Day II

Venue: Auditorio del IAFE, Instituto de Astronomía y Física del Espacio (CONICET-UBA). Pabellón IAFE, Ciudad Universitaria, CABA - Argentina.

Program:

10:00hs: Opening and presentation

10:15-11:15hs:Dr. Sebastián Nuza (IAFE)

Title: "Cosmological shock waves, galaxy clusters and their diffuse radio emission"

Abstract:

Cosmological simulations of structure formation predict the existence of shock waves linked to the evolution of the gaseous component in the cosmic web. These large-scale shock fronts can be broadly classified in two groups: those produced as a result of the accretion of material onto the potential wells determined by the dark matter distribution in the Universe, and those related to the merging of substructures naturally arising within the accepted cosmological hierarchical paradigm. Besides heating the gas at large scales, these shock fronts are ideal sites for particle acceleration which, in the presence of cosmic magnetic fields, may produce non-thermal emission. In this talk, I will discuss the formation of such fronts in Mpc-size astrophysical environments, as well as their link to the generation of large-scale diffuse radio emission. I will mainly focus on the diffuse emission produced within galaxy clusters, which are the most massive bound systems in the Universe, and turn out to be ideal astrophysical laboratories to study the nature and composition of the non-thermal component of cosmic gas.

11:15-11:45hs: Coffe

11:45-12:45hs:Dr. Daniel Supanitsky (ITEDA)

Title: "Constraints on the source models of ultrahigh energy cosmic rays from gamma-ray and neutrino observations"

Abstract:

The origin and nature of the ultrahigh energy cosmic rays (UHECR) are still unknown. However, a big progress have been achieved in past years due to the observations performed by the Pierre Auger and Telescope Array observatories. Above 1 EeV the observed energy spectrum presents two features: a hardening of the slope at about 4 EeV, which is known as the ankle and a suppression at approximately 40 EeV. The composition inferred from the experimental data, interpreted by using the current high energy hadronic interaction models, seems to be light below the ankle, showing a trend towards heavier nuclei for increasing values of the primary energy. Current high energy hadronic interaction models, updated by using the Large Hadron Collider data, are still subject to large systematic uncertainties, which makes difficult the interpretation of the experimental data in terms of composition. On the other hand, it is very well known that gamma rays and neutrinos are produced by UHECR during propagation from their sources, as a consequence of their interactions with the low energy photons of the radiation field present in the universe. The flux at Earth of these secondary particles is correlated with the UHECR composition. Therefore, both gamma-ray and neutrino observations can be used to constrain the source models of UHECR including the composition, in an independent way of the high energy hadronic interaction models. In this talk I will discuss recent results obtained by using gamma-ray and neutrino observations.

12:45-14:15hs: Lunch

14:30-15:30hs: Dra. María José Guzmán (IFLP-UNLP)

Title: “Cosmology in modified Teleparallel gravity”

Abstract:

Modified gravity theories are an active field of research today that encompasses multiple alternatives for the paradigms of modern cosmology and the problems of general relativity. Among them there are theories of gravity based on spacetimes with teleparallel structure, which utilize the tetrad as the dynamic variable instead of the metric. In this talk we will review the predictions of this class of theories in the field of cosmology. A special case of interest are f(T) theories of gravity, which were proposed more than a decade ago as an alternative to explain the accelerated expansion of the universe. In the context of high energy regimes, teleparallel deformations of the Born-Infeld type predict an exponential expansion of the scale factor at the beginning of the universe, and allow to smooth singularities that appear in various solutions of general relativity. Modified teleparallel gravity in all its forms have an intriguing and controversial feature: the loss of local Lorentz invariance, a topic that is recently under intense scrutiny. This characteristic can be understood as a preferential orientation of the field of tetrads for a given geometry. We will examine the relationship between this fact and the additional degree(s) of freedom that this type of theories presents.

15:30-16:00hs: Coffe

16:00-17:00hs: Dr. Gabriel León (OLP-FCAG-UNLP)

Title: “Observational constraints on inflationary potentials within the quantum collapse framework”

Abstract:

The inflationary paradigm is the most successful model for the generation of primordial perturbations. These perturbations have a purely quantum origin, while the inhomogeneities and anisotropies observed today exhibit a classical behavior. That situation is closely related to the quantum measurement problem, which in the cosmological setting appears in an exacerbated manner. A spontaneous collapse of the wave function can solve the measurement problem in quantum mechanics. In this presentation, we will analyze the theoretical predictions resulting from incorporating a specific collapse scheme into the inflationary Universe. In particular, the predictions for the scalar spectral index and the tensor-to-scalar ratio are different from the standard ones. Based on these predictions, we will show that the inflationary potentials allowed by recent observational data are different from the traditional approach.