3,283 research outputs found
Interaction of massless Dirac field with a Poincar\'e gauge field
In this paper we consider a model of Poincar\'e gauge theory (PGT) in which a
translational gauge field and a Lorentz gauge field are actually identified
with the Einstein's gravitational field and a pair of ``Yang-Mills'' field and
its partner, respectively.In this model we re-derive some special solutions and
take up one of them. The solution represents a ``Yang-Mills'' field without its
partner field and the Reissner-Nordstr\"om type spacetime, which are generated
by a PGT-gauge charge and its mass.It is main purpose of this paper to
investigate the interaction of massless Dirac fields with those fields. As a
result, we find an interesting fact that the left-handed massless Dirac fields
behave in the different manner from the right-handed ones. This can be
explained as to be caused by the direct interaction of Dirac fields with the
``Yang-Mills'' field. Accordingly, the phenomenon can not happen in the
behavior of the neutrino waves in ordinary Reissner-Nordstr\"om geometry. The
difference between left- and right-handed effects is calculated quantitatively,
considering the scattering problems of the massless Dirac fields by our
Reissner-Nordstr\"om type black-hole.Comment: 10pages, RevTeX3.
High Power Gamma-Ray Flash Generation in Ultra Intense Laser-Plasma Interaction
When high-intensity laser interaction with matter enters the regime of
dominated radiation reaction, the radiation losses open the way for producing
short pulse high power gamma ray flashes. The gamma-ray pulse duration and
divergence are determined by the laser pulse amplitude and by the plasma target
density scale length. On the basis of theoretical analysis and particle-in-cell
simulations with the radiation friction force incorporated, optimal conditions
for generating a gamma-ray flash with a tailored overcritical density target
are found.Comment: 12 pages, 5 figures Accepted for publication in Physical Review
Letters (this http://prl.aps.org/
Plant sexual reproduction during climate change: gene function in natura studied by ecological and evolutionary systems biology
Background It is essential to understand and predict the effects of changing environments on plants. This review focuses on the sexual reproduction of plants, as previous studies have suggested that this trait is particularly vulnerable to climate change, and because a number of ecologically and evolutionarily relevant genes have been identified. Scope It is proposed that studying gene functions in naturally fluctuating conditions, or gene functions in natura, is important to predict responses to changing environments. First, we discuss flowering time, an extensively studied example of phenotypic plasticity. The quantitative approaches of ecological and evolutionary systems biology have been used to analyse the expression of a key flowering gene, FLC, of Arabidopsis halleri in naturally fluctuating environments. Modelling showed that FLC acts as a quantitative tracer of the temperature over the preceding 6 weeks. The predictions of this model were verified experimentally, confirming its applicability to future climate changes. Second, the evolution of self-compatibility as exemplifying an evolutionary response is discussed. Evolutionary genomic and functional analyses have indicated that A. thaliana became self-compatible via a loss-of-function mutation in the male specificity gene, SCR/SP11. Self-compatibility evolved during glacial-interglacial cycles, suggesting its association with mate limitation during migration. Although the evolution of self-compatibility may confer short-term advantages, it is predicted to increase the risk of extinction in the long term because loss-of-function mutations are virtually irreversible. Conclusions Recent studies of FLC and SCR have identified gene functions in natura that are unlikely to be found in laboratory experiments. The significance of epigenetic changes and the study of non-model species with next-generation DNA sequencers is also discusse
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