935 research outputs found
Fermionic wave functions and Grassmann fields as possible sources of dark energy
We study a cosmological model with a fermionic field which can be interpreted
as a source of dark energy in the universe. Two different approaches were
considered, the first one with a massless fermionic field represented by a
standard wave-function and the second one where a massive field is a Grassmann
variable. {The first case naturally reduces to a XCDM model with a constant
equation of state parameter, while the last case reproduces a CDM model
for a massive field}, and in the massless limit, the intrinsic grassmannian
property of the field leads always to a vacuum equation of state parameter,
irrespective the specific form of the potential. Both cases leads to a dark
energy contribution of the fermionic sector. The models are totally compatible
with recent cosmological data from Supernovae, BAO and Hubble parameter
measurements. A brief study of linear evolution of density perturbations shows
that some of the small scale problems related to standard model can be at least
alleviated.Comment: 21 pages, 5 figures, final version publishe
Affine arithmetic-based methodology for energy hub operation-scheduling in the presence of data uncertainty
In this study, the role of self-validated computing for solving the energy hub-scheduling problem in the presence of multiple and heterogeneous sources of data uncertainties is explored and a new solution paradigm based on affine arithmetic is conceptualised. The benefits deriving from the application of this methodology are analysed in details, and several numerical results are presented and discussed
Germinação in vitro da mangabeira.
O objetivo do trabalho foi determinar as condições mais favoráveis para germinação in vitro de sementes inicial de plântulas de mangabeira.bitstream/CPATC/19572/1/bp-24.pd
Probing the time dependence of dark energy
A new method to investigate a possible time-dependence of the dark energy
equation of state is proposed. We apply this methodology to two of the most
recent data sets of type Ia supernova (Union2 and SDSS) and the baryon acoustic
oscillation peak at . For some combinations of these data, we show
that there is a clear departure from the standard CDM model at
intermediary redshifts, although a non-evolving dark energy component () cannot be ruled out by these data. The approach developed here may be
useful to probe a possible evolving dark energy component when applied to
upcoming observational data.Comment: 6 pages, 3 figures, LaTe
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