Pedro F. Gonzalez-Diaz

K-essential phantom energy: Doomsday around the corner?

In spite of its rather weird properties which include violation of the dominant-energy condition, the requirement of superluminal sound speed and increasing vacuum-energy density, phantom energy has recently attracted a lot of scientific and popular interests. In this Letter it is shown that in the framework of a general k-essence model, vacuum phantom energy leads to a cosmological scenario having negative sound speed and a big rip singularity, where the field potential also blows up, which might occur at an almost arbitrarily near time in the future that can still be comfortably accommodated within current observational constraints.

You need not be afraid of phantom energy

The author thanks Mariam Bouhmadi and Carmen L. Sigu¨enza for useful conversations. This work was supported by MCYT under Research Project No. BMF2002-03758.

Axion phantom energy

The existence of phantom energy in a universe which evolves to eventually show a big rip doomsday is a possibility which is not excluded by present observational constraints. In this paper it is argued that the field theory associated with a simple quintessence model is compatible with a field definition that is interpretable in terms of a rank-3 axionic tensor field, whenever we consider a perfect-fluid equation of state that corresponds to the phantom energy regime. Explicit expressions for the axionic field and its potential, both in terms of an imaginary scalar field, are derived, which show that these quantities both diverge at the big rip, and that the onset of phantom-energy dominance must take place just at present.

Unified dark energy thermodynamics: varying w and the −1-crossing

We investigate, in a unified and general way, the thermodynamic properties of dark energy with an arbitrary, varying equation-of-state parameter w(a). We find that all quantities are well defined and regular for every w(a), including the −1-crossing, with the temperature being negative in the phantom regime (w(a) −1). The density and entropy are always positive while the chemical potential can be arbitrary. At the −1-crossing, both temperature and chemical potential are zero. The temperature negativity can only be interpreted in the quantum framework. The regular behavior of all quantities at the −1-crossing leads to the conclusion that such a crossing does not correspond to a phase transition, but rather to a smooth crossover.

Achronal cosmic future

The spherically symmetric accretion of dark and phantom energy onto Morris-Thorne wormholes is considered. It is obtained that the accretion of phantom energy leads to a gradual increase of the wormhole throat radius which eventually overtakes the superaccelerated expansion of the Universe and becomes infinite at a time in the future before the occurrence of the big rip singularity. After that time, as it continues accreting phantom energy, the wormhole becomes an Einstein-Rosen bridge whose corresponding mass decreases rapidly and vanishes at the big rip.

Cndo/2 conformational calculation for conjugated and non-conjugated molecular systems

Abstract In order to check the effectiveness of the well known CNDO/2 method for predicting molecular conformations, twenty-six molecular systems, involving B, C, N, O, F, Si, S and Cl atoms, were studied. If these molecules are classified into three groups, according to simple rules, the CNDO/2 method is found to fail systematically in one of them. In this group the twisted bond is expected to be delocalized. It is concluded that the CNDO/2 method is not useful in predicting conformations of molecules in which the twisted bond is delocalized.

On the hydroxyl ions in apatites

Abstract The possible mechanism originating the stretching and librational bands of the OH groups in ir spectra of various apatites are discussed. On the basis of relating the νs frequency of the V3 hindered potential barrier, it is deduced that hydrogen bonds between the OH groups and the nearest Os of PO3−4 ions exist, and that they are responsible for the observed frequencies of the stretching and librational modes. The additional ir OH bands of heated nonstoichiometric hydroxylapatites are also discussed.

Phantom inflation and the “Big Trip”

Abstract Primordial inflation is regarded to be driven by a phantom field which is here implemented as a scalar field satisfying an equation of state p = ω ρ , with ω − 1 . Being even aggravated by the weird properties of phantom energy, this will pose a serious problem with the exit from the inflationary phase. We argue, however, in favor of the speculation that a smooth exit from the phantom inflationary phase can still be tentatively recovered by considering a multiverse scenario where the primordial phantom universe would travel in time toward a future universe filled with usual radiation, before reaching the big rip. We call this transition the “Big Trip” and assume it to take place with the help of some form of anthropic principle which chooses our current universe as being the final destination of the time transition.

Astronomical bounds on a future Big Freeze singularity

It was recently found that dark energy in the form of phantom generalized Chaplygin gas may lead to a new form of a cosmic doomsday, the Big Freeze singularity. Like the Big Rip singularity, the Big Freeze singularity would also take place at finite future cosmic time, but, unlike the Big Rip, it happens for a finite scale factor. Our goal is to test if a universe filled with phantom generalized Chaplygin gas can conform to the data of astronomical observations. We shall see that if the universe is only filled with generalized phantom Chaplygin gas with the equation of state p = −c2s2/ρα with α < −1, then such a model cannot be matched to the observational data; generally speaking, such a universe has an infinite age. To construct more realistic models, one actually need to add dark matter. This procedure results in cosmological scenarios which do not contradict the values of universe age and expansion rate and allow one to estimate how long we are now from the future Big Freeze doomsday.

Quantum state of the multiverse

A third quantization formalism is applied to a simplified multiverse scenario. A well-defined quantum state of the multiverse is obtained which agrees with standard boundary condition proposals. These states are found to be squeezed, and related to accelerating universes: they share similar properties to those obtained previously by Grishchuk and Siderov. We also comment on related works that have criticized the third quantization approach.