Lorentz Center - Baryogenesis and First Order Phase Transitions in the Early Universe from 29 Aug 2011 through 9 Sep 2011
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### Baryogenesis and First Order Phase Transitions in the Early Universe from 29 Aug 2011 through 9 Sep 2011

 Abstracts     Juergen Berges “Quantum Theory of Fermion Production after Inflation”   ---   Wilfried Buchmuller "Towards Quantum Leptogenesis"   We discuss thermal leptogenesis based on Kadanoff-Baym equations. Origin of the generated lepton asymmetry is the departure from equilibrium of the statistical propagator of the heavy Majorana neutrino, together with CP violating couplings. The effects of thermal damping due to gauge interactions are estimated.   ---   Pasquale Di Bari “Testing Leptogenesis with low energy neutrino experiments”     Marco Drewes “Dark Matter, Baryogenesis and Neutrino Oscillations from Right Handed Neutrinos”   We study in detail under which circumstances three generations of right handed neutrinos with masses below the electroweak scale, coupled to the Standard Model via the usual type-I seesaw Lagrangian, can simultaneously explain neutrino oscillations, dark matter and the baryon asymmetry of the universe. In large parts of the parameter space all three new particles may be detected directly or indirectly using present day experimental and observational techniques. Our results provide a guideline for experimental searches. Based on work in collaboration with Mikhail Shaposhnikov, Laurent Canetti and Tibor Frossard.   ---   Florian Gautier “Quantum properties of a non-Gaussian state”   In this talk, I will present the properties of a non-Gaussian density matrix for an O(N) scalar field in the context of the incomplete description picture. This is of relevance for studies of decoherence and entropy production in quantum field theory. In particular, I will focus on how the inclusion of the simplest non-Gaussian Correlator in the set of measured observables modifies the effective (Gaussian) description one can infer from the knowledge of the two-point fuctions only. I will show that one can compute exactly the matrix element of the  non-Gaussian density matrix at leading order in a 1/N expansion. This will allow me to discuss the quantum properties (purity, entripy, cohernece) of the corresponding state for arbitrarily strong non-Gaussianity.Finally I will show that if the Gaussian and the non-Gaussian observers essantially agree concerning quantum purity or correlation entropy, their conclusion can significantly differ for other, more detailed aspects such as the degree of quantum coherence of the system.   ---   David Jones “Leptogenesis in the two right-handed neutrino model revisited”   We revisit leptogenesis in the minimal non-supersymmetric type I see-saw mechanism with two right-handed (RH) neutrinos, including both light and heavy flavour effects and allowing both RH neutrinos $N_1$ and $N_2$ to contribute, rather than just the lightest RH neutrino $N_1$ that has hitherto been considered. Exploring the parameter space for this class of seesaw models, we find regions in which the $N_2$ contribution can dominate the contribution to leptogenesis, allowing the lightest right-handed neutrino mass to be lowered by about an order of magnitude, down to a minimum of $M_1\sim 7 \times 10^{10}\,{\rm GeV}$. We show that the new regions correspond to light sequential dominance, so the new results in our paper may be relevant to unified model building. Reference paper: Antusch. Di Bari, Jones, King, Arxiv 1107.xxxx   ---   Jose Miguel No “Electroweak Baryogenesis and Large Wall Velocitie”   ---   Hiren Patel “Gauge-independent Analysis of the Electroweak Phase Transition”   ---   Julien Serreau “Effective potential of O(N) scalar field in de Sitter geometry”   We study the quantum theory of an O(N) scalar field on de Sitter geometry at leading order in a non-perturbative 1/N-expansion. This resums the infinite series of so-called super-daisy loop diagrams. We obtain the de Sitter symmetric solutions of the corresponding, properly renormalized, dynamical field equations and compute the complete effective potential. Due to its self-interactions, the field acquires a strictly positive square mass which screens potential infra-red divergences. Moreover, strongly enhanced ultralong wavelength fluctuations prevent the existence of a spontaneously broken symmetry state in any dimension.   ---   Edward Shuryak "Multiquanta Bags, Sphalerons and  the CP Violation in the Hybrid Scenario of Baryogenesis"   In the scenario of cold electroweak baryogenesis, oscillations of the Higgs field lead to metastable domains of unbroken phase where the Higgs field nearly vanishes. Study of non-topological solitons made of large number ($\sim 1000$) of gauge quanta and heavy (top and anti-top) quarks,  called the $W-t-\bar{t}$ bags, have been made in detail and can be identified with them.  As real-time numerical studies had shown, sphalerons (topological transition events violating the baryon number) occur only inside those bags. The so called Carter-Ostrovsky-Shuryak sphalerons, with a variable size, can explain these simulations and the obtained sphaleron rate. Top-quark recycling" by sphalerons increases the baron number violation  rate, and it also directly couples the CP-odd asymmetry of top-minus-antotop population in the bag with the baryon asymmetry. We estimate the amount of CP violation in this scenario via the Cabibboâ€“Kobayashiâ€“Maskawa  (CKM) quark mixing matrix, in the 4-th order in weak $W$ diagrams describing interference of different quark flavor contributions. We found that there are multiple cancellations of diagrams lead to small but sign-definite effect in the 6-th order expansion over  flavor-dependent phases. Our estimates produce baryon asymmetry close to what is needed to explain the data. Our sign apparently is the correct one, as well.     ---   Michael Schmidt “Exercises with KB equations: Unobserved correlators generate entropy and decoherence in QFT”          [Back]