In this Letter we investigated the constraints imposed by the
GSL on modified Friedmann equations that arise from quantum
corrections to the entropy-area relation, Eq. (1). As is well known,
the GSL is a powerful tool to set bounds on astrophysical and cosmological
models—see e.g. [27–30].
Cosmological equations follow either from Jacobson’s approach,
that connects gravity to thermodynamics by associating Einstein
equations to Clausius relation (6), or Padmanabhan’s suggestion
that relates gravity (i.e., Einstein equations) to microscopic degrees
of freedom through the principle of equipartition of energy (2).
We analyzed two entropy-area terms, logarithmic (3), and powerlaw
corrections (4), the former coming from loop quantum gravity,
the latter from the entanglement of quantum fields.
Both quantum corrections have been widely investigated but,
since they come from very different techniques, one should not be
surprised that total agreement on these corrections is still missing.
In particular, there is a lack of consensus on the value of
the constant parameter α. Our work aimed to discriminate among
quantum corrections by requiring, via a classical analysis, the GSL
to be fulfilled throughout the evolution of the Universe. This sets
constraints on the value of the parameter.
We first investigated the intervals of values of α compatible
with the GSL by assuming that the DEC holds true for the perfect
fluid that sources the gravitational field of the FRW universe. In the
case of logarithmic corrections to the horizon entropy this gives a
wide range, in which positive values are largely favored, with no
upper bound in the case of the modified Friedmann equation derived
from Clausius relation. Negative values of α are consistent
with the GSL only up to α = −1/4, hence discarding two negative
values that have been suggested in the literature, namely,
In this Letter we investigated the constraints imposed by the
GSL on modified Friedmann equations that arise from quantum
corrections to the entropy-area relation, Eq. (1). As is well known,
the GSL is a powerful tool to set bounds on astrophysical and cosmological
models—see e.g. [27–30].
Cosmological equations follow either from Jacobson’s approach,
that connects gravity to thermodynamics by associating Einstein
equations to Clausius relation (6), or Padmanabhan’s suggestion
that relates gravity (i.e., Einstein equations) to microscopic degrees
of freedom through the principle of equipartition of energy (2).
We analyzed two entropy-area terms, logarithmic (3), and powerlaw
corrections (4), the former coming from loop quantum gravity,
the latter from the entanglement of quantum fields.
Both quantum corrections have been widely investigated but,
since they come from very different techniques, one should not be
surprised that total agreement on these corrections is still missing.
In particular, there is a lack of consensus on the value of
the constant parameter α. Our work aimed to discriminate among
quantum corrections by requiring, via a classical analysis, the GSL
to be fulfilled throughout the evolution of the Universe. This sets
constraints on the value of the parameter.
We first investigated the intervals of values of α compatible
with the GSL by assuming that the DEC holds true for the perfect
fluid that sources the gravitational field of the FRW universe. In the
case of logarithmic corrections to the horizon entropy this gives a
wide range, in which positive values are largely favored, with no
upper bound in the case of the modified Friedmann equation derived
from Clausius relation. Negative values of α are consistent
with the GSL only up to α = −1/4, hence discarding two negative
values that have been suggested in the literature, namely,
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