A Universe without Weak Interactions

SLAC-PUB-11795, hep-ph/0604027 A Universe Without Weak Interactions arXiv:hep-ph/0604027v1 4 Apr 2006 Roni Harnik 1 , Graham D. Kribs 2 , and Gilad Perez 3 1 Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94309 and Physics Department, Stanford University, Stanford, CA 94305 2 Department of Physics and Institute of Theoretical Science University of Oregon, Eugene, OR 97403 3 Theoretical Physics Group, Ernest Orlando Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720 roni@slac.stanford.edu, kribs@uoregon.edu, gperez@lbl.gov Abstract A universe without weak interactions is constructed that undergoes big-bang nucleosynthesis, matter domination, structure formation, and star formation. The stars in this universe are able to burn for billions of years, synthesize elements up to iron, and undergo supernova explosions, dispersing heavy elements into the interstellar medium. These definitive claims are supported by a detailed analysis where this hypothetical “Weakless Universe” is matched to our Universe by simultaneously adjusting Standard Model and cosmological parameters. For instance, chemistry and nuclear physics are essentially unchanged. The apparent habitability of the Weakless Universe suggests that the anthropic principle does not determine the scale of electroweak breaking, or even require that it be smaller than the Planck scale, so long as technically natural parameters may be suitably adjusted. Whether the multi-parameter adjustment is realized or probable is dependent on the ultraviolet completion, such as the string landscape. Considering a similar analysis for the cosmological constant, however, we argue that no adjustments of other parameters are able to allow the cosmological constant to raise up even remotely close to the Planck scale while obtaining macroscopic structure. The fine-tuning problems associated with the electroweak breaking scale and the cosmological constant therefore appear to be qualitatively different from the perspective of obtaining a habitable universe.