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We review the use of an exact renormalization group equation in quantum field theory and statistical physics. It describes the dependence of the free energy on an infrared cutoff for the quantum or thermal fluctuations. Non-perturbative solutions follow from approximations to the general form of the coarse-grained free energy or effective average action.… (More)

- Jürgen Berges
- 2002

We compute the nonequilibrium real-time evolution of an O(N)–symmetric scalar quantum field theory from a systematic 1/N expansion of the 2P I effective action to next-to-leading order, which includes scattering and memory effects. In contrast to the standard 1/N expansion of the 1P I effective action, the next-to-leading order expansion in presence of a… (More)

We discuss the Meissner effect for a color superconductor formed by cold dense quark matter. Though color and ordinary electromagnetism are broken in a color superconductor, there is a linear combination of the photon and a gluon that remains massless. Consequently, a color superconducting region may be penetrated by an external magnetic field. We show that… (More)

Calculations of nonequilibrium processes become more and more possible in quantum field theory from first principles. There has been important progress in our analytical understanding based on 2PI generating function-als. In addition, for the first time direct lattice simulations based on stochas-tic quantization techniques have been achieved. The… (More)

- J R Causse, J B Causse, +5 authors J M Bastide
- The American journal of otology
- 1989

The etiology of otospongiotic-otosclerotic disease is enzymatic; the proteolytic enzymes released by the otospongiotic-otosclerotic foci damage the inner ear and are also the basis of the bony rebuilding of the OW niche leading to stapedial fixation. The trigger may be an autoimmune process due to the reaction of the enchondral otic capsule against the… (More)

- Gert Aarts, Jürgen Berges
- 2001

Transport or kinetic equations are often derived assuming a quasi-particle (on-shell) representation of the spectral function. We investigate this assumption using a three-loop approximation of the 2P I effective action in real time, without a gradient expansion or on-shell approximation. For a scalar field in 1+1 dimensions the nonlinear evolution ,… (More)

- Jürgen Berges, Julien Serreau
- Physical review letters
- 2003

We present the first study of parametric resonance in quantum field theory from a complete next-to-leading order calculation in a 1/N expansion of the two-particle irreducible effective action, which includes scattering and memory effects. We present a complete numerical solution for an O(N)-symmetric scalar theory and provide an approximate analytic… (More)

- Gert Aarts, Daria Ahrensmeier, Rudolf Baier, Jürgen Berges, Julien Serreau
- 2002

We derive the nonequilibrium real-time evolution of an O(N) – invariant scalar quantum field theory in the presence of a nonvanishing expectation value of the quantum field. Using a systematic 1/N expansion of the 2P I effective action to next-to-leading order, we obtain nonperturbative evolution equations which include scattering and memory effects. The… (More)

We solve the nonequilibrium dynamics of a 3 + 1 dimensional theory with Dirac fermions coupled to scalars via a chirally invariant Yukawa interaction. The results are obtained from a systematic coupling expansion of the 2PI effective action to lowest non-trivial order, which includes scattering as well as memory and off-shell effects. The microscopic… (More)