NPAC (Nuclear/Particle/Astro/Cosmo) Forum

Event shapes characterize hadronic final states produced in e+ e- collisions. The two-jet kinematic endpoint of event shape distributions is particularly sensitive to the nonperturbative effects of hadronization. Soft-collinear effective theory provides the tools to factorize event shape distributions in the two-jet region into perturbatively-calculable and nonperturbative contributions. From the resulting factorization theorem we can deduce the extent to which these nonperturbative contributions are universal across different event shapes.

Speaker: Chris Lee LBL

 

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Room and Building: 
5280 Chamberlin

Experiments at the Large Hadron Collider (LHC) will begin in the second half of this year. This machine, along with the proposed International Linear Collider (ILC), will directly probe physics at the TeV energy scale. The discoveries and measurements made by these experiments can have interesting implications for cosmology. I will discuss two examples of this connection. First, if dark matter is composed of weakly interacting massive particles, these particles may be directly produced and studied at the LHC and the ILC. Second, precise measurements of the Higgs boson properties may allow us to understand the dynamics of the electroweak phase transition in the early universe, with important implications for baryogenesis. In both cases, I will stress the aspects of the connection that do not depend on the (presently unknown) details of the fundamental theory at the TeV scale.

Speaker: Maxim Perelstein Cornell

 

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Room and Building: 
4274 Chamberlin
Speaker: Pat Slane Harvard

 

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Room and Building: 
4274 Chamberlin

Sterile neutrinos are usually introduced to explain the masses of active neutrinos. If one of these fermions has mass of several keV, it can also account for the cosmological dark matter. The same particle can explain the observed velocities of pulsars, speed up the formation of the first stars and stir up supernova explosions. I will describe a mechanism for sterile neutrino production that involves a minimal extension of the Higgs sector by a gauge-singlet scalar. The relic abundance of sterile neutrinos is produced from decays of the singlet Higgs and does not depend on their mixing angle. The resulting dark matter is colder than the warm dark matter produced in neutrino oscillations. I will discuss the small-scale structure formation properties of these neutrinos and show that they comply with current observations. The presence of the gauge singlet in the Higgs sector has important implications for the electroweak phase transition, baryogenesis, and the upcoming experiments at the LHC.

Speaker: Kalliopi Petraki UCLA

 

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Room and Building: 
5280 Chamberlin
In this talk I discuss the formulation of the "minimal flavor violation" hypothesis in the lepton sector. I then construct the relevant low-energy effective field theory and analyze the phenomenological signatures of this scenario.
Speaker: Vincenzo Cirigliano Los Alamos

 

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Room and Building: 
4274 Chamberlin
Speaker: Christian Bauer LBNL & UC-Berkeley

 

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Room and Building: 
5280 Chamberlin Hall

The observation of neutrino oscillations is clear evidence for physics beyond the standard model. To make precise measurements of this phenomenon, neutrino oscillation experiments, including MiniBooNE, require an accurate description of neutrino charged current quasielastic (CCQE) cross sections to predict signal samples. Using a high-statistics sample of muon neutrino CCQE events, MiniBooNE finds that a simple Fermi gas model, with appropriate adjustments, accurately characterizes the CCQE events observed in a carbon-based detector. The extracted parameters include an effective axial mass, MA=1.23 +- 0.20GeV, that describes the four-momentum dependence of the axial-vector form factor of the nucleon, and a Pauli-suppression parameter, kappa=1.019 +- 0.011. Such a modified Fermi gas model may also be used by future accelerator-based experiments measuring neutrino oscillations on nuclear target.

Host: 
Teresa Montaruli
Speaker: Teppei Katori Indiana University

 

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Room and Building: 
4274 Chamberlin Hall

Nucleons in light nuclei have binding momenta smaller than the pion mass. In this energy regime, strong interactions can be described by effective field theories (EFTs) where all nuclear interactions are of contact type. I will discuss some of the features of these EFTs such as unusual renormalization leading to limit cycles, universal behavior in three-body systems, and a surprising amount of fine-tuning.

Speaker: Bira van Kolck University of Arizona

 

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Room and Building: 
4274 Chamberlin Hall

Reheating after inflation describes all the particle physics processes occurring from the decay of the inflaton up to the establishment of thermal equilibrium. Due to the strong model dependence, it is one of the most unknown stages in the history of the universe. It has been argued that SUSY flat directions are naturally excited during inflation, and that they slow down the thermalization of the inflaton decay products by providing a large effective mass to the fields they are coupled to. We discuss a nonperturbative decay channel for the flat directions which has been generally overlooked in the literature. It typically leads to a quick decay of the flat directions, and, consequently, to a suppression of their delaying effect for thermalization.

Speaker: Marco Peloso University of Minnesota

 

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Room and Building: 
4274 Chamberlin Hall
An observation of neutrinoless double beta decay would have profound consequences for our understanding of the lepton sector of the standard model. Double beta decay is only allowed if the neutrino and anti-neutrino are identical, which is a basic prediction of many extensions of the standard model, including many grand unified theories. Secondly, double beta decay could shed light on the scale of the neutrino mass spectrum. The EXO collaboration is developing sensitive searches for the double beta decay of Xenon-136. Our first experiment, EXO-200, is rapidly being constructed, and will be by far the largest double beta decay experiment ever attempted. We are also pursuing R&D to realize a system to tag the daughter barium nucleus of the decay using the techniques of single-ion spectroscopy. This would eliminate all conventional backgrounds, resulting in an ideal experiment.
Speaker: Carter Hall University of Maryland

 

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Room and Building: 
4274 Chamberlin Hall

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