A thermodynamic origin for the Cohen-Kaplan-Nelson bound

Understand

The Cohen-Kaplan-Nelson bound is imposed on the grounds of logical consistency (with classical General Relativity) upon local quantum field theories.

• This paper puts the bound into the context of a thermodynamic principle applicable to a field with a particular equation of state in an expanding universe.
• This is achieved without overtly appealing to either a decreasing density of states or a minimum coupling requirement, though they might still be consistent with the results described.
• We do so by defining an appropriate Helmholtz free energy which when extremized relative to a key parameter (the Hubble radius L) provides a scaling formula for the entropy with the Hubble radius (an exponent 'r' used in the text).