Physics & Astronomy Colloquium

The Galactic Ecosystem: connecting internal structure with formation history

Dr. Rachel Somerville Rutgers University The Galactic Ecosystem: connecting internal structure with formation history It has long been known that galaxies' internal structure is connected with their star formation activity in the nearby universe. Recent surveys have allowed us to study these correlations out to very large distances, allowing us for the first time to quantify these relationships over a significant span of cosmic time for statistically robust samples of objects. It has been known for several years that galaxies are growing in mass and radius, experiencing morphological transformation, and "downsizing" their star formation activity over cosmic time. Now, new observations are painting a picture in which the internal structure of galaxies (size and morphology) is intimately linked with their star formation activity and formation history. There are hints that the co-evolution of supermassive black holes with their host galaxies may be the driving force behind these correlations, but this remains controversial. While cosmological simulations set within the hierarchical formation scenario of Cold Dark Matter currently offer a plausible story for interpreting these observations, many puzzles remain. I will review recent insights gleaned from deep multi-wavelength surveys and state-of-the-art theoretical models and simulations, as well as highlight the open questions and challenges for the future.

Spinors, Strings and Superconductors: Challenges of a new era in Condensed Matter Physics

Dr. Piers Coleman Rutgers University Physics thrives on the strong convection of ideas between the lab and the cosmos, yet each new generation of physicist is surprised as it rediscovers the forgotten fact that discovery cuts across the boundaries of our specialities. Here, I shall argue that recent discoveries in particle, condensed matter and astronomy place us again at extraordinary juncture for a new convection of ideas. I shall try to sketch this pragmatic outlook from a condensed matter physics perspective, using examples drawn from my work and others. How some elegant equations from string theory and gravity led us to discover a novel phase transition in two dimensional Heisenberg magnets; how a discussion with a particle physicist suggested a new way of understanding heavy electron superconductors, and how the discovery of Ising electrons in the "hidden order" material, URu2Si2 suggests a form of order long thought to be forbidden - called "hastatic order".

Hidden Interactions of Quarks

Dr. Bogdan Dobrescu FNAL

The quarks feel all five types of boson-mediated interactions: electromagnetic, strong, weak, Higgs and gravitational. In this talk I will discuss theoretical and experimental constraints on hypothetical new interactions among quarks. Interactions of this type can be hidden if they have a very short range, or if they are very weak, or by other mechanisms such as momentum-dependent couplings. A related question is how strongly can quarks interact with dark matter.

Discovery of New and Old Thermoelectrics using First Principles Methods

 

 

Dr. David Singh Oak Ridge National Labs

There is increasing interest in thermoelectric materials motivated in part by recent progress and in part by the potential of these materials in various energy technologies. Thermoelectric performance is a multiply contra-indicated property of matter. For example, it requires (1) high thermopower and high electrical conductivity, (2) high electrical conductivity and low thermal conductivity and (3) low thermal conductivity and high melting point. The keys to progress are finding an optimal balance and finding ways of using complex electronic and phononic structures to avoid the counter-indications mentioned above. In this talk, I discuss some of the issues involved in the context of recent results. One key aspect is optimization of the doping level in a given thermoelectric material. While this has long been understood in terms of standard semiconductor parabolic band models, we find surprisingly different results for many thermoelectric materials when the actual first principles band structures are used. This has led to prediction of a number of useful thermoelectrics, some that are new, and surprisingly some that are old. This work was done in collaboration with David Parker, Xin Chen, Olivier Delaire and Mao-Hua Du and was supported by the Department of Energy through the S3TEC Energy Frontier Research Center.

 

 

The Astrophysics of Black Hole Spin

 

 

Dr. Reynolds University of Maryland In addition to providing vital clues as to the formation and evolution of black holes, the spin of black holes may be an important energy source in the Universe. Over the past couple of years, tremendous progress has been made in the realm of observational measurements of spin. I will describe these efforts with particular focus on the use of X-ray spectroscopy to probe the spin of supermassive black holes in active galactic nuclei (AGN). For the first time, we are obtaining hints about the distribution of spins across the population of supermassive black holes with some interesting and unexpected consequences. After discussing spin, I will also address questions related to the driving of relativistic jets from AGN and the jet-disk connection. I shall conclude by discussing future prospects enabled by Astro-H (to be launched in 2015) and LOFT/ATHENA+ (currently under consideration by ESA).

 

 

The Radon EDM Experiment

 

 

Dr. Tim Chupp University of Michigan A permanent electric dipole moment (EDM) of a particle or system would arise due to breaking of time-reversal (T), or equivalently charge-conjugation/parity (CP) symmetry. Over the past five decades, a number of experiments on the neutron, atoms and molecules have only set upper limits on EDMs, and the search continues, motivated in large part by the expectation that beyond Standard-Model physics CP violation is required to explain the baryon asymmetry of the universe. In addition, new techniques and access to systems in which the effects of CP violation would be greatly enhanced are driving the field forward. Systems that may be favorable for significant advances include the isotopes 225Ra and 221/223Rn, where the combination of significant octupole collectivity and relatively closely spaced opposite parity levels would increase the nuclear Schiff moment by orders of magnitude compared to other diamagnetic atoms, i.e. 199Hg. A number of technical and nuclear-structure issues must be addressed in order to assess the prospects for an experiment of significant impact. Among the technical challenges for the Radon-EDM program are developing an on-line EDM experiment at an isotope-production facility that will collect and make measurements on the short-lived species (half lives are approximately 25 min). We have developed and tested a system for high-efficiency collection and spin-exchange polarization of noble-gas isotopes that has been tested at the TRIUMF ISAC facility (experiment S929). Radon polarization techniques were studied at ISOLDE and Stony Brook, and spin-precession detection techniques are under development. Nuclear-structure issues include determining the octupole collectivity as well as the spacing of opposite parity levels. A series of experiments at ISOLDE (IS475 and IS552) have recently directly measured octupole collectivity in 220Rn and 224Ra leading to strengthened confidence in conclusions about the octupole enhancements. Experiments are also underway at NSCL at Michigan State University TRIUMF/ISAC to study the nuclear structure of isotopes in this mass region. I will report on progress on all these fronts and discuss recent developments in our studies of how we learn about the basic physical parameters of CP violation from the suite of EDM measurements.

 

 

Galaxy Build-up at Cosmic Dawn: New Insights from Ultra-Deep Hubble and Spitzer Observations

Dr. Pascal Oesch Space Telescope Science Institute

Thanks to ultra-deep observations with the WFC3/IR camera on Hubble the frontier of galaxies has recently been pushed out to z~9-12, only ~450 Myr from the Big Bang. From several large Hubble programs such as the HUDF09, CANDELS, or CLASH, we were able to identify large samples of more than 200 galaxies at z~7-8, and we are now starting to build up the sample sizes of z~9-11 galaxy candidates. In particular, the recent HUDF12 campaign further increased the depth of the WFC3/IR dataset over the Hubble Ultra-Deep Field (HUDF), and enabled us to detect a sample of nine very faint z>8 galaxy candidates in the HUDF. Additionally, the newly completed CANDELS data over GOODS-North now revealed four relatively bright z~9-10 sources, which are in tension with the previous UV LF determination from the GOODS-South field, indicating that star-formation in the early universe might have been very stochastic. Using all z>8 candidates in and around both GOODS fields, we infer that the cosmic star-formation rate density in galaxies with SFR>0.7Msol/yr decreases rapidly at z>8, dropping by an order of magnitude from z~8 to z~10. With complementing, ultra-deep Spitzer IRAC data, we are additionally able to infer the stellar mass densities out to z~8-10. In this talk I will highlight recent progress in exploring the high redshift frontier and in understanding the growth of galaxies in the first two billion years. In particular, I will present current constraints on the UV luminosity function of galaxies at z>8, and I will demonstrate the power of combining deep Hubble and Spitzer data to directly track the star-formation and mass build-up of z>=4 galaxies.

 

 

Controlled Magnetic Reversal and Emergent Metamagnetism in Permalloy Films Patterned into Artificial Quasicrystals

Dr. Lance Delong University of Kentucky

Ferromagnetic (FM) thin films patterned into periodic lattices of nanoscale holes or dots are candidated for UHD data storage media, an drelated wire network patterns are of fundamental interest as examples of controlled phase transitions in "artificial spin ice". Our recent Physical Review Letter reported an experimental study of the static and dynamic magnetic properties of FM permalloy thin films patterned as Penrose P2 (quasicrystal) tilings that exhibit long-range order, but aperiodic translational symmetry. Our DC magnetization and ferromagnetic resonance data constitute, we believe, the first experimental study of th espin wave dynamics of an artificial FM quasicrystalline thin film. Ground-breaking efforts were required to both pattern and deposit the sample film materials, and to execute large-scale numerical simulations of their static and dynamic behavior. This work demonstrates a new method for controlling the evolution of FM domain walls and spin wave spectra in magnetic media, in spite of a lack of periodic symmetry in an artificial quasicrystalline pattern. Simulations reveal a remarkably controlled sequence of reversals of individual film segments located on sublattices of the quasicrystal pattern, which may signal the occurence of true metamagnetic phase transitions in larger-area samples. These results directly imply FM films patterned as Penrose P2 tilings constitute a novel class of magnonic crystals whose magnon frequency dispersion and physical properties were heretofore unknown.

 

 

Quantum Tapestries

Dr. Matthew Fisher University of California, Santa Barbara

Quantum Tapestries Within each of Nature's crystals is an exotic quantum world of electrons weaving to and fro. Each crystal has its own unique tapestry, as varied as the crystals themselves. In some crystals the electrons weave an orderly quilt. Within others the electrons are seemingly entwined in an entangled web of quantum motion. In thi stalk I will describe the ongoing efforts to disentangle even Nature's most intricate quantum embroidery. Cutting-edge quantum many-body simulations together with recent ideas from quantum information theory, such as entangelment entropy, are enabling a coherent picture to emerge.

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