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Search Results: 1 - 10 of 54199 matches for " David Campo "
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Quantum corrections during inflation and conservation of adiabatic perturbations
David Campo
Physics , 2009, DOI: 10.1103/PhysRevD.81.043535
Abstract: The possibility that quantum corrections break the conservation of superhorizon adiabatic perturbations in single field inflation is examined. I consider the lowest order corrections from massless matter fields in the Hamiltonian formalism. Particular emphasis is therefore laid on the renormalization. The counterterms are the same as in the Lagrangian formalism. The renormalized value of the tadpole is zero. I find a possible secular dependence of the power spectrum at one loop due to the trace anomaly, but this result depends on the approximation of the modes and is inconclusive. The symmetry (not) violated by the quantum corrections is the invariance by dilatation. Perspectives on the backreaction problem are briefly discussed.
Problems with models of a fundamental length
David Campo
Physics , 2010,
Abstract: I critically examine various ad hoc models describing a fundamental minimal length at the level of the propagator. They violate causality and/or unitarity.
Quantum correlations in inflationary spectra and violation of bell inequalities
Campo, David;Parentani, Renaud;
Brazilian Journal of Physics , 2005, DOI: 10.1590/S0103-97332005000700016
Abstract: in spite of the macroscopic character of the fluctuation amplitudes, we show that the standard inflationary distribution of primordial density fluctuations still exhibits inherently quantum mechanical correlations (which cannot be mimicked by any classical stochastic ensemble). to this end, we propose a gedanken experiment for which certain bell inequalities are violated. we also compute the effect of decoherence and show that the violation persists provided that the decoherence lies below a certain non-vanishing threshold. moreover, there exists a higher threshold above which no violation of any bell inequalities can occur, so that the corresponding distributions can be interpreted as stochastic ensembles of classical fluctuations.
Why does the Unruh effect rely on Lorentz invariance, while Hawking radiation does not ?
David Campo,Nathaniel Obadia
Physics , 2010,
Abstract: We show that without Lorentz invariance, the Unruh effect does not exist. We use modified dispersion relations and describe in turn: the non-thermal nature of the vacuum (defined in the preferred frame) restricted to the Rindler wedge, the loss of the KMS property of the Wigthman function, the transition amplitudes and transition rates of a uniformaly accelerated detector. This situation seems to contrast with the Hawking radiation of acoustic black holes, which under certain assumptions has been shown to be robust to a breaking of Lorentz symmetry. We explain this discrepancy.
Quantum correlations in inflationary spectra and violation of Bell inequalities
David Campo,Renaud Parentani
Physics , 2005,
Abstract: In spite of the macroscopic character of the fluctuation amplitudes, we show that the standard inflationary distribution of primordial density fluctuations still exhibits inherently quantum mechanical correlations (which cannot be mimicked by any classical stochastic ensemble). To this end, we propose a Gedanken experiment for which certain Bell inequalities are violated. We also compute the effect of decoherence and show that the violation persists provided that the decoherence lies below a certain non-vanishing threshold. Moreover, there exists a higher threshold above which no violation of any Bell inequalities can occur, so that the corresponding distributions can be interpreted as stochastic ensembles of classical fluctuations.
Space-time correlations within pairs produced during inflation, a wave-packet analysis
David Campo,Renaud Parentani
Physics , 2003, DOI: 10.1103/PhysRevD.67.103522
Abstract: In homogeneous universes the propagation of quantum fields gives rise to pair creation of quanta with opposite momenta. When computing expectation values of operators, the correlations between these quanta are averaged out and no space-time structure is obtained. In this article, by an appropriate use of wave packets, we reveal the space-time structure of these correlations. We show that every pair emerges from vacuum configurations which are torn apart so as to give rise to two semi-classical currents: that carried by the particle and that of its `partner'. The partner's current lives behind the Hubble horizon centered around the particle. Hence any measurement performed within a Hubble patch would correspond to an uncorrelated density matrix, as for Hawking radiation. However, when inflation stops, the Hubble radius grows and eventually encompasses the partner. When this is realized the coherence is recovered within a patch. Our analysis applies to rare pair creation events as well as to cases leading to arbitrary high occupation numbers. Hence it might be applied to primordial gravitational waves which evolve into highly squeezed states.
Inflationary spectra and violations of Bell inequalities
David Campo,Renaud Parentani
Physics , 2005, DOI: 10.1103/PhysRevD.74.025001
Abstract: In spite of the macroscopic character of the primordial fluctuations, the standard inflationary distribution (that obtained using linear mode equations) exhibits inherently quantum properties, that is, properties which cannot be mimicked by any stochastic distribution. This is demonstrated by a Gedanken experiment for which certain Bell inequalities are violated. These violations are {\it in principle} measurable because, unlike for Hawking radiation from black holes, in inflationary cosmology we can have access to both members of correlated pairs of modes delivered in the same state. We then compute the effect of decoherence and show that the violations persist provided the decoherence level (and thus the entropy) lies below a certain non-vanishing threshold. Moreover, there exists a higher threshold above which no violation of any Bell inequality can occur. In this regime, the distributions are ``separable'' and can be interpreted as stochastic ensembles of fluctuations. Unfortunately, the precision which is required to have access to the quantum properties is so high that, {\it in practice}, an observational verification seems excluded.
Space-time correlations in inflationary spectra, a wave packet analysis
David Campo,Renaud Parentani
Physics , 2003, DOI: 10.1103/PhysRevD.70.105020
Abstract: The inflationary mechanism of mode amplification predicts that the state of each mode with a given wave vector is correlated to that of its partner mode with the opposite vector. This implies nonlocal correlations which leave their imprint on temperature anisotropies in the cosmic microwave background. Their spatial properties are best revealed by using local wave packets. This analysis shows that all density fluctuations giving rise the large scale structures originate in pairs which are born near the reheating. In fact each local density fluctuation is paired with an oppositely moving partner with opposite amplitude. To obtain these results we first apply a ``wave packet transformation'' with respect to one argument of the two point correlation function. A finer understanding of the correlations is then reached by making use of coherent states. The knowledge of the velocity field is required to extract the contribution of a single pair of wave packets. Otherwise, there is a two-folded degeneracy which gives three aligned wave packets arising from two pairs. The applicability of these methods to observational data is briefly discussed.
Analysis of the relation between organic products consumption and box schemes use in Alicante (Spain)  [PDF]
Fernando Vidal, David Bernardo López, Francisco José del Campo
Agricultural Sciences (AS) , 2011, DOI: 10.4236/as.2011.24065
Abstract: Box-schemes or organic food subscription plans consist on a regular delivery of a box of seasonal fruits and/or vegetables, preferably organic, cultivated in the vicinity at a specified point using subscription, The object of the present work is trying to examine whether there is a relationship between consumer knowledge about these short distribution channels and the consumption of organic products in the province of Alicante. A survey has been conducted among 400 usual food buyers in this Spanish province. It has been found that the consumption of organic products and the knowledge of such initiatives are linked. We recommend to companies that use this type of distribution channel to publicize its benefits.
Review of relative age effects and potential ways to reduce them in sport and education
David Gutiérrez Díaz del Campo
Retos : Nuevas Perspectivas de Educación Física, Deporte y Recreación , 2013,
Abstract: Differences on chronological age within a peer/age group are known as Relative Age, and its consecuences as Relative Age Effec (RAE). This article is a review of the most relevant publications in both the educative and sportive contexts. The decision of reviewing both contexts in the same article is based on the existence of many points in common between them. Furthermore when research is made on youth sport, all the participants are at the same time in the educational system. The hypothesis of the origin of RAE and possible solutions are discussed and analysed at the end of the paper. Besides the objective of compiling and analyse what literature says about RAE, this article has the aim of raisig awareness about this problem and wish of intervention in educators and sportive managers.
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