40 research outputs found
Auxiliary fields approach to shift-symmetric theories: the derivative theory and the crumpled-to-flat transition of membranes at two-loop order
We introduce a technique relying on the use of auxiliary fields in order to
eliminate explicit field-derivatives that plague the high orders
renormalization group treatment of shift-symmetric, derivative, theories. This
technique simplifies drastically the computation of fluctuations in such
theories. This is illustrated by deriving the two-loop renormalization group
equations and the three-loop anomalous dimension of the derivative
theory in , which is also relevant to describe the
crumpled-to-flat transition of polymerized membranes. Some features of this
transition are provided.Comment: 7 page
Spontaneous versus explicit replica symmetry breaking in the theory of disordered systems
We investigate the relation between spontaneous and explicit replica symmetry
breaking in the theory of disordered systems. On general ground, we prove the
equivalence between the replicon operator associated with the stability of the
replica symmetric solution in the standard replica scheme and the operator
signaling a breakdown of the solution with analytic field dependence in a
scheme in which replica symmetry is explicitly broken by applied sources. This
opens the possibility to study, via the recently developed functional
renormalization group, unresolved questions related to spontaneous replica
symmetry breaking and spin-glass behavior in finite-dimensional disordered
systems.Comment: 16 page
Heisenberg frustrated magnets: a nonperturbative approach
Frustrated magnets are a notorious example where the usual perturbative
methods are in conflict. Using a nonperturbative Wilson-like approach, we get a
coherent picture of the physics of Heisenberg frustrated magnets everywhere
between and . We recover all known perturbative results in a single
framework and find the transition to be weakly first order in . We compute
effective exponents in good agreement with numerical and experimental data.Comment: 5 pages, Revtex, technical details available at
http://www.lpthe.jussieu.fr/~tissie
Optimization of the derivative expansion in the nonperturbative renormalization group
We study the optimization of nonperturbative renormalization group equations
truncated both in fields and derivatives. On the example of the Ising model in
three dimensions, we show that the Principle of Minimal Sensitivity can be
unambiguously implemented at order of the derivative expansion.
This approach allows us to select optimized cut-off functions and to improve
the accuracy of the critical exponents and . The convergence of the
field expansion is also analyzed. We show in particular that its optimization
does not coincide with optimization of the accuracy of the critical exponents.Comment: 13 pages, 9 PS figures, published versio
A non perturbative approach of the principal chiral model between two and four dimensions
We investigate the principal chiral model between two and four dimensions by
means of a non perturbative Wilson-like renormalization group equation. We are
thus able to follow the evolution of the effective coupling constants within
this whole range of dimensions without having recourse to any kind of small
parameter expansion. This allows us to identify its three dimensional critical
physics and to solve the long-standing discrepancy between the different
perturbative approaches that characterizes the class of models to which the
principal chiral model belongs.Comment: 5 pages, 1 figure, Revte
Interacting fermions in self-similar potentials
We consider interacting spinless fermions in one dimension embedded in
self-similar quasiperiodic potentials. We examine generalizations of the
Fibonacci potential known as precious mean potentials. Using a bosonization
technique and a renormalization group analysis, we study the low-energy physics
of the system. We show that it undergoes a metal-insulator transition for any
filling factor, with a critical interaction that strongly depends on the
position of the Fermi level in the Fourier spectrum of the potential. For some
positions of the Fermi level the metal-insulator transition occurs at the non
interacting point. The repulsive side is an insulator with a gapped spectrum
whereas in the attractive side the spectrum is gapless and the properties of
the system are described by a Luttinger liquid. We compute the transport
properties and give the characteristic exponents associated to the frequency
and temperature dependence of the conductivity.Comment: 18 pages, 10 EPS figure
An international experience with single-operator cholangiopancreatoscopy in patients with altered anatomy
Background and study aims: The utility of digital single- operator cholangiopancreatoscopy (D-SOCP) in surgically altered anatomy (SAA) is limited. We aimed to evaluate the technical success and safety of D-SOCP in patients SAA.
Patients and methods: Patients with SAA who underwent D-SOCP between February 2015 and June 2020 were retrospectively evaluated. Technical success was defined as completing the intended procedure with the use of D-SOCP.
Results: Thirty-five patients underwent D-SOCP (34 D-SOC, 1 D-SOP). Bilroth II was the most common type of SAA (45.7 %), followed by Whipple reconstruction (31.4 %). Twenty-three patients (65.7 %) patients had prior failed ERCP due to the presence of complex biliary stone (52.2 %). A therapeutic duodenoscope was utilized in the majority of the cases (68.6 %), while a therapeutic gastroscope (22.7 %) or adult colonoscope (8.5 %) were used in the remaining procedures. Choledocholithiasis (61.2 %) and pancreatic duct calculi (3.2 %) were the most common indications for D-SOCP. Technical success was achieved in all 35 patients (100 %) and majority (91.4 %) requiring a single session. Complex interventions included electrohydraulic or laser lithotripsy, biliary or pancreatic stent placement, stricture dilation, and target tissue biopsies. Two mild adverse events occurred (pancreatitis and transient bacteremia).
Conclusions: In SAA, D-SOCP is a safe and effective modality to diagnose and treat complex pancreatobiliary disorders, especially in cases where standard ERCP attempts may fail