CIAR Cosmology & Gravity Program 2005
Annual Meeting
The Cosmic Quest for Fundamental Physics
Introduction
The 2005 CIAR Cosmology and Gravity Program’s annual meeting “The Cosmic Quest
for Fundamental Physics” was held in Mt. Tremblant, Quebec, from March 3 to 7. The
meeting once again saw a unique gathering of experts from all the fields in which the
program is active. Both experimental and theoretical progress in gravitational physics and
cosmology were reviewed at the meeting with a view to defining the program’s future
and core areas that will be the focus of the program over the coming years. All talks were
associated with Panels chaired by Program Member Moderators who ensured a lively
flow of presentation and discussion, with the overall theme always in mind.
Highlights of the Meeting
The Cosmic Microwave Background
Cosmology & Gravity Program Director Dick Bond, from the Canadian Institute for
Theoretical Astrophysics, gave an overview of the status of research in observational
cosmology and a summary of recent results from a number of experiments observing the
Cosmic Microwave Background (CMB). The CMB is a bath of relic radiation released
when the universe was only a few hundred thousand years old. Imprinted in the CMB are
small fluctuations that contain a wealth of information about the early universe.
Observations of these tiny ‘ripples’ underpin most of the revolutionary advances that
have occurred in the field of cosmology over the past decade.
Suzanne Staggs, a guest speaker from Princeton University, is involved in the planning
and building of a number of telescopes for studying the CMB, and she reviewed progress
on the development of two of them: the QUIET (Q/U Imaging ExperimenT) and ACT
(Atacama Cosmology Telescope) projects. These will both be operating in the Atacama
high-plateau desert in Chile and will be collecting some of the highest resolution images
of the microwave background by the end of the decade.
A fundamental prediction of the standard cosmological model is that photons emitted by
the CMB have a specific pattern of polarization on the sky. The detection of this pattern
is therefore a crucial step in verifying the current theories of the evolution of the universe.
QUIET will be observing the polarization of the CMB photons on unprecedented
arcminute scales. (An arcminute is a unit of angular measurement equal to one-sixtieth of
a degree.) Staggs also presented recent results from the CAPMAP experiment. This and
the CBI (Cosmic Background Imager) and DASI (Degree Angular Scale Interferometer)
experiments are the only ones to date with the required level of sensitivity to have
detected the polarization of the CMB. (One of the experimental highlights mentioned by
Bond in his opening talk and amplified by Program “reporter” Carlo Contaldi was the
CMB polarization results from the Cosmic Background Imager telescope and their
cosmological implications. The effort to analyze the CBI data is led by researchers at
CITA and the results, along with those from CAPMAP, were presented at the CIARsponsored COSMO04 conference held in Toronto in September 2004.)
Program member Barth Netterfield, from the University of Toronto, summarized the
progress in the analysis of data from the 2002 BOOMERANG flight, the results of which
are expected to be published later this year. BOOMERANG is a balloon-borne CMB
telescope which is flown from the Antarctic. The 2002 flight also targeted the observation
of the polarization of the CMB and will return the most detailed maps of the polarization
to date. The BOOMERANG results will complement the existing results from the DASI,
CBI and CAPMAP experiments. The BLAST experiment, another balloon-borne
telescope observing at infra-red wavelengths, was also reviewed by Netterfield. It will be
making its first science flight later in the year and will map the distribution of distant
galaxies.
Clusters & Galaxy Formation
Program members Gil Holder, from McGill University, and Henk Hoekstra, from the
University of Victoria, discussed the use of galaxy cluster observations in determining
the nature of dark energy. Dark energy is a form of energy whose existence has been
postulated to explain why the expansion of the universe appears to be accelerating. It
affects the number, size and distribution of clusters of galaxies. In the next few years, a
number of surveys will be producing large catalogs of clusters, which will yield
constraints on the nature and evolution of the dark energy. However, a careful
understanding of the physics involved in the formation and evolution of galaxy clusters
must be achieved before these results can be interpreted robustly, and much work is
focusing on this problem.
Much progress has been achieved in understanding the formation and evolution of
galaxies and clusters through huge simulations. A number of speakers presented results
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from a series of numerical simulations of galaxy formation and growth of structures in
the universe. The highlight of the session was the presentation of the latest simulation
carried out by the VIRGO consortium, the Millennium computation with over 10 billion
particles. This is the largest and most detailed simulation of its kind ever made. A number
of Cosmology and Gravity Program members are involved in the VIRGO collaboration,
including Julio Navarro from the University of Victoria and Carlos Frenk from the
University of Durham and program advisory committee member Simon White from the
Max Planck Institute for Astrophysics. More generally, the suite of simulations and their
analyses reported at the CIAR meeting represent the most advanced results in the field of
numerical cosmology (and numerical relativity). The scales simulated by the
cosmological codes range from a few thousand light years to many billions of light years
encompassing individual galaxy scales to, for the first time, most of the visible universe.
The work in this area is now shifting to ‘mining’ the wealth of information produced by
the simulations, a challenging computational problem in itself given the massive quantity
of data produced. The main task will be to compare the output of the simulations with
various cosmological observables such as the clustering of galaxies, the weak lensing of
light rays and to determine general characteristics of clusters of galaxies. This will be
crucial for being able to determine cosmological model parameters using future
observations of clusters and their distributions. These observations will include direct
measurements of the cluster X-ray emissions, the lensing effect surrounding them and
their small effect on the CMB. Frenk, Kauffmann, Navarro and White reported on
applications as varied as clusters, galaxy formation and evolution, through evidence for
tidal debris in our own Milky Way galaxy.
Much interaction between researchers at the meeting centred on new applications of the
simulation results to a variety of cosmological problems and a number of new
collaborations were set up. Alex Szalay, a program member from the John Hopkins
University, described his efforts towards the development of a ‘virtual observatory’
where a number of astrophysical observations could be stored for easy access by the
whole scientific community.
The problem of star formation, from both a theoretical and observational stand point, was
discussed by program member Richard Ellis, from Caltech, and guest speakers Guinevere
Kauffman, from the Max Planck Institute for Astrophysics, and Norm Murray, from the
Canadian Institute for Theoretical Astrophysics. Ellis presented new evidence of
significant star formation when the universe was only a few billion years old, which
would seem to support a shift in paradigm towards the existence of an early population of
first stars. This would also confirm evidence arising from CMB observations that the first
stars formed earlier than previously thought. Some models suggest that a population of
very massive stars, hundreds of times more massive than the sun, may have arisen at
these early times as the first generation of collapsed objects.
Particle Astrophysics & High Energy Astrophysics
Vicky Kaspi, a Cosmology & Gravity Program member from McGill University, gave an
update on her group’s work in interpreting observations of one of the most bizarre and
exciting astronomical objects ever seen, the double pulsar system known as PSRJ07370-
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3039, already discussed at last year’s Cosmology & Gravity annual meeting. The binary
system in which both stars happened to be pulsars (i.e. rotating neutron stars with very
strong magnetic fields that are misaligned with their axis of rotation) constitutes a unique
testing ground for the theory of gravitation due to the incredibly accurate timing of the xray ‘flashes’ released by such pulsars.
Guest speaker Norm Murray also reviewed a recent proposal published by Maxim
Lyutikov of McGill University and program member Chris Thompson of the Canadian
Institute for Theoretical Astrophysics, which explains some intriguing variability in the
system’s luminosity. Because the stars are so close together, Lyutikov and Thompson
propose that the interaction between their magnetic fields and the plasma surrounding
them leads to a complicated pattern of emission, resulting in the variability in the
observed luminosity. Their model fits the observations very closely. Program members
Lars Bildsten from the Kavli Institute for Theoretical Physics and Andrew Cumming
from McGill University also reviewed recent progress in the modeling of neutron stars
and their environments.
Advisory Committee Chair Art McDonald described the expansion plans for the world’s
deepest underground particle physics laboratory in Sudbury, Ontario. Building on the
success of the Solar Neutrino Observatory (SNO) at Sudbury, which confirmed the
theory of neutrino oscillations (the model whereby different types of neutrinos produced
deep inside the sun transform into each other as they travel towards the Earth), the
laboratory will be expanded to house more and larger detectors and to host a number of
different experiments which require the deep, underground environment.
Program member Mark Chen, from Queen’s University, also reviewed some of the future
experiments to be planned for the Sudbury site and their possible role in establishing a
link between cosmological neutrinos and dark energy.
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Weak Lensing and Supernovae Surveys
A number of program members involved in the Canada-France-Hawaii Telescope Legacy
Survey (CFHTLS) reviewed the progress of the observations and their analysis. The
survey is mapping a large patch of sky periodically. Its aim is to detect the highest
number of distant supernovae to determine the recent expansion history of the universe,
and to measure the subtle effect known as weak lensing.
Advisory committee member Chris Pritchet, from the University of Victoria, outlined the
progress in the supernovae search so far. Almost a hundred supernovae have been
detected. Some of the supernovae, known as Type 1a, are considered to be cosmological
‘standard candles’. This means that by measuring their luminosity researchers can
calculate quite precisely how far away they occurred. This enables cosmologists to
reconstruct the expansion of the universe for the past few billion years. These
observations have been the strongest indicator that the expansion has been accelerating,
possibly due to an unknown form of dark energy in the universe which could be related to
the prediction by Albert Einstein of a cosmological constant, something he considered to
have been his famous ‘greatest blunder’.
Program members Ludo Van Waerbeke, from the University of British Columbia, and
Henk Hoekstra described the progress of the weak lensing observations from the CanadaFrance-Hawaii Telescope (CFHT) Legacy Survey. When completed, this will be the
largest weak lensing survey carried out to date. The weak lensing effect is a small
distortion of the image of distant galaxies induced by the deflections of light from the
galaxies by the intervening matter between the galaxies and the Earth. In principle, the
mapping of the lensing provides a unique view of the dark matter in the universe, which
cannot be observed directly since it does not interact with visible matter that we are made
of.
The first measurements of weak lensing were achieved only a few years ago but already
this has become one of the most important fields in observational cosmology, at the
forefront of which are also involved a number of other CIAR Cosmology & Gravity
members such as Richard Ellis and Nick Kaiser of the University of Hawaii. The
observations have already yielded significant, independent constraints on cosmological
model parameters and it is expected that future measurements will open a unique window
onto the evolution of the dark energy form of matter.
Kaiser described the proposed PANSTARRS facility, multiple telescopes to be built in
Hawaii that would be used to produce the largest mappings of the weak lensing effect
covering a large fraction of the sky. The prototype for part of the telescope is complete
and undergoing testing and it is expected that ‘first light’ for the prototype will occur in
early 2006 with the full telescope being completed by the end of the decade.
String Theory and the Early Universe
Cosmology & Gravity Program member Lev Kofman, from the Canadian Institute for
Theoretical Astrophysics, opened the String Theory and Early Universe session with an
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overview of the increasing interactions between these two fields. Cosmology has become
one of the major testing grounds for fundamental theories, such as that of strings, with
many of the most innovative models for inflation – the period of exponential inflation in
the first few instants of the universe – now being inspired by a number of models of
string theory cosmology. Program member Rob Myers from the Perimeter Institute for
Theoretical Physics followed with an overview of the field of string theory.
Guest speakers Shamit Kachru and program member Eva Silverstein, both from Stanford
University, discussed some of their recent work, including the idea of the string theory
‘landscape’, in which the existence of a cosmological constant is explained through the
complexity of the dynamics of string theory.
Gary Horowitz, a Program Advisory Committee member based at the University of
California at Santa Barbara, described his research into the possible violation of the
cosmic censorship by hypothetical objects known as white holes. It is postulated that
white holes are formed at space-time singularities in a similar fashion to black holes, but
whereas the latter are surrounded by an event horizon and are therefore hidden from
view, the former are so-called “naked” singularities that have no such censorship. White
holes could occur under special circumstances if the singularities are formed from a
collapsing scalar field. These objects would be in direct violation of the well known
cosmic censorship hypothesis postulated by Stephen Hawking that states that all
singularities lie behind event horizons and that naked singularities cannot exist.
Gravitational Waves & Numerical Relativity
Guest speaker Scott Hughes, from the MIT, gave an overview of future experiments that
will attempt to measure gravitational waves. These waves are predicted by Einstein’s
theory of general relativity, but have not been measured yet as they require extremely
accurate observations of the displacement of test masses. They are the result of the
warping of space-time itself due to the movement of masses, and if measured, would
confirm the last unverified aspect of Einstein’s theories. Direct observations of gravity
waves are being attempted using very long laser interferometers measuring the distance
between two test masses in an experiment known as the LIGO (Laser Interferometer
Gravitational wave Observatory). Currently the experiment is slowly reaching the
required sensitivity at which it should start detecting the gravitational wave signature of
extreme events happening in the universe, such as the final instants of the merger
between black holes or a black hole and neutron stars.
Program member Matt Choptuik, from the University of British Columbia, and guest
speaker David Garfinkle, from Oakland University, gave an update on their continuing
efforts at simulating the formation and evolution of singularities that occur when massive
stars collapse into black holes. These simulations are also the only method researchers
can use to predict the gravity wave emission during mergers to compare with the
observations of detectors such as the LIGO facility or the space based LISA mission,
which is slated for launch in 2010. Choptuik highlighted the remarkable progress in
simulations of colliding relativistic objects made by Frans Pretorius of Caltech, updating
the earlier results reported by Frans at the CIAR04 meeting in Banff. (Pretorius is now a
Program member.)
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The meeting also had a highly interactive discussion on the future directions of the
Cosmology & Gravity Program and the field in general in view of its next five-year
period renewal. It ended with a very lively informal interaction among the string
theorists, numerical relativists, high energy and particle astrophysicists and physical
cosmologists on the role the interplay between developments in string theory and early
Universe physics to the observable world, especially as represented by the many Program
initiatives in experimental cosmology.
Links to research presented at the meeting
Neutrino Observatories:
SNO:
http://www.sno.phy.queensu.ca/
Galaxy Redshift Surveys:
SDSS:
http://www.sdss.org/
2dfGRS link:
http://magnum.anu.edu.au/~TDFgg/
CMB experiment links:
Ongoing:
WMAP:
http://map.gsfc.nasa.gov/
ACBAR:
http://cosmology.berkeley.edu/group/swlh/acbar/
BOOMERANG:
http://cmb.phys.cwru.edu/boomerang/
CBI:
http://www.astro.caltech.edu/~tjp/CBI/
DASI:
http://astro.uchicago.edu/dasi/
Future:
PLANCK:
ACT:
BICEP:
SPT:
http://www.rssd.esa.int/index.php?project=PLANCK
http://www.hep.upenn.edu/~angelica/act/act.html
http://www.astro.caltech.edu/~lgg/bicep_front.htm
http://astro.uchicago.edu/spt/
Telescopes:
Keck Observatory:
CFHT:
http://www2.keck.hawaii.edu/geninfo/about.html
http://www.cfht.hawaii.edu
Participants
Fellows
Dick Bond (CITA, Physical Cosmology)
Mark Chen (Queen’s University, Experimental Particle and Neutrino Astrophysics)
Matt Choptuik (UBC, Numerical Relativity)
Hugh Couchman (McMaster, Physical Cosmology)
Vicky Kaspi (McGill, Observational HEA)
Lev Kofman (CITA, Physical Cosmology)
Rob Myers (Perimeter Institute, String Theory)
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Julio Navarro (UVic, Physical Cosmology)
Barth Netterfield (UofT, Experimental Cosmology)
Ue-Li Pen (CITA, Physical Cosmology)
Bill Unruh (UBC, Gravity Theory)
Scholars
Andrew Cumming (McGIll, HEA)
Henk Hoekstra (UBC, Physical and Observational Cosmology)
Gil Holder (McGill, Physical Cosmology)
Amanda Peet (UofT, String Theory)
Ludo van Waerbeke (UBC, Physical Cosmology)
Associates
Lars Bildsten (KITP, High Energy Astrophysics)
Richard Ellis (Caltech, Observational Cosmology)
Carlos Frenk (Durham, Physical Cosmology)
David Garfinkle (Oakland University, Numerical Relativity)
Nick Kaiser (Hawaii, Physical Cosmology)
Luis Lehner (Louisiana, Numerical Relativity)
Eva Silverstein (Stanford/SLAC, String Theory)
Alex Szalay (Johns Hopkins, Physical Cosmology)
Reporter
Carlo Contaldi (CITA, Cosmology)
Advisory Board Members
Art McDonald (SNO Institute & Queen's University, Particle Astrophysics, Chair)
Gary Horowitz (University of California at Santa Barbara, String Theory, Gravity)
Scott Tremaine (Princeton, Astrophysical Dynamics)
Chris Pritchet (University of Victoria, Physical and Observational Cosmology)
Simon White (Max-Planck-Institut für Astrophysik, Physical Cosmology)
Guests
Scott Hughes (MIT, Gravity Waves)
Shamit Kachru (Stanford University, String Theory)
Guinevere Kauffman (Max-Planck-Institut für Astrophysik, Physical Cosmology)
Norm Murray (Canadian Institute for Theoretical Astrophysics, HEA & Planets)
Suzanne Staggs (Princeton University, Experimental Cosmology)
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