Abstract
We modify and extend an earlier proposal by Brown and Teitelboim to relax the effective cosmological term by nucleation of branes coupled to a three-index gauge potential. Microscopic considerations from string/M theory suggest two major innovations in the framework. First, the dependence of brane properties on the compactification of extra dimensions may generate a very small quantized unit for jumps in the effective cosmological term. Second, internal degrees of freedom for multiply coincident branes may enhance tunneling rates by exponentially large density of states factors. These new features essentially alter the relaxation dynamics. By requiring stability on the scale of the lifetime of the universe, rather than absolute stability, we derive a non-trivial relation between the supersymmetry breaking scale and the value of the cosmological term. It is plausibly, though not certainly, satisfied in Nature.
Highlights
Both the Casimir effect of quantum theory and the existence of symmetrybreaking condensates in both the strong and the electroweak sectors of the Standard Model indicate that empty space is a dynamical medium that ‘ought to’ have a large mass density, gravity, which couples universally to mass, does not reveal it
Various mechanisms have been proposed to address this problem, but so far none has won wide acceptance. This situation is especially challenging for string theory, and its conjectured non-perturbative definition M theory, in as much as string theory is proposed as a fully specified dynamical theory of gravity
In the two sections, we discuss features of string theory that may alleviate these difficulties: in Sec. 3 we describe the possibility of small charge densities and tensions arising from compactification, and in Sec. 4 we note the relevance of exponentially large density of states factors
Summary
Both the Casimir effect of quantum theory and the existence of symmetrybreaking condensates in both the strong and the electroweak sectors of the Standard Model indicate that empty space is a dynamical medium that ‘ought to’ have a large mass density, gravity, which couples universally to mass, does not reveal it. If the steps between adjacent false vacua are sufficiently small, and if there is a reason why vacuum decay stops or slows down dramatically as Λeff → 0, this mechanism could in principle relax a large microscopic cosmological term (arising from all sources other than the membrane-F field dynamics) to a value within observational bounds. In their pioneering work, Abbott, and Brown and Teitelboim, postulated dynamical entities ad hoc, with no richer context to enhance their credibility or connect them to other problems and facts of physics.
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