NPAC (Nuclear/Particle/Astro/Cosmo) Forum

Host: 
Stefan Westerhoff
Speaker: Segev BenZvi University of Wisconsin - Madison

 

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Room and Building: 
4274 Chamberlin
In July 2008, the International X-ray Observatory (IXO) was announced to the > astronomical community. IXO is a joint mission with participation from ESA, NASA and JAXA, superseding the US Constellation-X mission concept. IXO is dedicated to high resolution X-ray spectroscopy, with 100 times the throughput for high resolution spectroscopy of previous X-ray missions. The baseline for IXO features a single large X-ray mirror and an extensible optical bench with a 20-25m focal length and moveable focal plane. The instruments include an X-ray wide field imaging spectrometer, a high spectral resolution non-dispersive X-ray spectrometer, an X-ray grating spectrometer, a hard X-ray imaginer and an X-ray polarimeter.

I will discuss the IXO science objectives and how it will help answer the following questions: How do super-massive Black Holes grow and evolve? Does matter orbiting close to a Black Hole event horizon follow the predictions of General Relativity? What is the Equation of State of matter in Neutron Stars? How does Cosmic Feedback work and influence galaxy formation? How does galaxy cluster evolution constrain the nature of Dark Matter and Dark Energy? Where are the missing baryons in the nearby Universe? When and how were the
elements created and dispersed? How do high energy processes affect planetary formation and habitability? How do magnetic fields shape stellar exteriors and the surrounding environment? How are particles accelerated to extreme energies producing shocks, jets, and cosmic rays?
Host: 
Dan McCammon
Speaker: Randall Smith Harvard Smithsonian Center for Astrophysics

 

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Room and Building: 
4274 Chamberlin
The origin of flavor is one of the biggest mysteries of the Standard Model. Despite more than a half-century of data, we still have essentially no explanation for family replication in the Standard Model. Many theoretical models can incorporate or accommodate this replication, but very few actually explain/predict/require it. In this talk, I will describe some recent work on a possible new approach towards explaining the origin of family replication in the Standard Model.
Host: 
Sky Bauman and Lisa Everett
Speaker: Keith Dienes University of Arizona

 

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Room and Building: 
4274 Chamberlin

Particles near $10^{20}$ eV are the most energetic particles known to us in the universe, also called ultra high energy cosmic rays. Their observations have led us to build the largest detector systems in the world, in the South the Auger air-shower array, and in the North the Telescope Array, and perhaps soon Auger-North. With these and earlier arrays events have been detected of an energy up to $3 , 10^{20}$ eV, which is a macroscopic energy. There have been two predictions: one that due to interaction with the microwave background the spectrum should show a turnoff near $5 , 10^{19}$ eV; a turn-off has been confirmed by two experiments, HiRes and Auger. Second, that active galactic nuclei, possibly radio galaxies, should be the accelerators, based on the non-thermal optical spectra of knots and hot spots in radio galaxies; this is now tentatively confirmed by Auger, but contradicted by HiRes. I will go through some fundamental problems with the predictions, which teach us about active galactic nuclei and starburst galaxies. Apart from differentiating various remaining options, such as gamma ray bursts, how to generate these particles, and their source population, there is one major difficulty: the lack of understanding of the cosmological web of magnetic fields, which may influence the propagation of high energy particles; here it is especially important to understand the role of our local cosmic neighborhood and a possible galactic magnetic wind. It appears from MHD simulations that magnetic scattering leads to a steep distribution function of scattering angles of the deviation from a straight line path for the arriving particles, and also to a substantial delay time distribution. I will list and debate the merits of the closest candidate sources, Cen A, Vir A and For A. I will discuss the observational and theoretical limits for an exemplary set of models, the predictions like chemical abundances, that result from these models, and how present and future observations will test our conclusions, especially with the the Auger Array, the Telescope Array (TA), the neutrino observatory IceCube, the TeV Cherenkov $gamma$-ray telescopes, and the future space observatory EUSO. We face a number of exciting challenges for plasma physics, particle physics, cosmology, astronomy, and may attain better tools for our deep understanding of matter.

Host: 
Stefan Westerhoff
Speaker: Peter L. Biermann MPI Bonn

 

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Room and Building: 
4274 Chamberlin
In June 2007, MiniBooNE published results for a search for electron flavor neutrinos appearing in a predominantly muon neutrino beam. Although no excess of events was observed at an L/E consistent with a simple mixing interpretation of LSND, a > 3 sigma excess was observed at low energy. In the intervening time, MiniBooNE has acquired 3.3e20 POT delivered with the horn-focusing positively charged pions to create a predominantly antineutrino beam. The results from the recently unblinded nuebar appearance search will be discussed along with work that has transpired over the last year in understanding the low energy excess.
Host: 
Karsten Heeger & Mat Herndon
Speaker: Chris Polly University of Illinois Urbana-Champaign

 

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Room and Building: 
4274 Chamberlin
I will present ongoing work to incorporate the effects of very high excitation states of atomic hydrogen on the recombination history of the universe. After a review of recombination, I will discuss the relevance of cosmological recombination for CMB observables, our approach to the high-n problem, and preliminary results.&lt;br&gt;<br>
Host: 
Daniel Chung
Speaker: Daniel Grin Caltech

 

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Room and Building: 
4274 Chamberlin

I shall describe a bottom-up approach to modeling low-energy properties of QCD using holographic duality. Chiral symmetry and its breaking, QCD sum rules as well as asymptotic scaling are simultaneously realized in such models. The simplest model of this type gives a remarkably good fit to many low energy hadronic observables.

Host: 
M J Ramsey-Musolf
Speaker: Misha Stephanov U. Illinois Chicago

 

Available Downloads:

Room and Building: 
4274 Chamberlin
Extension of the minimal supersymmetric standard model (MSSM) that include a U(1)' gauge symmetry are motivated by top-down
constructions and offer an elegant solution to the MSSM mu problem.

In this talk I will describe some of the opportunities that such models offer, such as a new mechanism for mediation of supersymmetry breaking, as well as some of the challenges in constructing viable supersymmetric U(1)' models.
Host: 
Michael J. Ramsey-Musolf
Speaker: Gil Paz Institute for Advanced Study, Princeton

 

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Room and Building: 
4274 Chamberlin

Helium-8 (8He) is the most neutron-rich matter to have been synthesized on the Earth: it consists of two protons and six neutrons, and remains stable for an average of 0.2 seconds. It is often viewed as a 4He core with four additional neutrons orbiting at a relatively large distance, forming a halo. Because of its intriguing properties, 8He has the potential to reveal new aspects of the fundamental forces among the constituent nucleons. We have recently succeeded in laser trapping and cooling this exotic helium isotope, and have performed precision laser spectroscopy on individual trapped atoms. Based on the atomic frequency differences measured along the isotope chain 3He - 4He - 6He - 8He, the nuclear charge radius of 8He has now been determined for the first time. Comparing this result with the values predicted by a number of nuclear structure calculations, we test theoretical understanding of the nuclear forces in the extremely neutron-rich environment. Moreover, this method of capturing and probing atoms of rare isotopes is also applied to experiments that test fundamental symmetries and to applications of ultrasensitive trace analysis.

Host: 
Karsten Heeger
Speaker: Zheng-Tian Lu Argonne National Laboratory an University of Chicagod

 

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Room and Building: 
4274 Chamberlin

Baryon acoustic oscillations (BAO) in large galaxy surveys can provide an excellent standard ruler test to measure the cosmological distance scale, such as the angular diameter distance and the Hubble parameter, and therefore dark energy properties. This requires that we understand all of the physical effects that could alter the acoustic feature during the nonlinear evolution of structure. There are two important aspects of the nonlinear effects on BAO. First, the BAO signature is gradually reduced with time and in scale due to nonlinear growth of density fields, redshift distortions, and galaxy bias. Second, the various nonlinear effects may alter the observed BAO scale at low redshift, relative to the linear acoustic scale derived from the CMB, which would result in biased estimation of dark energy parameters. In this talk, I will present effects of such nonlinearities on BAO from N-body results: nonlinear growth and redshift distortions degrade the contrast of BAO while shifting BAO less than ~0.5% at z=0.3. I will show that most of these nonlinear effects can be reversed by a simple reconstruction scheme.I will also discuss the effect of galaxy bias on BAO.

Host: 
Peter Timbie
Speaker: Hee-Jong Seo Fermilab and U. Arizona

 

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Room and Building: 
5310 Chamberlin

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