Causality Violations in Lovelock Theories

Higher-derivative gravity theories, such as Lovelock theories, generalize Einstein's general relativity (GR). Modifications to GR are expected when curvatures are near Planckian and appear in string theory or supergravity. But can such theories describe gravity on length scales much larger than the Planck cutoff length scale? Here we find causality constraints on Lovelock theories that arise from the requirement that the equations of motion (EOM) of perturbations be hyperbolic. We find a general expression for the "effective metric" in field space when Lovelock theories are perturbed around some symmetric background solution. In particular, we calculate explicitly the effective metric for a general Lovelock theory perturbed around cosmological Friedman-Robertson-Walker backgrounds and for some specific cases when perturbed around Schwarzschild-like solutions. For the EOM to be hyperbolic, the effective metric needs to be Lorentzian. We find that, unlike for GR, the effective metric is generically not Lorentzian when the Lovelock modifications are significant. So, we conclude that Lovelock theories can only be considered as perturbative extensions of GR and not as truly modified theories of gravity. We compare our results to those in the literature and find that they agree with and reproduce the results of previous studies.Comment: Replaced to agree with the published version. Many typos corrected, text revised, results and conclusions unchange

RNA Polymerase-Binding and Transcription Initiation Sites Upstream of the Methyl Reductase Operon of Methanococcus vannielii

RNA Polymerase, purified from Methanococcus vannielii, was shown by exonuclease III footprinting to bind to a 49-base-pair (bp) region of DNA in the intergenic region upstream of mcrB. Sl nuclease protection experiments demonstrated that transcription Initiation in vivo occurs within this region at 32 or 33 bp 5' to the A T G translation initiation codon of mcrB and 19 or 20 bp 3' to a T A T A box

Трансформация исследований риска в сфере культуры в условиях глобализации

У статті розглянуто та охарактеризовано основні підходи до розуміння ризиків. На основі сучасних розробок в сфері дослідження ризику визначено та проаналізовано трансформації та поширення ризиків на всі суспільні відносини за умов динамічної модернізації суспільства. Визначено поле подальших досліджень даної проблеми.In the article basic approaches to understanding risks are considered and described. On the basis of modern risks research transformation and spreading risks in all social relations during dynamic social modernization are defined and analyzed. The field of subsequent researches of the given problem is defined.В статье рассмотрены и даны характеристики основным подходам к пониманию рисков. На основе современных разработок исследования риска определено и проанализированы трансформации и распространение рисков на все общественные отношения в условиях динамической модернизации общества. Определено поле дальнейших исследований данной проблемы

Farm Disease Outlook for 1953

Plant diseases have given us trouble for a long time, and they\u27ll be with us in one form or another in 1953. Here are the highlights of what may happen under different conditions and, in turn, what to do

Seed Cleaning and Treating Pays Off

Seed cleaning and treating is imperative- whether you do it yourself or have it done for you. It pays off in increased stands, fewer weeds and less trouble from certain diseases in oats, wheat, barley, flax, and rye