Expanding space-time and variable vacuum energy

8th International Workshop DICE2016: Spacetime - Matter - Quantum Mechanics

物理学;力学

Parmeggiani, Claudio^1

University of Milano-Bicocca - (UNIMIB), Italy^1

关键词: Acceleration/deceleration;    Cosmological modeling;    Energy density;    Expansion factors;    Friedmann equation;    Quantum field;    Space-time metric;    Zero-point energies;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/880/1/012024/pdf
DOI  :  10.1088/1742-6596/880/1/012024

学科分类：力学，机械学

来源: IOP

【 摘 要 】

The paper describes a cosmological model which contemplates the presence of a vacuum energy varying, very slightly (now), with time. The constant part of the vacuum energy generated, some 6 Gyr ago, a deceleration/acceleration transition of the metric expansion; so now, in an aged Universe, the expansion is inexorably accelerating. The vacuum energy varying part is instead assumed to be eventually responsible of an acceleration/deceleration transition, which occurred about 14 Gyr ago; this transition has a dynamic origin: it is a consequence of the general relativistic Einstein-Friedmann equations. Moreover, the vacuum energy (constant and variable) is here related to the zero-point energy of some quantum fields (scalar, vector, or spinor); these fields are necessarily described in a general relativistic way: their structure depends on the space-time metric, typically non-flat. More precisely, the commutators of the (quantum field) creation/annihilation operators are here assumed to depend on the local value of the space-time metric tensor (and eventually of its curvature); furthermore, these commutators rapidly decrease for high momentum values and they reduce to the standard ones for a flat metric. In this way, the theory is "gravitationally" regularized; in particular, the zero-point (vacuum) energy density has a well defined value and, for a non static metric, depends on the (cosmic) time. Note that this varying vacuum energy can be negative (Fermi fields) and that a change of its sign typically leads to a minimum for the metric expansion factor (a "bounce").