Physics & Astronomy Colloquium

Physics and Astronomy Colloquium: Neutrinos from Nuclear Reactors: Searches and Surprises

Nuclear reactors are very bright sources of neutrinos. The radioactive fission products are neutron rich, and beta decay back to the valley of stability while emitting (electron anti-)neutrinos along the way. This was how the neutrino was discovered, and how we verified that neutrino oscillations explained the Solar Neutrino Problem. More recently, the Daya Bay Reactor Neutrino Experiment discovered a new mode of neutrino oscillation, and the PROSPECT experiment is being planned to search for "sterile" neutrinos.

This talk will first review the basics of neutrinos, their detection, neutrino oscillations, and nuclear reactors as neutrino sources. We'll then take a tour of recent results and next steps, including some surprises in what we've learned about the reactor neutrino source itself.
 

Refreshments will be served in CP 179 at 3:15 PM

Date: 
Friday, September 18, 2015 - 3:30pm to 4:30pm
Location: 
CP155

The Structure and Evolution of Milky Way-Like Galaxies

Matthew Bershady University of Wisconsin

A small fraction of the universe's energy-density is comprised of normal matter. A still smaller fraction is bound into stars and gas that we can see and are responsible for life. This talk examines what we know about the baryon content of, and how stars assembled in, galaxies like the Milky Way (MW). Dynamical measurements from integral-field spectroscopy indicate the baryonic mass of spiral disks is small. Radiative-transfer modeling of dusty, edge-on galaxies reveals super-thin stellar disks previously missed. These findings yield a consistent picture of light disks with young luminosity-weighted stellar ages. A new census from the Sloan Digital Sky Survey-IV, now underway, will test how broadly these results apply to the galaxy population as a whole. This advance allows us to better place the MW in context of today's galaxy population, and to leverage the MW's unique archaeological record against observations of distant galaxies. A critical question that can be resolved is whether stellar age and abundance gradients in galaxy disks are the result of a settling process of decreasingly turbulent gas or dynamical heating.

Topological Insulators 101

 

 

Dr. Ganpathy Murthy University of Kentucky We thought we knew all there was to know about band insulators back in the 1930s. However, in the last 10 years we have learnt that there distinct types of band insulators in 2 and 3 dimensions. The distinction between these types is "topological", a term I will explain. I will introduce the idea of band topology in detail in 2D. I will then use the example of the integer quantum Hall effects to show that a topological insulator has edge states that are robust to disorder. Next I will introduce time-reversal invariance, which puts powerful constraints on band insulators. Once again, edge modes will prove to be extremely useful in characterizing the different types of band insulators. I will end up by talking about 3D topological insulators and some of the phenomenology associated with them.

 

 

Colloquium: The many facets of strongly coupled QFT: from QCD to Cosmology

Abstract: Quantum Field Theory is a universal language to describe a multitude of physical phenomena from elementary particle and condensed matter physics. Often apparent complexity of the described phenomena is attributed to strong coupling in the underlying QFT. Accordingly, understanding strongly-coupled dynamics became a universal theoretical challenge relevant for many areas of contemporary physics. Remarkably, the past decade was characterized by an accelerated development of several original approaches to this problem, leading to a plethora of new results. In my talk I will focus on several non-pertubative methods, most notably holographic correspondence, and describe recent progress and hot research topics. Refreshments will be served in CP 179 at 3:15 PM

Date: 
Friday, March 6, 2015 - 3:30pm to 4:30pm
Type of Event (for grouping events):

Enhancing Exoplanet Discovery and Characterization through Stellar Photometric “Flicker”

 

 

Dr. Fabienne Bastien Pennsylvania State University As a result of the high precision and cadence of surveys like MOST, CoRoT, and Kepler, we may now directly observe the very low-level light variations arising from stellar granulation in cool stars. Here, we discuss how this enables us to more accurately determine the physical properties of Sun-like stars, to understand the nature of surface convection and its connection to activity, and to better determine theproperties of planets around cool stars. Indeed, such sensitive photometric "flicker" variations are now within reach for thousands of stars, and we estimate that upcoming missions like TESS will enable such measurements for ~100 000 stars. We present recent results that tie “flicker” to granulation and enable a simple measurement of stellar surface gravity with a precision of 0.1 dex. We use this, together and solely with two other simple ways of characterizing the stellar photometric variations in a high quality light curve, to construct an evolutionary diagram for Sun-like stars from the Main Sequence on towards the red giant branch. We discuss further work that correlates “flicker” with stellar density, allowing the application of astrodensity profiling techniques used in exoplanet characterizationto many more stars. We also present results suggesting that the granulation of F stars must be magnetically suppressed in order to fit observations. Finally, we show that we may quantitatively predict a star's RV jitter using our evolutionary diagram, permitting the use of discovery light curves to help prioritize follow-up observations of transiting exoplanets.

 

 

The Universe as a Detector: What can we learn about fundamental physics from Cosmology?

 

 

Dr. Harsh Mathur Case Western Reserve University The imprint of primordial gravitational radiation on the cosmic microwave background polarization, if observed, is considered smoking gun proof of inflation. I will discuss how such an observation can not only provide information about the Universe in the epoch of inflation but also constrain theories of grand unification. In the second part of the talk I will discuss tests of gravity on scales ranging from the tabletop to the cosmological scale. Such tests may shed light on physics beyond the standard model.

 

 

Defects with Character: Majorana Local Modes in Condensed-Matter Systems

 

 

Dr. Bertrand Halperin Harvard University Theory predicts the existence of some peculiar phases of quantum condensed matter systems that have multiple degrees of freedom with very low energy, when localized “defects” are introduced. I shall focus on a class of these phases where each defect has half of a conventional degree of freedom, and the defects may be considered as sites for localized zero-energy states of a “Majorana fermion”. Such defects would also exhibit the intriguing property of “non-Abelian statistics” -- i.e., if various defects can be moved around each other, or if two identical defects can be interchanged, the result is a unitary transformation on the quantum mechanical state that depends on the order in which operations are performed but is insensitive to many other details. In my talk, I will try to explain these various concepts and discuss the attempts to realize them in condensed matter systems.

 

 

Rapid Arctic warming and extreme weather events in mid-latitudes: Are they connected?

 

 

Dr. Jennifer Francis Rutgers University In this presentation, I will discuss the hypothesis proposed by Francis and Vavrus (2012) that links rapid Arctic warming (so-called Arctic amplification) to changes in the large-scale atmospheric circulation in the northern hemisphere that favors more persistent weather patterns and a higher likelihood of extreme weather events such as droughts, cold spells, flooding, heavy snows, and heat waves. This hypothesis has been a topic of considerable controversy in recent months, particularly regarding its relationship to the unusual weather conditions that persisted in the winter of 2013/2014. I will discuss various aspects of this linkage, what we know and don't know, and present new related research.

 

 

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