This series consists of talks in the areas of Cosmology, Gravitation and Particle Physics.
The assumption of spatial homogeneity lies at the heart of the concordance cosmological model. But as I will discuss, truly solid empirical evidence for global (statistical) homogeneity is lacking, and tricky theoretical issues abound. I review a few recent advances in understanding the role inhomogeneity plays in cosmology, including some unexpected effects on light propagation, the death (and rebirth) of backreaction, and impending observational annoyances related to the lumpy local Universe.
One new frontier in cosmology is the frequency spectrum of the CMB. Future instruments may be precise enough to measure deviations from the nearly-perfect blackbody, measuring a chemical potential and thus probing energy injection at extremely high redshift. I will discuss ($\mu$ and $y$-type) CMB spectral distortions from the dissipation of entropy (isocurvature)-sourced acoustic modes. I will then discuss how a high-energy phase transition could also source such distortions.
The Planck satellite measurement of the cosmic microwave background has provided spectacular confirmation of the predictions of inflationary cosmology, putting inflation on a firm footing as the leading theory of the very early universe. I will discuss the implications of Planck for the simplest canonical single-field inflation models, which are favored by the data. Then I will discuss the most general question: How strong is the case that inflation is the "right" theory of the early universe?
The SDSS-III Baryon Oscillation Spectroscopic Survey, now nearly complete, is measuring the three-dimensional cosmic structure with 1.35 million new redshifts. Galaxy clustering measurements provide constraints on the cosmic expansion history through the baryon acoustic oscillation feature and the Alcock-Paczynski effect. In addition, the imprint of galaxy peculiar velocities on the observed galaxy clustering, "redshift-space distortions", provides a measurement of the growth rate of matter perturbations.
The Pan-STARRs supernova survey has discovered one of the largest samples of Type Ia supernovae. Measurements of the distances to these supernovae allow us to probe some of the most fundamental questions about the properties of the universe like what is dark energy. When combining measurements from various astrophysical probes, we find hints of interesting tension with the Lambda-CDM model. I discuss the various combinations of astrophysical probes and the source of this tension.
Direct observation of the small scale structure of matter in the Universe provides potentially important information about a wealth of physics, from complex galaxy evolution processes to fundamental particle properties of dark matter. Detecting this fine structure in dark matter, though, is notoriously difficult. Dark matter indirect detection--through observation of radiation products of particle annihilation--may be the most direct method for observing small scale structure.
After a short introduction to open inflation and the observed large-scale cosmic microwave anomalies, which have been confirmed by the Planck satellite, I'll argue that the anomalies are naturally explained in the context of a marginally-open, negatively curved universe. I'll look in particular at the dipole power asymmetry, and motivate that this asymmetry can happen if our universe has bubble nucleated in a phase transition during a period of early inflation, and, as a result, has open geometry.
The nature of dark matter is a fundamental problem in cosmology and particle physics. Many particle candidates have been devised over the course of the last decades, and are still at stake to be soon discovered or rejected. However, astronomical observations, in conjunction with the phenomenological efforts in astrophysical modeling, as well as in particle theories to explain them, have helped to pin down several key properties which any successful candidate has to have.
Fluctuations of the 21 cm brightness temperature before the formation of the first stars hold the promise of becoming a high-precision cosmological probe in the future. The growth of over densities is very well described by perturbation theory at that epoch and the signal can in principle be predicted to arbitrary accuracy for given cosmological parameters. Recently, Tseliakhovich and Hirata pointed out a previously neglected and important physical effect, due to the fact that baryons and cold dark matter (CDM) have supersonic relative velocities after recombination.
We observe a finite subvolume of the universe, so CMB and large scale structure data may give us either a representative or a biased sample of statistics in the larger universe. Mode coupling (non-Gaussianity) in the primordial perturbations can introduce a bias of parameters measured in any subvolume due to coupling to superhorizon background modes longer than the size of the subvolume. This leads to a "cosmic variance" of statistics on smaller scales, as the long-wavelength background modes vary around the global mean.