93 research outputs found
Electron Mass Anomalous Dimension at O(1/N^2_f) in Quantum Electrodynamics
The critical exponent corresponding to the renormalization of the composite
operator is computed in quantum electrodynamics at
O(1/\Nf^2) in arbitrary dimensions and covariant gauge at the non-trivial
zero of the -function in the large \Nf expansion and the exponent
corresponding to the anomalous dimension of the electron mass which is a gauge
independent object is deduced. Expanding in powers of
we check it is consistent with the known three loop perturbative
structure and determine the subsequent coefficients in the coupling constantComment: 12 pages (latex), 1 figure (available from author on request),
LTH-31
Anomalous dimension of non-singlet quark currents at O(1/Nf^2) in QCD
We compute the O(1/Nf^2) corrections to the flavour non-singlet quark
bilinear currents in QCD in arbitrary spacetime dimensions. Hence, the
anomalous dimension of the QED current is
deduced at four loops in the MSbar scheme up to one unknown parameter.Comment: 8 latex page
The Nambu-Jona-Lasinio Model at O(1/N^2)
We write down the anomalous dimensions of the fields of the
Nambu--Jona-Lasinio model or chiral Gross Neveu model with a continuous global
chiral symmetry for the two cases and
at in a expansion.Comment: 9 latex pages, 4 figures (available on request from the author),
LTH-308, (2 eqns corrected
Anomalous dimension of gluonic operator in polarized deep inelastic scattering at O(1/N_f)
We compute the O(1/N_f) correction to the predominantly gluonic flavour
singlet twist-2 anomalous dimension used in polarized deep inelastic
scattering. It is consistent with known two loop perturbation theory and we
determine the three loop contribution at O(1/N_f). The treatment of the
epsilon-tensor in the large N_f d-dimensional critical point formalism is also
discussed.Comment: 8 Latex pages, 1 postscript figur
Quark, Gluon and Ghost Anomalous Dimensions at O(1/N_f) in Quantum Chromodynamics
By considering the scaling behaviour of various Feynman graphs at leading
order in large \Nf at the non-trivial fixed point of the -dimensional
-function of QCD we deduce the critical exponents corresponding to the
quark, gluon and ghost anomalous dimensions as well as the anomalous dimensions
of the quark-quark-gluon and ghost-ghost-gluon vertices in the Landau gauge. As
the exponents encode all orders information on the perturbation series of the
corresponding renormalization group functions we find agreement with the known
three loop structure and, moreover, we provide new information at all
subsequent orders.Comment: 13 pages latex plus 3 figures (available from author on request),
LTH-31
Four loop MSbar mass anomalous dimension in the Gross-Neveu model
We compute the four loop term of the mass anomalous dimension in the two
dimensional Gross-Neveu model in the MSbar scheme. The absence of
multiplicative renormalizability which results when using dimensional
regularization means that the effect of the evanescent operator, which first
appears at three loops in the 4-point Green's function, has to be properly
treated in the construction of the renormalization group function. We repeat
the calculation of the three loop MSbar beta-function and construct the
beta-function of the evanescent operator coupling which corrects earlier
computations.Comment: 20 latex pages, 7 figure
QCD and QED renormalization group functions - a large N_f approach
The large N_f self-consistency programme is reviewed. As an application the
QCD beta-function is computed at O(1/N_f) and the anomalous dimensions of
polarized twist-2 singlet operators are determined at the same order.Comment: Talk given at DESY workshop QCD and QED in higher order; 8 pages
latex plus 1 figur
Anomalous Dimension of Non-Singlet Wilson Operators at O(1/N_f) in Deep Inelastic Scattering
We use the large N_f self consistency formalism to compute the
critical exponent corresponding to the renormalization of the flavour
non-singlet twist two Wilson operators which arise in the operator product
expansion of currents in deep inelastic processes. Expanding the
-dimensional expression in powers of the
coefficients of agree with the known two loop structure of the
corresponding renormalization group function and we deduce analytic expressions
for all moments, , at three and higher orders in perturbation theory in the
\overline{\mbox{MS}} scheme at .Comment: 13 Latex pages, 1 figure (available from author on request), LTH-32
Computation of quark mass anomalous dimension at O(1/N_f^2) in quantum chromodynamics
We present the formalism to calculate d-dimensional critical exponents in QCD
in the large N_f expansion where N_f is the number of quark flavours. It relies
in part on demonstrating that at the d-dimensional fixed point of QCD the
critical theory is equivalent to a non-abelian version of the Thirring model.
We describe the techniques used to compute critical two and three loop Feynman
diagrams and as an application determine the quark wave function, eta, and mass
renormalization critical exponents at O(1/N_f^2) in d-dimensions. Their values
when expressed in relation to four dimensional perturbation theory are in exact
agreement with the known four loop MSbar results. Moreover, new coefficients in
these renormalization group functions are determined to six loops and
O(1/N_f^2). The computation of the exponents in the Schwinger Dyson approach is
also provided and an expression for eta in arbitrary covariant gauge is given.Comment: 41 latex pages, 17 postscript figure
Renormalization properties of the mass operator A^2 in three dimensional Yang-Mills theories in the Landau gauge
Massive renormalizable Yang-Mills theories in three dimensions are analysed
within the algebraic renormalization in the Landau gauge. In analogy with the
four dimensional case, the renormalization of the mass operator A^2 turns out
to be expressed in terms of the fields and coupling constant renormalization
factors. We verify the relation we obtain for the operator anomalous dimension
by explicit calculations in the large N_f. The generalization to other gauges
such as the nonlinear Curci-Ferrari gauge is briefly outlined.Comment: 15 pages, 3 figure
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