K-essence: cosmology, causality and emergent geometry

k−Essence, superluminal propagation, causality and emergent geometry

The k-essence theories admit in general the superluminal propagation of the perturbations on classical backgrounds. We show that in spite of the superluminal propagation the causal paradoxes do not arise in these theories and in this respect they are not less safe than General Relativity.

Cosmic Walls and Filaments Formation in Modied Chaplygin Gas Cosmology

We want to study the perturbation growth of an initial seed of an ellipsoidal shape in Top-Hat collapse model of the structure formation in the Modied Chaplygin gas cosmology. Considering reasonable values of the constants and the parameters of the model under study, we can show that a very small deviation from spherical symmetry (ellipsoidal geometry) in the initial seed leads to a nal highly ...

Mythological analysis of kings’ metahuman adjectives in the historiography of the Safavid era

Iranian historiography after Islam indicates the attribution of some metahuman characteristics to kings. This attribution could be studied concerning the culture of the target society in addition to historiographical eloquence. Meanwhile, the two factors of repetition and the existence of similar features in Iran’s ancient cosmology indicate a kind of intellectual coherence. The main issue of t...

A no-go theorem for k-essence dark energy

We demonstrate that if k-essence can solve the coincidence problem and play the role of dark energy in the Universe, the fluctuations of the field have to propagate superluminally at some stage. We argue that this implies that successful k-essence models violate causality. It is not possible to define a time ordered succession of events in a Lorentz invariant way. Therefore, k-essence cannot ar...

Cosmology of F(T) Gravity and k-Essence