164 research outputs found
Complex Lagrangians and phantom cosmology
Motivated by the generalization of quantum theory for the case of
non-Hermitian Hamiltonians with PT symmetry, we show how a classical
cosmological model describes a smooth transition from ordinary dark energy to
the phantom one. The model is based on a classical complex Lagrangian of a
scalar field. Specific symmetry properties analogous to PT in non-Hermitian
quantum mechanics lead to purely real equation of motion.Comment: 11 pages, to be published in J.Phys.A, refs. adde
Classical and quantum Big Brake cosmology for scalar field and tachyonic models
We study a relation between the cosmological singularities in classical and
quantum theory, comparing the classical and quantum dynamics in some models
possessing the Big Brake singularity - the model based on a scalar field and
two models based on a tachyon-pseudo-tachyon field . It is shown that the
effect of quantum avoidance is absent for the soft singularities of the Big
Brake type while it is present for the Big Bang and Big Crunch singularities.
Thus, there is some kind of a classical - quantum correspondence, because soft
singularities are traversable in classical cosmology, while the strong Big Bang
and Big Crunch singularities are not traversable.Comment: final version, to appear in Phys. Rev.
Quantum cosmology with big-brake singularity
We investigate a cosmological model with a big-brake singularity in the
future: while the first time derivative of the scale factor goes to zero, its
second time derivative tends to minus infinity. Although we also discuss the
classical version of the model in some detail, our main interest lies in its
quantization. We formulate the Wheeler-DeWitt equation and derive solutions
describing wave packets. We show that all such solutions vanish in the region
of the classical singularity, a behaviour which we interpret as singularity
avoidance. We then discuss the same situation in loop quantum cosmology. While
this leads to a different factor ordering, the singularity is there avoided,
too.Comment: 24 pages, 7 figures, figures improved, references added, conceptual
clarifications include
Phantom universe from CPT symmetric QFT
Inspired by the generalization of quantum theory for the case of
non-Hermitian Hamiltonians with CPT symmetry, we construct a simple classical
cosmological scalar field based model describing a smooth transition from
ordinary dark energy to the phantom one
Tunneling in quantum cosmology: numerical study of particle creation
We consider a minisuperspace model for a closed universe with small and
positive cosmological constant, filled with a massive scalar field conformally
coupled to gravity. In the quantum version of this model, the universe may
undergo a tunneling transition through an effective barrier between regions of
small and large scale factor. We solve numerically the minisuperspace
Wheeler--De Witt equation with tunneling boundary conditions for the wave
function of the universe, and find that tunneling in quantum cosmology is quite
different from that in quantum mechanics. Namely, the matter degree of freedom
gets excited under the barrier, provided its interaction with the scale factor
is not too weak, and makes a strong back reaction onto tunneling. In the
semiclassical limit of small values of cosmological constant, the matter energy
behind the barrier is close to the height of the barrier: the system ``climbs
up'' the barrier, and then evolves classically from its top. These features are
even more pronounced for inhomogeneous modes of matter field. Extrapolating to
field theory we thus argue that high momentum particles are copiously created
in the tunneling process. Nevertheless, we find empirical evidence for the
semiclassical-type scaling with the cosmological constant of the wave function
under and behind the barrier.Comment: 29 pages, 17 figure
Spin-Raising Operators and Spin-3/2 Potentials in Quantum Cosmology
Local boundary conditions involving field strengths and the normal to the
boundary, originally studied in anti-de Sitter space-time, have been recently
considered in one-loop quantum cosmology. This paper derives the conditions
under which spin-raising operators preserve these local boundary conditions on
a 3-sphere for fields of spin 0,1/2,1,3/2 and 2. Moreover, the two-component
spinor analysis of the four potentials of the totally symmetric and independent
field strengths for spin 3/2 is applied to the case of a 3-sphere boundary. It
is shown that such boundary conditions can only be imposed in a flat Euclidean
background, for which the gauge freedom in the choice of the potentials
remains.Comment: 13 pages, plain-tex, recently appearing in Classical and Quantum
Gravity, volume 11, April 1994, pages 897-903. Apologies for the delay in
circulating the file, due to technical problems now fixe
The Complex Symmetry Gravitational Theory as a New Alternative of Dark Energy
We propose that complex symmetry gravitational theory (CSGT) explain the
accelerating expansion of universe. In this paper universe is taken as the
double complex symmetric space. Cosmological solution is obtained within CSGT.
The conditions of the accelerating expansion of universe are discussed within
CSGT. Moreover, the range of equation of state of matter is
given in the hyperbolic imaginary space.Comment: Latex 9 pages, submitted to International Journal of Theoretical
Physic
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