402 research outputs found
Invariance under complex transformations, and its relevance to the cosmological constant problem
In this paper we study a new symmetry argument that results in a vacuum state
with strictly vanishing vacuum energy. This argument exploits the well-known
feature that de Sitter and Anti- de Sitter space are related by analytic
continuation. When we drop boundary and hermiticity conditions on quantum
fields, we get as many negative as positive energy states, which are related by
transformations to complex space. The paper does not directly solve the
cosmological constant problem, but explores a new direction that appears
worthwhile.Comment: Some clarifications and references adde
The mathematical basis for deterministic quantum mechanics
If there exists a classical, i.e. deterministic theory underlying quantum
mechanics, an explanation must be found of the fact that the Hamiltonian, which
is defined to be the operator that generates evolution in time, is bounded from
below. The mechanism that can produce exactly such a constraint is identified
in this paper. It is the fact that not all classical data are registered in the
quantum description. Large sets of values of these data are assumed to be
indistinguishable, forming equivalence classes. It is argued that this should
be attributed to information loss, such as what one might suspect to happen
during the formation and annihilation of virtual black holes.
The nature of the equivalence classes is further elucidated, as it follows
from the positivity of the Hamiltonian. Our world is assumed to consist of a
very large number of subsystems that may be regarded as approximately
independent, or weakly interacting with one another. As long as two (or more)
sectors of our world are treated as being independent, they all must be
demanded to be restricted to positive energy states only. What follows from
these considerations is a unique definition of energy in the quantum system in
terms of the periodicity of the limit cycles of the deterministic model.Comment: 17 pages, 3 figures. Minor corrections, comments and explanations
adde
A symmetry for vanishing cosmological constant: Another realization
A more conventional realization of a symmetry which had been proposed towards
the solution of cosmological constant problem is considered. In this study the
multiplication of the coordinates by the imaginary number in the literature
is replaced by the multiplication of the metric tensor by minus one. This
realization of the symmetry as well forbids a bulk cosmological constant and
selects out dimensional spaces. On contrary to its previous
realization the symmetry, without any need for its extension, also forbids a
possible cosmological constant term which may arise from the extra dimensional
curvature scalar provided that the space is taken as the union of two
dimensional spaces where the usual 4-dimensional space lies at the intersection
of these spaces. It is shown that this symmetry may be realized through
spacetime reflections that change the sign of the volume element. A possible
relation of this symmetry to the E-parity symmetry of Linde is also pointed
out.Comment: The version to appear in PLB. The terms "non-orientable space" and
"extra-dimensional tranlation" are replaced by "space whose volume element
changes sign under extra dimensional reflections" and "extra dimensional
reflections", respectively; and typos are correcte
Vacuum driven accelerated expansion
It has been shown that an improved estimation of quantum vacuum energy can
yield not only acceptable but also experimentally sensible results. The very
idea consists in a straightforward extraction of gravitationally interacting
part of the full quantum vacuum energy by means of gauge transformations. The
implementation of the idea has been performed in the formalism of effective
action, in the language of Schwinger's proper time and the Seeley-DeWitt heat
kernel expansion, in the background of the Friedmann-Robertson-Walker geometry.Comment: 11 pages, 2 figures, minor improvements, final preprint version,
published version:
http://www3.interscience.wiley.com/journal/120847180/abstract, devoted to the
memory of professor Ryszard Raczka on the occasion of the 11th anniversary of
his deat
Human papillomavirus and natural history of cervical intraepithelial neoplasia : clinical consequences
Cervical cancer is the second most common cancer in women world-wide after breast
cancer. Each year, there are approximately 437,000 new cases of invasive cancer of the
cervix diagnosed and more than 200,000 women die from the disease, 79% of which occur in
developing countries. In the Netherlands approximately 715 new cases of cervical cancer
are diagnosed each year with an age-standardised incidence rate of 8,6 new cases per
1 00,000 women. The age-standardised mortality rate for the Netherlands has been estimated
at 2,4 deaths per 1 00,000 women with a total of 234 deaths reported in 1995. The average
age-standardised mortality rate of developing countries is 2,5 f1mes that of industrialised
areas
A symmetry for vanishing cosmological constant
Two different realizations of a symmetry principle that impose a zero
cosmological constant in an extra-dimensional set-up are studied. The symmetry
is identified by multiplication of the metric by minus one. In the first
realization of the symmetry this is provided by a symmetry transformation that
multiplies the coordinates by the imaginary number i. In the second realization
this is accomplished by a symmetry transformation that multiplies the metric
tensor by minus one. In both realizations of the symmetry the requirement of
the invariance of the gravitational action under the symmetry selects out the
dimensions given by D = 2(2n+1), n=0,1,2,... and forbids a bulk cosmological
constant. Another attractive aspect of the symmetry is that it seems to be more
promising for quantization when compared to the usual scale symmetry. The
second realization of the symmetry is more attractive in that it is posible to
make a possible brane cosmological constant zero in a simple way by using the
same symmetry, and the symmetry may be identified by reflection symmetry in
extra dimensions.Comment: Talk in the conference IRGAC 2006, 2nd International Conference on
Quantum Theories and Renormalization Group in Gravity and Cosmology,
Barcelon
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
Renormalization-group running cosmologies and the generalized second law
We explore some thermodynamical consequences of accelerated universes driven
by a running cosmological constant (CC) from the renormalization group (RG).
Application of the generalized second law (GSL) of gravitational thermodynamics
to a framework where the running of the CC goes at the expense of energy
transfer between vacuum and matter, strongly restricts the mass spectrum of a
(hypothetical) theory controlling the CC running. We find that quantum effects
driving the running of the CC should be dominated by a trans-planckian mass
field, in marked contrast with the GUT-scale upper mass bound obtained by
analyzing density perturbations for the running CC. The model shows compliance
with the holographic principle.Comment: 8 pages, final version to appear in Phys. Lett.
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