An alternative singularity-free cosmological scenario from cusp geometries

We study an alternative geometrical approach on the problem of classical cosmological singularity. It is based on a generalized function $f (x, y) = x^{2} + y^{2} = (1 - z)z^{n}$ which consists of a cusped coupled isosurface. Such a geometry is computed and discussed into the context of Friedmann singularity-free cosmology where a pre-big bang scenario is considered. Assuming that the mechanism of cusp formation is described by non-linear oscillations of a pre-big bang extended very high energy density field ($> 3 \times 10^{94} kg/m^{3}$), we show that the action under the gravitational field follows a tautochrone of revolution, understood here as the primary projected geometry that alternatively replaces the Friedmann singularity in the standard big bang theory. As shown here this new approach allows us to interpret the nature of both matter and dark energy from first geometric principles.Comment: Proceedings of Sixth International School on Field Theory and Gravitation-2012 - by American Institute of Physic

Group galaxy number density profiles far out: is the 'one-halo' term NFW out to >10>10 virial radii?

While the density profiles (DPs) of $\Lambda$CDM haloes obey the NFW law out to roughly one virial radius, $r_{\rm vir}$, the structure of their outer parts is still poorly understood, since the 1-halo term describing the halo itself is dominated by the 2-halo term representing the other haloes picked up. Using a semi-analytical model, we measure the real-space `1-halo' number DP of groups out to $20\,r_{\rm vir}$ by assigning each galaxy to its nearest group with mass above $M_{\rm a}$, in units of the group $r_{\rm vir}$. If $M_{\rm a}$ is small (large), the outer DP of groups falls rapidly (slowly). We find that there is an optimal $M_{\rm a}$ for which the stacked DP resembles the NFW model to $0.1$ dex accuracy out to $\simeq 13\,r_{\rm vir}$. We find similar long-range NFW surface DPs (out to $\simeq 10\,r_{\rm vir}$) in the SDSS observations using a galaxy assignment scheme that combines the non-linear virialized regions of groups with their linear outer parts. The optimal $M_{\rm a}$ scales as the minimum mass of the groups that are stacked to the power $0.25-0.3$. Our results suggest that the NFW model does not solely originate from violent relaxation. Moreover, populating haloes with galaxies using HOD models must proceed out to larger radii than usually done.Comment: 5 pages, 4 figures. Accepted for publication in MNRAS Letters. Final version including discussion on the backsplash radiu

A new gravitational N-body simulation algorithm for investigation of cosmological chaotic advection

Recently alternative approaches in cosmology seeks to explain the nature of dark matter as a direct result of the non-linear spacetime curvature due to different types of deformation potentials. In this context, a key test for this hypothesis is to examine the effects of deformation on the evolution of large scales structures. An important requirement for the fine analysis of this pure gravitational signature (without dark matter elements) is to characterize the position of a galaxy during its trajectory to the gravitational collapse of super clusters at low redshifts. In this context, each element in an gravitational N-body simulation behaves as a tracer of collapse governed by the process known as chaotic advection (or lagrangian turbulence). In order to develop a detailed study of this new approach we develop the COsmic LAgrangian TUrbulence Simulator (COLATUS) to perform gravitational N-body simulations based on Compute Unified Device Architecture (CUDA) for graphics processing units (GPUs). In this paper we report the first robust results obtained from COLATUS.Comment: Proceedings of Sixth International School on Field Theory and Gravitation-2012 - by American Institute of Physic

Stellar Population Properties of ETGs in Compact Groups of Galaxies

We present results on the study of the stellar population in Early-Type galaxies (ETGs) belonging to 151 Compact Groups (CGs). We also selected a field sample composed of 846 ETGs to investigate environmental effects on galaxy evolution. We find that the dependences of mean stellar ages, [Z/H] and [$\alpha$/Fe] on central stellar velocity dispersion are similar, regardless where the ETG resides, CGs or field. When compared to the sample of centrals and satellites from the literature, we find that ETGs in GCs behave similarly to centrals, especially those embedded in low-mass haloes ($M_{h} < 10^ {12.5}M_{\odot}$). Except for the low-mass limit, where field galaxies present a Starforming signature, not seen in CGs, the ionization agent of the gas in CG and field galaxies seem to be similar and due to hot, evolved low-mass stars. However, field ETGs present an excess of H$\alpha$ emission relative to ETGs in CGs. Additionally, we performed a dynamical analysis, which shows that CGs present a bimodality in the group velocity dispersion distribution - a high and low-$\sigma$ mode. Our results indicate that high-$\sigma$ groups have a smaller fraction of spirals, shorter crossing times, and a more luminous population of galaxies than the low $\sigma$ groups. It is important to emphasize that our findings point to a small environmental impact on galaxies located in CGs. The only evidence we find is the change in gas content, suggesting environmentally-driven gas loss.Comment: 21 pages, 18 Figure

SIR-SI model with a Gaussian transmission rate: Understanding the dynamics of dengue outbreaks in Lima, Peru

Introduction Dengue is transmitted by the Aedes aegypti mosquito as a vector, and a recent outbreak was reported in several districts of Lima, Peru. We conducted a modeling study to explain the transmission dynamics of dengue in three of these districts according to the demographics and climatology. Methodology We used the weekly distribution of dengue cases in the Comas, Lurigancho, and Puente Piedra districts, as well as the temperature data to investigate the transmission dynamics. We used maximum likelihood minimization and the human susceptible-infected-recovered and vector susceptible-infected (SIR-SI) model with a Gaussian function for the infectious rate to consider external non-modeled variables. Results/principal findings We found that the adjusted SIR-SI model with the Gaussian transmission rate (for modelling the exogenous variables) captured the behavior of the dengue outbreak in the selected districts. The model explained that the transmission behavior had a strong dependence on the weather, cultural, and demographic variables while other variables determined the start of the outbreak. Conclusion/significance The experimental results showed good agreement with the data and model results when a Bayesian-Gaussian transmission rate was employed. The effect of weather was also observed, and a strong qualitative relationship was obtained between the transmission rate and computed effective reproduction number Rt

SIR-SI model with the Gaussian exogenous variable and climatic conditions adjusted for 2017.

The adjusted analysis without the exogenous variable is in green, and the adjusted analysis with model 4 is in red.</p

Values of the adjusted parameters for each model in the experiments.

Values of the adjusted parameters for each model in the experiments.</p

Fig 5 -

Cross-correlation between temperature and cases: Comas in (A) 2017 and (B) 2020, Lurigancho in (C) 2017 and (D) 2019, Puente de Piedra in (E) 2020, and (F) the total. The vertical red line indicates the point of maximum correlation.</p