Entanglement and Expansion

We study the entanglement entropy resulting from tracing out local degrees of freedom of a quantum scalar field in an expanding universe. It is known that when field modes become superhorizon during inflation they evolve to increasingly squeezed states. We argue that this causes the entanglement entropy to grow continuously as successive modes cross the horizon. The resulting entropy is proportional to the total duration of inflation. It is preserved during a subsequent radiation or matter dominated era, and thus it may be relevant for today's universe. We demonstrate explicitly these features in a toy model of a scalar field in 1+1 dimensions.Comment: 42 pages, 8 figures. v2: references adde

Entanglement of Harmonic Systems in Squeezed States

The entanglement entropy of a free scalar field in its ground state is dominated by an area law term. It is noteworthy, however, that the study of entanglement in scalar field theory has not advanced far beyond the ground state. In this paper, we extend the study of entanglement of harmonic systems, which include free scalar field theory as a continuum limit, to the case of the most general Gaussian states, namely the squeezed states. We find the eigenstates and the spectrum of the reduced density matrix and we calculate the entanglement entropy. Finally, we apply our method to free scalar field theory in 1+1 dimensions and show that, for very squeezed states, the entanglement entropy is dominated by a volume term, unlike the ground-state case. Even though the state of the system is time-dependent in a non-trivial manner, this volume term is time-independent. We expect this behaviour to hold in higher dimensions as well, as it emerges in a large-squeezing expansion of the entanglement entropy for a general harmonic system.Comment: 44 pages + 29 pages appendix, 13 figure

A solution of the coincidence problem based on the recent galactic core black hole mass density increase

A mechanism capable to provide a natural solution to two major cosmological problems, i.e. the cosmic acceleration and the coincidence problem, is proposed. A specific brane-bulk energy exchange mechanism produces a total dark pressure, arising when adding all normal to the brane negative pressures in the interior of galactic core black holes. This astrophysically produced negative dark pressure explains cosmic acceleration and why the dark energy today is of the same order to the matter density for a wide range of the involved parameters. An exciting result of the analysis is that the recent rise of the galactic core black hole mass density causes the recent passage from cosmic deceleration to acceleration. Finally, it is worth mentioning that this work corrects a wide spread fallacy among brane cosmologists, i.e. that escaping gravitons result to positive dark pressure.Comment: 14 pages, 3 figure

Broomrape Species Parasitizing Odontarrhena lesbiaca (Brassicaceae) Individuals Act as Nickel Hyperaccumulators

The elemental defense hypothesis supports that metal hyperaccumulation in plant tissues serves as a mechanism underpinning plant resistance to herbivores and pathogens. In this study, we investigate the interaction between Odontarrhena lesbiaca and broomrape parasitic species, in the light of the defense hypothesis of metal hyperaccumulation. Plant and soil samples collected from three serpentine sites in Lesbos, Greece were analyzed for Ni concentrations. Phelipanche nowackiana and Phelipanche nana were found to infect O. lesbiaca. In both species, Ni concentration decreased gradually from tubercles to shoots and flowers. Specimens of both species with shoot nickel concentrations above 1000 mg.kg−1 were found, showing that they act as nickel hyperaccumulators. Low values of parasite to O. lesbiaca leaf or soil nickel quotients were observed. Orobanche pubescens growing on a serpentine habitat but not in association with O. lesbiaca had very low Ni concentrations in its tissues analogous to excluder plants growing on serpentine soils. Infected O. lesbiaca individuals showed lower leaf nickel concentrations relative to the non-infected ones. Elevated leaf nickel concentration of O. lesbiaca individuals did not prevent parasitic plants to attack them and to hyperaccumulate metals to their tissues, contrary to predictions of the elemental defense hypothesis