Why include -xi*H in the equation of state?

AI Thread Summary
The discussion centers on the inclusion of the term -xi*H in the equation of state for a perfect fluid, which is typically expressed as p=w*rho. The term -xi*H is introduced to analyze the dynamics of the system, specifically focusing on the time evolution of density (rho) and the Hubble parameter (H). The relevance of this term lies in its utility for examining the equations for the time derivatives of density and Hubble parameter, allowing for a more comprehensive understanding of the cosmological dynamics. The conversation emphasizes that this inclusion is not about modifying the cosmological constant but rather about solving the dynamical system for rho and H. Ultimately, the term enhances the analysis of cosmological behavior in the context of single fluid cosmology.
odd-socks
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I'm aware that the equation of state for a perfect fluid (when considering single fluid cosmology) is p=w*rho

However I've come across an equation of state of p=w*rho - xi*H, H being Hubble's parameter. However I cannot find an explanation of why you can put this in? Can anyone explain this to me please?

Thanks
 
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It is irrelevant. You wish to inject it into the cosmological constant?
 
its to look at equations for rhodot (d rho/dt) and Hdot (dH/dt) so solve as a dynamical system for rho and H
 

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