Sinks in the landscape, Boltzmann brains and the cosmological constant problem
Abstract
This paper extends a recent investigation of the string theory landscape (Ceresole et al 2006 Phys. Rev. D 74 086010), where it was found that the decay rate of de Sitter (dS) vacua to a collapsing space with a negative vacuum energy can be quite large. The parts of space that experience a decay to a collapsing space, or to a Minkowski vacuum, never return back to dS space. The channels of irreversible vacuum decay serve as sinks for the probability flow. The existence of such sinks is a distinguishing feature of the string theory landscape. We describe relations between several different probability measures for eternal inflation taking into account the existence of the sinks. The local (comoving) description of the inflationary multiverse suffers from the socalled Boltzmann brain (BB) problem unless the probability of the decay to the sinks is sufficiently large. We show that some versions of the global (volumeweighted) description do not have this problem even if one ignores the existence of the sinks. We argue that if the number of different vacua in the landscape is large enough, the anthropic solution of the cosmological constant problem in the string landscape scenario should be valid for a broad class of the probability measures which solve the BB problem. If this is correct, the solution of the cosmological constant problem may be essentially measureindependent. Finally, we describe a simplified approach to the calculations of anthropic probabilities in the landscape, which is less ambitious but also less ambiguous than other methods.
To the memory of Eugene Feinberg, who was trying to make a bridge between science, philosophy and art.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 January 2007
 DOI:
 10.1088/14757516/2007/01/022
 arXiv:
 arXiv:hepth/0611043
 Bibcode:
 2007JCAP...01..022L
 Keywords:

 High Energy Physics  Theory;
 Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Phenomenology
 EPrint:
 42 pages, 5 figures, the paper is substantially extended, a section on the cosmological constant is addeed