NPAC (Nuclear/Particle/Astro/Cosmo) Forum

Thursday, March 25th, 2010
Host: 
Baha Balantekin
Speaker: David Ernst Vanderbilt University

 

Available Downloads:

Room and Building: 
4274 Chamberlin

The assumed isotropy of galactic cosmic rays has been topic of investigation since the seventies, when an O(10^-3 - 10^-4) anisotropy in arrival direction has been observed for the first time. The wide energy range of this observations (from tens of GeV to hundreds of TeV) has raised questions on the origin of this phenomenon. While we can generically claim that the responsible of this anisotropy is to be connected to the structure of the Local Interstellar Medium, and specifically to the Local Interstellar Magnetic Field (within about 0.1-1.0 pc ~ 20,000 - 200,000 AU), we still suffer from the lack of knowledge of the properties of our local environment. Only recently, with the observation of O(10-30 degrees) excess of cosmic rays by MILAGRO and with the first high statistics observation of the southern sky by IceCube, the topic is gaining renewed attention. The possibility that the ~100's TeV galactic cosmic ray anisotropy might be connected to the blast from a nearby supernova, in connection with the anomalies in the observed positron fraction and electron spectrum is very appealing and will be discussed.

Host: 
Michael Ramsey-Musolf
Speaker: Paolo Desiati University of Wisconsin at Madison

 

Available Downloads:

Room and Building: 
5310 Chamberlin
Over the last few years the Bayesian statistics has played an increasingly important role in astronomical data analyses, from classifying quasars to fitting cosmological models to WMAP data. One aspect of Bayesian statistical methods used to classify astronomical objects is that traditionally they assume that the object being classified falls into a finite set of modeled (or known) astronomical objects. However, astronomical research continually reveals new, unexplained phenomena; new large-scale surveys coming up in the next decade (such as the Dark Energy Survey, the Large Synoptic Survey Telescope, the Joint Dark Energy Mission, etc.) are expected to greatly enrich our catalog of understood (or at least modeled) astronomical objects. In my
talk, I will first review the two approaches to statistics, Bayesian and Frequentist. I will describe how and why the Bayesian approach has been so successful in astronomy in general, and in particular how the Bayesian approach can be extended to account for as yet unmodeled objects. I will then show how this method can be used to quantify the differences in the spectra of
Ultra-Luminous Infra-Red Galaxies (ULIRGs) and aid in the identification of Type Ia supernovae, a staple of modern cosmological research. I will also discuss how network diagrams and graph theory can be used in conjunction with these Bayesian methods to enhance our understanding of the evolution of ULRGs
and Type Ia supernovae.
Host: 
Stefan Westerhoff
Speaker: Brian Connolly University of Pennsylvania

 

Available Downloads:

Room and Building: 
5280 Chamberlin
Astrophysical results obtained by the Fermi Large Area telescope
mission in the first year of its mission are presented. In its first year the LAT has detected more than 10 million gamma-rays above 100 MeV and more than 1000 point sources, many of which were studied individually. These studies cover a wide range of astrophysical objects, like AGN, GRB, Starburst Galaxies, Pulsars, their Nebulae and Supernova Remnants. Besides individual objects, the properties of the diffuse emission from our own galaxy and beyond have been analyzed, yielding
new insights into the propagation of cosmic rays and the nature of the extragalactic diffuse emission.
Host: 
Albrecht Karle
Speaker: Markus Ackermann

 

Available Downloads:

Room and Building: 
5310 Chamberlin Hall
Study of Acoustic Ultra-high energy Neutrino Detection (SAUND) phase II uses 1000km^2 of ocean as a neutrino detector. SAUND<br>
aims to detect comic ray neutrinos of GZK energies and beyond<br>
(&gt;10^18eV) acoustically by utilizing the ocean water as the target and an existing US Navy underwater microphone array as sensors. A DAQ system was developed and deployed in 2005. The experiment ran during 2006 and 2007, collecting over 1 TB of data with over 100 days of cumulative livetime. A study of the ocean ambient noise was performed using SAUND data, characterising the background for neutrino signals. Data analysis to isolate signals is performed in parallel to Monte Carlo studies of the detector to optimize cut efficiencies and set a neutrino flux limit in the ultra-high energy region.
Host: 
Teresa Montaruli
Speaker: Naoko Kurahashi Stanford

 

Available Downloads:

Room and Building: 
5310 Chamberlin
Seismic imaging is a technology used worldwide by the oil industry to look into the subsurface and determine underground structures and their potential for oil and gas production. Time-lapse seismic monitoring is a relatively new technology that consists of carefully repeating a seismic image months to years after production starts and looking for changes that indicate where production did or did not occur to help guide future operations. <br>
<br>
Production of oil and gas is often accompanied by a large reduction in the reservoir fluid pressure that in some cases leads to compaction as large as several meters. The deformation of the reservoir layers is coupled to the adjacent rocks and leads to changes in the stress and strain fields that extend a great distance away from the reservoir. Time-lapse seismic measurements through these rocks show large variations that are useful for monitoring the distribution of deformation within the reservoir.<br>
<br>
The compaction induces seismic velocity changes that are observed on many different wave types including conventional P-P reflection seismic, P-S mode converted seismic, and surface waves such as the Scholte wave and refracted compressional waves. Using geomechanical models that predict changes in stress and strain fields within the earth we can start to understand the factors that control the changes in seismic velocities. We find that simple non-linear relationships between velocity and strain produce forward models that match many of our observations. <br>
<br>
Host: 
Balantekin
Speaker: Paul Hatchell Shell International E&P, Research and Development, Houston, TX

 

Available Downloads:

Room and Building: 
2103 Chamberlin (tentative) (coffee & cookies at 3:30)

Why do baryon resonance multiplets exist, and what controls their formation and decays? It is natural to consider them as merely excited states of some three-quark or meson-nucleon potential. But these are just simplistic quantum-mechanical pictures that recognize neither the full field-theoretical complexities of QCD nor the extremely brief lifetimes of resonances due to quark pair production. Both of these issues are addressed by the 1/Nc expansion of QCD, where Nc is the number of color charges. Constraints arising at large Nc on meson-baryon scattering amplitudes not only create linear relationships between them, thus linking distinct partial waves and their embedded resonances, but also restrict the possible resonant decay channels. I present strong experimental evidence in favor of this approach, describe the multiplet structure that it predicts, and show how to perform the analysis beyond the strict large Nc limit by incorporating 1/Nc-suppressed effects. This program has been developed to the point that now one possesses a full effective field theory formalism for physics in the baryon resonance region.

Host: 
Michael Ramsey-Musolf
Speaker: Richard Lebed Arizona State University

 

Available Downloads:

Room and Building: 
5310 Chamberlin
In the first part of this talk, I will discuss theoretical predictions of various SUSY GUT models for lepton flavor violation. Including the WMAP dark matter constraints, lower bounds on the branch fractions of these LFV rare charged lepton decays can be obtained. Furthermore, a next generation MECO-like experiment turns out to be the more robust way in distinguishing various GUT models.<br>
<br>
In the second part of the talk, I will focus on flavor violation in RS models. Generically, RS models suffer from strong constraints due to the presence of the FCNCs at tree-level. Furthermore, these models require fine tuning in order to get large neutrino mixing. I will present a model based on the double tetrahedral family symmetry which successfully avoids the tree-level FCNCs in both quark and lepton sectors. In addition, our model gives rise to realistic masses and mixing angles for both quarks and leptons.
Host: 
Michael Ramsey-Musolf
Speaker: Mu-Chun Chen U. C. Irvine

 

Available Downloads:

Room and Building: 
2301 Sterling Hall
The fact that the QED vacuum is unstable via the production of
electron-positron pairs in the presence of an external electric field is one of the first non-trivial predictions of QED, due to Heisenberg and Euler, and later formalized by Schwinger. This non-perturbative effect has implications and analogies in QCD and gravitational physics. However, the effect is so weak that it has still not been directly observed. But recent experimental progress in ultra-intense laser systems has brought us
tantalizingly close to seeing this non-perturbative particle production. I will review the current status and describe some new theoretical ideas aimed at making this process accessible.
Host: 
Michael Ramsey-Musolf
Speaker: Gerald Dunne University of Connecticut

 

Available Downloads:

Room and Building: 
4274 Chamberlin
Astrophysical evidence on a variety of distance scales clearly shows that we cannot account for a large fraction of the mass of the universe. This matter is "dark", not emitting or absorbing any electromagnetic radiation. A compelling explanation for this missing mass is the existence of Weakly Interacting Massive Particles (WIMPs).

These particles are well motivated by particle physics theories beyond the Standard Model, and the discovery of WIMPs would have enormous impact on both astrophysics and particle physics. WIMPs, if they exist, would occasionally interact with normal matter. With a mass in the range of 1 to 1000 times the mass of the proton, and moving at speeds relative to the Earth on the order of 200 km/s, WIMPs would only deposit a small amount of energy when scattering with nuclei.

Detectors that are low in radioactivity and sensitive to small energy depositions can search for the rare nuclear recoil events predicted by WIMP models. In recent years, several new efforts on direct dark matter detection have begun in which the detection material is a noble liquid. Advantages include: large nuclear recoil signals in both scintillation and ionization channels, good scalability to large target masses, effective discrimination against gamma ray backgrounds, easy purification, and reasonable cost.
Host: 
Karsten Heeger
Speaker: Dan McKinsey Yale University

 

Available Downloads:

Room and Building: 
4274 Chamberlin

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