project title: | Properties of the Lorentz invariant quantum vacuum. |
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project leader: | Prof. Frans Klinkhamer |

access given (in days): | 7 |

access used (in days): | 4 |

status: | COMPLETED |

local host: | Prof. Grigory Volovik |

home institution: | University of Karlsruhe, Karlsruhe |

country of institution: | Germany |

starting date (yyyy-mm-dd): | 2008-03-27 |

objectives: | We are planning to study the self-sustained quantum vacuum -- the vacuum state which can be stable in the absense of external environment. We ate interested in the relativistic vacua which obey Lorent invariance. Different types of the dynamical variable, which chracterizes such a vacuum, will be considered. The main advantage of such vacua is that the adjustment of the vacuum variable to the thermodynamic equilibrium leads to nullification of the vacuum energy density without any fine-tuning. This property of the vacuum can be used as the natural solution of the main cosmological constant problem: why the present vacuum energy is by more 120 orders of magnitude smaller than estimated using the conventional quantum field theory. The effective theory of such vacuua will be constructed. |

achievements: | We found that though the vacuum energy density is governed by processes in the deep ultraviolet vacuum, the thermodynamics of the vacuum energy can be described by a relatively minor extension of the low-energy (infrared) effective theory, namely, by the introduction of a constant vacuum variable. In other words, the cosmological constant problem belongs to the realm of infrared physics. We introduced spacetime-independent variable which characterizes a Lorentz-invariant self-sustained quantum vacuum. For a perfect (Lorentz-invariant) quantum vacuum, the self-tuning of this variable nullifies the effective energy density which enters the low-energy gravitational field equations, and thus nullifies the cosmological constant. The observed small but nonzero value of the cosmological constant is then explained as corresponding to the effective energy density of an imperfect quantum vacuum (perturbed by, e.g., the presence of thermal matter). The paper about that has been published: F.R. Klinkhamer, G.E. Volovik, Self-tuning vacuum variable and cosmological constant, Phys. Rev. D 77, 085015 (2008). |