13 research outputs found
Triad representation of the Chern-Simons state in quantum gravity
We investigate a triad representation of the Chern-Simons state of quantum
gravity with a non-vanishing cosmological constant. It is shown that the
Chern-Simons state, which is a well-known exact wavefunctional within the
Ashtekar theory, can be transformed to the real triad representation by means
of a suitably generalized Fourier transformation, yielding a complex integral
representation for the corresponding state in the triad variables. It is found
that topologically inequivalent choices for the complex integration contour
give rise to linearly independent wavefunctionals in the triad representation,
which all arise from the one Chern-Simons state in the Ashtekar variables. For
a suitable choice of the normalization factor, these states turn out to be
gauge-invariant under arbitrary, even topologically non-trivial
gauge-transformations. Explicit analytical expressions for the wavefunctionals
in the triad representation can be obtained in several interesting asymptotic
parameter regimes, and the associated semiclassical 4-geometries are discussed.
In restriction to Bianchi-type homogeneous 3-metrics, we compare our results
with earlier discussions of homogeneous cosmological models. Moreover, we
define an inner product on the Hilbert space of quantum gravity, and choose a
natural gauge-condition fixing the time-gauge. With respect to this particular
inner product, the Chern-Simons state of quantum gravity turns out to be a
non-normalizable wavefunctional.Comment: Latex, 30 pages, 1 figure, to appear in Phys. Rev.
The exact cosmological solution to the dynamical equations for the Bianchi IX model
Quantum geometrodynamics in extended phase space describes phenomenologically
the integrated system ``a physical object + observation means (a gravitational
vacuum condensate)''. The central place in this version of QGD belongs to the
Schrodinger equation for a wave function of the Universe. An exact solution to
the ``conditionally-classical'' set of equations in extended phase space for
the Bianchi-IX model and the appropriate solution to the Schrodinger equation
are considered. The physical adequacy of the obtained solutions to existing
concepts about possible cosmological scenarios is demonstrated. The
gravitational vacuum condensate is shown to be a cosmological evolution factor.Comment: LaTeX, 14 pages, to be published in Int. J. Mod. Phys.
The linearization of the Kodama state
We study the question of whether the linearization of the Kodama state around
classical deSitter spacetime is normalizable in the inner product of the theory
of linearized gravitons on deSitter spacetime. We find the answer is no in the
Lorentzian theory. However, in the Euclidean theory the corresponding
linearized Kodama state is delta-functional normalizable. We discuss whether
this result invalidates the conjecture that the full Kodama state is a good
physical state for quantum gravity with positive cosmological constant.Comment: 14 pages, statement on the corresponding Yang-Mills case correcte
Evolution of the Scale Factor with a Variable Cosmological Term
Evolution of the scale factor a(t) in Friedmann models (those with zero
pressure and a constant cosmological term Lambda) is well understood, and
elegantly summarized in the review of Felten and Isaacman [Rev. Mod. Phys. 58,
689 (1986)]. Developments in particle physics and inflationary theory, however,
increasingly indicate that Lambda ought to be treated as a dynamical quantity.
We revisit the evolution of the scale factor with a variable Lambda-term, and
also generalize the treatment to include nonzero pressure. New solutions are
obtained and evaluated using a variety of observational criteria. Existing
arguments for the inevitability of a big bang (ie., an initial state with a=0)
are substantially weakened, and can be evaded in some cases with Lambda_0 (the
present value of Lambda) well below current experimental limits.Comment: 29 pages, 12 figures (not included), LaTeX, uses Phys Rev D style
files (revtex.cls, revtex.sty, aps.sty, aps10.sty, prabib.sty). To appear in
Phys Rev
Exact quantum states for the diagonal Bianchi type IX model with negative cosmological constant
Follow-up regimes for sick-listed employees: A comparison of nine north-western European countries
The Covid-19 pandemic has revealed the importance of social protection systems, including income security, when health problems arise. The aims of this study are to compare the follow-up regimes for sick-listed employees across nine European countries, and to conduct a qualitative assessment of the differences with respect to burden and responsibility sharing between the social protection system, employers and employees. The tendency highlighted is that countries with shorter employer periods of sick-pay typically have stricter follow-up responsibility for employers because, in practice, they become gatekeepers of the public sickness benefit scheme. In Germany and the UK, employers have few requirements for follow-up compared with the Nordic countries because they bear most of the costs of sickness absence themselves. The same applies in Iceland, where employers carry most of the costs and have no obligation to follow up sick-listed employees. The situation in the Netherlands is paradoxical: employers have strict obligations in the follow-up regime even though they cover all the costs of the sick-leave themselves. During the pandemic, the majority of countries have adjusted their sick-pay system and increased coverage to reduce the risk of spreading Covid-19 because employees are going to work sick or when they should self-quarantine, except for the Netherlands and Belgium, which considered that the current schemes were already sufficient to reduce that risk
Follow-up regimes for sick-listed employees : A comparison of nine north-western European countries
The Covid-19 pandemic has revealed the importance of social protection systems, including income security, when health problems arise. The aims of this study are to compare the follow-up regimes for sick-listed employees across nine European countries, and to conduct a qualitative assessment of the differences with respect to burden and responsibility sharing between the social protection system, employers and employees. The tendency highlighted is that countries with shorter employer periods of sick-pay typically have stricter follow-up responsibility for employers because, in practice, they become gatekeepers of the public sickness benefit scheme. In Germany and the UK, employers have few requirements for follow-up compared with the Nordic countries because they bear most of the costs of sickness absence themselves. The same applies in Iceland, where employers carry most of the costs and have no obligation to follow up sick-listed employees. The situation in the Netherlands is paradoxical: employers have strict obligations in the follow-up regime even though they cover all the costs of the sick-leave themselves. During the pandemic, the majority of countries have adjusted their sick-pay system and increased coverage to reduce the risk of spreading Covid-19 because employees are going to work sick or when they should self-quarantine, except for the Netherlands and Belgium, which considered that the current schemes were already sufficient to reduce that risk