Found 93 talks archived in Cosmology

The concordance model of cosmology with its constituents dark matter and dark Energy is an established description of some anomalous observations. However, a series of additional contradictions indicate that the current view is far from satisfactory. Rather than describing observations with new numbers, it is argued that science should reflect its method, considering the fact that real progress was usually achieved by simplification. History, not only with the example of the epicycles, has shown many times that creating new ad-hoc concepts dominated over putting in doubt what had been established earlier. Also critical astrophysicists often believe that lab-tested particle physics has reliable evidence for its model. It is argued instead that the very same sociological and psychological mechanisms have been at work and brought particle physics in a still more deperate situation long ago. As an example, a couple of absurdities of the recent Higgs boson announcements are outlined. It seems inevitable that physics needs a new culture of data evaluation, raw data and source code must become equally transparent and openly accessible.

I will discuss how the acoustic oscillations that propagate in the photon-baryon fluid during the first million years of the Universe provide a robust method for measuring the cosmological distance scale. The distance that the sound can travel can be computed to high precision and creates a signature in the late-time clustering of matter that serves as a standard ruler. Galaxy clustering results from the Sloan Digital Sky Survey reveal this feature, giving a geometric distance to a redshift of 0.3 and an accurate measurement of Omega_matter. I will review our recent work on the theory and practice of the acoustic oscillation method and our latest cosmology results from SDSS-II. I will then present SDSS-III, which will use the acoustic method to produce 1% distance measurements in order to map the curvature and expansion history of the Universe and measure the evolution of dark energy.

The European Space Agency's Planck satellite was launched on 14 May 2009, and has been surveying the sky stably and continuously since 13 August 2009. Its performance is well in line with expectations, and it will continue to gather scientific data until the end of its cryogenic lifetime. I will present the first scientific results of the mission, which appeared as a series of 26 papers at the beginning of this year 2011, covering a variety of astrophysical topics. In particular, I will focus on the results on galactic diffuse emissions, as well as the first results on galaxy clusters detected by means of the Sunyaev-Zeldovich effect.

I revisit the claim of Dark Energy detection after stacking CMB data on the angular position of voids and superclusters in Sloan Data. I examine the theoretically expected amplitude for the ISW-induced signal and explore its scale dependence. I next confront these predictions with results obtained from real WMAP data, and evaluate the degree of agreement and the possible presence of contaminants. In a more general context, I address the possibility of unveiling the signature of Dark Energy on the CMB by looking at isolated regions on the sky hosting high-threshold projected under/over-densities: this constitutes a novel approach since it is less sensitive to large angle systematics commonly present in large scale structure surveys.

In this talk I will review the subject of cosmological inflation, a period of early accelerated expansion. I will discuss Friedmann-Robertson-Walker cosmology and the horizon and flatness problems, and introduce inflation as a solution to those problems. I will also discuss the generation of  the primordial (scalar and tensor) spectrum of perturbations which provides the seeds for the large scale structure in the Universe. I will review quickly the status of observations in relation to the inflationary parameters, and then the implications for model building.

I will review some theoretical ideas in Cosmology different to the standard "Big Bang": the Quasi-steady State model, Plasma Cosmology model, non-cosmological redshifts, alternatives to non-baryonic dark matter and/or dark energy, and others. Some open problems of Cosmology within the standard model will also be summarized.

In the first part of this talk I will present a historical review of the CMB observations, one of the most powerful cosmological probes. Following the first talk of this series, where Jose Alberto described the basic parameters that define the standard cosmological model, I will here summarize the constraints to these parameters that have been derived from these observations. I will also describe the current challenges in this field, in particular the detection of the inflation's B-mode signal through CMB polarization observations, as well as the experiments that have been developed worldwide to this aim, including IAC's QUIJOTE. In the second part, I will focus on the so-called ``missing baryon problem'', i.e. the fact that the half of the expected baryon content of the local universe remains yet undetected. I will describe the theoretical studies that provide hints on where these baryons could be located, and the observational efforts that have been undertaken in this regard.

This is the first talk of a series of four aimed to discuss about Cosmology. Here, I will review the basic concepts of the standard cosmological model, which will be further discussed in the following talks, as well as the observational evidence in support of the Lambda-CDM model. As the subject is very broad, I will focus the discussion on topics related with inflation, dark matter and dark energy. Moreover, I will mainly discuss large scale structure probes.

The extragalactic background light (EBL) is of fundamental importance both for understanding the entire process of galaxy evolution and for gamma-ray astronomy, but the overall spectrum of the EBL between 0.1 and 1000 microns has never been determined directly from galaxy spectral energy distribution (SED) observations over a wide redshift range. Galaxy SED-type fractions from z=0.2-1 are estimated from a multi-wavelength sample from the AEGIS collaboration that allows a new determination of the evolving EBL. Then, the transparency of the Universe to very high energy (VHE) gamma-ray photons is derived. We find the maximum transparency of the Universe allowed by the standard framework. This result challenges current VHE observations of high redshift blazars. A solution to this problem is discussed utilizing VHE spectra of the highest redshift blazars assuming the existence of a plausible dark matter candidate known as axion-like particle.