Authors: Renan I. Boschetti
Abstract:
We generated a Log-Normal galaxy map for two different tracers and obtained from this map the monopole and quadrupole for each tracer. With these observables we performed an MCMC in order to measure the growth rate of density perturbations. Our main goal in the future is to study modified gravity, with the same technique, by measuring the growth rate.
Authors: Luciano Combi (IAR, Pereyra, Argentina) and Eduardo M. Gutiérrez (IAR, Pereyra, Argentina).
Abstract: There are several non-equivalent models that attempt to describe a black hole immerse in an expanding background. These models exhibit different causal structures for a given cosmological scale factor and their physical interpretation is non-trivial. The orbits of particles and photons around the collapsed system are also important to explore the astrophysical applications of these metrics. In this work, we investigate bounded geodesics for three different metrics representing a Schwarzschild black hole embedded in a FLRW universe. We analyze the existence of circular orbits and we solve numerically the motion equations in order to compare the evolution of test particle through the cosmological history of the universe in each of these models.
Author: Edilson de Carvalho Filho (ON, Rio de Janeiro, Brazil).
Abstract: The Baryon Acoustic Oscillation (BAO) phenomenon imprinted a characteristic scale to the spatial distribution of matter. Here we follow a quasi model-independent approach to measure the transversal BAO mode at high redshift using the three-point angular correlation function (3PACF). This analysis is only possible now with the quasars catalog from the twelfth data release (DR12Q) from the Sloan collaboration, because it is dense enough (in redshift space) to measure the angular BAO signature with high statistical significance and acceptable precision. Our analyses considering quasars in the redshift interval z=[2.20,2.25] produced the angular BAO scale at 1.45º \pm 0.37º in the 3PACF with two sides of triangle fixed at 1.0º and 1.5º.
Author: Martín de los Rios (IATE, Córdoba, Argentina) and Mariano Javier de Leon Dominguez Romero (IATE, Córdoba, Argentina).
Abstract: In this work we present the first measurement of the spatial distribution of the cosmological parameters performed with Machine Learning Techniques.
This approach has the advantage of reduce the cpu-time involved in the parameters estimation without losing precision. Taking into account that is very simple to add more cosmological probes within this formalism, this work is the first step to an automatic method for the estimation of the cosmological parameters using different cosmological probes.
Author: Caroline Guandalin (IF-USP, São Paulo, Brazil).
Abstract: We are developing a code that will compute the bispectrum of mock catalogs of multiple tracers of large-scale structure. By comparing
the spectra and bispectra of the different tracers we will measure
physical parameters such as non-Gaussianities at the same time as we
measure the biases of those tracers, breaking some of the relevant
degeneracies.
Author: María José Guzmán Monsalve (IAFE, Buenos Aires, Argentina).
Abstract: f(T) gravity, a kind of modified teleparallel theory of gravity, has attracted a lot of attention in the recent years due to its hability to predict an early accelerated expansion of the Universe without resorting to an inflaton field, and since it allows to smooth black-hole singularities for certain schemes. This theory is a generalization of the teleparallel equivalent of general relativity, a dynamical theory for the tetrad or vielbein, and it is based in the torsion of the Weitzenböck connection, describing a spacetime with zero curvature but non-vanishing torsion. This theory is not local Lorentz invariant; that is, the equations of motion are sensible to local Lorentz transformations of the tetrad in the tangent space. We will present recent findings concerning to McVittie and FLRW solutions and its relation with the additional degrees of freedom of the theory.
Author: Jiamin Hou (Max Planck Institute for Extraterrestrial Physics, Garching/Munich, Germany).
Abstract: We explore the cosmological implications of anisotropic clustering measurements of the quasar sample from Data Release 14 of the Sloan Digital Sky Survey IV Extended Baryon Oscillation Spectroscopic Survey (eBOSS) in configuration space. The ~147,000 quasar sample observed by eBOSS offers a direct tracer of the density field and bridges the gap of previous BAO measurements between redshift 0.8 < z < 2.2. By analysing the two-point correlation function characterized by clustering wedges xi_w_i(s) and multipoles xi_ell(s), we measure the angular diameter distance, Hubble parameter and cosmic structure growth rate. We define a systematic error budget for our measurements based on the analysis of N-body simulations and mock catalogues. Based on the DR14 large scale structure quasar sample at the effective redshift z_eff=1.52, we find the growth rate of cosmic structure f\sigma_8(z_eff)=0.396 \pm 0.079, and the geometric parameters D_V(z)/r_d=26.47 \pm 1.23, and F_AP(z)=2.53 \pm 0.22, where the uncertainties include both statistical and systematic errors. These values are in excellent agreement with the best-fitting standard LCDM model to the latest cosmic microwave background data from Planck.
Author: Tomás Hough (FCAGLP, La Plata, Argentina).
Abstract: Several internal self-regulated processes affect the content of the hot gas halo and the cold gas disc of galaxies.
The former is reduced by gas cooling, contributing to increase the cold gas reservoir, which in turn is reduced by star formation and supernova feedback.
When a galaxy is accreted into a more massive halo and becomes a satellite, external physical processes, like ram pressure and tidal stripping, become important in removing the galaxy's hot and cold gas, hence affecting its
star formation rate. The time-scale in which a satellite galaxy is quenched (e.g., is transformed from star-forming to passive) due to these processes depends both on its stellar mass
and its evolutionary stage, which is tied to the orbital evolution and the mass growth of the main host halo.
Our analysis of the quenching time-scales helps to understand how star formation quenching occurs.
Author: Leonardo Leitao (IFIBA, Buenos Aires, Argentina).
Abstract: There are several projects to build Gravitational Waves (GWs) spaceborne detectors as LISA. A frequency signal in the detection range would be generated in the electroweak scale. This work focuses on GWs generation from the electroweak phase transition.
Author: Gabriel León (FCAGLP, La Plata, Argentina).
Abstract: We reevaluate the predictions of inflation regarding primordial gravity waves, which should appear as B-modes in the CMB, in light of the fact that the standard inflationary paradigm is unable to account for the transition from an initially symmetric state into a non-symmetric outcome. We show that the incorporation of an element capable of explaining such a transition dramatically alters the prediction for the shape and size of the B-mode spectrum. In particular, we find that by adapting a realistic objective collapse model to the situation at hand, the B-mode spectrum gets strongly suppressed with respect to the standard prediction.
Author: Martha Lippich Golobart (Max-Planck Institute for Extraterrestial Physics, Garching/Munich, Germany).
Abstract: The Euclid survey will provide galaxy-clustering measurements over large cosmic volumes to unprecedented statistical uncertainty. In order to infer cosmological parameters from the analysis of galaxy clustering the knowledge of the associated covariance matrix is essential. Therefore, the production of thousands of independent realizations is required, since noise due to the finite number of realizations will propagate into the final cosmological parameter constraints. Running a large number of N-body simulations is expensive in terms of run-time and memory, hence fast approximate schemes for gravitational structure formation and evolution will likely be used. We present a detailed comparison of the covariance matrices of anisotropic two-point correlation function measurements, which are obtained from several fast approximate methods including ICE-COLA, Halogen, Peak Patch, PINOCCHIO, PATCHY, as well as a simple Gaussian model and a log-normal mock catalogue.
Author: Rafael Christ Lopes (IFUSP, São Paulo, Brazil).
Abstract: We investigate the spherical collapse model in a class of modified gravity (MG) models, namely the $f(R)$ scenario. We have computed numerically the density contrast (delta) at the moment of turnaround (delta(t)). We also illustrate the main differences between MG and the LCDM model. We show that (delta(t)) is sensitive to MG evidencing the potential of the turnaround radius as an observable that can reveal differences between these GR and MG. We also compute the turnaround radius in both the context of LCDM and f(R), and argue that by measuring the turnaround radius in large-scale structures we can constrain the parameters of f(R) models.
Author: Pablo López (IATE, Córdoba, Argentina).
Abstract: Dark matter halos (DM) are the largest virialized structures in the Universe. Their internal dynamics are linked to the history of the galaxies, groups and clusters which form on their potential wells, but also to the large-scale structure of the Universe. Therefore, understanding the dynamical properties of halos becomes a keystone in any cosmological and galaxy formation model. The tidal torque theory (TTT) naturally relates the origin and evolution of angular momentum to the characteristics of the environment in which DM halos formed. Even though TTT is the most accepted model on the current paradigm, its validity range is limited to the early times of structure formation, and its predictions contrast in several aspects with measurements obtained from cosmological simulations on their non-linear stages. In this work, we study and characterize systematic deviations from the TTT model performing a statistical analysis of different DM halo populations in a cosmological simulation. We find that the classification according to their angular momentum growth results in samples with different levels of clustering and radically different distributions of spin parameters. Based on this classification, we find a strong correlation between the angular momentum history and the well known mass dependent alignment between the angular momentum direction and the large-scale structure. Our study suggests that a secondary tidal torque mechanism could be acting during the non-linear stages of halo formation.
Author: Geferson Lucatelli (FURG, Rio Grande, Brazil).
Abstract: Classification of galaxies can help understand their formation and evolution. We use a nonparametric morphometry approach to investigate the presence of multicomponent in galaxies, like bulges and disks.
One basic diagnostic tool consist in calculating the curvature k(R) of the galaxy surface brightness profile I(R); From k(R) we can identify the presence of more than one photometric component and their relative size, thus allowing the estimation of bulge to disk ratio, which is a crucial parameter to understand galaxy structure.
Alternatively, we also measure non standard entropies in the galaxy image with the purpose of identifying substructures in the light distribution. Our measurements are accomplished with the {Morfometryka} algorithm. Our first steps consists in applying the technique to synthetic mock images of galaxies in order to understand how the measuremtens are correlated with implicit parameters. We then follow by applying it to observations.
Author: Nahuel Miron-Granese (UBA, Buenos Aires, Argentina).
Abstract: We consider the evolution of the gravitational wave spectrum for super-Hubble modes in interaction with a relativistic fluid, which is regarded as an effective description of fluctuations in a light scalar minimally coupled field, during the earliest epoch of the radiation dominated era after the end of inflation. We obtain the initial conditions for gravitons and fluid from quantum fluctuations at the end of inflation, and assume instantaneous reheating. We model the fluid by using relativistic causal hydrodynamics. There are two dimensionful parameters, the relaxation time $\tau$ and temperature. In particular we study the interaction between gravitational waves and the nontrivial tensor (spin 2) part of the fluid energy-momentum tensor. Our main result is that the new dimensionful parameter $\tau$ introduces a new relevant scale which distinguishes two kinds of super-Hubble modes. For modes with $H^{−1} < \lambda < \tau$ the fluid-graviton interaction increases the amplitude of the primordial gravitational wave spectrum at the electroweak transition by a factor of about $1.3$ with respect to the usual scale invariant spectrum.
Author: Carolina Negrelli (FCAGLP, La Plata, Argentina).
Abstract: We perform a test of the Modified Gravity theory of John Moffat (MOG) within our own Galaxy, the Milky Way, adopting the well known “Rotation Curve” method. We use the dynamics of observed tracers within the disk to determine the gravitational potential as a function of galactocentric distance, and compare that with the potential that is expected to be generated by the visible component only (stars and gas) under different “flavors” of the MOG theory, making use of a state-of-the-art setup for both the observed tracers and baryonic morphology. Our analysis shows that in its original formulation the theory fails to reproduce the observed rotation curve with an extremely high statistical significance. An additional test, performed with a modification of the theory to account for a self-consistent evaluation of the Milky Way mass, also falls short of solving the discrepancy. We conclude that in none of its present formulation, the MOG theory is able to explain the observed Rotation Curve of the Milky Way.
Author: Andres Daniel Perez (IFIBA, Buenos Aires, Argentina).
Abstract: Axino and gravitino particles are among the most promising candidates from supersymmetry (SUSY) frameworks to solve the dark matter identity problem. Both of them can easily evade the stringent direct detection limits and provoke fundamental changes in the cosmology of the Universe. Whether either, axino or gravitino, is the lightest supersymmetric particle (LSP) and the other is the next-to-LSP (NLSP) an exciting interplay arise. Moreover, distinct cosmological scenarios befall depending on the era in which the NLSP decays to the LSP in a so-called decaying dark matter model (DDM). If the decay takes place between recombination and present era, stringent constraints exist, and studies claim that DDM models can relax some cosmological tensions. Furthermore, the breaking of R-parity in SUSY models implies that the LSP, either the gravitino or the axino, can decay to a neutrino and a photon, giving a potentially detectable signal. In this work, we carry out a complete analysis of the parameter space for SUSY models considering constraints from cosmological observations, $\gamma$-ray experiments, and neutrino physics. In particular, we pay careful attention to the $\mu$ from $\nu$ supersymmetric model ($\mu\nu$SSM), which solves the $\mu$ problem of SUSY frameworks and reproduces neutrino observed data, only using couplings with right-handed neutrinos $\nu$'s. Finally, we show that either, the gravitino or the axino can produce a $\gamma$-ray signal detectable by the proposed e-Astrogam mission, and in a particular parameter region, a double 'smoking gun' could be present simultaneously from both candidates.
Author: Marcos Ramirez (INENCO, Salta, Argentina).
Abstract: In this work we construct new solutions of the Einstein-Gauss-Bonnet field equations in an isotropic Shiromizu-Maeda-Sasaki brane-world setting which represent a couple of Z2-symmetric vacuum thin shells splitting from the central brane, and explore the main properties of the dynamics of the system. The matching of the separating vacuum shells with the brane-world is as smooth as possible and all matter fields are restricted to the brane. We prove the existence of these solutions, derive the criteria for their existence, analyse some fundamental aspects or their evolution and demonstrate the possibility of constructing cosmological examples that exhibit this feature at early times. We also comment on the possible implications for cosmology and the relation of this system with the thermodynamic instability of highly symmetric vacuum solutions of Lovelock theory.
Author: R.R.Rosa, R.R. de Carvalho, P.H. Barchi, R.A. Sautter (INPE- Brazil)
Abstract: This paper presents machine learning experiments performed over results of galaxy classification into elliptical (E) and spiral (S) with morphological parameters: concentration (CN), asymmetry metrics (A3), smoothness metrics (S3), entropy (H) and gradient pattern analysis parameter (GA). Except concentration, all parameters performed a image segmentation pre-processing. For supervision and to compute confusion matrices, we used as true label the galaxy classification from GalaxyZoo. With a 48145 objects dataset after pre-processing (44760 galaxies labelled as S and 3385 as E), we performed experiments with Support Vector Machine (SVM) and Decision Tree (DT). Whit a 1962 objects balanced dataset, we applied K-means and Agglomerative Hierarchical Clustering. All experiments with supervision reached an Overall Accuracy, OA ≥ 97%.
Author: Henrique Rubira (USP, S\~ao Paulo, Brazil).
Abstract: We present the 3Loops effective field theory of LSS. Until now the EFTofLSS was done only until 2Loops.
Author: Simony Santos da Costa (ON, Rio de Janeiro, Brazil).
Abstract: The current available Cosmic Microwave Background (CMB) data show an anomalously low value of the CMB temperature fluctuations at large angular scales (l< 40). This lack of power is not explained by the minimal LCDM model, and one of the possible mechanisms explored in the literature to address this problem is the presence of features in the primordial power spectrum (PPS) motivated by the early universe physics. In this work, we analyse a set of cutoff inflationary PPS models using a Bayesian model comparison approach in light of the latest CMB data from the Planck Collaboration. Our results show that the
standard power-law parameterisation is preferred over all models considered in the analysis, which motivates the search for alternative explanations for the observed lack of power in the CMB anisotropy spectrum.
Author: Rodrigo Voivodic (IFUSP, São Paulo, Brazil).
Abstract: We develop a new method to construct nonlinear catalog. This method is based in the halo model and excursion set ideas where we construct the halo catalog from the initial gaussian conditions and put dark matter particles (or galaxies) in these halos to obtain, in a fast way, a nonlinear catalog that mimics the N-body simulated catalogs.
Author: Lucas Zenocratti (FCAGLP, La Plata, Argentina).
Abstract: Early type galaxies constitute one of the largest populations inhabiting groups and clusters in the local Universe. Thus, their study might provide important clues to understand the process of formation and evolution of structures in the Universe. Results from a statistical analysis on this type of galaxies in numerical simulations within cosmological context will be presented. Integrated properties of such simulated systems will be analyzed at redshift z=0 in order to establish the main astrophysical processes which detetermine their evolution. The ability of models to reproduce observational results will be also tested.