Multi-tracer surveys of large-scale structure and the J-PAS survey Raul Abramo (IF - USP)
Astrophysical surveys are targeting an increasing number of different types of galaxies and other extragalactic
objects. The potential of these surveys is significantly improved by this wide variety of tracers of the large-scale
structure, and in fact our understanding about the formation of these objects, as well as their environments, is
becoming increasingly intertwined with the cosmological applications of these datasets. Additional advantages of
multi-tracer surveys of the cosmos are the enhanced constraints on cosmological parameters, which can even appear
to violate the bounds imposed by cosmic variance. I will show how this is possible, which parameters can benefit
from the multi-tracer analysis, and what are the constraints which can be achieved by the next generation of
astrophysical surveys. In particular, I will discuss how these ideas can be employed in J-PAS (the Javalambre
Physics of the Accelerating Universe Astrophysical Survey), which, starting in 2015, will use narrow-band filters
to obtain a low-resolution spectrum of 1/5 of the whole sky.
Scalar self-force in Schwarzschild spacetime Marc Casals (ICRA - CBPF)
The centers of most galaxies host supermassive black holes which are eagerly devouring smaller astrophysical
objects in their vicinity and emitting gravitational waves in the process. The detection of these waves would open up a
unique window into our Universe. In the extreme mass-ratio limit, the inspiral can be viewed as the smaller object deviating
from a geodesic of the background spacetime of the supermassive black hole due to the action of its own field, the self-force.
In this talk we will introduce novel methods for the calculation of the self-force which are based on the Green function of
the wave equation obeyed by field perturbations of the background spacetime. We will focus on the case of a scalar charge in
Schwarzschild spacetime, which serves as a useful toy-model for the gravitational case. We will present a spectroscopy analysis
of the Green function, which includes characteristic resonances ('quasinormal modes') and a branch cut in the complex-frequency
plane. We will apply this analysis to reveal geometrical properties of wave propagation on a black hole spacetime and to calculate
the scalar self-force.
Shape of black holes María Eugenia Gabach (FaMAF - UNC, IFEG - CONICET)
It is well known that celestial bodies tend to be spherical due to gravity and that rotation produces
deviations from this sphericity. We explore these issues on axisymmetric black holes, both in stationary and
dynamical regimes. We find that black hole rotation indeed manifests in the widening of their central regions,
limits their global shapes and enforces their whole geometry to be close to the extreme-Kerr horizon geometry at
almost maximal rotational speed. The results, which are based on the stability inequality, depend only on the
horizon area and angular momentum. In particular they are entirely independent of the surrounding geometry of the
space-time and of the presence of matter satisfying the strong energy condition. We also discuss the relations and
applications of this result to the Hoop conjecture.
New geometries for the characterization of dark matter phenomena Osvaldo Moreschi (UNC)
The standard characterization of dark matter phenomena is through models that
assume the generally accepted cold dark matter model.
However, when studying dark matter phenomena with different techniques one
often finds non-trivial disagreement among the measurements. Notably, when estimating
the matter content in a region using gravitational
weak lensing effects and dynamical studies, the different techniques do not coincide
in the estimated value. These problems might be related to the way one normally deals
with inhomogeneities in cosmology.
We will comment briefly on the inherent problems involved in the notion of averaging of tensors;
that contribute to unexpected terms in the energy momentum tensor. In a previous study of weak
lensing we have noticed that a spacelike contribution
of the energy-momentum tensor has been neglected in previous works. We will present some new
geometries that involve new kind of energy momentum tensors
which are suitable for the description of dark matter phenomena.
Precision Cosmology with Voids Santiago Patiri (IANIGLA - CONICET)
In recent years, significant progress has been made in the accuracy of measurements of cosmological
parameters, thanks mainly to new CMB experiments and large scale galaxy surveys, resulting in a new
era for Cosmology known as “Precision Cosmology”. In order to keep improving results, it is essential
to measure the parameters with different techniques and data.
In this presentation I discuss a novel method to constrain cosmological parameters using the large
underdensities found in the large scale structure of the Universe, the so-called voids. In particular,
I show how to constrain the values of Sigma_8 and Omega_m h, and present results obtained using data
from the Sloan Digital Sky Survey. I also discuss work in progress on constraining other parameters
such as the equation of state for Dark Energy and non-Gaussianity.
Measuring sigma_8 with Weak Lensing of Supernovae Miguel Quartin (IF - UFRJ)
Soon the number of type Ia supernovae (SNe) measurements should surpass $10^5$. Understanding weak
lensing effects in these objects will then be more important than ever. Although SNe lensing is usually
seen as a source of systematic noise in this talk I will show how this noise can be in fact turned into signal.
To accomplish this I will first describe how we were able to accurately model the lensing effects and provide
simple analytical fits to describe it. I will then show that the non-gaussianity introduced by lensing in the SNe
Hubble diagram dispersion is basically modulated by Omega_m0 and sigma_8. Finally, I will argue that the modelling
of such non-gaussianity allows for an independent measurement of sigma_8 with supernova data and present a first
measurement with real data.
Radiation Production and Stochastic Effects during Inflation Rudnei Ramos (IF - UERJ)
Nonisentropic inflation models are characterized by radiation production due to the decay of fields
coupled to the inflaton during inflation and that might sustain a thermal radiation bath as a result
of the dissipative particle production. The presence of the radiation bath can impact on the dynamics
of inflation and, consequently, on the observable quantities measured from the cosmic microwave background
radiation. In particular, the amplitude of primordial curvature perturbations is enhanced and this is
particularly significant when a non-trivial statistical ensemble of inflaton fluctuations is also maintained.
Since gravitational modes are decoupled from the radiation bath for energies well below the Planck scale,
the presence of the thermal radiation bath and/or a non vanishing statistical ensemble for the inflaton generically
lowers the tensor-to-scalar ratio and yields a modified consistency relation for warm inflation, as well as changing
the tilt of the scalar spectrum. This is able to alter the landscape of observationally allowed inflationary models,
with for example the quartic chaotic potential being in very good agreement with the Planck results for nearly-thermal
inflaton fluctuations, whilst essentially ruled out for an underlying vacuum state. Besides of dissipative effects,
these are also accompanied by stochastic fluctuations. Both the origin and the impact of these effects on the inflationary
dynamics is explained in this talk.
Concepts and science drivers of the Cherenkov Telescope Array Adrián Rovero (IAFE - CONICET)
The Cherenkov Telescope Array (CTA) is the next generation ground-based instrument for the
observation of very-high-energy gamma rays. It will provide an order of magnitude more sensitivity
in an extended energy range (20 GeV to 100 TeV) than currently operating instruments (VERITAS, MAGIC, HESS).
The CTA will cover the full sky by constructing two observatories, one in each hemisphere, composed of more
than a hundred Cherenkov telescopes of three different sizes. With improved sensitivity and angular resolution
CTA will help to address a number of important open questions in astrophysics and fundamental physics.
This talk will present the basic concepts of CTA and highlight some of its science drivers.
Quantum Gravity with Higher Derivatives and the Problem of Massive Ghosts Ilya L. Shapiro (IF - UFJF)
The main problem of Quantum Gravity is the conflict between
renormalizability and unitarity. The quantum version of GR is
non-renormalizable, and when we provide renormalizability by
introducing higher derivatives, the particle spectrum of the
theory includes massive unphysical ghosts. Removing the ghosts
from the spectrum leads to violated unitarity. In order to
check whether the ghosts really pose a danger, one can explore
the dynamics of metric perturbations (gravitational waves) at
the tree-level in the theory with higher derivatives. In the
recent papers we have shown that, in case of the cosmological
background, there are no traces of ghosts beyond the Planck
scale. Now we try to formulate the problem in a more general
setting and explore more general backgrounds and more general
higher derivative theories, corresponding to a superrenormalizable
versions of quantum gravity.
Neutrino emission from Gamma-Ray Bursts Florencia L. Vieyro (IAR - CONICET)
Gamma-ray bursts (GRBs) are the most violent and energetic events in the universe. Short GRBs seem to be
the result of the final merger of two compact objects, whereas long GRBs are probably associated with the
gravitational collapse of very massive stars (collapsars).
The central engine of a GRB can collimate relativistic jets that propagate inside the stellar envelope.
Although the location of the exact region where the gamma rays are created is still under debate, it is
widely accepted that the prompt emission has a different origin from the afterglow emission. The latter
is produced at much longer distances from the central engine, where the jet is decelerated by its
interaction with the interstellar medium.
The prompt gamma-ray radiation and the afterglows are likely generated by relativistic electrons accelerated
in shock fronts. The same shocks should also accelerate baryons leading to neutrino production, a distinctive
signature of hadronic interactions.
In this talk I shall review different scenarios where neutrinos with energies from MeV to EeV can be produced
in the collapse of massive stars and the subsequent processes. I shall also briefly discuss the case of short GRBs.