Low Vacuum Energy Research Articles

An explanation for the tiny value of the cosmological constant and the low vacuum energy density

The paper aims to provide an explanation for the tiny value of the cosmological constant and the low vacuum energy density to represent the dark energy. To accomplish this, we will search for a fundamental principle of symmetry in space-time by means of the elimination of the classical idea of rest, by including an invariant minimum limit of speed in the subatomic world. Such a minimum speed, unattainable by particles, represents a preferred reference frame associated with a background field that breaks down the Lorentz symmetry. The metric of the flat space-time shall include the presence of a uniform vacuum energy density, which leads to a negative pressure at cosmological length scales. Thus, the equation of state for the cosmological constant [$p$(pressure)$=- \epsilon$ (energy density)] naturally emerges from such a space-time with an energy barrier of a minimum speed. The tiny values of the cosmological constant and the vacuum energy density will be successfully obtained, being in agreement with the observational results of Perlmutter, Schmidt and Riess.

Flux compactifications grow lumps

The simplest flux compactifications are highly symmetric---a $q$-form flux is wrapped uniformly around an extra-dimensional $q$-sphere. In this paper, we investigate solutions that break the internal SO($q+1$) symmetry down to SO$(q)\times\mathbb Z_2$; we find a large number of such lumpy solutions, and show that often at least one of them has lower vacuum energy, larger entropy, and is more stable than the symmetric solution. We construct the phase diagram of lumpy solutions, and provide an interpretation in terms of an effective potential. Finally, we provide evidence that the perturbatively stable vacua have a non-perturbative instability to spontaneously sprout lumps; we give an estimate of the decay rate and argue that generically it is exponentially faster than all other known decays.

Thin-shell bubbles and information loss problem in anti de Sitter background

We study the motion of thin-shell bubbles and their tunneling in anti de Sitter (AdS) background. We are interested in the case when the outside of a shell is a Schwarzschild-AdS space (false vacuum) and the inside of it is an AdS space with a lower vacuum energy (true vacuum). If a collapsing true vacuum bubble is created, classically it will form a Schwarzschild-AdS black hole. However, this collapsing bubble can tunnel to a bouncing bubble that moves out to spatial infinity. Then, although the classical causal structure of a collapsing true vacuum bubble has the singularity and the event horizon, quantum mechanically the wavefunction has support for a history without any singularity nor event horizon which is mediated by the non-perturbative, quantum tunneling effect. This may be regarded an explicit example that shows the unitarity of an asymptotic observer in AdS, while a classical observer who only follows the most probable history effectively lose information due to the formation of an event horizon.

PROPERTIES OF A FUTURE SUSY UNIVERSE

In the string landscape picture, the effective potential is characterized by an enormous number of local minima of which only a minuscule fraction are suitable for the evolution of life. In this "multiverse", random transitions are continually made between the various minima with the most likely transitions being to minima of lower vacuum energy. The inflationary era in the very early universe ended with such a transition to our current phase which is described by a broken supersymmetry and a small, positive vacuum energy. However, it is likely that an exactly supersymmetric (susy) phase of zero vacuum energy as in the original superstring theory also exists and that, at some time in the future, there will be a transition to this susy world. In this article we make some preliminary estimates of the consequences of such a transition.

Effects of phase transitions on the evolution of the early universe

In spontaneously broken gauge theories, the gauge symmetry is restored at high temperatures, i.e., in the early universe. As the universe cools, it undergoes a phase transition from the symmetric to asymmetric phase. We examine two interesting cosmological effects of such phase transitions in detail. First, the latent heat released in the SU(2) x U(1)..-->..U(1) phase transition will decrease the previously generated baryon number to entropy ratio. This decrease is calculated as a function of the Higgs meson mass, and the range of Higgs masses for which this decrease is significant (and perhaps unacceptably large) is found. Second, the observation that the present universe has a low vacuum energy density (cosmological constant) implies that, prior to symmetry breakdown, the universe had a very large vacuum energy density, and this large energy density may have had an effect on the expansion of the universe. We show that, in any phase transition, there exists a range of parameters for which the vacuum energy dominates the radiation energy for a short time, causing an exponential cosmic expansion; the corresponding range of Higgs masses in SU(2) x U(1) is found. A suggestion that the large vacuum energy could reverse the collapse of a collapsingmore » universe is investigated, and it is shown that such a ''bounce'' will not occur within the framework of perturbative gauge theories, unless the vacuum energy always dominates the radiation density before the bounce, a condition not satisfied by our present universe.« less