Cosmic Microwave Background: Past, Future, and Present

I explain the origin and evolution of anisotropies in the Cosmic Microwave Background (CMB) and argue that upcoming experiments will measure cosmological and fundamental parameters very accurately. Most of the paper focuses on present data, which strongly suggest that the universe is flat. Several arguments are given to prove that present data sets are not contaminated by systematics. New techniques to compare different experiments visually are introduced. These are illustrated for two years of the MSAM and Python experiments.Comment: 19 pages, 9 figures, plenary talk at Lepton-Photon 99, to be published in International Journal of Modern Physic

Coherent Phase Argument for Inflation

Cosmologists have developed a phenomenally successful picture of structure in the universe based on the idea that the universe expanded exponentially in its earliest moments. There are three pieces of evidence for this exponential expansion -- {\it inflation} -- from observations of anisotropies in the cosmic microwave background. First, the shape of the primordial spectrum is very similar to that predicted by generic inflation models. Second, the angular scale at which the first acoustic peak appears is consistent with the flat universe predicted by inflation. Here I describe the third piece of evidence, perhaps the most convincing of all: the phase coherence needed to account for the clear peak/trough structure observed by the WMAP satellite and its predecessors. I also discuss alternatives to inflation that have been proposed recently and explain how they produce coherent phases.Comment: 16 pages, 13 figures, Invited Talk at Fourth Tropical Workshop, Cairns, Australia, June 200

Backgrounds and Projected Limits from Dark Matter Direct Detection Experiments

A simple formula is introduced which indicates the amount by which projections of dark matter direct detection experiments are expected to be degraded due to backgrounds.Comment: 4 pages, 3 figures, code available at http://home.fnal.gov/~dodelson/dm.htm

The Real Problem with MOND

Gravitational potentials in the cosmos are deeper than expected from observed visible objects, a phenomenon usually attributed to dark matter, presumably in the form of a new fundamental particle. Until such a particle is observed, the jury remains out on dark matter, and modified gravity models must be considered. The class of models reducing to MOdified Newtonian Dynamics (MOND) in the weak field limit does an excellent job fitting the rotation curves of galaxies, predicting the relation between baryonic mass and velocity in gas-dominated galaxies, and explaining the properties of the local group. Several of the initial challenges facing MOND have been overcome, while others remain. Here I point out the most severe challenge facing MOND.Comment: 6 pages, 1 figure, Honorable Mention, Gravity Research Foundation 2011 Award

A Robust Approach to Constraining Dark Matter from Gamma-Ray Data

Photons produced in the annihilations of dark matter particles can be detected by gamma-ray telescopes; this technique of indirect detection serves as a cornerstone of the upcoming assault on the dark matter paradigm. The main obstacle to the extraction of information about dark matter from the annihilation photons is the presence of large and uncertain gamma-ray backgrounds. We present a new technique for using gamma-ray data to constrain the properties of dark matter that makes minimal assumptions about the dark matter and the backgrounds. The technique relies on two properties of the expected signal from annihilations of the smooth dark matter component in our galaxy: 1) it is approximately rotationally symmetric around the axis connecting us to the Galactic Center, and 2) variations from the mean signal are uncorrelated from one pixel to the next. We apply this technique to recent data from the Fermi telescope to generate constraints on the dark matter mass and cross section for a variety of annihilation channels. We quantify the uncertainty introduced into our constraints by uncertainties in the halo profile and by the possibility that the halo is triaxial. The resultant constraint, the flux F \leq 4.5\times10^-6 cm^-2 s^-1 sr^-1 for energies between 1 and 100 GeV at an angle 15 degrees away from the Galactic Center, translates into an upper limit on the velocity weighted annihilation cross section of order 10^-25 cm^3 s^-1 depending on the annihilation mode.Comment: 13 pages, 8 figure