arXiv subjects

Marcello Porta

Publications and source records attributed to Marcello Porta.

42 records · Page 3Linked to original sources

arXiv2010

Anomalous behavior in an effective model of graphene with Coulomb interactions

We analyze by exact Renormalization Group (RG) methods the infrared properties of an effective model of graphene, in which two-dimensional massless Dirac fermions propagating with a velocity smaller than the speed of light interact with a three-dimensional quantum electromagnetic field. The fermionic correlation functions are written as series in the running coupling constants, with finite coefficients that admit explicit bounds at all orders. The implementation of Ward Identities in the RG scheme implies that the effective charges tend to a line of fixed points. At small momenta, the quasi-particle weight tends to zero and the effective Fermi velocity tends to a finite value. These limits are approached with a power law behavior characterized by non-universal critical exponents.

cond-mat.str-el↗

arXiv2010

Lattice gauge theory model for graphene

The effects of the electromagnetic (e.m.) electron-electron interactions in half-filled graphene are investigated in terms of a lattice gauge theory model. By using exact Renormalization Group methods and lattice Ward Identities, we show that the e.m. interactions amplify the responses to the excitonic pairings associated to a Kekulé distortion and to a charge density wave. The effect of the electronic repulsion on the Peierls-Kekulé instability, usually neglected, is evaluated by deriving an exact non-BCS gap equation, from which we find evidence that strong e.m. interactions among electrons facilitate the spontaneous distortion of the lattice and the opening of a gap.

cond-mat.str-el↗

arXiv2010

Absence of interaction corrections in graphene conductivity

The exact vanishing of the interaction corrections to the zero temperature and zero frequency conductivity of graphene in the presence of weak short range interactions is rigorously established.

cond-mat.str-el↗

arXiv2010

Borel summability of $ϕ^{4}_{4}$ planar theory via multiscale analysis

We review the issue of Borel summability in the framework of multiscale analysis and renormalization group, by discussing a proof of Borel summability of the $ϕ^{4}_4$ massive euclidean planar theory; this result is not new, since it was obtained by Rivasseau and 't Hooft. However, the techniques that we use have already been proved effective in the analysis of various models of consended matter and field theory; therefore, we take the $ϕ^{4}_4$ planar theory as a toy model for future applications.

math-ph↗

arXiv2010

Studio della misura di Sinai-Ruelle-Bowen in un sistema semplice

In this thesis we discuss some applications of the theory of Anosov systems to nonequilibrium statistical mechanics. In particular, we perform a perturbative check of the Gallavotti-Cohen fluctuation relation for a simple Anosov system; we find that the lack of differentiability of the time reversal operator implies a violation of the Gallavotti-Cohen fluctuation relation.

math-ph↗

arXiv2009

Fluctuation Theorem, non linear response and the regularity of time reversal symmetry

The Gallavotti - Cohen Fluctuation Theorem (FT) implies an infinite set of identities between correlation functions that can be seen as a generalization of Green Kubo formula to the nonlinear regime. As an application, we discuss a perturbative check of the FT relation through these identities for a simple Anosov reversible system; we find that the lack of differentiability of the time reversal symmetry implies a violation of the Gallavotti - Cohen fluctuation relation. Finally, a brief comparison with Lebowitz - Spohn FT is reported.

cond-mat.stat-mech↗