1,680 research outputs found
Dark Matter Prediction from Canonical Quantum Gravity with Frame Fixing
We show how, in canonical quantum cosmology, the frame fixing induces a new
energy density contribution having features compatible with the (actual) cold
dark matter component of the Universe. First we quantize the closed
Friedmann-Robertson-Walker (FRW) model in a sinchronous reference and determine
the spectrum of the super-Hamiltonian in the presence of ultra-relativistic
matter and a perfect gas contribution. Then we include in this model small
inhomogeneous (spherical) perturbations in the spirit of the Lemaitre-Tolman
cosmology. The main issue of our analysis consists in outlining that, in the
classical limit, the non-zero eigenvalue of the super-Hamiltonian can make
account for the present value of the dark matter critical parameter.
Furthermore we obtain a direct correlation between the inhomogeneities in our
dark matter candidate and those one appearing in the ultra-relativistic matter.Comment: 5 pages, to appear on Modern Physics Letters
The role of the time gauge in the 2nd order formalism
We perform a canonical quantization of gravity in a second-order formulation,
taking as configuration variables those describing a 4-bein, not adapted to the
space-time splitting. We outline how, neither if we fix the Lorentz frame
before quantizing, nor if we perform no gauge fixing at all, is invariance
under boost transformations affected by the quantization.Comment: 4 pages, Proceedings of the II Stueckelberg Worksho
Dualism between Physical Frames and Time in Quantum Gravity
In this work we present a discussion of the existing links between the
procedures of endowing the quantum gravity with a real time and of including in
the theory a physical reference frame. More precisely, as first step, we
develop the canonical quantum dynamics, starting from the Einstein equations in
presence of a dust fluid and arrive to a Schroedinger evolution. Then, by
fixing the lapse function in the path integral of gravity, we get a
Schroedinger quantum dynamics, of which eigenvalues problem provides the
appearance of a dust fluid in the classical limit. The main issue of our
analysis is to claim that a theory, in which the time displacement invariance,
on a quantum level, is broken, is indistinguishable from a theory for which
this symmetry holds, but a real reference fluid is included.Comment: 9 pages, submitted to Mod. Phys. Lett. A, major replacements in
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Deep feature extraction for representing and classifying time series cases: Towards an interpretable approach in haemodialysis
A fuzzy approach to similarity in Case-Based Reasoning suitable to SQL implementation
The aim of this paper is to formally introduce a notion of acceptance and similarity,
based on fuzzy logic, among case features in a case retrieval system. This is pursued
by rst reviewing the relationships between distance-based similarity (i.e. the
standard approach in CBR) and fuzzy-based similarity, with particular attention
to the formalization of a case retrieval process based on fuzzy query specication.
In particular, we present an approach where local acceptance relative to a feature
can be expressed through fuzzy distributions on its domain, abstracting the actual
values to linguistic terms. Furthermore, global acceptance is completely grounded
on fuzzy logic, by means of the usual combinations of local distributions through
specic dened norms. We propose a retrieval architecture, based on the above notions
and realized through a fuzzy extension of SQL, directly implemented on a
standard relational DBMS. The advantage of this approach is that the whole power
of an SQL engine can be fully exploited, with no need of implementing specic
retrieval algorithms. The approach is illustrated by means of some examples from
a recommender system called MyWine, aimed at recommending the suitable wine
bottles to a customer providing her requirements in both crisp and fuzzy way
General Relativity as Classical Limit of Evolutionary Quantum Gravity
We analyze the dynamics of the gravitational field when the covariance is
restricted to a synchronous gauge. In the spirit of the Noether theorem, we
determine the conservation law associated to the Lagrangian invariance and we
outline that a non-vanishing behavior of the Hamiltonian comes out. We then
interpret such resulting non-zero ``energy'' of the gravitational field in
terms of a dust fluid. This new matter contribution is co-moving to the slicing
and it accounts for the ``materialization'' of a synchronous reference from the
corresponding gauge condition. Further, we analyze the quantum dynamics of a
generic inhomogeneous Universe as described by this evolutionary scheme,
asymptotically to the singularity. We show how the phenomenology of such a
model overlaps the corresponding Wheeler-DeWitt picture. Finally, we study the
possibility of a Schr\"odinger dynamics of the gravitational field as a
consequence of the correspondence inferred between the ensemble dynamics of
stochastic systems and the WKB limit of their quantum evolution. We demonstrate
that the time dependence of the ensemble distribution is associated with the
first order correction in to the WKB expansion of the energy spectrum.Comment: 23 pages, to appear on Class. Quant. Gra
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