S. Andergassen
Title: Nonequilibrium current and relaxation dynamics of a charge-fluctuating
Abstract: We study the steady-state current in a minimal model for a quantum
dot dominated by charge fluctuations and analytically describe the time
evolution into this state. The current is driven by a finite bias voltage V
across the dot, and two different renormalization group methods are used to
treat the local Coulomb interaction. The corresponding flow equations can
be solved analytically which allows to identify all microscopic cutoff
scales. Exploring the entire parameter space we find rich non-equilibrium
physics which cannot be understood by simply considering the bias voltage
as an infrared cutoff. For the experimentally relevant case of left-right
asymmetric couplings, the current generically shows a power-law suppression
for large V. The relaxation dynamics towards the steady state features
characteristic oscillations as well as an interplay of exponential and
power-law decay.
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L. Bartosch
Title: Ward identities and skeleton equations in the functional renormalization
Abstract: We use the functional renormalization group approach with partial
bosonization in the particle-particle channel to study the effect of order
parameter fluctuations on the BCS-Bose-Einstein condensate (BEC) crossover
of superfluid fermions in three dimensions. Our approach is based on a new
truncation of the vertex expansion where the renormalization group flow of
bosonic two-point functions is closed by means of Dyson-Schwinger equations
and the superfluid order parameter is related to the single-particle gap
via a Ward identity. We explicitly calculate the chemical potential, the
single-particle gap, and the superfluid order parameter at the unitary point
and compare our results with experiments and previous calculations.
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M. Birse
Title: Functional RG for few-body physics
Abstract: TBA
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J.-P. Blaizot
Title: Flow equations with momentum dependent vertex functions
Abstract: In this talk I shall discuss truncation schemes of the exact
renormalization group flow equations that allow for the treatment of the
momentum dependence of the n-point functions. Applications will be presented
to the critical O(N) model, and to field theory at finite temperature.
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J. Braun
Title: Universal scaling laws for QCD with many flavors
Abstract: QCD with many quark flavors has drawn a lot of attention in the
past few years. In this talk we discuss many-flavor QCD in the chiral limit
and present universal scaling laws for physical observables such as the
critical temperature or the chiral condensate as a function of the flavor
number near the conformal window. We argue on general grounds that the
associated critical exponents are all interrelated and can be determined
from the critical exponent of the running gauge coupling at the
Caswell-Banks-Zaks infrared fixed point.
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N. Dupuis
Title: Renormalization-group approach to lattice models
Abstract: We propose a modification of the non-perturbative
renormalization-group (NPRG) which applies to lattice models. Contrary
to the usual NPRG approach where the initial condition of the RG flow is
the mean-field solution, the lattice NPRG uses the (local) limit of
decoupled sites as the (initial) reference system. In the long-distance
limit, it is equivalent to the usual NPRG formulation and therefore yields
identical results for the critical properties. We discuss both a lattice
field theory defined on a $d$-dimensional hypercubic lattice and classical
spin models. The simplest approximation, the local potential approximation,
is sufficient to obtain the critical temperature and the magnetization of
the 3D Ising, XY and Heisenberg models to an accuracy of the order of one
percent. We briefly comment on the application of the lattice NPRG to
interacting bosons (Bose-Hubbard model).
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T. Gasenzer
Title: Critical dynamics and turbulence in ultracold atomic gases
Abstract: Turbulent dynamics in an ultracold Bose gas, in two and three
spatial dimensions, is analysed by means of statistical simulations using
classical field equations. A special focus is set on the infrared
regime of large-scale excitations following universal power-law
distributions distinctly different from those of commonly known weak
wave-turbulence phenomena. The infrared power laws which have been
predicted within an analytic field-theoretic approach based on the 2PI
effective action, are discussed in comparison to the well-known
Kolmogorov scaling of vortical motion. These phenomena of strong
turbulence can in principle be observed with technologies available to
date in the physics of ultracold atomic gases.
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C. Husemann
Title: Effective Interaction Vertex of the 2D Hubbard Model at Weak Coupling
Abstract: We identify leading contributions in the scale dependent interaction
vertex of the 2D (t,t')-Hubbard model and separate them from remainder terms.
The former are expanded in boson exchange interactions of fermion bilinears,
such as Cooper pairs or spin operators. In a combined RG flow both boson
exchange and remainder interactions are calculated for the repulsive Hubbard
model at weak coupling. The momentum dependence of the remainder term is
analyzed in detail. Besides momentum we also allow a partial frequency
dependence of the boson exchange interactions. In dependence on next to
nearest neighbor hopping and electron filling we find antiferromagnetism,
d-wave superconductivity, and ferromagnetism.
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Y. Igarashi
Title: Ginsparg-Wilson type realization of chiral symmetry in ERG
Abstract: Ginsparg-Wilson type realization of chiral symmetry for sigma
model is discussed in continuum theory. Non-linear transformations needed
for reduction of chiral transformations to those of the standard form are
found. The Polchinski flow equations expressed in terms of new variables
is given.
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S. Jakobs
Title: Nonequibrium functional RG for the Anderson impurity model
Abstract: TBA
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P. Jakubczyk
Title: Turning a First Order Quantum Phase Transition Continuous:
Abstract: We analyze a quantum phase transition between normal metal and
a quantum nematic phase. Renormalization group approach based on the
standard expansion of the effective potential in powers of the order
parameter is not applicable in this case. Employing functional RG, we
show that fluctuation effects change the predicted order of the phase
transition, revealing the critical quantum fluctuations, which are absent
according to mean-field studies.
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P. Kopietz
Title: Spectral function and quasiparticle damping of interacting bosons
Abstract: We employ the functional renormalization group to study dynamical
properties of the two-dimensional Bose gas. Our approach is free of infrared
divergences, which plague the usual diagrammatic approaches, and is consistent
with the exact Nepomnyashchy identity, which states that the anomalous
self-energy vanishes at zero frequency and momentum. We recover the correct
infrared behavior of the propagators and present explicit results for the
spectral line-shape, from which we extract the quasi-particle dispersion
and damping.
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D. Litim
Title: Perspectives for asymptotically safe gravity
Abstract: TBA
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W. Metzner
Title: RG flow for symmetry breaking in interacting Fermi systems
Abstract: I review various ways of treating spontaneous symmetry breaking
in interacting Fermi systems within the exact renormalization group framework.
Using fermionic superfluids as a prototype for a broken continuous symmetry,
I discuss purely fermionic flow equations as well as coupled flows of fermions
and their (bosonic) order parameter fluctuations.
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Y. Meurice
Title: Fisher's zeros as boundary of RG flows in complex coupling space
Abstract: We discuss the possibility of extending the RG flows to complex
coupling spaces. We argue that the Fisher's zeros are located at the boundary
of the complex basin of attraction of IR fixed points. We support this
picture with numerical calculations at finite volume for 2D O(N) models in
the large-N limit and the hierarchical Ising model using the two-lattice
matching method. We present numerical evidence supporting the idea that,
as the volume increases, the Fisher's zeros of 4-dimensional pure gauge
SU(2) lattice gauge theory with a Wilson action, stabilize at a distance
larger than 0.1 from the real axis in the complex beta=4/g^2 plane. We show
that when a positive adjoint term is added, the zeros get closer to the
real axis. We compare the situation with the U(1) case. We discuss the
implications of this new framework for proofs of confinement and searches
for nontrivial IR fixed points in models beyond the standard model.
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D. Mouhanna
Title: Crumpling transition and flat phase of polymerized phantom membranes
Abstract: Polymerized membranes form a particularly rich domain of
statistical physics. Due to their nontrivial elastic properties they
exhibit nontrivial critical behaviours first, they undergo a phase
transition between a crumpled phase at high temperature and a flat phase
at low temperature with orientational order between the normals of the
membrane. Second, amazingly, due to the existence of long-range forces
mediated by phonons, the correlations functions in the flat phase display
a nontrivial infrared scaling behaviour. Accordingly, the lower critical
dimension above which an order can develop appears to be smaller than 2.
I show how a nonperturbative renormalization group approach of polymerized
membranes allows to explore all these behaviours in a unified way.
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E. Mottola
Title: The Trace Anomaly, Dynamical Vacuum Energy and Effective Action
Abstract: TBA
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A. Parola
Title: Renormalization of microscopic Hamiltonians
Abstract: A review of the Hierarchical Reference Theory of fluids (HRT) is
presented. I will first discuss how to generalize
the basic concepts of Wilson's momentum shell integration method to
microscopic models, both on and off lattice. This allows to retain
information of non universal properties throughout the renormalization
process by avoiding any coarse-graining procedure and the mapping onto effective
models.
Sharp and smooth cut-off prescriptions will be contrasted.
Then I will introduce a simple non perturbative approximation to the exact HRT
equations
(in the same spirit of the Local Potential Approximation)
showing results for some specific statistical model.
The behavior at the first order transition and the convexity requirement
of the free energy will be also discussed.
I will then generalize HRT to quantum systems, comparing the results with
field theoretical methods for the case of Heisenberg antiferromagnets.
Some open problem and perspective for future work will be finally offered.
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R. Percacci
Title: Flow of couplings in 3-dimensional topologically massive gravity
Abstract: Unlike pure Einstein-Hilbert gravity in 3d, which has no
propagating degrees of freedom, topologically massive gravity is a
nontrivial theory. I will describe the RG flow of this theory, which
has three couplings. It exhibits asymptotic safety in a domain where
perturbation theory is probably still reliable. Some technical issues
will be highlighted.
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M. Pietroni
Title: Resummation methods in cosmological perturbation theory
Abstract: The distribution of matter at low redshift and at O(100 Mpc) scales
carries information on crucial aspects of our Universe, such as its recent
expansion history, neutrino masses, non-gaussianity of the primordial statistics
of the perturbations, and the nature of Dark Matter and Dark Energy. In order
to accurately describe the relevant observables, density perturbations have to
be resummed at all orders, since they are close to non-linear in these regimes.
I will review and compare the different approaches which have been proposed in
the recent years, most of which make use of field theoretical tools, such as
Feynman diagrams and RG techniques. I will also discuss some recent results on
the distribution of Dark Matter halos, and compare them with N-body simulations.
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M. Pletyukhov
Title: Real-time renormalization group approach to the time evolution of
Abstract: We address the problem of how a quantum local interacting
dissipative system evolves towards nonequilibrium stationary state.
Applying the recently established method of real-time renormalization
group (RTRG) we study the real-time evolution of observables after a
sudden switching of a coupling to reservoirs with chemical potentials
+V/2 and -V/2 in two basic models. In particular, we consider the anisotropic
Kondo model (both antiferromagnetic and ferromagnetic) and interacting
resonant-level model (IRLM) which are the minimal models for the study of
spin and charge fluctuations, respectively. We derive analytic expressions
for all time scales and find that 1) all observables (spin, current, dot
population) decay with both relaxation and decoherence rates, 2) bias voltage
V appears as an important energy scale for the dynamics setting the frequency
of oscillatory behavior, 3) the decay is not purely exponential but is rather
accompanied by the power-law decay.
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J. Polchinski
Title: The Holographic Wilson Renormalization Group
Abstract: The holographic principle implies the emergence of quantum gravity
from a nongravitational theory in one fewer dimension. In AdS/CFT, the
radial dimension emerges from the energy scale of the field theory. We
develop the parallels between radial evolution in AdS space and the Wilson
RG in the field theory.
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O. Rosten
Title: A new perspective on quantum field theory from the ERG
Abstract: TBA
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F. Saueressig
Title: Evaluating functional renormalization group equations via off-diagonal
Abstract: The derivation of explicit beta-functions from an exact functional
RG equation is often inhibited by the occurrence of operator traces which
include non-minimal or higher-derivative differential operators. In this
talk, I will outline a systematic method for evaluating such traces
based on off-diagonal heat-kernel techniques. The approach is
exemplified by computing the ghost wave-function renormalization in
asymptotically safe Quantum Gravity.
The talk will be based on work in progress in collaboration with D.
Benedetti, K. Groh and P. Machado.
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M. Scherer
Title: Non-Gaussian Fixed-Points in Chiral Yukawa Systems - Critical
Abstract: TBA
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D. Schuricht
Title: Non-equilibrium transport through quantum dots: The effect of
Abstract: TBA
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H. Sonoda
Title: Wilson-Fisher fixed point for the Yukawa model in 3 dimensions
Abstract: TBA
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G. Tarjus
Title: Nonperturbative functional RG of the random field Ising model:
Abstract: TBA
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N. Tetradis
Title: Resummation of cosmological perturbations and the cosmological model
Abstract: TBA
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M. Tissier
Title: A linear realization of the BRST symmetry
Abstract: When applying the techniques of the nonperturbative renormalization
group to systems with a non-abelian gauge invariance, we face the problem
that the gauge-fixed action has a symmetry (the BRST symmetry) which is
realized non-linearly. Being non-linear, this symmetry is difficult to
handle in the NPRG formalism because quadratic regulators explicitly break
it. We will present a model which is equivalent to the usual Yang-Mills
theory in the low energy limit, but where the BRST symmetry is realized
linearly. We show that this equivalence results from decoupling of massive
modes, much as the non-linear sigma model is related witj the linear sigma
model when the massive (sigma) mode is frozen. We will discuss how this idea
can be implemented to make explicit non-perturbative studies of non-abelian
gauge theories.
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S.-W. Tsai
Title: Renormalization-group studies of cold fermions and BEC mixtures
Abstract: The spectacular progress in the physics of cold atoms has
allowed experimental access to the study of quantum gases, and mixtures
of quantum gases with different statistics. Inter-atom interactions can be
tuned by external fields, and Hubbard-models can be created in optical
lattices. In mixtures of quantum gases, one species may mediate interactions
between atoms of another species, leading to the occurrence of competing
quantum phases, such as BCS pairing and density-wave states. These mediated
interactions are typically frequency dependent, and retardation effects may
play an important role. These effects are studied using a functional
renormalization-group approach. I will discuss some of the rich phase
diagram of these system, focusing on effects of interactions, dimensionality,
and lattice geometry.
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A. Wipf
Title: Supersymmetric Flows for Supersymmetric Field Theories
Abstract: We study supersymmetric Yukawa models with the functional RG
formulated in terms of an exact and manifestly off-shell supersymmetric
flow equation for the effective action. For the 2d-supersymmetric Wess-Zumino
models with one supercharge we relate the dynamical breaking of supersymmetry
to an RG relevant control parameter of the superpotential. Supersymmetry
gives rise to a new superscaling relation between the critical exponent
associated with the control parameter and the anomalous dimension of the
field. The models exhibit a surprisingly rich fixed-point structure with a
discrete number of fixed-point superpotentials. Each fixed-point superpotential
is characterized by its number of nodes and by the number of RG relevant
directions. For the 3d-models we determine the phase-transition line separating
the supersymmetric from the non-supersymmetric phase. In addition we determine
the finite-temperature phase diagram for the restoration of the global
Z2-symmetry.
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