cal O}(\mu^4)$. To suppress rapid vacuum decay, gravitational Lorentz violation must occur at scales near $\mu$, and inflation can produce the required initial conditions by emptying the ghost sector. The scenario yields testable predictions for sub-millimeter gravity and connects early-universe dynamics to late-time vacuum energy.

Abstract

We study a symmetry, schematically Energy -> - Energy, which suppresses matter contributions to the cosmological constant. The requisite negative energy fluctuations are identified with a "ghost" copy of the Standard Model. Gravity explicitly, but weakly, violates the symmetry, and naturalness requires General Relativity to break down at short distances with testable consequences. If this breakdown is accompanied by gravitational Lorentz-violation, the decay of flat spacetime by ghost production is acceptably slow. We show that inflation works in our scenario and can lead to the initial conditions required for standard Big Bang cosmology.