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Friday, February 3rd 2017

2:00 pm:

by Jurgen Eser, Florian Divotgey, Dirk H. Rischke

We use the functional renormalization group (FRG) technique to explore the characteristics of the so-called extended linear sigma model (eLSM). This model is an effective description of the strong interaction in terms of quarks and mesonic felds. Besides scalars and pseudoscalars, it also features vector and axial-vector mesons.

The first part focuses on the restoration of chiral symmetry in the context of the transition from hadronic matter to the quark-gluon plasma in the phase diagram of quantum chromodynamics (QCD). Results on the order of the chiral phase transition in the presence of vector and axial-vector mesons will be presented. Vector mesons are of particular interest since modifications related to chiral symmetry restoration affect their in-medium spectral properties, which can be detected via decays into dileptons. Effects of the axial anomaly and the explicit breaking of chiral symmetry due to nonzero quark masses are also studied. The mass degeneracy of chiral partners beyond the phase boundary and the phase diagram as a function of the temperature and the quark-chemical potential will be shown.

The second part sheds light on the low-energy limit of the eLSM. We consider the influence of wave-function renormalization factors and couplings beyond the local potential approximation. The infrared-relevant couplings can be associated with the corresponding low-energy constants of QCD.

Friday, February 10th 2017

11:15 am:

Friday, February 17th 2017

11:15 am:

Tuesday, February 21st 2017

11:30 am:

Rapid advances in automation, robotization, computerization are changing local and global job markets. Worldwide, the youth are struggling to understandand define a meaningful role for themselves and a promising future for their families. While the future for the innovators, leaders and entrepreneurs is brighter than ever before, a large majority are becoming pessimistic and losing hope. This talk will examine existing trends and correlate many of the current challenges---jobs, poverty, population, migration, climate change, environmental degradation, etc.--- to ask the question, is liberal democracy under threat.

Friday, February 24th 2017

11:15 am:

Friday, March 3rd 2017

11:15 am:

Friday, March 10th 2017

1:30 pm:

Cosmic microwave background Stage-IV experiments and thirty-meter-class telescopes will come on line in the next decade. The convolution of these data sets will provide on order 1% precision for observables related to neutrino cosmology. Beyond Standard Model (BSM) physics could manifest itself in slight deviations from the standard predictions of quantities such as the neutrino energy density and the primordial abundances from Big Bang Nucleosynthesis (BBN). In this talk, I will argue for the need for precise and accurate numerical calculations of BBN. I will first show the detailed evolution of the neutrino spectra as they go out of equilibrium with the plasma. The spectra are important in changing the ratio of neutrons to protons. I will show how sensitive the primordial mass fraction of helium is to the weak interaction rates which evolve the neutron-to-proton ratio. Finally, I will present an example of how BSM physics can affect BBN by instituting an asymmetry between neutrinos and antineutrinos, commonly characterized by a lepton number.

Friday, March 24th 2017

11:15 am:

Friday, March 31st 2017

11:15 am:

Motivated by our earlier estimate that shows an enormous degree of overlap among neutrino wave packets (WPs) from astrophysical sources, I will present a derivation of vacuum oscillation probability for detecting one neutrino from a pair of neutrino WPs which are described by an anti-symmetric 2-particle wave function. I will begin by briefly reviewing the oscillation probability in the one-particle framework and recast the probability as the expectation value of a projection operator which projects a neutrino WP state onto the detected WP state. In the two-particle framework, such expectation value can be computed with the help of the density matrix of the 2-particle wave function. Additional interference terms in the derived oscillation probability appear to be invariant under arbitrary re-phasing of the relevant WP states but these terms will nevertheless vanish due to the orthogonality between the two neutrino WPs. Therefore, the derived oscillation probability reduces to a simple sum of one-particle oscillation probabilities.

Friday, April 14th 2017

11:15 am:

We study collective two-flavor oscillations of an isotropic gas of monochromatic neutrinos and antineutrinos. We analytically solve for the eigenstates at fixed neutrino density and perform stability analyses of these states. We use the stable eigenstates to understand the flavor evolution of the dense neutrino gas above the proto-neutron star in a core-collapse supernova or above the accretion disk in a neutron-star merger.

Friday, April 21st 2017

11:15 am:

After a successful core-collapse supernova a neutrino-driven wind develops from the nascent neutron star. Neutrino-driven winds are a possible astrophysical site for the synthesis of the lighter heavy elements (26 < Z < 47) which are associated to the r-process and at least one additional process. Despite the fast process in the last years the astrophysical and nuclear physics uncertainties are still relatively large. We study the impact of the astrophysical uncertainties on the nucleosynthesis in the wind and have a special focus on the formation of 92,94Mo and 96,98Ru. The Mo and Ru p-isotopes have raised interest because their nucleosynthesis origin in the solar system is a long lasting mystery. We present the necessary conditions for the synthesis of 92,94Mo and 96,98Ru and show whether the wind can explain their solar system abundances. Moreover, we show that (alpha,n) reactions are critical to redistribute matter in neutron-rich winds. In the absence of experiments most (alpha,n) reaction rates are calculated with statistical models, and thus contain some uncertainties. Our results show that (alpha,n) rate uncertainties are crucial for the abundances. Since the nucleosynthesis path is close to stability, individual critical reactions can be measured with new radioactive beam facilities in the near future.

Friday, April 28th 2017

11:15 am:

Friday, September 8th 2017

10:10 am:

Friday, September 15th 2017

10:10 am:

Friday, September 22nd 2017

10:10 am:

Friday, September 29th 2017

10:10 am:

Friday, October 6th 2017

10:10 am:

Friday, October 13th 2017

10:10 am:

Monday, October 16th 2017

1:25 pm:

The perturbative series for finite-temperature field theories has very poor convergence properties and one needs a way to reorganize it. In this talk, I review one way of reorganizing the perturbative series thermal QCD, namely hard-thermal-loop perturbation theory (HTLpt). I will present results for the pressure, trace anomaly, speed of sound and the quark susceptibilities from a 3-loop HTLpt calculation. A careful comparison with available lattice data shows good agreement for a number of physical quantities.

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