155 research outputs found
Dark Matter & Dark Energy from a single scalar field: CMB spectrum and matter transfer function
The dual axion model (DAM), yielding bot DM and DE form a PQ-like scalar
field solving the strong CP problem, is known to allow a fair fit of CMB data.
Recently, however, it was shown that its transfer function exhibits significant
anomalies, causing difficulties to fit deep galaxy sample data. Here we show
how DAM can be modified to agree with the latter data set. The modification
follows the pattern suggested to reconcile any PQ-like approach with gravity.
Modified DAM allows precise predictions which can be testable against future
CMB and/or deep sample data.Comment: 15 pages, 8 figures, accepted for publication in JCA
A machine learning enabled multi-fidelity platform for the integrated design of aircraft systems
The push toward reducing the aircraft development cycle timemotivates the development of collaborative frameworks that enable themore integrated design of aircraft and their systems. The ModellIng and Simulation tools for Systems IntegratiONon Aircraft (MISSION) project aims to develop an integratedmodelling and simulation framework. This paper focuses on some recent advancements in theMISSION project and presents a design framework that combines a filtering process to down-select feasible architectures, amodeling platformthat simulates the power system of the aircraft, and a machine learning-based clustering and optimization module. This framework enables the designer to prioritize different designs and offers traceability on the optimal choices. In addition, it enables the integration of models at multiple levels of fidelity depending on the size of the design space and the accuracy required. It is demonstrated for the electrification of the Primary Flight Control System (PFCS) and the landing gear braking system using different electric actuation technologies. The performance of different architectures is analyzed with respect to key performance indicators (fuel burn, weight, power). The optimization process benefits from a data-driven localization step to identify sets of similar architectures. The framework demonstrates the capability of optimizing across multiple, different system architectures in an efficient way that is scalable for larger design spaces and larger dimensionality problems
Thermal and Economic Efficiency of Progressive Retrofit Strategies for School Buildings by a Statistical Analysis based Tool
Design alternatives in air conditioned buildings may be easily compared just by summing the hourly consumption of primary energy, while quantitative approachs for bioclimatic design strategies are difficult to be assessed and compared. A actively heated and passively cooled school building is considered as an application field of a novel methodology to promote an informed choice about the retrofit strategies to be adopted for buildings, defined as the Gained Comfort Cost (GCC). A functional and significant unit (i.e. a classroom), is used to test different energy retrofit solutions and their performances were compared with a baseline, in terms of the capacity to reduce the indoor air temperature variation. The novel methodology is a visual tool allowing to understand the “distance” of indoor conditions from comfort; the retrofit strategies are promoted to reduce this distance considering however the associated costs (LCC) to deal with actual feasibility
Scalar field-perfect fluid correspondence and nonlinear perturbation equations
The properties of dynamical Dark Energy (DE) and, in particular, the
possibility that it can form or contribute to stable inhomogeneities, have been
widely debated in recent literature, also in association to a possible coupling
between DE and Dark Matter (DM). In order to clarify this issue, in this paper
we present a general framework for the study of the nonlinear phases of
structure formation, showing the equivalence between two possible descriptions
of DE: a scalar field \phi self-interacting through a potential V(\phi) and a
perfect fluid with an assigned negative equation of state w(a). This enables us
to show that, in the presence of coupling, the mass of DE quanta may increase
where large DM condensations are present, so that also DE may partake to the
clustering process.Comment: 16 pages, accepted for publication in JCA
Le Chatelier-Braun principle in cosmological physics
Assuming that dark energy may be treated as a fluid with a well defined
temperature, close to equilibrium, we argue that if nowadays there is a
transfer of energy between dark energy and dark matter, it must be such that
the latter gains energy from the former and not the other way around.Comment: 6 pages, revtex file, no figures; version accepted for publication in
General Relativity and Gravitatio
Dynamical Dark Energy simulations: high accuracy Power Spectra at high redshift
Accurate predictions on non--linear power spectra, at various redshift z,
will be a basic tool to interpret cosmological data from next generation mass
probes, so obtaining key information on Dark Energy nature. This calls for high
precision simulations, covering the whole functional space of w(z) state
equations and taking also into account the admitted ranges of other
cosmological parameters; surely a difficult task. A procedure was however
suggested, able to match the spectra at z=0, up to k~3, hMpc^{-1}, in
cosmologies with an (almost) arbitrary w(z), by making recourse to the results
of N-body simulations with w = const. In this paper we extend such procedure to
high redshift and test our approach through a series of N-body gravitational
simulations of various models, including a model closely fitting WMAP5 and
complementary data. Our approach detects w= const. models, whose spectra meet
the requirement within 1% at z=0 and perform even better at higher redshift,
where they are close to a permil precision. Available Halofit expressions,
extended to (constant) w \neq -1 are unfortunately unsuitable to fit the
spectra of the physical models considered here. Their extension to cover the
desired range should be however feasible, and this will enable us to match
spectra from any DE state equation.Comment: method definitely improved in semplicity and efficacy,accepted for
publication on JCA
Dark Matter and Dark Energy from the solution of the strong CP problem
The Peccei Quinn (PQ) solution of the strong CP problem requires the
existence of axions, which are a viable candidate for Dark Matter. Here we show
that, if the Nambu Goldstone potential of the PQ model is replaced by a
potential V(|\Phi|) admitting a tracker solution, the scalar field |\Phi| can
account for Dark Energy, while the phase of \Phi yields axion Dark Matter. Such
Dark Matter and Dark Energy turn out to be weakly coupled. If V is a SUGRA
potential, the model essentially depends on a single parameter, the energy
scale \Lambda. Once we set \Lambda \simeq 10^{10} GeV, at the quark--hadron
transition, |\Phi| naturally passes through values suitable to solve the strong
CP problem, later growing to values providing fair amounts of Dark Matter and
Dark Energy. In this model, the linear growth factor, from recombination to
now, is quite close to \LambdaCDM. The selected \Lambda value can be an
indication of the scale where the soft breaking of SUSY occurred.Comment: 10 pages, 5 figures Revised abstract and added new section on
fluctuation evolution. Phys Rev Lett (in press
Cosmic Microwave Background Polarization and reionization: constraining models with a double reionization
Neutral hydrogen around high-z QSO and an optical depth tau ~ 0.17 can be
reconciled if reionization is more complex than a single transition at z ~ 6-8.
Tracing its details could shed a new light on the first sources of radiation.
Here we discuss how far such details can be inspected through planned
experiments on CMB large-scale anisotropy and polarization, by simulating an
actual data analysis. By considering a set of double reionization histories of
Cen (2003) type, a relevant class of models not yet considered by previous
works, we confirm that large angle experiments rival high resolution ones in
reconstructing the reionization history. We also confirm that reionization
histories, studied with the prior of a single and sharp reionization, yield a
biased tau, showing that this bias is generic. We further find a monotonic
trend in the bias for the models that we consider, and propose an explanation
of the trend, as well as the overall bias. We also show that in long-lived
experiments such a trend can be used to discriminate between single and double
reionization patterns.Comment: 8 pages, 11 figures. Substantial rewriting, replaced with accepted
version. To be published in A&
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