Colloquium

Colloquium: Balancing the Cluster Baryon Budget

The deep gravitational potential wells of clusters of galaxies should capture fair samples of the total baryon fraction of the Universe, unless other physical processes drive baryons out of clusters. Thus precision measurements of the baryon fraction, particularly as a function of cluster mass, can reveal the history of baryon flux into and out of clusters. How those baryons are then apportioned between stars and intracluster gas---the star formation efficiency---informs models of cluster assembly and massive galaxy evolution, as well as efforts to use the cluster gas fraction to constrain the mass density and dark energy equation of state parameters. Even the partitioning of the stellar baryons alone, in and out of galaxies, tests models of cluster galaxy evolution, as intracluster stars are the final, unambiguous signature of stars stripped from cluster galaxies during tidal encounters. We have discovered that intracluster stars are a significant part of the stellar baryons in clusters and poorer groups of galaxies. I will present new work characterizing the properties of this previously unexplored component, as well as the consequences for the cluster baryon budget and its relationship to the Universal value.

Date: 
Friday, October 20, 2017 - 3:30pm to 4:30pm
Location: 
CP 155
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Colloquium

Date: 
Friday, April 28, 2017 - 3:30pm to 4:30pm
Location: 
CP155
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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.

 

 

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.

 

 

Science Policy in America

 

 

Dr. Tyler Glembo The American Physical Society Science Policy in America Fundamental scientific research, as a majority federally funded initiative, is becoming more deeply embedded in politics. Since the end of the Space Race, funding of basic physical sciences research as a percent GDP has continuously declined, indicating that policy makers see funding scientific research as less of a priority than they once did. Indeed, a lack of understanding about both science and how science is done amongst members of Congress has led to both reduced prioritization and also to misguided attempts at regulation, such as making peer review a public process and considering Congressional oversight for specific grants. Here we will examine a few current issues in science policy and the need for physicists to effectively weigh in on such policy issues. We will also consider the positive or negative effects such public engagement may have on our scientific careers and ways in which you can get involved.

 

 

Unravelling the Mysteries of Neutrinos

Dr. Stephen Parke Fermilab Neutrinos are the most numerous massive particles in the Universe. Their masses are very tiny, no larger than one millionth the mass of the electron. Are they like all the known massive fermions, being four component particles, or are they a new type of fermion never seen before, a two component fermion? Are there only only three neutrinos or are there more species of neutrinos? Of the three neutrinos we know of, we have determined part of the massing pattern but not the completely pattern. Also we have measured some of their mixing parameters with reasonable precision via neutrino oscillation experiments but not all. Do neutrinos violate CP in neutrino oscillations? Can neutrinos help explain the baryon-antibaryon asymmetry of the Universe? I will address many of the important questions about the neutrinos and how the future Fermilab program will address some of these questions.

 

 

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