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Manuel Reenders

Publications and source records attributed to Manuel Reenders.

6 recordsLinked to original sources
arXiv2002

Large N planar or bare vertex approximation and critical behavior of a SU(N) invariant four-fermion model in 2+1 dimensions

A four-fermion model in 2+1 dimensions describing N Dirac fermions interacting via SU(N) invariant N^2-1 four-fermion interactions is solved in the leading order of the 1/N expansion. The 1/N expansion corresponds to 't Hoofts topological 1/N expansion in which planar Feynman diagrams prevail. For the symmetric phase of this model, it is argued that the planar expansion corresponds to the ladder approximation. A truncated set of Schwinger-Dyson equations for the fermion propagator and composite boson propagator representing the relevant planar diagrams is solved analytically. The critical four-fermion coupling and various critical exponents are determined as functions of N. The universality class of this model turns out to be quite distinct from the Gross-Neveu model in the large N limit.

hep-th↗
arXiv2002

Compositional and orientational ordering in rod-coil diblock copolymer melts

The phase behavior of a melt of monodisperse rod-coil diblocks is studied. We derive a Landau free energy functional for both a compositional and a nematic order parameter. The excluded volume interaction between the rod blocks is modeled by an attractive Maier-Saupe interaction. The incompatibility between rod- and coil blocks is modeled by the usual Flory-Huggins interaction. For a large volume fraction of the rods, a transition from isotropic to nematic to smectic C is observed upon decreasing the temperature, whereas for small rod volume fraction, spherical, hexagonal, and lamellar structures prevail. In the smectic C phase, the rod orientation angle with respect to the lamellar normal increases rapidly from 35 to 40 degrees close to the nematic/smectic-C phase boundary to values between 45 and 55 degrees.

cond-mat.soft↗
arXiv2001

Nonperturbative infrared dynamics of three-dimensional QED with a four-fermion interaction

A non-linear Schwinger-Dyson (SD) equation for the gauge boson propagator of massless QED in one time and two spatial dimensions is studied. It is shown that the nonperturbative solution leads to a nontrivial renormalization-group infrared fixed point quantitatively close to the one found in the leading order of the 1/N expansion, with N the number of fermion flavors. In the gauged Nambu-Jona-Lasinio (GNJL) model an equation for the Yukawa vertex is solved in an approximation given by the one-photon exchange and an analytic expression is derived for the propagator of the scalar fermion-antifermion composites. Subsequently, the mass and width of the scalar composites near the phase transition line are calculated as functions of the four-fermion coupling g and flavor number N. The possible relevance of these results for describing particle-hole excitations, in particular antiferromagnetic correlations, observed in the underdoped cuprates, is briefly discussed.

hep-ph↗
arXiv2000

Nontriviality of Abelian gauged Nambu-Jona-Lasinio models in four dimensions

We study a particular class of Abelian gauged Nambu-Jona-Lasinio models with global U_L(N)xU_R(N) symmetry, where N is the number of fermion flavors. We show, by treating the gauge interaction in the ladder approximation and four-fermion interactions in the leading order of the 1/N expansion, that the renormalization-group beta function of the U(1) gauge coupling has ultraviolet stable fixed points for sufficiently large N. This implies the existence of a nontrivial continuum limit.

hep-th↗
arXiv1999

Dynamical symmetry breaking in the gauged Nambu-Jona-Lasinio model

The mechanism of dynamical chiral symmetry breaking is studied in the Abelian version of the gauged Nambu-Jona-Lasinio model in four dimensions. The most interesting feature of the gauged Nambu-Jona-Lasinio model is the appearance of relevant (renormalizable) four-fermion interactions near a critical curve separating a chiral symmetric and a dynamically chiral symmetry broken phase. The first three chapters of the thesis are introductory. Chapter 4 is based on hep-th/9712123. In an attempt to go beyond standard mean field approximations for four-fermion interactions, the 1/N expansion is utilized in chapter 5. Within the 1/N expansion, where N is the number of fermion flavors, it is shown that the renormalization group beta function of the U(1) gauge coupling has ultra-violet stable fixed points for sufficiently large N. This implies that the gauged Nambu-Jona-Lasinio model is a rare example of a nontrivial nonasymptotically free gauge field theory in four dimensions.

hep-th↗