19,828 research outputs found
Acceleration and Deceleration in Curvature Induced Phantom Model of the Late and Future Universe, Cosmic Collapse as Well as its Quantum Escape
Here, cosmology of the late and future universe is obtained from
-gravity with non-linear curvature terms and ( being the
Ricci scalar curvature). It is different from -dark enrgy models, where
non-linear curvature terms are taken as gravitational alternative of dark
energy. In the present model, neither linear nor no-linear curvature terms are
taken as dark energy. Rather, dark energy terms are induced by curvature terms
in the Friedmann equation derived from -gravitational equations. It has
advantage over - dark energy models in the sense that the present model
satisfies WMAP results and expands as during matter-dominance.
So, it does not have problems due to which -dark energy models are
criticized. Curvature-induced dark energy, obtained here, mimics phantom.
Different phases of this model, including acceleration and deceleration during
phantom phase, are investigated here.It is found that expansion of the universe
will stop at the age ( being the present
age of the universe) and after this epoch, it will contract and collapse by the
time . Further,it is shown that universe will
escape predicted collapse (obtained using classical mechanics) on making
quantum gravity corrections relevant near collapse time due to extremely high
energy density and large curvature analogous to the state of very early
universe. Interestingly, cosmological constant is also induced here, which is
very small in classical domain, but very high in quantum domain.Comment: 33 page
Fractal Propagators in QED and QCD and Implications for the Problem of Confinement
We show that QED radiative corrections change the propagator of a charged
Dirac particle so that it acquires a fractional anomalous exponent connected
with the fine structure constant. The result is a nonlocal object which
represents a particle with a roughened trajectory whose fractal dimension can
be calculated. This represents a significant shift from the traditional Wigner
notions of asymptotic states with sharp well-defined masses. Non-abelian
long-range fields are more difficult to handle, but we are able to calculate
the effects due to Newtonian gravitational corrections. We suggest a new
approach to confinement in QCD based on a particle trajectory acquiring a
fractal dimension which goes to zero in the infrared as a consequence of
self-interaction, representing a particle which, in the infrared limit, cannot
propagate.Comment: To appear in Brazilian Journal of Physics, special edition for the
proceedings of IRQCD, Rio de Janeiro, 5-9 June 200
Saturation of Transverse Energy per Charged Hadron and Freeze-Out Criteria in Heavy-Ion Collisions
For beam energies from SPS to RHIC, the transverse energy per charged
particle, , saturates at a value of approximately 0.8 GeV.
A direct connection between this value and the freeze-out criterium GeV for the primordial energy and particle number in the hadronic
resonance gas model is established.Comment: 7pages 5 figure
Incidence of Agromyza obtusa Malloch in different varieties of Arhar (Cajanus cajan) (Diptera: Agromyzidae).
Aus unseren Beobachtungen geht klar hervor, dass das stĂ€rkste Vorkommen von Agromyza obtusa Malloch bei den frĂŒhen VarietĂ€ten von Cajanus cajan im Dezember und bei den spĂ€ten VarietĂ€ten im MĂ€rz festzustellen ist.The above observations clearly indicatet that the maximum incidence of Agromyza obtusa Malloch was recorded during the month December in early varieties and March in late varieties of Cajanus cajan
Structure of the species-energy relationship
The relationship between energy availability and species richness (the species-energy relationship) is one of the best documented macroecological phenomena. However, the structure of species distribution along the gradient, the proximate driver of the relationship, is poorly known. Here, using data on the distribution of birds in southern Africa, for which species richness increases linearly with energy availability, we provide an explicit determination of this structure. We show that most species exhibit increasing occupancy towards more productive regions (occurring in more grid cells within a productivity class). However, average reporting rates per species within occupied grid cells, a correlate of local density, do not show a similar increase. The mean range of used energy levels and the mean geographical range size of species in southern Africa decreases along the energy gradient, as most species are present at high productivity levels but only some can extend their ranges towards lower levels. Species turnover among grid cells consequently decreases towards high energy levels. In summary, these patterns support the hypothesis that higher productivity leads to more species by increasing the probability of occurrence of resources that enable the persistence of viable populations, without necessarily affecting local population densities
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