Graduate seminar on topical areas in modern astrophysics and
cosmology. Each semester a different topic of current special
interest is selected. Participants in this seminar discuss papers
given by seminar members (in rotation). Several faculty members also
participate.
Note: Participation for three semesters is required to obtain
credit for this course.
The angular power spectrum is a standard tool in analyzing CMB anisotropies.
In this talk I will discuss the mathematical formalisms used to characterize
CMB anisotropies, with particular emphasis on the angular power spectrum and
E-B decomoposition of CMB polarization. In order to fully understand the CMB
anistoropies, accurate theoretical predictions are needed for comparison with
the observed data. In the second part of the talk I will discuss linear perturbation
theory and show how it is applied to calculate CMB anisotropies from initial
density perturbations.
Check out the Power Point presentation online!
The positions and amplitudes of the acoustic peaks in the CMB
temperature power spectrum contain enough information to allow
simultaneous determination of the cosmological parameters, of which we
are mainly intersted in H_o, Omega_Baryon, Omega_Matter, and
Omega_Lambda. In this talk I hope to elucidate the main physical
processes behind the acoustic peaks and isolate their effects on the
most interesting cosmological parameters. We will do this by analyzing
a two-fluid approximation pioneered by Uros Seljak that allows us to
illuminate the relevant physical effects more transparently than in an
exact solution. We will also show some engaging (CMBFAST generated)
animations from Max Tegmark and Wayne Hu to help visualize the effects
of parameter changes on the temperature power spectrum. Ultimately, we
will explore parameter degeneracies and identify which parameters the
CMB measurements are most sensitive to. "Anisotropies 3" - Christopher Pilman In addition to the CMB anisotropies due to density distributions
which have already been discussed, gravity waves also play an important
if smaller role in the anisotropies of the CMB. In this talk I will introduce
the basic physics behind the gravity waves which influence the CMB, explain
the effects that they have on the thermal power spectrum, and explore their
effects on the polarization spectrum. Specifically, I will discuss the theoretical
differences between tensor and scalar contributions to the CMB power spectrum,
show (with animations) how the variation of gravitational parameters alters
the modeled results, and delineate the usefulness of the polarization data
and E- and B-modes, particularly for resolving degeneracies
of analysis which ignore gravity contributions.
CMB experiments have progressed from Penzias and Wilson's
measurement of an isotropic excess temperature to detection of
temperature and polarization anisotropy on scales as small as an
arcminute. We will review the history of CMB experiments and discuss
the technologies and methods of current CMB temperature and
polarization instruments. We will cover the various mapping
strategies and detection methods and briefly present the latest power
spectra.
This page was last updated on Tue Apr 8 21:27:48 EDT 2003
Schedule for Spring'2003:
``Organizational meeting'' - Kris Stanek, Matias Zaldarriaga
0. January 29th, 2003Abstract:
How the course is organized. Motivation for the topic. Scheduling the
talks.General reading material for the Semester:
``An Introduction to the CMB'' - James Battat1. January 29th, 2003(Some sample calculations that may be of use)
Abstract:
The Cosmic Microwave Background has been cosmology's Giving Tree.
Since its discovery by Penzias and Wilson in 1965, varied studies of
CMB properties have offered stiff constraints on cosmological models.
Current work helps push forward the accuracy of cosmology. This talk
will provide a basic context within which the importance of CMB
studies can be easily understood. I will cover some history of the
research, as well as a summarized history of the Universe to give a
broad, inclusive understanding of the creation and evolution of the
CMB.
Reading material:
Useful Textbooks
``The CMB Frequency Spectrum'' - Mark Hartman2. February 5th, 2003Abstract:
To a first approximation, the CMB is an isotropic blackbody radiator
with a temperature of 2.725 +/- 0.002 K. Within experimental errors,
the spectrum holds to the thermal Planck law over nearly three decades
in wavelength. Given that most cosmological parameters are nefariously
difficult to pin down, any measurement good to better than 1% should
contain a wealth of information.
This talk will examine the CMB in the context of a (near) perfect
blackbody spectrum. In particular, I will review the history and
difficulties of the measurements after (and before!) Penzias and
Wilson in 1965, ask why the afterglow from the hot Big Bang should be
thermalized, present mechanisms which could give rise to non-thermal
distortions, place limits on the distortions actually observed from
COBE and other experiments and show how these limits constrain the
processes by which energy is dumped into the universe at different
epochs.
Reading material:
``Anisotropies 1'' - Kamson
Lai3. February 12th, 2003Abstract:
Reading material:
``CMB Anisotropies II: Attack of the C_l ones'' - Andrew Friedman4. February 19th, 2003
And you might recognize one of your professors here!
Abstract:
Reading material:
5. February 26th,
2003Abstract:
Reading material:
"Experiments 1" Parts A and B - Dan
Marrone and Shinae Park6. March 5th, 2003Abstract:
Reading material:
Instrument papers for some CMB temperature experiments:
Polarization Experiments:
``Experiments 2'' - Jonathan Devor
7. March 12th, 2003Abstract:
Before extracting useful CMB information from the WMAP images, one needs
to first “clean up” the data. We will discuss the way the WMAP team managed
the detector and foreground noise and compare their results with more sophisticated
approaches that have been recently proposed. These issues of data reduction,
traditionally far from the limelights, are now being scrutinized as possible
culprits for the surprising values seen in the low order multipoles and
other possible artifacts. We will conclude the talk with a brief overview
of how the CMB results help constrain the values of the cosmological parameters
and further validate the CDM model.
Reading material:
``Inflation'' - Daniel Babich8. March 19th, 2003 Abstract:
Inflation, which postulates that the universe underwent a brief period
of superluminal expansion, simultaneously solves several problems of
the hot Big Bang model and provides a mechanism to create the
inhomogeneities that we observe in the CMB. This talk will describe
how inflation solves these problems and will outline how it produces
the super-horizon, adiabatic and Gaussian fluctuations that have been
recently observed in WMAP.Reading material:
Spring Break
``SZ (clusters)'' - Vit
Hradecky9. April 2nd, 2003 Abstract:
The Sunyaev-Zel'dovich effect (SZE) is emerging as a powerful tool for
cosmology. I will review the physics of the thermal and kinematic SZE and
discuss the anisotropies and polarization they introduce into the CMB.
To date the SZE has been successfully used in combination with X-ray
observations as a distance estimator and to measure the baryon fraction
in galaxy clusters. The most exciting potential of the SZE is to detect
clusters to high redshift and to constrain the dark energy equation of
state. I will discuss theoretical work done along these lines, and
describe current and future instruments for studying the SZE.
Reading material:
``Secondary effects'' - Deborah Freedman
10. April 9th, 2003 Abstract:
As the CMB photons travel from the surface of last scattering to
our detectors today, the photons must pass through a Universe full of
intervening matter. The intervening matter, including clusters,
heated moving gas, and other features of large scale structure, create
secondary anisotropies in the CMB power spectrum. It is possible to
model and sometimes to measure the interaction of the CMB with the
various forms of matter along the way. In this talk, I will discuss what
causes the secondary anisotropies and what effects are expected. The
secondary anisotropies that are produced fall into two categories:
scattering off electrons and gravitational interactions. In particular,
I will describe the Ostriker-Vishniac (OV) effect, the Sunyaev-Zel'dovich
effect from large-scale structure, and patchy reionization, which are
examples of scattering secondaries. I will also describe the
gravitational secondary of lensing. Reading material:
``Foregrounds'' - Slavko Bogdanov
11. April 16th, 2003 Abstract:
Reading material:
``Future Experiments'' - Ryan Hickox12. April 23rd, 2003 Abstract:
Reading material:
``Other Backgrounds'' - Jenny Greene13. April 30th, 2003 Abstract:
Reading material:
Questions or Comments? Send an
e-mail to kstanek@cfa.harvard.edu.
