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Lisa Randall

Publications and source records attributed to Lisa Randall.

6 recordsLinked to original sources
PubMed2005

Relaxing to three dimensions.

We propose a new selection principle for distinguishing among possible vacua that we call the "relaxation principle." The idea is that the Universe will naturally select among possible vacua through its cosmological evolution, and the configuration with the biggest filling fraction is the likeliest. We apply this idea to the question of the number of dimensions of space. We show that under conventional (but higher-dimensional) Friedmann-Robertson-Walker evolution, a universe filled with equal numbers of branes and antibranes will naturally come to be dominated by 3-branes and 7-branes. We show why this might explain the number of dimensions that are experienced in our visible Universe.

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PubMed2004

Dynamical approach to the cosmological constant.

We consider a dynamical approach to the cosmological constant. There is a scalar field with a potential whose minimum occurs at a generic, but negative, value for the vacuum energy, and it has a nonstandard kinetic term whose coefficient diverges at zero curvature as well as the standard kinetic term. Because of the divergent coefficient of the kinetic term, the lowest energy state is never achieved. Instead, the cosmological constant automatically stalls at or near zero. The merit of this model is that it is stable under radiative corrections and leads to stable dynamics, despite the singular kinetic term. The model is not complete, however, in that some reheating is required. Nonetheless, our approach can at the very least reduce fine-tuning by 60 orders of magnitude or provide a new mechanism for sampling possible cosmological constants and implementing the anthropic principle.

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PubMed2003

Extranatural inflation.

We present a new model of inflation in which the inflaton is the extra component of a gauge field in a 5D theory compactified on a circle. The chief merit of this model is that the potential comes only from nonlocal effects so that its flatness is not spoiled by higher-dimensional operators or quantum gravity corrections. The model predicts a red spectrum (n approximately 0.96) and a significant production of gravitational waves (r approximately 0.11). We also comment on the relevance of this idea to quintessence.

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PubMed2002

Extra dimensions and warped geometries.

The field of extra dimensions, as well as the hypothesized sizes of extra dimensions, have grown by leaps and bounds over the past few years. I summarize the new results and the reasons for the recent activity in this field. These include the observations that extra dimensions can be macroscopic or even infinite in size. Another new development is the application of extra dimensions to the determination of particle physics parameters and properties.

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PubMed2002

Unification and hierarchy from 5D anti-de Sitter space.

We show that perturbative high scale unification and a solution to the hierarchy problem are possible with extra dimensions in the context of the warped geometry of 5D anti-de Sitter space ( AdS(5)). This is possible because the couplings for bulk gauge bosons run logarithmically below the AdS(5) curvature scale. The calculation is done in five dimensions, rather than in the effective theory, which is strongly coupled above the TeV scale.

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