219 research outputs found
Switching model with two habitats and a predator involving group defence
Switching model with one predator and two prey species is considered. The
prey species have the ability of group defence. Therefore, the predator will be
attracted towards that habitat where prey are less in number. The stability
analysis is carried out for two equilibrium values. The theoretical results are
compared with the numerical results for a set of values. The Hopf bifuracation
analysis is done to support the stability results
Non-adiabatic geometrical quantum gates in semiconductor quantum dots
In this paper we study the implementation of non-adiabatic geometrical
quantum gates with in semiconductor quantum dots. Different quantum information
enconding/manipulation schemes exploiting excitonic degrees of freedom are
discussed. By means of the Aharanov-Anandan geometrical phase one can avoid the
limitations of adiabatic schemes relying on adiabatic Berry phase; fast
geometrical quantum gates can be in principle implementedComment: 5 Pages LaTeX, 10 Figures include
Thick de Sitter 3-Branes, Dynamic Black Holes and Localization of Gravity
The embedding of a thick de Sitter 3-brane into a five-dimensional bulk is
studied, assuming a scalar field with potential is present in the bulk. A class
of solutions is found in closed form that can represent a thick de Sitter
3-brane interpolating either between two dynamical black holes with a topology or between two Rindler-like spacetimes with a topology. The gravitational field is localized in a small region near
the center of the 3-brane. The analysis of graviton fluctuations shows that a
zero mode exists and separates itself from a set of continuous modes by a mass
gap. The existence of such a mass gap is shown to be universal. The scalar
perturbations are also studied and shown to be stable.Comment: the study of scalar perturbations and some relevant references have
been added. The most used definition for mass in de Sitter space has been
adopte
The Large Magellanic Cloud and the Distance Scale
The Magellanic Clouds, especially the Large Magellanic Cloud, are places
where multiple distance indicators can be compared with each other in a
straight-forward manner at considerable precision. We here review the distances
derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing
Binaries, and show that the results from these distance indicators generally
agree to within their errors, and the distance modulus to the Large Magellanic
Cloud appears to be defined to 3% with a mean value of 18.48 mag, corresponding
to 49.7 Kpc. The utility of the Magellanic Clouds in constructing and testing
the distance scale will remain as we move into the era of Gaia.Comment: 23 pages, accepted for publication in Astrophysics and Space Science.
From a presentation at the conference The Fundamental Cosmic Distance Scale:
State of the Art and the Gaia Perspective, Naples, May 201
Large-scale magnetic fields from inflation in dilaton electromagnetism
The generation of large-scale magnetic fields is studied in dilaton
electromagnetism in inflationary cosmology, taking into account the dilaton's
evolution throughout inflation and reheating until it is stabilized with
possible entropy production. It is shown that large-scale magnetic fields with
observationally interesting strength at the present time could be generated if
the conformal invariance of the Maxwell theory is broken through the coupling
between the dilaton and electromagnetic fields in such a way that the resultant
quantum fluctuations in the magnetic field has a nearly scale-invariant
spectrum. If this condition is met, the amplitude of the generated magnetic
field could be sufficiently large even in the case huge amount of entropy is
produced with the dilution factor as the dilaton decays.Comment: 28 pages, 5 figures, the version accepted for publication in Phys.
Rev. D; some references are adde
Current constraints on Cosmological Parameters from Microwave Background Anisotropies
We compare the latest observations of Cosmic Microwave Background (CMB)
Anisotropies with the theoretical predictions of the standard scenario of
structure formation. Assuming a primordial power spectrum of adiabatic
perturbations we found that the total energy density is constrained to be
while the energy density in baryon and Cold Dark
Matter (CDM) are and ,
(all at 68% C.L.) respectively. The primordial spectrum is consistent with
scale invariance, () and the age of the universe is
Gyrs. Adding informations from Large Scale Structure and
Supernovae, we found a strong evidence for a cosmological constant
and a value of the Hubble parameter
. Restricting this combined analysis to flat universes, we put
constraints on possible 'extensions' of the standard scenario. A gravity waves
contribution to the quadrupole anisotropy is limited to be (95%
c.l.). A constant equation of state for the dark energy component is bound to
be (95% c.l.). We constrain the effective relativistic degrees
of freedom and the neutrino chemical potential and (massless neutrinos).Comment: The status of cosmological parameters before WMAP. In press on Phys.
Rev. D., Rapid Communication, 6 pages, 5 figure
Production and dilution of gravitinos by modulus decay
We study the cosmological consequences of generic scalar fields like moduli
which decay only through gravitationally suppressed interactions. We consider a
new production mechanism of gravitinos from moduli decay, which might be more
effective than previously known mechanisms, and calculate the final
gravitino-to-entropy ratio to compare with the constraints imposed by
successful big bang nucleosynthesis (BBN) etc., taking possible hadronic decays
of gravitinos into account. We find the modulus mass smaller than
TeV is excluded. On the other hand, inflation models with high reheating
temperatures GeV can be compatible with BBN thanks
to the late-time entropy production from the moduli decay if model parameters
are appropriately chosen.Comment: 18 pages, 4 figures, to appear in Phys. Rev.
Cosmic acceleration from second order gauge gravity
We construct a phenomenological theory of gravitation based on a second order
gauge formulation for the Lorentz group. The model presents a long-range
modification for the gravitational field leading to a cosmological model
provided with an accelerated expansion at recent times. We estimate the model
parameters using observational data and verify that our estimative for the age
of the Universe is of the same magnitude than the one predicted by the standard
model. The transition from the decelerated expansion regime to the accelerated
one occurs recently (at ).Comment: RevTex4 15 pages, 1 figure. Accepted for publication in Astrophysics
& Space Scienc
Simplifying Algebra in Feynman Graphs, Part III: Massive Vectors
A T-dualized selfdual inspired formulation of massive vector fields coupled
to arbitrary matter is generated; subsequently its perturbative series modeling
a spontaneously broken gauge theory is analyzed. The new Feynman rules and
external line factors are chirally minimized in the sense that only one type of
spin index occurs in the rules. Several processes are examined in detail and
the cross-sections formulated in this approach. A double line formulation of
the Lorentz algebra for Feynman diagrams is produced in this formalism, similar
to color ordering, which follows from a spin ordering of the Feynman rules. The
new double line formalism leads to further minimization of gauge invariant
scattering in perturbation theory. The dualized electroweak model is also
generated.Comment: 39 pages, LaTeX, 8 figure
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