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Search Results: 1 - 10 of 330668 matches for " Marina Cortês "
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The Universe as a Process of Unique Events
Marina Cortês,Lee Smolin
Physics , 2013, DOI: 10.1103/PhysRevD.90.084007
Abstract: We describe a new class of models of quantum space-time based on energetic causal sets and show that under natural conditions space-time emerges from them. These are causal sets whose causal links are labelled by energy and momentum and conservation laws are applied at events. The models are motivated by principles we propose govern microscopic physics which posit a fundamental irreversibility of time. One consequence is that each event in the history of the universe has a distinct causal relationship to the rest; this requires a novel form of dynamics which an be applied to uniquely distinctive events. We hence introduce a new kind of deterministic dynamics for a causal set in which new events are generated from pairs of progenitor events by a rule which is based on extremizing the distinctions between causal past sets of events. This dynamics is asymmetric in time, but we find evidence from numerical simulations of a 1+1 dimensional model, that an effective dynamics emerges which restores approximate time reversal symmetry. Energetic causal set models differ from other spacetime-free causal set approaches, e.g. Ref. [1] proposed causal sets based on quantum information processing systems, and Ref. [2] proposed causal sets constructed out of standard model particles. Finally we also present a natural twistorial representation of energetic causal sets.
Energetic Causal Sets
Marina Cortês,Lee Smolin
Physics , 2013, DOI: 10.1103/PhysRevD.90.044035
Abstract: We propose an approach to quantum theory based on the energetic causal sets, introduced in Cort\^{e}s and Smolin (2013). Fundamental processes are causal sets whose events carry momentum and energy, which are transmitted along causal links and conserved at each event. Energetic causal set models differ from other spacetime-free causal set approaches, e.g. Ref. [2] proposed causal sets based on quantum information processing systems, and Ref. [3] proposed causal sets constructed out of standard model particles. Fundamentally there are amplitudes for causal processes in energetic causal sets, but no space-time. An embedding of the causal processes in an emergent space-time arises only at the semiclassical level. Hence, fundamentally there are no commutation relations, no uncertainty principle and, indeed, no $\hbar$. All that remains of quantum theory is the relationship between the absolute value squared of complex amplitudes and probabilities. Consequently, we find that neither locality, nor non locality, are primary concepts, only causality exists at the fundamental level.
Del síntoma a la enfermedad: elevación de transaminasas
Cortés Marina,R.B.;
Pediatría Atención Primaria , 2009, DOI: 10.4321/S1139-76322009000700015
Abstract: increased transaminases (ast-alt) is a common finding in paediatric clinical practice. sometimes detection occurs in patients of any age with no symptoms of liver or biliary disease, following an analytical requested for another reason. we report the case of a 9 year old girl, on whom analytical tests were performed in an attempt to establish the aetiology of a skin reaction. this reaction appeared during a course of an antibiotic treatment for pneumonia. after elevated transaminases and subsequent confirmation in subsequent analytical, applies the study protocol and is diagnosed with wilson's disease.
Viable inflationary models ending with a first-order phase transition
Marina Cortês,Andrew R. Liddle
Physics , 2009, DOI: 10.1103/PhysRevD.80.083524
Abstract: We investigate the parameter space of hybrid inflation models where inflation terminates via a first-order phase transition causing nucleation of bubbles. Such models experience a tension from the need to ensure nearly scale invariant density perturbations, while avoiding a near scale-invariant bubble size distribution which would conflict observations. We perform an exact analysis of the different regimes of the models, where the energy density of the inflaton field ranges from being negligible as compared to the vacuum energy to providing most of the energy for inflation. Despite recent microwave anisotropy results favouring a spectral index less than one, we find that there are still viable models that end with bubble production and can match all available observations. As a by-product of our analysis, we also provide an up-to-date assessment of the viable parameter space of Linde's original second-order hybrid model across its full parameter range.
Old Dark Energy
Marina Cortês,Eric V. Linder
Physics , 2009, DOI: 10.1103/PhysRevD.81.063004
Abstract: Dark energy dynamics in the recent universe is influenced by its evolution through the long, matter dominated expansion history. A particular dynamical property, the flow variable, remains constant in several classes of scalar field models as long as matter dominates; the dark energy is only free to diverge in behavior at recent times. This gives natural initial conditions for Monte Carlo studies of dark energy dynamics. We propose a parametrization for the later evolution that covers a wide range of possible behaviors, is tractable in making predictions, and can be constrained by observations. We compare the approach to directly parametrizing the potential, which does not take into account the maturity of the dark energy dynamics.
Cosmic microwave background anomalies in an open universe
Andrew R Liddle,Marina Cortês
Physics , 2013, DOI: 10.1103/PhysRevLett.111.111302
Abstract: We argue that the observed large-scale cosmic microwave anomalies, discovered by WMAP and confirmed by the Planck satellite, are most naturally explained in the context of a marginally-open universe. Particular focus is placed on the dipole power asymmetry, via an open universe implementation of the large-scale gradient mechanism of Erickcek et al. Open inflation models, which are motivated by the string landscape and which can excite `super-curvature' perturbation modes, can explain the presence of a very-large-scale perturbation that leads to a dipole modulation of the power spectrum measured by a typical observer. We provide a specific implementation of the scenario which appears compatible with all existing constraints.
Non-parametric Dark Energy Degeneracies
Renée Hlozek,Marina Cortês,Chris Clarkson,Bruce Bassett
Physics , 2008, DOI: 10.1007/s10714-007-0548-6
Abstract: We study the degeneracies between dark energy dynamics, dark matter and curvature using a non-parametric and non-perturbative approach. This allows us to examine the knock-on bias induced in the reconstructed dark energy equation of state, w(z), when there is a bias in the cosmic curvature or dark matter content, without relying on any specific parameterisation of w. Even assuming perfect Hubble, distance and volume measurements, we show that for z > 1, the bias in w(z) is up to two orders of magnitude larger than the corresponding errors in Omega_k or Omega_m. This highlights the importance of obtaining unbiased estimators of all cosmic parameters in the hunt for dark energy dynamics.
On the prior dependence of constraints on the tensor-to-scalar ratio
Marina Cortês,Andrew R. Liddle,David Parkinson
Physics , 2011, DOI: 10.1088/1475-7516/2011/09/027
Abstract: We investigate the prior dependence of constraints on cosmic tensor perturbations. Commonly imposed is the strong prior of the single-field inflationary consistency equation, relating the tensor spectral index nT to the tensor-to-scalar ratio r. Dropping it leads to significantly different constraints on nT, with both positive and negative values allowed with comparable likelihood, and substantially increases the upper limit on r on scales k = 0.01 Mpc^-1 to 0.05 Mpc^-1, by a factor of ten or more. Even if the consistency equation is adopted, a uniform prior on r on one scale does not correspond to a uniform one on another; constraints therefore depend on the pivot scale chosen. We assess the size of this effect and determine the optimal scale for constraining the tensor amplitude, both with and without the consistency relation.
Comprehensive analysis of the simplest curvaton model
Christian T. Byrnes,Marina Cortês,Andrew R. Liddle
Physics , 2014, DOI: 10.1103/PhysRevD.90.023523
Abstract: We carry out a comprehensive analysis of the simplest curvaton model, which is based on two non-interacting massive fields. Our analysis encompasses cases where the inflaton and curvaton both contribute to observable perturbations, and where the curvaton itself drives a second period of inflation. We consider both power spectrum and non-Gaussianity observables, and focus on presenting constraints in model parameter space. The fully curvaton-dominated regime is in some tension with observational data, while an admixture of inflaton-generated perturbations improves the fit. The inflating curvaton regime mimics the predictions of Nflation. Some parts of parameter space permitted by power spectrum data are excluded by non-Gaussianity constraints. The recent BICEP2 results [1] require that the inflaton perturbations provide a significant fraction of the total perturbation, ruling out the usual curvaton scenario in which the inflaton perturbations are negligible, though not the admixture regime where both inflaton and curvaton contribute to the spectrum.
Categorización social y cogniciones infantiles sobre la pobreza en ni?os: una mirada desde el esencialismo psicológico
Amar,José J.; Abello,Raimundo; Martínez,Marina B.; Monroy,Ernesto; Cortés,Omar; Crespo,Fernando;
Investigación y Desarrollo , 2011,
Abstract: we present preliminary results of a study about the early presence of essentialism as the basis for social categorization of poverty, in a purposive sample of 121 children's body five to seven years, from the high and low socioeconomic levels in barranquilla, colombia. after application of the scales, there was no evidence of essentialist thinking, and no significant differences associated with age, gender or socioeconomic status, except in the capacity of self-categorization. the results suggest that children identified poverty as a category, but they are based on external circumstances to establish the membership to the category.
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