Vacuum energy and cosmological constant in QFT in curved spacetime

Understand

The cosmological constant term (CC), $\Lambda$, is a pivotal ingredient in the standard model of cosmology or $\Lambda$CDM, but it is a rigid quantity for the entire cosmic history.

• This is unnatural and inconsistent.
• Different theoretical and phenomenological conundrums suggest that the $\Lambda$CDM necessitates further theoretical underpinning to cope with modern observations.
• An interesting approach is the framework of the `running vacuum model' (RVM).