Energy conditions and cosmic acceleration

Abstract

In general relativity, the energy conditions are invoked to restrict general energy-momentum tensors Tµν in different frameworks, and to derive general results that hold in a variety of general contexts on physical grounds. We show that in the standard Friedmann-Lemaître-Robertson-Walker (FLRW) approach, where the equation of state of the cosmological fluid is unknown, the energy conditions provide model-independent bounds on the behavior of the distance modulus of cosmic sources as a function of the redshift for any spatial curvature. We use the most recent type Ia supernovae (SNe Ia) observations, which include the new Hubble Space Telescope SNe Ia events, to carry out a model-independent analysis of the energy conditions violation in the context of the standard cosmology. We show that both the null (NEC), weak (WEC) and dominant (DEC) conditions, which are associated with the existence of the so-called phantom fields, seem to have been violated only recently (z 0.2), whereas the condition for attractive gravity, i.e., the strong energy condition (SEC) was firstly violated billions of years ago, at z 1.PACS numbers: 98.80. Es, 98.80.Jk

The generalized second law of thermodynamics in the accelerating universe

“…In order to shed some light on the generalized second law in the universe from the obser- The dashed line was plotted by choosing H 0 = 72Kms −1 Mpc −1 , which is the central value of different observations for the present Hubble parameter and this value was also taken in plotting the distance modulus in [11]. It is interesting to see that the data follow the line, but are not exactly on the line.…”

“…Recently, the SNe Ia data have been used to examine the energy conditions' violation in the context of the standard cosmology [11,12].…”

Energy conditions in modified f(G) gravity

“…The well-known Raychaudhuri equations could be considered to discuss the viability of various forms of ECs [43][44][45]. Some of the literature review of ECs were discussed by using the classical ECs of general relativity (GR) like the phantom fields potential [46], the history of expanding universe [47][48][49][50][51][52] and the pattern movement of deceleration parameters [53,54]. The various expression for ECs are derived in f (R) gravity [55] and using these formalism and techniques, some authors have pointed out some issues (cosmological) in f (R) gravity [56][57][58].…”

ENERGY CONDITIONS IN f(R) GRAVITY AND BRANS–DICKE THEORIES

“…where T m µν is the stress-energy tensor of the normal matter as expressed in equation (5). Variation of action (19) with respect to φ gives…”

“…For example, the Hawking-Penrose singularity theorems invoke the WEC and SEC [3], whereas the proof of the second law of black hole thermodynamics requires the NEC [4]. Another example comes from cosmology [5] where energy conditions are studied by using red shifts.…”