Physics Department
Spring 2005 Colloquium Schedule
Speaker: Prof. Chetan Nayak, UCLA
Title: Topological Quantum Computation
Abstract can be found here
Speaker: Dr. Martin Kruczenski, Brandeis University
Title: The string/gauge theory correspondence and ferromagnetic spin chains
Abstract can be found here
Speaker: Dr. Joshua Colwell, University of Colorado, Laboratory for Atmospheric and Space Physics
Title: The Cassini-Huygens Mission to Saturn: Overview and a Closer Look at Saturn's Rings
Abstract can be found here
Speaker: Dr. Andrei Gritsan, LBL
Title: B Meson Decays to Vector Particles: a New Window on Fundamental Interactions
Abstract can be found here
Speaker: Dr. Vadim Oganesyan, Princeton University
Title: On fluctuation diamagnetism and pseudogap of high temperature superconductors
Abstract can be found here
Speaker: Dr. Anatoli Polkovnikov, Harvard University
Title: Superfluid-insulator transition in a moving system of interacting bosons
Abstract can be found here
Speaker: Dr. Oliver DeWolfe, Princeton University
Title: Flux Compactifications of String Theory: Toward Phenomenology and Cosmology
Abstract can be found here
Speaker: Dr. Eva Halkiadakis, University of Rochester
Title: An experimentalist's view of particle physics at the energy frontier
Abstract can be found here
Speaker: Prof. Karyn Le Hur, Sherbrooke University, Québec, Canada
Title: Condensed Matter at Mesoscopic Scale
Abstract can be found here
Speaker: Dr. Kevin Stenson, University of Colorado
Title: The Search for Pentaquarks
Abstract can be found here
Speaker: Dr. Joseph Formaggio, University of Washington, Seattle
Title: The Three Phases of SNO
Abstract can be found here
Speaker: Dr. Kaustubh Agashe, John Hopkins University
Title: Particle Physics from a Warped Extra Dimension
Abstract can be found here
Speaker: Dr. Heather J. Lewandowski, NIST/JILA, University of Colorado
Title: Creating Cold Molecules to Constrain the Evolution of the Fine Structure Constant
Abstract can be found here
Spring Break
Speaker: Prof. Peter Palffy-Muhoray
Title: Liquid Crystal Institute, Kent State University
Abstract can be found here
Speaker: Prof. Michael Peskin, SLAC, Stanford
Title: The International Linear Collider: The Next Step in High-Energy Electron-Positron Physics
Abstract can be found here
Speaker: Dr. Brian O'Reilly, Caltech (LIGO Livingston Observatory)
Title: Recent Progress at LIGO
Abstract can be found here
Speaker: Prof. Glennys Farrar
Title: New clues to the origin of ultra-high energy cosmic rays
Abstract can be found here
Speaker:
Title:
Abstract can be found here
Professor Chetan Nayak, UCLA. January 12, 2005
Topological Quantum Computation
The computational power of a quantum-mechanical Hilbert space is potentially
far greater than that of any classical device. However, it is difficult
to harness it because much of the quantum information contained in a system
is encoded in phase relations which one might expect to be easily destroyed
by its interactions with the outside world (`decoherence'). Therefore, one
must keep the error rate low and represent information redundantly so that
errors can be diagnosed and corrected. Remarkably, there are phases of electrons
(`topological phases') in which this can occur automatically. Topological
phases occur in the quantum Hall regime and may occur in other correlated
electronic materials. In these phases, the low-energy states are sensitive
only to the topology of the system, so interactions with the environment,
which are presumably local, cannot cause errors. Some examples of such phases
will be discussed as well as some ideas about how quantum information could
be stored and manipulated in them.
Dr. Martin Kruczenski, Brandeis University. January
19, 2005
The string/gauge theory correspondence and ferromagnetic spin chains
It has long been suspected that strings play a role in understanding the
low energy limit of non-abelian gauge theories and in particular in describing
hadrons as bound states of quarks and gluons. This idea has recently been
made precise by the AdS/CFT correspondence which provides a concrete example
of the relation between gauge and string theories.
After reviewing these ideas I am going to concentrate in two aspects of
the correspondence:
First, in the way in which, for certain theories, quarks can
be incorporated and their bound states can be computed.
Second, in a procedure that allows to derive an effective action
for a string directly from the field theory. Here, the ferromagnetic (spin
1/2) Heisenberg chain plays a central role: on one hand it arises naturally
in the field theory and on the other, it can be seen that its low energy
excitations (spin waves) can be interpreted as strings. It therefore provides
a bridge between both descriptions.
Dr. Joshua Colwell, University of Colorado, LASP.
January 26, 2005
The Cassini-Huygens Mission to Saturn: Overview and a Closer Look at
Saturn's Rings
The Cassini spacecraft, carrying the ESA-built Huygens probe, entered Saturn
orbit on June 30, 2004, and the Huygens probe successfully landed on the
surface of Saturn's large moon Titan on January 14, 2005. In the first six
and a half months of this international mission new moons have been discovered
orbiting Saturn, ring dynamics have been observed in unprecedented detail,
the nature of Titan's surface has been revealed, and temporal variability
has been seen both in Saturn's atmosphere and its magnetosphere. Answers
to some of the questions raised by the Voyager spacecraft are starting to
emerge, but with them come even more new questions. For example, Cassini
observations suggest that the dark material mysteriously covering half of
the moon Iapetus is exogenic rather than endogenic, but the ultimate origin
remains unknown, and a new ridge of unknown origin has been discovered nearly
circling the moon.
One of Cassini's 12 instruments is an ultraviolet imaging spectrograph
built at CU. I will present an overview of the Cassini-Huygens mission and
initial observations of Saturn's moons, rings, and magnetosphere with an
emphasis on the UV observations. Special attention will be given to UV observations
of Saturn's rings which provide the highest resolution measurements of the
structure of the rings. These observations enable precise measurements of
the ring surface mass density which in conjunction with other data help
constrain the age of the rings. Future Cassini observations will hopefully
resolve the fundamental questions of the age and origin of Saturn's rings
which are currently unknown.
Dr. Andrei Gritsan, LBL. February 2, 2005
B Meson Decays to Vector Particles: a New Window on Fundamental Interactions
Fundamental particles and their interactions are the necessary building
blocks in understanding our Universe, its existence and evolution. B-factory
experiments produce abundant samples of B mesons to study fundamental interactions.
CP-violation measurements can be represented on the "Unitarity Triangle."
One angle of the triangle is now known to about 4%. The best measurements
for the second angle were expected to come from the simple decay of a B
meson into two pions. Instead, the best measurements have come from the
decay of B mesons into a pair of spin-one resonances, B->rho rho. Another
decay to a pair of vector mesons, B->phi K* is found to have polarization
not consistent with expectations. Could this be a sign of New Physics? This
opens a completely new approach to CP violation studies and search for new
fundamental interactions.
Dr. Vadim Oganesyan, Princeton University. February
9, 2005
On fluctuation diamagnetism and pseudogap of high temperature superconductors
High temperature superconductivity in the cuprates is a major puzzle in
the theory of condensed matter. One of the key questions concerns the nature
of the so-called pseudogap region in their phase diagrams. In this talk
I will review the issues here and focus on incipient superconductivity as
an explanation for the pseudogap. I will describe work on detecting such
superconductivity via diamagnetism, motivated by recent measurements in
the cuprates by the Ong group at Princeton. I will show an analysis of the
diamagnetic response near the celebrated Kosterlitz-Thouless transition
provides a coherent explanation of data on the highly two dimensional cuprate
BSSCO2212.
Dr. Anatoli Polkovnikov, Harvard University. February
16, 2005
Superfluid-insulator transition in a moving system of interacting bosons
Cold atomic systems with their high tunability and nearly perfect isolation
from environment became very attractive for studying strongly correlated
systems. Particularly exciting is the possibility to address problems of
quantum dynamics far from equilibrium, which are beyond the reach of conventional
condensed matter systems.
Most of theoretical studies of dynamics in these systems employ essentially
classical (Gross-Pitaevskii) equations of motion. At the same time in equilibrium
a lot is known about various quantum regimes, where the classical description
does not work. In this talk I will discuss a problem where both quantum
and dynamic effects are important. In particular, I will describe a moving
system of interacting bosons in a periodic optical lattice potential and
generalize the conventional superfluid-Mott insulator transition to this
highly non-equilibrium situation. I will discuss implications of our results
to recent and future experiments.
Dr. Oliver DeWolfe, Princeton University. February
21, 2005
Flux Compactifications of String Theory: Toward Phenomenology and Cosmology
String theory is a leading candidate for a theory of quantum gravity, but
it is fundamentally ten-dimensional. Obtaining a realistic four-dimensional
model has long been a goal. "Compactifying" six dimensions has many desirable
features, but has suffered from the significant problem of unfixed moduli,
gravitationally coupled scalar fields with no potential that are inconsistent
with experiment. We discuss recent progress toward solving this problem.
Compactifications are threaded with generalized electromagnetic fields called
"fluxes," long an unexploited feature of the theory, which can generate
a potential for the moduli. A rich set of isolated vacua emerges. We consider
the properties of these vacua, as well as efforts toward realizing in them
realistic particle phenomenology and cosmologies such as inflation.
Dr. Eva Halkiadakis, University of Rochester.
February 23, 2005
An experimentalist's view of particle physics at the energy frontier
Fermilab's Tevatron is currently the highest energy proton-anti-proton
collider in the world, until the Large Hadron Collider at CERN turns on
in 2007. CDF is one of two large multipurpose detectors designed to detect
these high energy collisions, and will allow us to study the fundamental
building blocks of nature.
The W and Z bosons, the top quark and the yet-to-be discovered Higgs boson
are the most massive particles in the Standard Model. W and Z boson measurements
are significant probes of the Standard Model and the prediction of the Higgs
boson mass hinges on the precise measurements of the W boson and top quark
masses. I will describe the characteristics of the W and Z bosons and the
top quark as we identify them in the CDF detector and how we measure their
properties. I will review the status of a few of these measurements from
the CDF collaboration from the ongoing Run II of the Tevatron.
Prof. Karyn Le Hur, Sherbrooke University, Québec,
Canada. February 28, 2005
Condensed Matter at the Mesoscopic Scale
We scrutinize electrical properties of devices (solids) with dimensions
ranging from several micronmeters down to few nanometers. Those devices
are bigger than atoms but not big enough to obey Ohm's formula. Landauer
demonstrated that the conductance of such mesoscopic conductors coupled
to macroscopic reservoir leads is always quantized in units of 2e^2/h (the
"contact resistance") where is "e" is the charge of the electron. In this
talk, we will focus on two classes of mesoscopic conductors, namely the
one-dimensional mesoscopic conductors and the quantum dots which embody
artificial atoms. We address interesting issues like: correlated effects
at a quantum point contact, interference effects with electron waves and
measurement of the electron life-time, realization of charge and spin qubits
with solid-state devices, emergence of new entanglement mechanisms and consequences
on transport, and teleportation of Cooper pairs through mesoscopic setups.
Dr. Kevin Stenson, University of Colorado. March
1, 2005
The Search for Pentaquarks
So far, all matter containing quarks can be understood as being composed
of a quark and an antiquark (mesons) or three quarks (baryons). From
what we understand, however, nothing prevents the existence of more
exotic states such as four, five, or six quark combinations. I will
present an overview of the current status of the search for pentaquarks,
of which evidence has been seen from a dozen collaborations. I will
also present results of searches using data from the FOCUS experiment.
Dr. Joseph Formaggio, University of Washington,
Seattle. March 2, 2005
The Three Phases of SNO
The past few years have been an incredible time for neutrino physics.
Recent results from the Sudbury Neutrino Observatory in Canada and from
the KamLAND experiment in Japan have changed the landscape of weak
interactions by providing overwhelming evidence that neutrinos from the
sun undergo oscillations -the quantum mechanical process by which a
neutrino of one type spontaneously changes into another. During my talk,
I will review the current status of neutrino oscillations, with special
emphasis on the recent solar neutrino experimental results of the
Sudbury Neutrino Observatory. The talk will then continue with how new
and upcoming experiments plan to tackle some of the remaining mysteries
of this elusive particle.
Dr. Kaustubh Agashe, John Hopkins University. March 9, 2005
Particle Physics from a Warped Extra Dimension
In the Standard Model of particle physics, a condensate of a
particle known as the Higgs
boson determines the range of the weak nuclear force. However, one
finds that quantum
corrections shift this range to a much smaller value than observed.
I will describe how the idea of the Higgs boson being a composite
can solve this ``hierarchy problem''. Remarkably, under certain
circumstances, this scenario has a
dual and simpler description in terms of a warped higher dimensional
spacetime.
I will show that the same set-up also naturally explains the
basic structure of quarks and leptons
via their profiles in the extra dimension.
In this model, the idea of grand unification of the
fundamental forces works very well and also naturally leads to an
exotic particle
that may be the dark matter of the universe.
Thus, this framework may solve several of
the fundamental puzzles of nature. I will describe
how we will test it in experiments.
Dr. Heather J. Lewandowski, NIST/JILA, University
of Colorado. March 16, 2005
Creating Cold Molecules to Constrain the Evolution of the Fine
Structure Constant
The advent of laser cooling and Bose-Einstein condensation has transformed
atomic physics. Cold molecules, with their richer internal structure, offer
many new exciting research opportunities including high resolution spectroscopy,
precision measurements, and novel collision studies. We create cold molecules
by using the well understood phenomenon of supersonic expansion to cool
molecules and the Stark effect to slow the resulting molecules into the
rest frame of the laboratory.
Theories that try to unify gravity with the other fundamental forces predict
variations in the fundamental constants over time, including the fine structure
constant. Comparing measurements of OH transition frequencies at cosmological
distances with laboratory based measurements can give a limit of the time
variation of the fine structure constant. We have made the most precise
measurements of microwave transitions in the ground state of OH to complement
the astronomical observations.
Prof. Peter Palffy-Muhoray, Liquid Crystal Institute,
Kent State University. March 30, 2005
Light induced phenomena in liquid crystal rubbers
Liquid crystal elastomers are orientationally ordered elastic solids.
Because of the strong coupling between orientational order and mechanical
strain, they are extremely responsive to external stimuli. We present
observations of light-induced deformations and related phenomena in these
materials, and discuss the underlying physics. Modelling the dynamic
response is an interesting and challenging problem. We describe our efforts
to construct a continuum model, and present preliminary results of
simulations. We consider potential applications based on the unique features
of these materials.
Prof. Michael Peskin, SLAC and Stanford University.
April 6, 2005
The International Linear Collider:
The Next Step in High-Energy Electron-Positron Physics
One of the important developments in elementary particle physics over the
past ten years has been the precision study of the weak interactions through
experiments in e+e- annihilation. The weak interactions are parity-violating,
and so spin observables have played a key role in this program. Now, building
on the successes of this study, particle physicists have proposed the construction
of a giant e+e- linear collider, which will use the same tools to explore
deeper into the structure of the weak interactions and even beyond them.
In this colloquium, I will first describe some of the recent precision weak-interaction
experiments and the questions they raise that might be answered at higher
energies. I will then describe the International Linear Collider (ILC) Project.
Finally, I will describe experiments that can be carried out at the ILC
that bear on the mysteries of the Higgs boson, cosmic dark matter, and other
major issues of particle physics.
Dr. Brian O'Reilly, Caltech (LIGO Livingston Observatory).
April 13, 2005
Recent Progress at LIGO
The LIGO experiment is designed to search for gravitational waves arising
from astrophysical phenomena. The detectors are km-scale suspended mass
interferometers located in Hanford, WA and Livingston, LA. At design sensitivity
these interferometers will measure displacements on the order of $1.5\times
10^{-9} m/\sqrt{Hz}$. LIGO has already conducted a series of scientific
observation runs and has published upper limits for several types of signals.
I will present an overview of the apparatus design and commissioning along
with recent published results.
Prof. Glennys Farrar, New York University, Center for
cosmology and particle physics April 20, 2005
New clues to the origin of ultra-high energy cosmic rays
A cluster of 4-5 ultra-high cosmic ray events has recently been
isolated, which provides tentative answers to several important
questions about the nature and origin of these mysterious particles.
I will discuss the evidence that these events have a common source
versus being a random coincidence and explain how analyzing the spread
in their arrival directions allows one to place constraints on cosmic
magnetic fields which are otherwise inaccessible to study. Candidate
sources and insight provided by the Sloan Digital Sky Survey will be
discussed. The energy spectrum of the clustered events is an important
clue to their origin, as will be explained. Several popular models for
the origin of UHECRs can be excluded.