Talks & Events
KICP Colloquia: 2013
Covering the Bases
One of the principal aims of cosmology today is to seek subtle correlations in primordial perturbations, beyond the standard two-point correlation that has been mapped precisely already, that may hint at new physics beyond that in the simplest single-field slow-roll models. I will describe in this talk a new class of such correlations and how they may be sought with galaxy surveys and in the CMB. I will then turn my attention to a new formalism, total-angular-momentum (TAM) waves, that my collaborators and I have recently developed. In most of the literature, cosmological perturbations are decomposed into Fourier modes, or plane waves. However, for calculations that aim to produce predictions for angular correlations on a spherical sky, a decomposition into TAM waves provides a far more direct and intuitive route from theory to observations. I will describe the formalism and illustrate with applications to cosmic shear, three-point correlation functions, and redshift-space distortions.
New CMB Results from the South Pole Telescope
The South Pole Telescope (SPT) recently completed a 2500 square degree survey of the sky in the 3mm, 2mm and 1.4 mm bands with an unprecedented combination of resolution, area, and sensitivity. The data from this survey has enabled a number of studies, including the most precise measurement of the sub-degree primordial CMB anisotropy to date. This talk will review this measurement and the resulting cosmological constraints. The new SPT data, in conjunction with data from the WMAP satellite and low-redshift measurements, leads to strong constraints on the number of neutrino-like particle species present in the early universe, the sum of the neutrino masses, and the shape of the power spectrum of primordial density fluctuations. I will also give a brief update on the status of SPTpol, the new polarization-sensitive receiver on the SPT.
CMB Results from WMAP and ACT
Acoustic processes in the plasma which pervades the early Universe govern the shape of the anisotropy of the cosmic background which has been measured by WMAP and other probes, notably ACT and the South Pole Telescope. I'll describe what we have learned, and what we have not learned from precise measurements of the temperature and polarization anisotropy of the CMB. Once the Universe became transparent, these acoustic signals stopped propagating. The density variations associated with them have remained fixed in co-moving (expanding) coordinates. I'll finish by talking about CHIME, the Canadian Hydrogen Intensity Mapping Experiment, CHIME, a collaboration to build a novel radio telescope designed to measure these same acoustic features at the much later epoch when cosmic acceleration from dark energy is important.
Shedding light on dark matter and astrophysical sources with gamma-ray anisotropy
Gamma rays probe the most energetic processes in the universe and are a promising tool to search for signatures of new physics. One current mystery in high-energy astrophysics is the origin of the diffuse gamma-ray background. The contribution of undetected sources is expected to induce small-scale anisotropies in this emission, and these may provide a means of identifying and constraining the properties of its contributors. I will review the results of the first anisotropy analysis of the diffuse gamma-ray background measured by the Fermi Large Area Telescope, and highlight the new constraints this measurement has placed on high-energy source populations, focusing on implications for blazar population models and for a signal from the annihilation or decay of dark matter particles. I will also present new multi-wavelength techniques for unraveling contributors to diffuse emission.
The secret lives of galaxy clusters
Galaxy clusters have the potential to be highly accurate probes of cosmological parameters. However, they are also very interesting astrophysical objects in their own right! The properties that make clusters irritating to those who wish to use them for cosmology - deviations from sphericity and hydrostatic equilibrium, shocks, mergers, and a variety of baryonic processes - provide a tremendous amount of information about these massive beasts. I will present recent efforts to understand the effects that correctly modeling the properties of gas in cosmological simulations have on the observable properties of clusters, focusing on shocks and the non-thermal components of the intracluster medium, including cosmic rays and magnetic fields.
Towards 1% measurements of cosmological distances with cosmic sound
Measuring the accelerated expansion of the Universe with the goal of better understanding its underlying physics is one of the leading programs in cosmology today. The baryon acoustic oscillation technique is one of the foremost tools in our toolbox today. This talk will explain the underlying physics of this method and the reasons it is extremely robust to observational and theoretical systematic errors. I will then present the latest results from the SDSS and BOSS surveys, currently the most precise distance constraints from this method. These will include a new analysis technique to undo the effects of the nonlinear evolution of the density field and partially ''reconstruct'' the initial density field, and can reduce the distance errors by a factor of 1.7. I will discuss the implications of these measurements, and will conclude by discussing prospects for improvements in the immediate and not-so-immediate future.
Effective Field Theories for Fluids and Superfluids
I will present a novel field theoretical framework that captures the long-distance and low frequency dynamics of hydrodynamical systems. The approach is that of effective field theories, whose building blocks are the long-distance degrees of freedom and symmetries. Possible applications include questions in condensed matter physics, heavy-ion collisions, astrophysics, cosmology, and quantum hydrodynamics. Finally, this formulation naturally invites (and answers) new questions in classical hydrodynamics.
Dark Matter at Colliders
While 27% of the Universe is made of dark matter, the particle identity of the dark matter still remains a mystery. Collider studies offers a complementary tool to explore the nature of the dark matter, in addition to dark matter direct and indirect detections. In this talk, I will discuss the collider studies of the dark matter, focusing on how to observe dark matter signals, and how to distinguish dark matter scenarios.
In the first part of the talk I will discuss the model-independent approach for the monojet/monophoton plus missing ET signals, as well as model-dependent signatures of dark matter produced in the cascade decay chain of parent particles. The second part of the talk will focus on the study of distinguishing multiple component dark matter with traditional single particle dark matter.
Observation of High Energy Neutrinos at IceCube
Cosmic rays above the ankle (10^18 eV) are the universe's most energetic particles and must be produced in the universe's most energetic objects -- but which ones? and how? Neutrinos should be produced in whatever the cosmic accelerators are and should provide unique insights into their production mechanisms. Recent searches for high-energy (> 100 TeV) neutrinos at the antarctic IceCube neutrino observatory have produced the first evidence for a neutrino population beyond what is readily explained by neutrino production in the Earth's atmosphere from cosmic ray interactions, including the observation of several events with energies above 1 PeV -- the highest energy neutrinos ever observed. This talk will discuss the current status of these astrophysical neutrino searches in IceCube and prospects for the future.
I will discuss consistency tests of the standard LCDM paradigm in light of the comparison between recent Planck CMB results and local measurements, using alternative models as foils.
Neutrino Quantum Spookiness: Collapsing Stars, Supernovae, and the Cosmos
Collapsing stellar cores and the early universe are fantastic engines for generating neutrinos, ghostlike
particles which interact with matter only through the aptly named weak interaction and gravitation. However, neutrinos can more than make up for these feeble interactions with huge numbers. They can even come to dominate the energetics and element synthesis in the early universe and supernovae. But the way neutrinos interact with matter depends on which of three "flavors" they come in, i.e., electron, muon, or tau flavor. We therefore must determine how neutrino flavor changes as these particles move through their surroundings. This is a tricky, new kind of quantum mechanics problem. The advent of supercomputers has allowed us to follow this process in places, like supernova cores, where the flavor states of the neutrinos determine how flavor changes. And yes, this process is fiercely nonlinear. The results are startling and unexpected. Neutrinos can undergo collective flavor oscillations, producing signatures akin to domain formation in familiar condensed systems like ferromagnets. These signatures, if detected, could give us insights into astrophysical processes, like where the elements come from, but also into as yet unmeasured fundamental particle physics and cosmology issues, e.g., the neutrino mass hierarchy, the neutrino magnetic moment, and dark matter. Future high precision measurements, especially of the cosmic background radiation, promise to box-in many currently outstanding issues in neutrino physics.
Cosmic Calibration or: How I Learned to Stop Worrying and Love Supercomputers
Cosmology is now entering one of its most scientifically exciting phases. Decades of surveying the sky have culminated in the celebrated "Cosmological Standard Model". Yet, two of its key pillars, dark matter and dark energy -- together accounting for 95% of the mass-energy of the Universe -- remain mysterious. Deep fundamental questions demand answers: What is dark matter made of? Why is the Universe's expansion rate accelerating? Should general relativity be modified? What is the nature of primordial fluctuations? What is the exact geometry of the Universe? Next-generation observatories will open new routes to understand the true nature of the "Dark Universe". These observations will pose tremendous challenges on many fronts -- from the sheer size of the data that will be collected (more than a hundred Petabytes) to its modeling and interpretation. The interpretation of the data requires sophisticated simulations on the world's largest supercomputers. The cost of these simulations, the large number of modeling parameters, the uncertainties in our modeling abilities, and the fact that we have only one Universe that we can observe opposed to carrying out controlled experiments, all come together to create a major test for the process of scientific inference.
In this talk I will give a very brief introduction to the Dark Universe and outline the challenges ahead. To combat these challenges, close cross-disciplinary collaborations between physicists, statisticians, and computer scientists will be crucial. I will discuss two key advances brought about by successful collaboration: (i) the development of HACC, a new N-body code that enables us to carry out very large cosmological simulations, and (ii) the cosmic calibration framework which melds sophisticated statistical methods with simulation and modeling inputs to attack the problem of scientific inference.
Testing Gravity by Poking the Moon with a Laser
Laser range measurements between the earth and the moon have provided some of our best tests to date of general relativity and gravitational phenomenology--including the equivalence principle, the time-rate-of-change of the gravitational constant, the inverse square law, and gravitomagnetism. APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) is now collecting measurements at the unprecedented precision of one millimeter, which will produce order-of-magnitude improvements in a variety of gravitational tests. Experimental performance, evidence for dust-induced degradation of the reflectors, finding the lost Soviet Lunokhod 1 reflector, project status and science outlook will be discussed.