Superfluidity in many fermion systems: Exact renormalisation group treatment

The application of the exact renormalisation group to symmetric as well as asymmetric many-fermion systems with a short-range attractive force is studied. Assuming an ansatz for the effective action with effective bosons, describing pairing effects a set of approximate flow equations for the effective coupling including boson and fermionic fluctuations has been derived. The phase transition to a phase with broken symmetry is found at a critical value of the running scale. The mean-field results are recovered if boson-loop effects are omitted. The calculations with two different forms of the regulator are shown to lead to a similar results. We find that, being quite small in the case of the symmetric many-fermion system the corrections to mean field approximation becomes more important with increasing mass asymmetry.Comment: Talk given at the IVth International Conference on Quarks and Nuclear Physics (QNP06), Madrid, 5-10 June 200

Superfluidity within Exact Renormalisation Group approach

The application of the exact renormalisation group to a many-fermion system with a short-range attractive force is studied. We assume a simple ansatz for the effective action with effective bosons, describing pairing effects and derive a set of approximate flow equations for the effective coupling including boson and fermionic fluctuations. The phase transition to a phase with broken symmetry is found at a critical value of the running scale. The mean-field results are recovered if boson-loop effects are omitted. The calculations with two different forms of the regulator was shown to lead to similar results.Comment: 17 pages, 3 figures, to appear in the proceedings of Renormalization Group 2005 (RG 2005), Helsinki, Finland, 30 Aug - 3 Sep 200

Linking the Quark Meson Model with QCD at High Temperature

We model the transition of a system of quarks and gluons at high energies to a system of quarks and mesons at low energies in a consistent renormalization group approach. Flow equations interpolate between the physics of the high-temperature degrees of freedom and the low-temperature dynamics at a scale of 1 GeV. We also discuss the dependence of the equation of state on baryon density and compare our results with recent lattice gauge simulations.Comment: 11 pages, 4 figures additional discussion of the second order phase transitio

Dynamics of broken symmetry lambda phi^4 field theory

We study the domain of validity of a Schwinger-Dyson (SD) approach to non-equilibrium dynamics when there is broken symmetry. We perform exact numerical simulations of the one- and two-point functions of lambda phi^4 field theory in 1+1 dimensions in the classical domain for initial conditions where < phi(x) > not equal to 0. We compare these results to two self-consistent truncations of the SD equations which ignore three-point vertex function corrections. The first approximation, which sets the three-point function to one (the bare vertex approximation (BVA)) gives an excellent description for < phi(x) > = phi(t). The second approximation which ignores higher in 1/N corrections to the 2-PI generating functional (2PI -1/N expansion) is not as accurate for phi(t). Both approximations have serious deficiencies in describing the two-point function when phi(0) > .4.Comment: 10 pages, 6 figure

The system overview tool of the Joint COntrols Project (JCOP) framework

For each control system of the Large Hadron Collider (LHC) experiments, there will be many processes spread over many computers. All together, they will form a distributed system with around 150 computers organized in a hierarchical fashion. A centralized tool has been developed for supervising, identification of errors and troubleshooting such a large system. A quick response to abnormal situations will be crucial to maximize the physics usage. This tool gathers data from all the systems via several paths (e.g., process monitors, internal database), and after some processing, presents it in different views. Correlations between the different views are provided to help to understand complex problems that involve more than one system. It is also possible to filter the information presented to the shift operator according to several criteria (e.g. node, process type, process state). Alarms are raised when undesired situations are found. The data gathered is stored in the historical archive for further analysis

Uniqueness of infrared asymptotics in Landau gauge Yang-Mills theory

We uniquely determine the infrared asymptotics of Green functions in Landau gauge Yang-Mills theory. They have to satisfy both, Dyson-Schwinger equations and functional renormalisation group equations. Then, consistency fixes the relation between the infrared power laws of these Green functions. We discuss consequences for the interpretation of recent results from lattice QCD.Comment: 24 pages, 8 figure

Transport coefficients from the 2PI effective action

We show that the lowest nontrivial truncation of the two-particle irreducible (2PI) effective action correctly determines transport coefficients in a weak coupling or 1/N expansion at leading (logarithmic) order in several relativistic field theories. In particular, we consider a single real scalar field with cubic and quartic interactions in the loop expansion, the O(N) model in the 2PI-1/N expansion, and QED with a single and many fermion fields. Therefore, these truncations will provide a correct description, to leading (logarithmic) order, of the long time behavior of these systems, i.e. the approach to equilibrium. This supports the promising results obtained for the dynamics of quantum fields out of equilibrium using 2PI effective action techniques.Comment: 5 pages, explanation in introduction expanded, summary added; to appear in PR

The Phase Structure of the Polyakov--Quark-Meson Model

The relation between the deconfinement and chiral phase transition is explored in the framework of an Polyakov-loop-extended two-flavor quark-meson (PQM) model. In this model the Polyakov loop dynamics is represented by a background temporal gauge field which also couples to the quarks. As a novelty an explicit quark chemical potential and N_f-dependence in the Polyakov loop potential is proposed by using renormalization group arguments. The behavior of the Polyakov loop as well as the chiral condensate as function of temperature and quark chemical potential is obtained by minimizing the grand canonical thermodynamic potential of the system. The effect of the Polyakov loop dynamics on the chiral phase diagram and on several thermodynamic bulk quantities is presented.Comment: 13 pages, 12 figures, RevTex4; discussion of mu-dependence extended, references added, version to be published in PR

On the 2-point function of the O(N) model

The self-energy of the critical 3-dimensional O(N) model is calculated. The analysis is performed in the context of the Non-Perturbative Renormalization Group, by exploiting an approximation which takes into account contributions of an infinite number of vertices. A very simple calculation yields the 2-point function in the whole range of momenta, from the UV Gaussian regime to the scaling one. Results are in good agreement with best estimates in the literature for any value of N in all momenta regimes. This encourages the use of this simple approximation procedure to calculate correlation functions at finite momenta in other physical situations