38 research outputs found
Designing Horndeski and the effective fluid approach
We present a family of designer Horndeski models, i.e. models that have a
background exactly equal to that of the CDM model but perturbations
given by the Horndeski theory. Then, we extend the effective fluid approach to
Horndeski theories, providing simple analytic formulae for the equivalent dark
energy effective fluid pressure, density and velocity. We implement the dark
energy effective fluid formulae in our code EFCLASS, a modified version of the
widely used Boltzmann solver CLASS, and compare the solution of the
perturbation equations with those of the code hi_CLASS which already includes
Horndeski models. We find that our simple modifications to the vanilla code are
accurate to the level of with respect to the more complicated
hi_CLASS code. Furthermore, we study the kinetic braiding model both on and off
the attractor and we find that even though the full case has a proper
CDM model limit for large , it is not appropriately smooth, thus
causing the quasistatic approximation to break down. Finally, we focus on our
designer model (HDES), which has both a smooth CDM limit and
well-behaved perturbations, and we use it to perform Markov Chain Monte Carlo
analyses to constrain its parameters with the latest cosmological data. We find
that our HDES model can also alleviate the soft tension between the
growth data and Planck 18 due to a degeneracy between and one of its
model parameters that indicates the deviation from the CDM model.Comment: 31 pages, 9 figures, 5 tables, comments welcome. The codes used in
the analysis of this paper can be found at
https://members.ift.uam-csic.es/savvas.nesseris/efclass.html and at
https://github.com/wilmarcardonac/EFCLAS
The traces of anisotropic dark energy in light of Planck
We study a dark energy model with non-zero anisotropic stress, either linked
to the dark energy density or to the dark matter density. We compute
approximate solutions that allow to characterise the behaviour of the dark
energy model and to assess the stability of the perturbations. We also
determine the current limits on such an anisotropic stress from the cosmic
microwave background data by the Planck satellite, and derive the corresponding
constraints on the modified growth parameters like the growth index, the
effective Newton's constant and the gravitational slip.Comment: 29 pages, 10 figures; matches version accepted for publication in
JCA
Momentum transfer in the dark sector and lensing convergence in upcoming galaxy surveys
We investigated a cosmological model that allows a momentum transfer between
dark matter and dark energy. The interaction in the dark sector mainly affects
the behaviour of perturbations on small scales while the background evolution
matches the CDM solution. As a result of the momentum transfer, these kinds
of models help alleviating the discrepancy in the standard model,
but do not resolve the so-called tension. We confirm that this is indeed
the case by computing cosmological constraints. While our analysis tends to
favour values lower than in CDM, we do not find evidence
for a non-vanishing momentum transfer in the dark sector. Since upcoming galaxy
surveys will deliver information on scales and red-shift relevant for testing
models allowing momentum transfer in the dark sector, we also carried out
forecasts using different survey configurations. We assessed the relevance of
neglecting lensing convergence when modelling the angular power
spectrum of number counts fluctuations . We found that
not including in analyses leads to biased constraints () of cosmological parameters even when including information from
other experiments. Incorrectly modelling might lead to
spurious detection of neutrino masses and exacerbate discrepancies in and
.Comment: 26 pages, 8 figures, 8 tables. Comments welcome Updated versio
Holographic energy density, dark energy sound speed, and tensions in cosmological parameters: and
Interesting discrepancies in cosmological parameters are challenging the
success of the CDM model. Direct measurements of the Hubble constant
using Cepheid variables and supernovae turn out to be higher than
inferred from the Cosmic Microwave Background (CMB). Weak galaxy lensing
surveys consistently report values of the strength of matter clustering
lower than values derived from the CMB in the context of
CDM. In this paper we address these discrepancies in cosmological
parameters by considering Dark Energy (DE) as a fluid with evolving equation of
state , constant sound speed squared
, and vanishing anisotropic stress . Our
is derived from the Holographic Principle and can
consecutively exhibit radiation-like, matter-like, and DE-like behaviour, thus
affecting the sound horizon and the comoving angular diameter distance, hence
. Here we show DE sound speed plays a part in the matter clustering
behaviour through its effect on the evolution of the gravitational potential.
We compute cosmological constraints using several data set combinations
including primary CMB, CMB lensing, redshift-space-distortions, local
distance-ladder, supernovae, and baryon acoustic oscillations. In our analysis
we marginalise over and find
is excluded at . For our baseline
result including the whole data set we found and in good
agreement (within ) with low redshift probes. Our constraint
for the baryon energy density is however in
tension with BBN constraints. We conclude evolving DE also having non-standard
clustering properties [e.g., ] might be relevant
for the solution of current discrepancies in cosmological parameters.Comment: 28 pages, 12 figures, 3 tables. References adde
Lensing convergence and anisotropic dark energy in galaxy redshift surveys
Analyses of upcoming galaxy surveys will require careful modelling of
relevant observables such as the power spectrum of galaxy counts in harmonic
space . We investigate the impact of disregarding relevant
relativistic effects by considering a model of dark energy including constant
sound speed, constant equation of state , and anisotropic stress. Here we
show that neglecting the effect of lensing convergence will lead to substantial
shifts in cosmological parameters such as the galaxy bias , the value of
the dark energy equation of state today , and the Hubble constant .
Interestingly, neglecting the effect of lensing convergence in this kind of
models results in shifting downwards, something which could shed light on
the current tension between local and CMB determinations of the Hubble
constant.Comment: 13 pages, 3 figures, comments welcom
Unraveling the effective fluid approach for models in the subhorizon approximation
We provide explicit formulas for the effective fluid approach of
theories, such as the Hu & Sawicki and the designer models. Using the latter
and simple modifications to the CLASS code, which we call EFCLASS, in
conjunction with very accurate analytic approximations for the background
evolution, we obtain competitive results in a much simpler and less error-prone
approach. We also derive the initial conditions in matter domination and we
find they differ from those already found in the literature for a constant
model. A clear example is the designer model that behaves as CDM in
the background, but has nonetheless dark energy perturbations. We then use the
aforementioned models to derive constraints from the latest cosmological data,
including supernovae, BAO, CMB, and growth-rate data, and find they are
statistically consistent to the CDM model. Finally, we show that the
viscosity parameter in realistic models is not constant as commonly
assumed, but rather evolves significantly over several orders of magnitude,
something which could affect forecasts of upcoming surveys.Comment: 24 pages, 12 figures, 5 tables. Changes match published version. The
codes used in the analysis can be found at
https://members.ift.uam-csic.es/savvas.nesseris/efclass.html and
https://github.com/wilmarcardonac/EFCLAS
Lensing convergence and the neutrino mass scale in galaxy redshift surveys
We demonstrate the importance of including the lensing contribution in galaxy clustering analyses with large galaxy redshift surveys. It is well known that radial cross-correlations between different redshift bins of galaxy surveys are dominated by lensing. But we show here that also neglecting lensing in the autocorrelations within one bin severely biases cosmological parameter estimation with redshift surveys. It leads to significant shifts for several cosmological parameters, most notably the scalar spectral index and the neutrino mass scale. Especially the latter parameter is one of the main targets of future galaxy surveys.Peer reviewe
Using machine learning to compress the matter transfer function
The linear matter power spectrum connects theory with large scale
structure observations in cosmology. Its scale dependence is entirely encoded
in the matter transfer function , which can be computed numerically by
Boltzmann solvers, and can also be computed semi-analytically by using fitting
functions such as the well-known Bardeen-Bond-Kaiser-Szalay (BBKS) and
Eisenstein-Hu (EH) formulae. However, both the BBKS and EH formulae have some
significant drawbacks. On the one hand, although BBKS is a simple expression,
it is only accurate up to , which is well above the precision goal
of forthcoming surveys. On the other hand, while EH is as accurate as required
by upcoming experiments, it is a rather long and complicated expression. Here,
we use the Genetic Algorithms (GAs), a particular machine learning technique,
to derive simple and accurate fitting formulae for the transfer function
. When the effects of massive neutrinos are also considered, our
expression slightly improves over the EH formula, while being notably shorter
in comparison.Comment: 12 pages, 7 figures, 2 tables. Changes match published versio
La evolución de la cognición humana en la obra de Michael Tomasello
RESUMEN: La conjunción de las ciencias cognitivas y la biologÃa evolutiva ha legitimado y popularizado en la comunidad cientÃfica la pregunta por la evolución de la mente o de la cognición humana. La discusión ha girado en torno a dos grandes perspectivas: quienes afirman que la mente humana tiene rasgos que le son particulares (no observados en otras especies), y quienes sostienen que las diferencias entre la cognición humana y las de otras especies animales sólo son un asunto de grado (como lo creÃa Darwin). En este trabajo se aborda una propuesta sobre la evolución cognitiva humana que no es claramente ubicable en las dos perspectivas mencionadas: la de Michael Tomasello. El abordaje presenta el siguiente orden: en primer lugar, se hará una descripción pormenorizada de los principales argumentos de la propuesta; en segundo lugar, se presentarán algunas crÃticas relacionadas con sus fundamentos teóricos y experimentales y, en tercer lugar, se hará una contrastación entre la propuesta de Michael Tomasello y la de Steven Mithen, que son semejantes en cuanto a su ubicación difusa dentro de las dos grandes perspectivas mencionadas, pero difieren en su
explicación de la trayectoria evolutiva que dio paso a lo que, hoy por hoy, es la cognición humana.ABSTRACT: The junction between Cognitive Sciences and Evolutionary Biology has legitimated and popularized, in the scientific community, the question about evolution of mind or human cognition. This debate has revolve around two points of view: those who say that human mind has unique traits (not observed in other species), and those who claim that differences between human cognition and that of other species is a matter of degree and not of kind (as Darwin believed). This work adresses an hypothesis about human cognitive evolution that is not clearly classifiable in the points of view mentioned earlier: the hypothesis of Michael Tomasello. The present work has the following order: first, a detailed description of the main arguments will be made; second, some critical words will be said related with his theoretical and experimental foundations and, third, a contrastation between Tomasello's hypothesis and that of Steven Mithen will be made, because they are similar in their fuzzy position inside the two big perspectives, but they differ in their explanation of the evolutionary route that gave birth to what we currently know as human cognition.RESUMEN: La conjunción de las ciencias cognitivas y la biologÃa evolutiva ha legitimado y popularizado en la comunidad cientÃfica la pregunta por la evolución de la mente o de la cognición humana. La discusión ha girado en torno a dos grandes perspectivas: quienes afirman que la mente humana tiene rasgos que le son particulares (no observados en otras especies), y quienes sostienen que las diferencias entre la cognición humana y las de otras especies animales sólo son un asunto de grado (como lo creÃa Darwin). En este trabajo se aborda una propuesta sobre la evolución cognitiva humana que no es claramente ubicable en las dos perspectivas mencionadas: la de Michael Tomasello. El abordaje presenta el siguiente orden: en primer lugar, se hará una descripción pormenorizada de los principales argumentos de la propuesta; en segundo lugar, se presentarán algunas crÃticas relacionadas con sus fundamentos teóricos y experimentales y, en tercer lugar, se hará una contrastación entre la propuesta de Michael Tomasello y la de Steven Mithen, que son semejantes en cuanto a su ubicación difusa dentro de las dos grandes perspectivas mencionadas, pero difieren en su explicación de la trayectoria evolutiva que dio paso a lo que, hoy por hoy, es la cognición humana
Aprovechamiento de barcia para realización de pre-emulsiones como materia prima
Aprovechar la barcia de res que es un material sin utilidad para el proceso productivo y que es vendido a 90 / kilo para hacer concentrado de comida animal; a partir de este material se elabora una pre-emulsión y se genera una nueva materia prima cárnica, la cual ingresa al proceso como pre-emulsión, incrementando las posibilidades de abastecimiento para el negocio.
Para el desarrollo de la propuesta se utiliza el método de diseño experimental, donde se tendrán variables controlables y fijas en la formulación de la preemulsión. Las variables fijas son las materias primas definidas y estandarizadas como lo son la barcia de res, sal, polvo praga y tripolifosfato de sodio y las variables controlables para lograr una pre-emulsión barcia estable serán la proteÃna concentrada de soya y agua; la metodologÃa de validación utilizada es la de panel sensorial triangular, con la participación de panelistas entrenados, que evaluaran el producto piloto escogido con la aplicación parcial de la pre-emulsión barcia en reemplazo de materia prima cárnica, chequeando que no hayan modificaciones en las caracterÃsticas organolépticas del producto terminado.
Esta propuesta tiene dos justificaciones que para actualidad son muy necesarias, la primera desde la obtención de procesos limpios, por la no generación de residuos sólidos, no impactando ambientalmente y la segunda es el aprovechamiento de los materiales resultantes del proceso productivo que no son utilizados en el mismo, optimizando los procesos y recursos, mejorando los costos, siendo más competitivos en el mercado. El alcance de esta propuesta tiene una cobertura de producción y distribución dentro del negocio cárnico, con aplicación de la pre-emulsión y cumplimientos de la misma en parámetros de inocuidad, calidad y proceso bien definidos en las diferentes formulaciones, con la limitación que el volumen elaboración de la pre-emulsión depende de la generación de la barcia.
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Para el desarrollo de esta propuesta es necesario conocer el principio en la elaboración de emulsiones y para tal fin es primordial seleccionar el emulsionante apropiado (Charalambous Doxastakis, 1989; Dickinson, 1992; Hasenhuettl, 1997; Stauffer, 1999; Krog ySparso, 2004). (McClements, 2005); En la actualidad existe un gran número de emulsionantes como ingredientes alimentarios y cada uno tiene su propia y única caracterÃsticas y el rango óptimo de las aplicaciones (Hasenhuettl y Hartel, 1997; Krog y Sparso, 2004). (McClements, 2005).
Se aplica conceptos de gestión empresarial y formulación de proyectos, donde se evidencie la factibilidad de la propuesta, fundamentándose en encontrar posibilidades para el negocio.
Otro valor agregado de la propuesta es que los costos de los productos en los cuales se aplicara la pre-emulsión serán reducidos, dando un mayor margen de utilidad y generando un ahorro para el negocio cárnico, de igual manera se aplicara todas las etapas aprendidas a través de la carrera identificando las oportunidades y riesgos a los que se puede enfrentar