Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session MA: Frontiers in Nuclear Theory |
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Chair: Lawrence Cardman, Jefferson Lab Room: Simmons Ballroom 2-3 |
Sunday, October 26, 2008 10:30AM - 11:06AM |
MA.00001: QCD energy-momentum tensor correlators and viscosity Invited Speaker: An accurate lattice determination of the energy-momentum tensor two-point function is now possible in the pure gauge theory due to an efficient algorithm and powerful computing resources. At finite temperature, the temporal correlators are related by Kubo formulas to transport properties of the quark-gluon plasma, namely shear and bulk viscosity. The latter play a central role in interpreting data from heavy ion collisions at RHIC and LHC. The Euclidean correlators can also be confronted with two opposite pictures of the plasma formed at these colliders: the weakly coupled asymptotic-temperature regime, and the strongly coupled regime studied in supersymmetric gauge theories by AdS/CFT methods. Finally, I will discuss the prospects of calculating the correlators in full QCD. [Preview Abstract] |
Sunday, October 26, 2008 11:06AM - 11:42AM |
MA.00002: The Baryon Resonance Spectrum and the $1/N_c$ Expansion Invited Speaker: 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 $1/N_c$ expansion of QCD, where $N_c$ is the number of color charges. Constraints arising at large $N_c$ 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 $N_c$ limit by incorporating $1/N_c$-suppressed effects. [Preview Abstract] |
Sunday, October 26, 2008 11:42AM - 12:18PM |
MA.00003: Universality in Nuclear Physics and Leading Corrections Invited Speaker: Effective field theories (EFT) are the ideal tool to calculate observables of systems with a separation of two scales. The ratio of these scales can be used as a small expansion parameter and observables can therefore be calculated in a controlled expansion which allows reliable error estimates. One such separation of scales familiar in nuclear physics is the sizable difference between the nucleon-nucleon scattering length and the associated interaction range $r\sim 1/m_\pi$. In the last decade an EFT has been developed which allows for a precise calculation of observables of low-energy nuclear systems. This EFT is built up from contact interactions only and is the appropriate framework for systems with relative momenta $k \ll 1/|r|$. Systems with a large scattering length have recently also gained a lot of interest in atomic physics. The possibility to change the two-body scattering length if a Feshbach resonance can be exploited gives the oppurtunity to analyze many- and few-body systems with a tunable interaction strength. In my talk I will present recent results obtained with this EFT. In particular, I will discuss universal relations for spin-1/2 fermions which can be derived using the well-known operator product expansion and which apply to neutron matter at very low densities. I will then consider the three-nucleon case and discuss how observables can be calculated to higher order in the EFT expansion and how these finite range effects impact the universal limit of this EFT. If time allows I will present results for electromagnetic observables calculated within this framework. [Preview Abstract] |
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