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Utilizza questo identificativo per citare o creare un link a questo documento:
http://hdl.handle.net/10761/936

Data:  2feb2012 
Autori:  Messina, Emanuele 
Titolo:  Non perturbative renormalization of firmion theories 
Abstract:  The present work is devoted to the study of the nonperturbative renormalization of quantum
field theories (QFT) of selfinteracting fermions,
which is investigated with the help of a fermion Wilsonian RG method.
By starting with the appropriate scale dependent action S_k for fermion models and performing a nontrivial extension of previous techniques, a new renormalization group (RG) equation for a generalized N flavors GrossNeveu model in 2 ¿ d ¿ 4 dimensions is established.
The renormalizability of such a model is related to the
existence of a nonGaussian fixed point of the RG equations, which
turns out also to be related to the critical point of the
chiral symmetry breaking.
Within the Wilson RG approach to critical phenomena, the
critical exponents of the GrossNeveu model are computed by considering the behaviour of the running mass m(k) and Fermi constant G(k)
around such a nonGaussian fixed point (with divergent correlation length).
By means our approach, this model can be
studied even far from the applicability domain of other traditional analytical tools (as epsilon or 1/N expansion) relying on the bosonization
of the model.
The RG equations for the running mass m(k) and Fermi constant G(k)
are numerically studied in
the whole (G, m) plane. From this analysis, in turns out that the physics of the chiral
phase transition can be described well in terms of a crossover phenomenon triggered by
the presence of an infinitesimal bare mass.
The impact of higher powers operators (¿¿)^4 in the Wilsonian potential is also considered.
In the large N limit,
the failure of the hyperscaling and the presence of
a logarithmic behaviour at d=4 dimensions with the scale of the quartic operator (¿¿)^4 are thus recovered in our RG fermion language.
By considering the impact of odd interaction terms in the potential, the marginality
of the cubic operator in d = 3 dimensions is also recovered. The anomalous dimension of this
operator is computed and found to be in agreement with results given in the literature at
the next to leading order in the 1/N expansion.
Finally the Wilsonian RG equation is extended to theories which involve both fermions
and bosons. For N=1 and d=4 this equation coincides with that found in
literature. A nontrivial FP which should describe the chiral transition for
d<4 is then found.
If, however, a four Fermi interaction term is added to the Yukawa theory,
an intriguing and unexpected result is found. Namely, the nonperturbative
scaling of the running Fermi constant G(k) triggers the appearence of a
nonGaussian fixed point which heals the triviality of the Yukawa coupling
in d=4 dimensions. 
In  Area 02  Scienze fisiche

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