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Poster Section
I Workshop on Current Challenges in
Cosmology:
Inflation and the Origin of the CMB Anomalies
Cali, May 18-22, 2015
May 13, 2015
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fN L calculation for two-field models through the moment transport equations
Carlos Alberto Sierra Ordonez
Universidad Industrial de Santander
[email protected]
Abstract
When using the δN formalism for calculating cosmological parameters, it is well known
the difficulty of obtaining the expressions for the amount of expansion and its derivatives
since there does not exist a standard methodology for its calculation; moreover, it is necessary to take into account the numerical bias incurred if finite differences are employed
for a numerical implementation and the initial conditions are not adequate. In this work,
we present a standardization for that calculation that starts with a proper gauge transformation of the temporal variable, such that the amount of expansion derivatives do not
evolve in time, leaving this role to the field perturbations and their correlation functions.
The usage of an almost-gaussian probability density allows us to reproduce the required
statistics to calculate the evolution of the two and there-point curvature perturbation correlations. This calculus is made possible through the moment transport equations which
are a direct consequence from the probability density conservation. We apply the method
to a certain type of two-field inflationary models.
New Geometric Representations of the CMB 2pcf
Andre L. D. Froes
Universidade Estadual de Londrina
[email protected]
Abstract
When searching for deviations of statistical isotropy in CMB, a popular strategy is to
write the two-point correlation function (2pcf) as the most general function of four spherical
angles (i.e., two unit vectors) in the celestial sphere. Then, using a basis of bipolar spherical
harmonics, statistical anisotropy will show up if and only if any coefficient of the expansion
with non-trivial bipolar momentum is detected although this detection will not in general
elucidate the origin of the anisotropy. In this work we show that two new sets of four
angles and basis functions exist which completely specifies the 2pcf, while, at the same
time, offering a clearer geometrical interpretation of the mechanisms generating the signal.
Since the coefficients of these expansions are zero if and only if isotropy holds, they act
as a simple and geometrically motivated null test of statistical isotropy. After illustrating
the properties of these multipolar power spectra with numerical simulations, we report the
results of a simple null test of isotropy using the temperature data released by the Planck
team.
2
Dynamical dark energy and galaxy formation
Luciano Casarini
Universidade Federal do Espirito Santo
[email protected]
Abstract
The influence of Dark Energy parametrization on galaxy formation must be taken into
account, especially in the era of precision cosmology. The different background evolutions
can (depending on the behavior of the DE equation of state) either enhance or quench star
formation with respect to a LCDM model, at a level similar to the variation of the stellar
feedback parametrization, with strong effects on the final galaxy rotation curves.
Cosmological evolution of a Gauss-Bonnet vector dark energy
Enzo Solis Gonzales
Universidad del Atl´antico
[email protected]
Abstract
We explore the possibility that the current accelerated expansion of the universe is due
to the presence of a cosmic vector field coupled to the Gauss-Bonnet invariant and the
Einstein’s Tensor. Under certain conditions the model can be solved by analytical method
and can fit the recent observation for the Hubble parameter H(z), and the state parameter
w(z). The most general model is solved by numerical methods where furthermore is considered a particular potential, a divergence term and the contribution for the matter for a
study of a late times
3
Constraints on dark energy models from CMB Shift Parameter and LSS Growth
Rate measurements
Alexander Bonilla1 , Jorge E. Garc´ıa2 , Juan Maga˜
na3
[email protected], [email protected], [email protected]
1
Departamento de Ciencias Naturales y Exactas, Fundaci´on Universidad Aut´onoma de
Colombia
2
Departamento de F´ısica, Facultad de Ciencias, Universidad Nacional de Colombia.
3
Instituto de F´ısica y Astronom´ıa, Facultad de Ciencias, Universidad de Valpara´ıso, Chile
Abstract
We make use of the most recent observational data from CMB (Plank 13 + WMAP 9) and
LSS (SDSS, WiggleZ, 6dFGS), to put cosmological constraints on different dark energy
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models (ΛCDM , wCDM, CPL, IDE, EDE). The CMB Shift Parameter (R = l1T T /lT1 T )
is used as cosmological test to probe the cosmic expansion from the time of decoupling
(foton-hadron, z ≈ 1090). Moreover, under the assumption that general relativity is the
correct theory of gravity, we use the Linear Growth Factor Structure (D+ ) as cosmological test, through of the Growth Rate Data g(a) ≡ aD0 (a)/D(a) and Growth Parameter
Aobs (z) = f (z)σ8 (z). As complementary tests we use Mass Gas Fracction (fgas ) and SNIa
(Union2.0). The cosmological models are based on paradigm of dark energy, in which this
strange energy density is responsible for the accelerated expansion of the universe. We
study the expansion history trougth of different probes as: deceleration parameter q(z),
Om(z) diagnostic and evolution of ρDE (z), where we found that at low redshift appears
an anomalous behavior of slowdown, which occurs in models with evolution of dark energy
density with redshift. The same time we simulate the growth structure with Gadget2 to
different values of cosmological parameters to each model, where we can study the evolution of the structure at low redshift. Furthermore, we explore the goodness of fit DGP,
which is one of the most popular cosmological models of modified gravity.
Power spectrum of causal primordial magnetic fields with helicity
Hector Hortua
Universidad Nacional de Colombia
[email protected]
Abstract
In this work we compute the exact power spectrum of primordial magnetic fields generated after inflation including the helical contribution.We also show such a effect on the
CMB anisotropy and we compare this result with previous treatment for the non- helical
case.
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Dynamical systems applied to vector fields in the framework of the Horndeski’s
theory
Andres A. Navarro Leon
Universidad Industrial de Santander
[email protected]
Abstract
The presence of anomalies in the observations of WMAP and Planck satellites about
the cosmic microwave background (CMB) creates the possibility that the universe has
a preferred direction, so cosmological models constructed from scalar fields only cannot
explain these new features of the CMB. A possible way to explain these anomalies is by
building inflationary models that involve vector fields since, due to their inherent nature,
they introduce the notion of a spatial direction. Based on the pioneering idea, initially
explored by Horndeski in 1974, where the most general possible action involving a scalar
field and gravity was found, where the equations of motion are, at most, of second order (in
order to avoid the Ostrogradski’s instabilities), we propose to find the most general action,
involving a scalar field, SU(2) vector fields, and gravity and to study the cosmologies
associated with the resulting models. Because of the significant increment in the number
of degrees of freedom due to the introduction of vector fields, studying the inflationary
dynamics of these models can become quite complicated; an alternative to address this
technical difficulty is to study the resultant models by means of the concepts of the theory
of dynamical systems, mainly stability. In summary, by means of analytical and numerical
techniques, and the use of the theory of dynamical systems, we propose to analyze the
resultant cosmologies obtained from finding the mentioned most general Horndeskis action
and to check if the obtained models generate inflationary periods long enough to solve
the classical problems of the standard cosmology. Additionally, we propose to determine
the predictions made by these models regarding the anisotropic expansion and its possible
relation with the anomalies in the CMB.
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Bosonic structure of F-term supersymmetric cosmic strings in a realistic GUT
context
Erwan Allys
Institut d’Astrophysique de Paris
[email protected]
Abstract
Cosmic strings, i.e. linear topological defects which are expected to form during the
Spontaneous Symmetry Breaking (SSB) of Grand Unified Theory (GUT), permit to probe
particle physics up to energies around 101 6 GeV: the lack of observational signatures
provide serious constraints for those theories. Until now, only toy-models have been used
to describe strings, assuming a minimal field content necessary to form them. However,
an actual implementation of their microscopic structure in a realistic particle physic and
cosmological context could give new insights. For example, the property to have the scale
of formation of the strings as only characteristic energy can be wrong, due to possible
contributions of higher energy fields. Moreover, a more complicated microscopic structure,
stemming from the condensation of some GUT fields in the strings, could lead to a more
complicated phenomenology for the bosonic currents which can appear in their core. We
present general results which can be obtained when studying these cosmic strings, first in
a general Supersymmetric (SUSY) GUT with standard or hybrid inflation, and then in a
given SO(10) example, focusing on the bosonic sector of these theories.
Evolution of bi-gravity theories in Bianchi I universes
Josue Motoa Manzano
Universidad del Valle
[email protected]
Abstract
In this work we studied the behavior of a ghost free bigravity theory build on a Bianchi
I metric for both worlds. We describe a two world system (two metric systems) each one
with its own matter content and only coupled by gravity. To do such estudy, we build a
dynamical system and solve it numerically on a variety of initial conditions, such as, type
of matter content, amount of matter content, amount of shear content, ratio of matter and
shear content between the two worlds.
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Dark energy from Gauss-Bonnet and nonminimal couplings
L. N. Granda and D. F. Jimenez
Universidad del Valle
[email protected]
Abstract
We consider a scalar-tensor model of dark energy with Gauss-Bonnet and nonminimal
couplings. Exact cosmological solutions were found in the absence of potential that give
equations of state of dark energy consistent with current observational constraints, but
with different asymptotic behaviors depending on the couplings of the model. A detailed
reconstruction procedure is given for the scalar potential and the Gauss-Bonnet coupling
for any given cosmological scenario. In particular we consider conditions for the existence
of a variety of cosmological solutions with accelerated expansion, including quintessence,
phantom, de Sitter, and Little Rip. For the case of quintessence and phantom we have
found a scalar potential of the Albrecht-Skordis type, where the potential is an exponential
with a polynomial factor.
Semiclassical States in Loop Quantum Cosmology
Edison Montoya
Universidad Industrial de Santander
[email protected]
Abstract
The spatially flat Friedman-Robertson-Walker (FRW) cosmological model with a massless scalar field in loop quantum cosmology admits a description in terms of a completely
solvable model. This has been used to prove that: i) the quantum bounce that replaces
the big bang singularity is generic; ii) there is an upper bound on the energy density for all
states and iii) semiclassical states at late times had to be semiclassical before the bounce.
Here we consider a family of exact solutions to the theory, corresponding to generalized
coherent Gaussian and squeezed states. We analyze the behavior of basic physical observables and impose restrictions on the states based on physical considerations. These turn
out to be enough to select, from all the generalized coherent states, those that behave
semiclassical at late times
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