Physics and Astronomy Colloquium

semester, 2010


Wednesday, January 20th 2010
3:35 pm:
There will be no colloquium this week.

Wednesday, January 27th 2010
3:35 pm:
Speaker: Maxim Pospelov, Perimeter Institute for Theoretical Physics
Subject: Dark Forces
Refreshments served in Room 216 Physics after colloquium

The Universe's energy budget is dominated by dark energy and dark matter. The existence of a dark force, a new interaction between dark matter particles, is another possibility that has recently attracted a lot of attention. I will review current motivations for the dark force, and describe various theoretical ideas for directly testing its existence in the collider and fixed target experiments.


Wednesday, February 3rd 2010
3:35 pm:
There will be no colloquium this week.

Wednesday, February 10th 2010
3:35 pm:
Speaker: Nemanja Kaloper
Subject: Out of Darkness: The Quest for Lambda
Refreshments served in Room 216 Physics after colloquium

Recent astronomical observations are forcing us to face the cosmological constant problem, which is perhaps the greatest challenge of modern fundamental physics. Solving it seems to require a paradigm shift in our thinking about nature. In this talk I will start with a review of the experimental evidence which forces us to really address the cosmological constant problem. Through a survey of historical evolution of our understanding of the physics of cosmological constant and vacuum energy, I will outline the salient physical features of the problem and the assumptions which it rests upon. From the viewpoint of the "standard" effective field theory, the key obstacle is nicely summed up in the venerated Weinberg no-go theorem, which explains why the physics of the cosmological constant is so elusive. Reviewing it, I will discuss the ideas often seen in our modern attempts to find solutions, reflecting on the landscape approach, and why people might wish to modify gravity.


Tuesday, February 16th 2010
3:35 pm:
Speaker: Prof. A. Yu. Grosberg, NYU
Subject: Fractal organization of DNA in the cell: theoretical prediction, experimental confirmation, computer simulation ... and still many open questions.
Refreshments served in Room 216 Physics after colloquium

Fractal organization of DNA in the cell: theoretical prediction, experimental confirmation, computer simulation ... and still many open questions.

Each cell of our body contains about 2 meters of DNA packed in a micron size nucleus. It was predicted a long time ago that this DNA has to be organized as a crumpled globule in which polymer chain has fractal dimension 3. Recent experiment confirmed the prediction. Theory based on the topological properties of DNA also explains the phenomenon of chromosome territories. However, more detailed experiments as well as computer simulations of the model systems, particularly related to the dynamics of DNA in crumpled globule state, challenge physicists with new tough questions.

3:35 pm:
Speaker: Prof. A. Yu. Grosberg, NYU
Subject: Fractal organization of DNA in the cell: theoretical prediction, experimental confirmation, computer simulation ... and still many open questions.
Refreshments served in Room 216 Physics after colloquium

Fractal organization of DNA in the cell: theoretical prediction, experimental confirmation, computer simulation ... and still many open questions.

Each cell of our body contains about 2 meters of DNA packed in a micron size nucleus. It was predicted a long time ago that this DNA has to be organized as a crumpled globule in which polymer chain has fractal dimension 3. Recent experiment confirmed the prediction. Theory based on the topological properties of DNA also explains the phenomenon of chromosome territories. However, more detailed experiments as well as computer simulations of the model systems, particularly related to the dynamics of DNA in crumpled globule state, challenge physicists with new tough questions.

3:35 pm:
Speaker: Prof. A. Yu. Grosberg, NYU
Subject: Fractal organization of DNA in the cell
Refreshments served in Room 216 Physics after colloquium

Each cell of our body contains about 2 meters of DNA packed in a micron size nucleus. It was predicted a long time ago that this DNA has to be organized as a crumpled globule in which polymer chain has fractal dimension 3. Recent experiment confirmed the prediction. Theory based on the topological properties of DNA also explains the phenomenon of chromosome territories. However, more detailed experiments as well as computer simulations of the model systems, particularly related to the dynamics of DNA in crumpled globule state, challenge physicists with new tough questions.


Wednesday, February 17th 2010
3:35 pm:
Speaker: Michel Janssen, University of Minnesota
Subject: Jordan and the wave-particle duality of light.
Refreshments served in Room 216 Physics after colloquium

In 1909, Einstein derived a formula for the mean-square energy fluctuation in black-body radiation. This formula is the sum of a wave term and a particle term. In a famous joint paper with Born and Heisenberg submitted in late 1925, Pascual Jordan used the new matrix mechanics to show that one recovers both these terms in a simple model of quantized waves. This result not only solved Einstein’s puzzle about the wave-particle duality of light, it also provided striking evidence for matrix mechanics and a strong argument for field quantization. After reviewing Einstein’s early work on fluctuations in black-body radiation, I present Jordan’s result and the curious story of its reception. Rather than being hailed as a major contribution to quantum theory, Jordan’s result met mostly with skepticism, even from his co-authors. I will argue that the skeptics were wrong.


Wednesday, February 24th 2010
3:35 pm:
Speaker: Raymond Orbach, Energy Institute, University of Texas at Austin
Subject: Energy Security: From Deal Killers to Game Changers
Refreshments served in Room 216 Physics after colloquium

Five energy security "deal killers" are identified: 1) Global warming and CO2 emissions from fossil fuel combustion; 2) Intermittent energy sources (wind, solar) and the presence and stability of the grid; 3) Penetration of plant defenses to produce transportation fuels from biomass; 4) Mimicking nature: artificial photosynthesis for solar energy to fuels; and 5) Spent fuel from nuclear power reactors. Transformational basic research is required to successfully change the ground rules, to transform these "deal killers" into "game changers." They are: 1) Offsetting carbon capture and storage costs through enhanced oil recovery and methane generation from high temperature geothermal saline aquifers; 2) Electrical energy storage, through batteries and super-capacitors; 3) Genetic modification of plant cell walls, and catalytic methods for transforming plant sugars into fuels; 4) Separation of solar-induced electrons from holes, and catalysis to produce fuels; and 5) Closing the nuclear fuel cycle. Basic research can revolutionize our approach to carbon-free energy by enhancing nature to achieve energy security.

Biography: Dr. Raymond Lee Orbach is Director of The University of Texas at Austin’s Energy Institute, a multi-disciplinary institute that combines the strengths of the university’s schools and colleges to advance solutions to today’s energy-related challenges. He will also have joint appointments as a professor with tenure in the Department of Mechanical Engineering, Cockrell School of Engineering; the Department of Physics, College of Natural Sciences; and the Jackson School of Geosciences. Orbach was sworn in as the Department of Energy’s first under secretary for science in June 2006. He was the chief scientist of the Department of Energy, and adviser to Secretary Samuel W. Bodman on science policy as well as all scientific aspects of the Department of Energy, including basic and applied research ranging from nuclear energy, to environmental clean-up of Cold War legacy sites, to defense programs. Orbach was responsible for planning, coordinating and overseeing the Energy Department’s research and development programs and its 17 national laboratories, as well as the department’s scientific and engineering education activities. Orbach also was responsible for the department’s implementation of the president’s American Competitiveness Initiative, designed to help drive continued U.S. economic growth. of Energy (DOE).

There will be a live webcast of this colloquium, here


Wednesday, March 3rd 2010
3:35 pm:
Speaker: Haiyan Gao, Duke University and Triangle Universities Nuclear Laboratory
Subject: A New Search for Neutron Electric Dipole Moment (nEDM)
Refreshments served in Room 216 Physics after colloquium

A new experiment is being planned to search for the neutron Electric Dipole Moment (nEDM) with an unprecedented sensitivity. The proposed search aims at a two orders of magnitude improvement over the current experimental limit. A search for a non-zero value of the neutron EDM is a direct search of the time reversal symmetry (T) violation. It provides a unique insight into CP (Charge conjugation and parity) violation because of the CPT theorem. The Standard Model (SM) prediction for the neutron EDM is below the current experimental limit by several orders of magnitude. However, many proposed models of electroweak interaction which are extensions beyond the SM predict much larger values of neutron EDM. The new experiment has the potential to reduce the acceptable range of predictions by two orders of magnitude. Furthermore, if new sources of CP violation are present in nature beyond the Standard Model and are relevant to hadronic systems, this experiment offers a unique opportunity to measure a non-zero value of nEDM. The current understanding of the baryogenesis suggests that other sources of CP violation might exist in nature beyond the Standard Model and beyond what have been observed so far. To explain the baryon number asymmetry in the universe through the grand unified theory or electroweak baryogenesis, substantial New Physics in the CP violation sector is required. In this talk, I will discuss this new experiment following a brief review of previous neutron EDM experiments.


Wednesday, March 10th 2010
3:35 pm:
Speaker: Takashi Imai, Mcmaster University and Canadian Institute for Advanced Research
Subject: Iron: the most unlikely suspect for high temperature superconductivity
Refreshments served in Room 216 Physics after colloquium

During the 2008 APS March Meeting in New Orleans, a rumor spread like wildfire: "a new type of high temperature superconductor was discovered!" To the astonishment of condensed matter physicists, the new superconductor turned out to contain the most unlikely suspect among all the transition metal elements: iron, a synonym of ferromagnetic metals. Despite intense research efforts over the last 2 years around the globe, we are still far from understanding the mechanism of high temperature superconductivity in the new iron-based systems. In this talk, I will describe the exciting developments in this emerging research field


Wednesday, March 17th 2010
3:35 pm:
No colloquium this week. Spring Break

Wednesday, March 24th 2010
3:35 pm:
Speaker: Mitchell Luskin, University of Minnesota
Subject: Predictive Atomistic-to-Continuum Coupling Methods
Refreshments served in Room 216 Physics after colloquium

Many materials problems require the accuracy of atomistic modeling in small regions, such as the neighborhood of a crack tip. However, these localized defects typically interact with a much larger region through long-ranged elastic fields. These regions are too large to be computed atomistically. Many methods have been proposed to compute solutions to these multiscale problems by coupling atomistic models near a localized defect with continuum models where the deformation is nearly uniform.

The development of coupling methods for crystalline materials that are reliable and accurate for configurations near the onset of lattice instabilities such as dislocation formation has been particularly challenging. I will present theory developed with Matthew Dobson and Christoph Ortner to assess currently utilized methods and to propose more reliable, accurate, and efficient methods.


Wednesday, March 31st 2010
3:35 pm:
Speaker: Vladimir Savinov, University of Pittsburgh
Subject: Probing the Nature of Neutrinos and Other Fun Stuff with ATLAS at the LHC.
Refreshments served in Room 216 Physics after colloquium

Processes with high transverse momentum leptons and jets are predicted by many Beyond the Standard Model (BSM)scenarios including leptoquarks, Left-Right Symmetry and various models of Grand Unification. Such theoretical models extend the application of Quantum Field Theory to energies far above the Electroweak Symmetry Breaking (EWSB) energy scale and seek to provide a more elegant description of the fundamental forces. I will present preliminary results of studies performed with the ATLAS detector at the LHC, where we attempt to address questions about the origin of masses and the nature of the known neutrinos, the origin of CP violation and its role in baryogenesis, the origin of flavor and other fundamental questions beyond EWSB.


Wednesday, April 7th 2010
3:35 pm:
Speaker: Dam Thanh Son, University of Washington
Subject: Viscosity, quark gluon plasma, and string theory
Refreshments served in Room 216 Physics after colloquium

Viscosity is a very old concept which was introduced to physics by Navier in the 19th century. However, in strongly coupled systems viscosity is extremely difficult to compute ab initio. In this talk I will describe some recent surprising developments in string theory which allow one to compute the viscosity for a class of strongly interacting fluids not too dissimilar to the quark gluon plasma. I will describe efforts to measure the viscosity and other physical properties of the quark gluon plasma at the Relativistic Heavy Ion Collider.


Wednesday, April 14th 2010
3:35 pm:
Speaker: Albert Libchaber, The Rockefeller University
Subject: The Origin of Life: from geophysics to biology?
Refreshments served in Room 216 Physics after colloquium

One of the deepest and most controversial questions of our time is that of the origin of life. In this lecture a hypothesis is presented, according to which the temperature gradients existing in the earth - which led to plate tectonics and the formation of undersea thermal vents - also led to the evolution of life around these vents. Movies and data will be shown of experiments in which all stages of this scenario are presented: how thermal
gradients led to plate tectonics, to DNA amplification in thermal vents, to polymerization of peptides at high pressure and to the organization of bacteria. This mixture of physics, chemistry, and biology illustrates how life could originate without the intervention of the sun, driven only by geophysical thermal gradients.


Wednesday, April 21st 2010
3:35 pm:
Speaker: Chandra Varma, UC Riverside (Honorary Doctorate of Science Presentation)
Subject: Quantum Phase Transitions or You Gotta Love Singularities.
Refreshments served in Room 216 Physics after colloquium

In recent years, a variety of phenomena in systems of interacting fermions is understood by fluctuations towards phase transitions to a broken symmetry in the limit of zero temperature. For example, the high temperature superconductivity phenomena is known to be associated with such fluctuations. Such fluctuations require a quantum-mechanical theory of critical fluctuations unlike the theory of fluctuations near classical phase transitions which is one of the great and beautiful solved problems of the 20th century. I will try to provide a simple and concise account of the difference between classical and quantum phase transitions and fluctuations. Remarkably, many observed quantum-critical phenomena manifests itself in a separation of time and space variables with critical fluctuations only in time. Although the universality class of such criticality is unknown, the fluctuations associated with high temperature superconductivity have been solved and shown to be due to a proliferation of a new class of topological defects which have for good reason been called "warps". It is expected that the general elucidation of such criticality will influence wide fields in physics just as understanding classical critical phenomena did.


Wednesday, April 28th 2010
3:35 pm:
There will be no colloquium this week.

Wednesday, May 5th 2010
3:35 pm:
Speaker: Leo Kadanoff, James Franck Institute, University of Chicago and the Perimeter Institute Waterloo, Ontario, Canada
Subject: Phase Transitions: Scales, Universality, Singularities, and Renormalization
Refreshments served in Room 216 Physics after colloquium

In present-day physics, the renormalization method, as developed by Kenneth G. Wilson, serves as the primary means for constructing the connections between theories at different length scales. This method is rooted in both particle physics and the theory of phase transitions. It was developed to supplement mean field theories like those developed by van der Waals and Maxwell, followed by Landau. Sharp phase transitions are necessarily connected with singularities in statistical mechanics, which in turn require infinite systems for their realization. (I call this result the extended singularity theorem.) A discussion of this point apparently marked a 1937 meeting in Amsterdam celebrating van der Waals. Mean field theories neither demand nor employ spatial infinities in their descriptions of phase transitions. Another theory is required that weds a breaking of internal symmetries with a proper description of spatial infinities. The renormalization (semi-)group provides such a wedding. Its nature is described. The major ideas surrounding this point of view are described including especially scaling, universality, and theory-reduction.


Wednesday, May 12th 2010
3:35 pm:
There will be no colloquium this week.

Wednesday, September 8th 2010
3:35 pm:
There will be no colloquium this week.

Wednesday, September 15th 2010
3:35 pm:
Speaker: Julio Navarro, University of Victoria
Subject: Dark Matter under a Numerical Microscope
Refreshments served in Room 216 Physics after colloquium

Dark matter is one of the basic ingredients of our current paradigm for the growth of structure. In this scenario, dark matter halos are the basic units of non-linear structures---such as galaxies---in the present Universe. I will report results from the latest numerical simulations of galaxy-scale dark halos. These state-of-the-art simulations achieve resolutions high enough that a number of previously pending questions regarding the structure and substructure of dark matter halos can now be addressed with confidence. Tests demonstrate detailed convergence for (sub)structures well below a millionth the mass of the final system, below the mass scale associated with even the faintest galaxies known. I will discuss applications of this simulation series, such as accurate characterization of the expected signal both in Earth-bound experiments designed to detect dark matter directly, and in indirect detection experiments which attempt to image dark matter annihilation radiation at gamma-ray wavelengths.


Wednesday, September 22nd 2010
3:35 pm:
Speaker: N. David Mermin, Cornell University
Subject: What has quantum mechanics to do with factoring?
Refreshments served in Room 216 Physics after colloquium

Quantum computer science will be introduced in the context of its most sensational algorithm: the highly efficient factoring routine discovered by Peter Shor. I will emphasize those features of Shor's procedure that puzzled, surprised, and charmed me in the course of my own efforts to better understand how it does its magic. The subject offers some offbeat glimpses of both quantum mechanics and computation.


Wednesday, September 29th 2010
3:35 pm:
Speaker: Jenny Hoffman, Harvard University
Subject: Scanning Tunneling Spectroscopy and Vortex Imaging in the Iron-Pnictide High-Tc Superconductors
Refreshments served in Room 216 Physics after colloquium

In 2008, 22 years after the discovery of high-Tc superconductivity in the cuprates, superconductivity was discovered up to 55K in a second family of materials: the iron-pnictides. This new discovery has generated tremendous excitement for several reasons. First, there is hope that the iron-pnictides will finally provide the foil necessary to understand the enormous yet puzzling body of research on the cuprates. Second, initial reports of low anisotropy and strong vortex pinning in these new materials have spurred optimism that the iron-pnictides may finally lead to the widespread technological applications which have been elusive for cuprates. In this talk, I will summarize the current state of iron-pnictide research, before presenting our own work: the first scanning tunneling spectroscopic imaging study of a single crystal iron-pnictide superconductor in high magnetic fields. We observe a static disordered vortex lattice at, and demonstrate that vortices are pinned in the bulk of this material, a promising observation for practical applications.


Wednesday, October 6th 2010
3:35 pm:
Speaker: Professor Joel Moore, UC Berkeley
Subject: The Birth of Topological Insulators
Refreshments served in Room 216 Physics after colloquium

Wednesday, October 13th 2010
3:35 pm:
Speaker: Guido Mueller, University of Florida
Subject: The Laser Interferometer Space Antenna (LISA)
Refreshments served in Room 216 Physics after colloquium

LISA is a joint NASA/ESA space project aimed at the detection of gravitational waves in the mHz frequency region. Super-massive black hole mergers, neutron star binaries, and extreme mass ratio inspirals are among the most prominent known LISA sources but its exceptional sensitivity virtually guarantees many unexpected signals from many currently unknown sources. LISA consists of three spacecraft (SC) separated by around 5 Gm in a triangular formation. Each SC houses two 4cm cubes made from a Gold-Platinum alloy. These cubes are in near perfect free fall and shielded from all external forces. They form the end points of laser interferometer which will measure changes in their distances with 10 pm/rtHz sensitivity. This concept has not changed I will give an overview of the scientific merits of LISA, will describe the mission concept, and discuss the current status of LISA.


Wednesday, October 20th 2010
3:35 pm:
Speaker: Professor Vincent Noireaux, University of Minnesota
Subject: Development of an artificial cell to study some information and self-organization processes.
Refreshments served in Room 216 Physics after colloquium

Living cells are characterized by three components: the information, the compartment and the metabolism. One way to understand the cooperative link between these parts is to use a bottom-up approach, which consists of assembling a synthetic cell from scratch with the basic molecules of life.
I will present an approach to construct an artificial cell, which emphasizes the biophysical properties of genetic and non-genetic processes found in living organisms. Unlike other information systems, such as electrical circuits, gene networks are not constructed with elementary blocks that can be repeated. I will show how elementary gene circuits can be built in vitro with a cell-free toolbox and I will discuss the dynamical properties of these circuits. Molecular self-organization is a non-genetic process critical for any living cell. I will present a quantitative method to study the self-assembly of membrane proteins.


Wednesday, October 27th 2010
3:35 pm:
Speaker: Jeremiah Mans , University of Minnesota
Subject: First Physics Results from the LHC
Refreshments served in Room 216 Physics after colloquium

On March 30, the Large Hadron Collider commenced collision operations at a center-of-mass energy of 7 TeV, seven thousand times the mass of the proton. With this event, fifteen years of design and construction came to an end -- a mammoth project designed to answer questions about the nature of mass and to search for an understanding of dark matter. I discuss briefly discuss the physics goals of the LHC and present the first experimental results from the LHC covering our understanding of electroweak physics and the structure of the proton as well as searches for physics beyond the Standard Model. I will discuss the recent observation of a ridge structure in proton-proton collisions and the prospects for discoveries in the coming year.


Wednesday, November 3rd 2010
3:35 pm:
Speaker: Martin Greven
Subject: Unconventional magnetism in the copper-oxide high-temperature superconductors
Refreshments served in Room 216 Physics after colloquium

Magnetic correlations might cause the superconductivity in the mysterious copper-oxides and are generally believed to be antiferromagnetic. Following our success in growing sizable crystals of the model compound HgBa2CuO4+δ, we used elastic neutron scattering to demonstrate the universal existence of a novel type of magnetic order in superconducting samples. Unlike antiferromagnetism, this order does not break the translational invariance of the crystal lattice. Using inelastic neutron scattering, we subsequently discovered several excitations that appear to be fundamental collective modes associated with the unusual magnetic order. Our findings are consistent with a particular type of order involving circulating charge currents and with the notion that the phase diagram of the copper-oxides is controlled by an underlying quantum critical point -- a zero-temperature phase transition as a function of the hole-carrier density.


Wednesday, November 10th 2010
3:35 pm:
Speaker: William Hendee Medical College of Wisconsin;
Subject: Medical Physics: The Past and the Present
Refreshments served in Room 216 Physics after colloquium

Wednesday, November 17th 2010
3:35 pm:
Speaker: Eric Hudson, MIT
Subject: Stability in a Turbulent (Fermi) Sea: The Ever More Remarkable High Temperature Superconductors
Refreshments served in Room 216 Physics after colloquium

For over two decades high temperature superconductivity has captured the attention of scientists the world round. However, rather than finding a simple explanation for the properties of these materials, as was done for their low temperature cousins half a century ago, intensive research has instead led to an increasingly complex picture of materials characterized by an intricate phase diagram, full of competing or coexisting states, yet still dominated by a superconducting state which persists, at least in some materials, almost half way to room temperature. In this talk I will describe nanoscale investigations of the electronic structure of high temperature superconductors using scanning tunneling microscopy (STM). We have recently found that a still not understood high temperature phase in these materials, the pseudogap, is characterized by strong charge inhomogeneity. Surprisingly, although this disorder persists into the superconducting state, it does not seem to perturb coexisting homogeneous superconductivity. The resolution of this apparent contradiction gives new insight into the onset of superconductivity and its relationship with the pseudogap phase.


Wednesday, November 24th 2010
3:35 pm:
There will be no colloquium this week.

Wednesday, December 1st 2010
3:35 pm:
There will be no colloquium this week.

Wednesday, December 8th 2010
3:35 pm:
Speaker: Prof. Csaba Csaki, Cornell University
Subject: Searching for the mechanism of electroweak symmetry breaking
Refreshments served in Room 216 Physics after colloquium

The standard model of particle physics has been one of the greatest scientific achievements of the 20th century. Nevertheless most particle physicists think that the model is not complete. The generation of mass is included in an ad-hoc way, which does not even seem to be stable under quantum corrections. In this talk I first review the standard model and the Higgs mechanism thought to be responsible for particle masses. Then I explain the reasons for being dissatisfied with this picture. In the bulk of the talk I will present several ideas that could complement the standard model, including supersymmetric and extra dimensional models, and explain how the mass generation mechanism is incorporated/affected in such models and their variants.


Wednesday, December 15th 2010
3:35 pm:
Speaker: Uwe-Jens Wiese, Institute for Theoretical Physics, Albert Einstein Center for Fundamental Physics, Bern University, Switzerland
Subject: Discrete Quantum Systems and Emergent Field Theories: From Graphene to Antiferromagnets and QCD
Refreshments served in Room 216 Physics after colloquium

Discrete quantum systems play an important role in both condensed matter and particle physics. Nonrelativistic electrons hopping on a honeycomb lattice provide us with the Dirac cones of graphene. In the presence of strong Coulomb repulsion, electrons hopping on a bipartite lattice form an antiferromagnet which may turn into a high-temperature superconductor upon doping. Quantum Chromodynamics (QCD) --- the theory of the strong interaction --- can be regularized beyond perturbation theory by replacing space-time by a 4-dimensional lattice. Quarks, anti-quarks, and gluons propagating on the discrete lattice are confined inside protons and neutrons, and also form very light pions. Just as the pions in QCD, the magnons in an antiferromagnet, or the light fermions in graphene are described quantitatively by an emergent field theory. By numerical simulations of the underlying discrete quantum systems, one can accurately determine the low-energy parameters of the effective theories. Calculations in the effective theory then provide analytic insight into the nonperturbative dynamics of these interesting systems from condensed matter and particle physics.


Wednesday, December 22nd 2010
3:35 pm:
There will be no colloquium this week. Finals week.

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