The Fate of the Universe: Dark Energy Dilution?

We study the possibility that dark energy decays in the future and the universe stops accelerating. The fact thatthe cosmological observations prefer an equation of state of dark energy smaller than -1 can be a signal that dark energy will decay in the future. This conclusion is based in interpreting a w<-1 as a signal of dark energy interaction with another fluid. We determine the interaction through the cosmological data and extrapolate it into the future. The resulting energy density for dark energy becomes rho=a^{-3(1+w)}e^{-\beta(a-1)}, i.e. it has an exponential suppression for a >> a_o=1. In this scenario the universe ends up dominated by this other fluid, which could be matter, and the universe stops accelerating at some time in the near future.Comment: 5 pages, 3 figure

Notes on Polyphylia Harris with a description of a new species (Coleoptera: Scarabaeidae: Melolonthinae)

Polyphylla aeolus La Rue, new species, is described from the Kelso Sand Dunes, Mojave Desert, San Bernardino County, California, U.S.A. Illustrations of dorsal habitus, significant morphological details, and adult genitalic forms are provided. A description of the type locality including geographical and ecological parameters is presented. Taxonomic problems within the genus and limitations of recently proposed methods of species identification are discussed. A modified key is provided to distinguish the new species. The heretofore undescribed females of Polyphylla anteronivea Hardy, P. mescalerensis Young, P. nubila Van Dyke, and P. pottsorum Hardy, are described. The larval host of P. erratica Hardy is reported, and the adult female is redescribed from pristine specimens. A dorsal habitus illustration of each female is provided. Bionomic and distributional data are presented for Polyphylla avittata Hardy, P. cavifrons LeConte, P. hirsuta Van Dyke, P. monahansensisHardy, P. petiti Guerin, P. stellata Young, andP. squamiventris Cazier

A f(R) gravity without cosmological constant

In this work we consider the possibility of describing the current evolution of the universe, without the introduction of any cosmological constant or dark energy (DE), by modifying the Einstein-Hilbert (EH) action. In the context of the f(R) gravities within the metric formalism, we show that it is possible to find an action without cosmological constant which exactly reproduces the behavior of the EH action with cosmological constant. In addition the f(R) action is analytical at the origin having Minkowski and Schwarzschild as vacuum solutions. The found f(R) action is highly non-trivial and must be written in terms of hypergeometric functions but, in spite of looking somewhat artificial, it shows that the cosmological constant, or more generally the DE, is not a logical necessity.Comment: 5 pages, no figure

Relativity of representations in quantum mechanics

Only the position representation is used in introductory quantum mechanics and the momentum representation is not usually presented until advanced undergraduate courses. To emphasize the relativity of the representations of the abstract formulation of quantum mechanics, two examples of representations related to the operators aX+(1-a)P and (XP+PX)/2 are presented.Comment: 10 pages, no figures, accepted in Am.J.Phy