arXiv subjects

Matthieu Tissier

Publications and source records attributed to Matthieu Tissier.

At least 55 records · Page 3Linked to original sources

arXiv2013

Fixed points and their stability in the functional renormalization group of random field models

We consider the zero-temperature fixed points controlling the critical behavior of the $d$-dimensional random-field Ising, and more generally $O(N)$, models. We clarify the nature of these fixed points and their stability in the region of the $(N,d)$ plane where one passes from a critical behavior satisfying the $d\rightarrow d-2$ dimensional reduction to one where it breaks down due to the appearance of strong enough nonanalyticities in the functional dependence of the cumulants of the renormalized disorder. We unveil an intricate and unusual behavior.

cond-mat.dis-nn↗

arXiv2013

Three-point correlation functions in Yang-Mills theory

We investigate the three-point correlation functions of Yang-Mills theory in the Landau gauge, with a particular emphasis on the infrared regime. The effect of the Gribov copies is accounted for by adding a mass term for the gluons in the Faddeev-Popov action in the Landau gauge. We perform a one-loop calculation for the ghost-antighost-gluon and three-gluon correlation functions. These analytic results are compared with the available lattice data and give a very satisfying agreement.

hep-th↗

arXiv2013

Critical scaling in random-field systems: 2 or 3 independent exponents?

We show that the critical scaling behavior of random-field systems with short-range interactions and disorder correlations cannot be described in general by only two independent exponents, contrary to previous claims. This conclusion is based on a theoretical description of the whole (d,N) domain of the d-dimensional random-field O(N) model and points to the role of rare events that are overlooked by the proposed derivations of two-exponent scaling. Quite strikingly, however, the numerical estimates of the critical exponents of the random field Ising model are extremely close to the predictions of the two-exponent scaling, so that the issue cannot be decided on the basis of numerical simulations.

cond-mat.dis-nn↗

arXiv2013

Dimensional reduction and its breakdown in the 3-dimensional long-range random field Ising model

We investigate dimensional reduction, the property that the critical behavior of a system in the presence of quenched disorder in dimension d is the same as that of its pure counterpart in d-2, and its breakdown in the case of the random-field Ising model in which both the interactions and the correlations of the disorder are long-ranged, i.e. power-law decaying. To some extent the power-law exponents play the role of spatial dimension in a short-range model, which allows us to probe the theoretically predicted existence of a nontrivial critical value separating a region where dimensional reduction holds from one where it is broken, while still considering the physical dimension d=3. By extending our recently developed approach based on a nonperturbative functional renormalization group combined with a supersymmetric formalism, we find that such a critical value indeed exists, provided one chooses a specific relation between the decay exponents of the interactions and of the disorder correlations. This transition from dimensional reduction to its breakdown should therefore be observable in simulations and numerical analyses, if not experimentally.

cond-mat.dis-nn↗

arXiv2012

Avalanches and dimensional reduction breakdown in the critical behavior of disordered systems

We investigate the connection between a formal property of the critical behavior of several systems in the presence of quenched disorder, known as "dimensional reduction", and the presence in the same systems at zero temperature of collective events known as "avalanches". Avalanches generically produce nonanalyticities in the functional dependence of the cumulants of the renormalized disorder. We show that this leads to a breakdown of the dimensional reduction predictions if and only if the fractal dimension characterizing the scaling properties of the avalanches is exactly equal to the difference between the dimension of space and the scaling dimension of the primary field, e.g. the magnetization in a random field model. This is proven by combining scaling theory and functional renormalization group. We therefore clarify the puzzle of why dimensional reduction remains valid in random field systems above a nontrivial dimension (but fails below), always applies to the statistics of branched polymer and is always wrong in elastic models of interfaces in a random environment.

cond-mat.dis-nn↗

arXiv2012

Lifting the Gribov ambiguity in Yang-Mills theories

We propose a new one-parameter family of Landau gauges for Yang-Mills theories which can be formulated by means of functional integral methods and are thus well suited for analytic calculations, but which are free of Gribov ambiguities and avoid the Neuberger zero problem of the standard Faddeev-Popov construction. The resulting gauge-fixed theory is perturbatively renormalizable in four dimensions and, for what concerns the calculation of ghost and gauge field correlators, it reduces to a massive extension of the Faddeev-Popov action. We study the renormalization group flow of this theory at one-loop and show that it has no Landau pole in the infrared for some - including physically relevant - range of values of the renormalized parameters.

hep-th↗

arXiv2011

Nonperturbative Functional Renormalization Group for Random Field Models. III: Superfield formalism and ground-state dominance

We reformulate the nonperturbative functional renormalization group for the random field Ising model in a superfield formalism, extending the supersymmetric description of the critical behavior of the system first proposed by Parisi and Sourlas [Phys. Rev. Lett. 43, 744 (1979)]. We show that the two crucial ingredients for this extension are the introduction of a weighting factor, which accounts for ground-state dominance when multiple metastable states are present, and of multiple copies of the original system, which allows one to access the full functional dependence of the cumulants of the renormalized disorder and to describe rare events. We then derive exact renormalization group equations for the flow of the renormalized cumulants associated with the effective average action.

cond-mat.stat-mech↗

arXiv2011

Nonperturbative Functional Renormalization Group for Random Field Models. IV: Supersymmetry and its spontaneous breaking

We apply the nonperturbative functional renormalization group (NP-FRG) in the superfield formalism that we have developed in the preceding paper to study long-standing issues concerning the critical behavior of the random field Ising model. Through the introduction of an appropriate regulator and a supersymmetry-compatible nonperturbative approximation, we are able to follow the supersymmetry, more specifically the superrotational invariance first unveiled by Parisi and Sourlas [Phys. Rev. Lett. 43, 744 (1979)], and its spontaneous breaking along the RG flow. Breaking occurs below a critical dimension dDR \simeq 5.1, and the supersymmetry-broken fixed point that controls the critical behavior then leads to a breakdown of the "dimensional reduction" property. We solve the NP-FRG flow equations numerically and determine the critical exponents as a function of dimension down to d < 3, with a good agreement in d = 3 and d = 4 with the existing numerical estimates.

cond-mat.stat-mech↗

arXiv2011

An Infrared Safe perturbative approach to Yang-Mills correlators

We investigate the 2-point correlation functions of Yang-Mills theory in the Landau gauge by means of a massive extension of the Faddeev-Popov action. This model is based on some phenomenological arguments and constraints on the ultraviolet behavior of the theory. We show that the running coupling constant remains finite at all energy scales (no Landau pole) for $d>2$ and argue that the relevant parameter of perturbation theory is significantly smaller than 1 at all energies. Perturbative results at low orders are therefore expected to be satisfactory and we indeed find a very good agreement between 1-loop correlation functions and the lattice simulations, in 3 and 4 dimensions. Dimension 2 is shown to play the role of an upper critical dimension, which explains why the lattice predictions are qualitatively different from those in higher dimensions.

hep-th↗

arXiv2011

Supersymmetry and its spontaneous breaking in the random field Ising model

We provide a resolution of one of the long-standing puzzles in the theory of disordered systems. By reformulating the functional renormalization group (FRG) for the critical behavior of the random field Ising model in a superfield formalism, we are able to follow the associated supersymmetry and its spontaneous breaking along the FRG flow. Breaking is shown to occur below a critical dimension $d_{DR}\simeq 5.1$ and leads to a breakdown of the "dimensional reduction" property. We compute the critical exponents as a function of dimension and give evidence that scaling is described by three independent exponents.

cond-mat.stat-mech↗

arXiv2011

Hierarchical Reference Theory of critical fluids in disordered porous media

We consider the equilibrium behavior of fluids imbibed in disordered mesoporous media, including their gas-liquid critical point when present. Our starting points are on the one hand a description of the fluid/solid-matrix system as a quenched-annealed mixture and on the other hand the Hierarchical Reference Theory (HRT) developed by A. Parola and L. Reatto to cope with density fluctuations on all length scales. The formalism combines liquid-state statistical mechanics and the theory of systems in the presence of quenched disorder. A straightforward implementation of the HRT to the quenched-annealed mixture is shown to lead to unsatisfactory results, while indicating that the critical behavior of the system is in the same universality class as that of the random-field Ising model. After a detour via the field-theoretical renormalization group approach of the latter model, we finally lay out the foundations for a proper HRT of fluids in a disordered porous material.

cond-mat.stat-mech↗

arXiv2010

Infrared propagators of Yang-Mills theory from perturbation theory

We show that the correlation functions of ghosts and gluons for the pure Yang-Mills theory in Landau gauge can be accurately reproduced for all momenta by a one-loop calculation. The key point is to use a massive extension of the Faddeev-Popov action. The agreement with lattice simulation is excellent in d=4. The one-loop calculation also reproduces all the characteristic features of the lattice simulations in d=3 and naturally explains the pecularities of the propagators in d=2.

hep-ph↗

arXiv2009

A linear realization of the BRST symmetry

In this Letter, we propose a model which is equivalent to the Yang-Mills theory at long distances but for which all symmetries are realized linearly. On top of the gauge and Fadeev-Popov ghosts fields, the model presents several massive fields, all of which can be merged in a unique vector field with support in a curved superspace. The equivalence of this model with the gauge-fixed Yang-Mills theory is shown to result from the decoupling of these extra massive modes at small momenta. Most of the symmetries of Yang-Mills theory, including the famous BRST symmetry, can be interpreted in this way as isometries of the superspace.

hep-th↗

arXiv2008

Gauged supersymmetries in Yang-Mills theory

In this paper we show that Yang-Mills theory in the Curci-Ferrari-Delbourgo-Jarvis gauge admits some up to now unknown local linear Ward identities. These identities imply some non-renormalization theorems with practical simplifications for perturbation theory. We show in particular that all renormalization factors can be extracted from two-point functions. The Ward identities are shown to be related to supergauge transformations in the superfield formalism for Yang-Mills theory. The case of non-zero Curci-Ferrari mass is also addressed.

hep-th↗

arXiv2007

Non-Perturbative Functional Renormalization Group for Random Field Models and Related Disordered Systems. I: Effective Average Action Formalism

We have developed a nonperturbative functional renormalization group approach for random field models and related disordered systems for which, due to the existence of many metastable states, conventional perturbation theory often fails. The approach combines an exact renormalization group equation for the effective average action with a nonperturbative approximation scheme based on a description of the probability distribution of the renormalized disorder through its cumulants. For the random field $O(N)$ model, the minimal truncation within this scheme is shown to reproduce the known perturbative results in the appropriate limits, near the upper and lower critical dimensions and at large number $N$ of components, while providing a unified nonperturbative description of the full $(N,d)$ plane, where $d$ is the spatial dimension.

cond-mat.stat-mech↗

arXiv2007

Non-Perturbative Functional Renormalization Group for Random Field Models and Related Disordered Systems. II: Results for the Random Field O(N) Model

We study the critical behavior and phase diagram of the $d$-dimensional random field O(N) model by means of the nonperturbative functional renormalization group approach presented in the preceding paper. We show that the dimensional reduction predictions, obtained from conventional perturbation theory, break down below a critical dimension $d_{DR}(N)$ and we provide a description of criticality, ferromagnetic ordering and quasi-long range order in the whole $(N,d)$ plane. Below $d_{DR}(N)$, our formalism gives access to both the typical behavior of the system, controlled by zero-temperature fixed points with a nonanalytic dimensionless effective action, and to the physics of rare low-energy excitations ("droplets"), described at nonzero temperature by the rounding of the nonanalyticity in a thermal boundary layer.

cond-mat.stat-mech↗

arXiv2006

Two-loop Functional Renormalization Group of the Random Field and Random Anisotropy O(N) Models

We study by the perturbative Functional Renormalization Group (FRG) the Random Field and Random Anisotropy O(N) models near $d=4$, the lower critical dimension of ferromagnetism. The long-distance physics is controlled by zero-temperature fixed points at which the renormalized effective action is nonanalytic. We obtain the beta functions at 2-loop order, showing that despite the nonanalytic character of the renormalized effective action, the theory is perturbatively renormalizable at this order. The physical results obtained at 2-loop level, most notably concerning the breakdown of dimensional reduction at the critical point and the stability of quasi-long range order in $d<4$, are shown to fit into the picture predicted by our recent non-perturbative FRG approach.

cond-mat.stat-mech↗

arXiv2005

A unified picture of ferromagnetism, quasi-long range order and criticality in random field models

By applying the recently developed nonperturbative functional renormalization group (FRG) approach, we study the interplay between ferromagnetism, quasi-long range order (QLRO) and criticality in the $d$-dimensional random field O(N) model in the whole ($N$, $d$) diagram. Even though the "dimensional reduction" property breaks down below some critical line, the topology of the phase diagram is found similar to that of the pure O(N) model, with however no equivalent of the Kosterlitz-Thouless transition. In addition, we obtain that QLRO, namely a topologically ordered "Bragg glass" phase, is absent in the 3--dimensional random field XY model. The nonperturbative results are supplemented by a perturbative FRG analysis to two loops around $d=4$.

cond-mat.other↗