62 research outputs found
Topological entropy for some isotropic cosmological models
The chaotical dynamics is studied in different Friedmann-Robertson- Walker
cosmological models with scalar (inflaton) field and hydrodynamical matter. The
topological entropy is calculated for some particular cases. Suggested scheme
can be easily generalized for wide class of models. Different methods of
calculation of topological entropy are compared.Comment: Final version to appear in Phys. Rev D. Minor changes, typos
corrected; 29 pages with 2 eps figure
Gravitons in One-Loop Quantum Cosmology: Correspondence Between Covariant and Non-Covariant Formalisms
The discrepancy between the results of covariant and non-covariant one-loop
calculations for higher-spin fields in quantum cosmology is analyzed. A
detailed mode-by-mode study of perturbative quantum gravity about a flat
Euclidean background bounded by two concentric 3-spheres, including
non-physical degrees of freedom and ghost modes, leads to one-loop amplitudes
in agreement with the covariant Schwinger-DeWitt method. This calculation
provides the generalization of a previous analysis of fermionic fields and
electromagnetic fields at one-loop about flat Euclidean backgrounds admitting a
well-defined 3+1 decomposition.Comment: 29 pages, latex, recently appearing in Physical Review D, volume 50,
pages 6329-6337, November 1994. The authors apologize for the delay in
circulating the paper, due to technical problems now fixe
Relativistic Gauge Conditions in Quantum Cosmology
This paper studies the quantization of the electromagnetic field on a flat
Euclidean background with boundaries. One-loop scaling factors are evaluated
for the one-boundary and two-boundary backgrounds. The mode-by-mode analysis of
Faddeev-Popov quantum amplitudes is performed by using zeta-function
regularization, and is compared with the space-time covariant evaluation of the
same amplitudes. It is shown that a particular gauge condition exists for which
the corresponding operator matrix acting on gauge modes is in diagonal form
from the beginning. Moreover, various relativistic gauge conditions are studied
in detail, to investigate the gauge invariance of the perturbative quantum
theory.Comment: 26 pages, plain TeX, no figure
Comment about UV regularization of basic commutators in string theories
Recently proposed by Hwang, Marnelius and Saltsidis zeta regularization of
basic commutators in string theories is generalized to the string models with
non-trivial vacuums. It is shown that implementation of this regularization
implies the cancellation of dangerous terms in the commutators between Virasoro
generators, which break Jacobi identity.Comment: LaTeX, 9 pages, no figures, submitted to Physics Letters
A generalisation of the Heckmann - Schucking cosmological solution
An exact solution of the Einstein equations for a Bianchi -I universe in the
presence of dust, stiff matter and cosmological constant, generalising the
well-known Heckmann-Schucking solution is presented. PACS: 04.20-q; 04.20.Dw
Keywords: Exact cosmological solutionsComment: LaTeX file, 10 pages. Physics Letters B, to appea
Quantum origin of the early inflationary Universe
We give a detailed presentation of a recently proposed mechanism of
generating the energy scale of inflation by loop effects in quantum cosmology.
We discuss the quantum origin of the early inflationary Universe from the
no-boundary and tunneling quantum states and present a universal effective
action algorithm for the distribution function of chaotic inflationary
cosmologies in both of these states. The energy scale of inflation is
calculated by finding a sharp probability peak in this distribution function
for a tunneling model driven by the inflaton field with large negative constant
of non-minimal interaction. The sub-Planckian parameters of this peak
(the mean value of the corresponding Hubble constant , its
quantum width and the number of inflationary
e-foldings ) are found to be in good correspondence with the
observational status of inflation theory, provided the coupling constants of
the theory are constrained by a condition which is likely to be enforced by the
(quasi) supersymmetric nature of the sub-Planckian particle physics model.Comment: 43 pages, LaTeX, figures not include
Hamiltonian BFV-BRST theory of closed quantum cosmological models
We introduce and study a new discrete basis of gravity constraints by making
use of harmonic expansion for closed cosmological models. The full set of
constraints is splitted into area-preserving spatial diffeomorphisms, forming
closed subalgebra, and Virasoro-like generators. Operatorial Hamiltonian
BFV-BRST quantization is performed in the framework of perturbative expansion
in the dimensionless parameter which is a positive power of the ratio of
Planckian volume to the volume of the Universe. For the (N+1) - dimensional
generalization of stationary closed Bianchi-I cosmology the nilpotency
condition for the BRST operator is examined in the first quantum approximation.
It turns out, that certain relationship between dimensionality of the space and
the spectrum of matter fields emerges from the requirement of quantum
consistency of the model.Comment: 28 pages, LaTe
Palatini approach to 1/R gravity and its implications to the late Universe
By applying the Palatini approach to the 1/R-gravity model it is possible to
explain the present accelerated expansion of the Universe. Investigation of the
late Universe limiting case shows that: (i) due to the curvature effects the
energy-momentum tensor of the matter field is not covariantly conserved; (ii)
however, it is possible to reinterpret the curvature corrections as sources of
the gravitational field, by defining a modified energy-momentum tensor; (iii)
with the adoption of this modified energy-momentum tensor the Einstein's field
equations are recovered with two main modifications: the first one is the
weakening of the gravitational effects of matter whereas the second is the
emergence of an effective varying "cosmological constant"; (iv) there is a
transition in the evolution of the cosmic scale factor from a power-law scaling
to an asymptotically exponential scaling ; (v) the energy density of the matter field scales as ; (vi) the present age of the Universe and the
decelerated-accelerated transition redshift are smaller than the corresponding
ones in the CDM model.Comment: 5 pages and 2 figures. Accepted in PR
Effective equations of motion and initial conditions for inflation in quantum cosmology
We obtain effective equations of inflationary dynamics for the mean inflaton
and metric fields in the no-boundary and tunneling quantum states of the
Universe. In the slow roll approximation (taking the form of the local
Schwiger-DeWitt expansion) effective equations follow from the Euclidean
effective action on the DeSitter gravitational instanton. Effective equations
are applied in the model of the inflaton scalar field coupled to the GUT sector
of matter fields and also having a strong nonminimal coupling to the curvature.
The inverse of its big negative nonminimal coupling constant, serves as a small
parameter of the slow roll expansion and semiclassical expansion of quantum
gravitational effects. As a source of initial conditions we use a sharp
probability peak recently obtained in the one-loop approximation for the
no-boundary and tunneling quantum states and belonging (in virtue of a strong
nonminimal coupling) to the GUT energy scale much below the Planck scale. The
obtained equations in the tunneling quantum state predict a finite duration of
inflationary stage compatible with the observational status of inflation
theory, whereas for the no-boundary state they lead to the infinite
inflationary epoch with a constant inflaton field.Comment: 23 pages, LaTe
Cosmological Unparticle Correlators
We introduce and study an extension of the correlator of unparticle matter
operators in a cosmological environment. Starting from FRW spaces we specialize
to a de Sitter spacetime and derive its inflationary power spectrum which we
find to be almost flat. We finally investigate some consequences of requiring
the existence of a unitary boundary conformal field theory in the framework of
the dS/CFT correspondence.Comment: 8 pages, 1 figure, to appear on Phys. Lett.
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