4,241 research outputs found
Astrophysical and Cosmological Tests of Quantum Theory
We discuss several proposals for astrophysical and cosmological tests of
quantum theory. The tests are motivated by deterministic hidden-variables
theories, and in particular by the view that quantum physics is merely an
effective theory of an equilibrium state. The proposed tests involve searching
for nonequilibrium violations of quantum theory in: primordial inflaton
fluctuations imprinted on the cosmic microwave background, relic cosmological
particles, Hawking radiation, photons with entangled partners inside black
holes, neutrino oscillations, and particles from very distant sources.Comment: 25 pages. Amendment to section 7. Contribution to: "The Quantum
Universe", special issue of Journal of Physics A, dedicated to Prof. G.-C.
Ghirardi on the occasion of his seventieth birthda
Inflationary Cosmology as a Probe of Primordial Quantum Mechanics
We show that inflationary cosmology may be used to test the statistical
predictions of quantum theory at very short distances and at very early times.
Hidden-variables theories, such as the pilot-wave theory of de Broglie and
Bohm, allow the existence of vacuum states with non-standard field fluctuations
('quantum nonequilibrium'). We show that inflationary expansion can transfer
microscopic nonequilibrium to macroscopic scales, resulting in anomalous power
spectra for the cosmic microwave background. The conclusions depend only weakly
on the details of the de Broglie-Bohm dynamics. We discuss, in particular, the
nonequilibrium breaking of scale invariance for the primordial (scalar) power
spectrum. We also show how nonequilibrium can generate primordial perturbations
with non-random phases and inter-mode correlations (primordial
non-Gaussianity). We address the possibility of a low-power anomaly at large
angular scales, and show how it might arise from a nonequilibrium suppression
of quantum noise. Recent observations are used to set an approximate bound on
violations of quantum theory in the early universe.Comment: 44 pages. Minor changes in v
Effect of metal clusters on the swelling of gold-fluorocarbon-polymer composite films
We have investigated the phenomenon of swelling due to acetone diffusion in
fluorocarbon polymer films doped with different gold concentrations below the
percolation threshold. The presence of the gold clusters in the polymer is
shown to improve the mixing between the fluorocarbon polymer and the acetone,
which is not a good solvent for this kind of polymers. In order to explain the
experimental results the stoichiometry and the morphology of the polymer--metal
system have been studied and a modified version of the Flory--Huggins model has
been developed
Comparing unconstrained parametrization methods for return covariance matrix prediction
Forecasting covariance matrices is a difficult task in many research fields since the predicted matrices should be at least positive semidefinite. This problem can be overcome by including constraints in the predictive model or through a parametrization of the matrices to be predicted. In this paper, we focus on the latter approach in a financial application and analyse four parametrizations of the covariance matrices of asset returns. The aim of the manuscript is to understand if the parametrizations of the covariance matrices exhibit differences in terms of predictive accuracy. To this end, we critically analyse their predictive performance through both a Monte Carlo simulation and an empirical application with daily and weekly realized covariance matrices of stock assets. Our findings highlight that the Cholesky decomposition and the parametrization recently introduced by Archakov and Hansen are the overall best-performing methods in terms of forecasting accuracy
Analysing spatiotemporal patterns of Covid-19 confirmed deaths at the NUTS-2 regional level
During the ongoing Covid-19 pandemic, understanding the spatiotemporal patterns of the virus is crucial for policymakers to intervene promptly. The relevance of spatial proximity in the spread of the pandemic necessitates adequate tools, and noisy data must be properly treated. This study proposes obtaining clusters of European regions using smoothed curves of daily deaths from March 2020-March 2022. A functional representation of the curves
Photoemission tuning of nanodiamond particles treated in variable percentages of - plasmas
This work deals with photochatodes (PCs) based on as-received and treated nanodiamond (ND) particles, 250 nm in size. The aim of this study is the hydro-, hydro-/nitro- and nitro-genation of NDs performed in microwave plasmas adding different percentages (0, 50 and 100 %) to pure gas. Untreated and treated NDs are dispersed in solvents such as 1,2-dichloroethane and deionized water, and then deposited, as continuous layers, on p-Si and kapton substrates by the pulsed spray technique. The produced layers are characterized by Raman, photoluminescence spectroscopies and photoemission measurements. The quantum efficiency (QE), a merit figure for photocathodes, is assessed in the UV spectral range from 146 to 210 nm. The results show an enhancement of the photoemission for PCs based on hydro-, hydro-/nitro- and nitro-genated NDs that exhibit at 146 nm QE values of about 23, 21 and 13 %, respectively. The advantage of nitrogenated PCs is the good stability to air exposure against their lowest QE values
Alveolar recruitment manoeuvre in laterally recumbent anaesthetized sheep.
General anaesthesia in laterally recumbent sheep under spontaneous ventilating may cause hypoxaemia as previously reported.
The stepwise ARM followed by mechanical ventilation with PEEP at 5 cmH2O, improves the oxygenation indices and decrease the amount of venous admixture evaluated by the F-shunt.
The positive effects of the ARM are still present in most of the animals at recovery
A first experimental test of de Broglie-Bohm theory against standard quantum mechanics
De Broglie - Bohm (dBB) theory is a deterministic theory, built for
reproducing almost all Quantum Mechanics (QM) predictions, where position plays
the role of a hidden variable. It was recently shown that different coincidence
patterns are predicted by QM and dBB when a double slit experiment is realised
under specific conditions and, therefore, an experiment can test the two
theories. In this letter we present the first realisation of such a double slit
experiment by using correlated photons produced in type I Parametric Down
Conversion. Our results confirm QM contradicting dBB predictions
Signal-Locality and Subquantum Information in Deterministic Hidden-Variables Theories
It is proven that any deterministic hidden-variables theory, that reproduces quantum theory for a 'quantum equilibrium' distribution of hidden variables, must predict the existence of instantaneous signals at the statistical level for hypothetical 'nonequilibrium ensembles'. This 'signal-locality theorem' generalises yet another feature of the pilot-wave theory of de Broglie and Bohm, for which it is already known that signal-locality is true only in equilibrium. Assuming certain symmetries, lower bounds are derived on the 'degree of nonlocality' of the singlet state, defined as the (equilibrium) fraction of outcomes at one wing of an EPR-experiment that change in response to a shift in the distant angular setting. It is shown by explicit calculation that these bounds are satisfied by pilot-wave theory. The degree of nonlocality is interpreted as the average number of bits of 'subquantum information' transmitted superluminally, for an equilibrium ensemble. It is proposed that this quantity might provide a novel measure of the entanglement of a quantum state, and that the field of quantum information would benefit from a more explicit hidden-variables approach. It is argued that the signal-locality theorem supports the hypothesis, made elsewhere, that in the remote past the universe relaxed to a state of statistical equilibrium at the hidden-variable level, a state in which nonlocality happens to be masked by quantum noise
- …