Status of twist-2 operator dimensions at O(1/N_f)

We review the computation of the anomalous dimensions of the twist-2 unpolarized operators in the large N_f expansion. Results are discussed for the predominantly gluonic singlet operator and the O(1/N_f) part of the 3-loop splitting function is given.Comment: 4 latex pages, contribution to DIS 9

Critical exponent omega in the Gross-Neveu-Yukawa model at O(1/N)

The critcal exponent $\omega$ is evaluated at $O(1/N)$ in $d$-dimensions in the Gross-Neveu model using the large $N$ critical point formalism. It is shown to be in agreement with the recently determined three loop $\beta$-functions of the Gross-Neveu-Yukawa model in four dimensions. The same exponent is computed for the chiral Gross-Neveu and non-abelian Nambu-Jona-Lasinio universality classes.Comment: 16 latex pages, 5 figures, typos corrected and text adde

Eight dimensional QCD at one loop

The Lagrangian for a non-abelian gauge theory with an $SU(N_{\! c})$ symmetry and a linear covariant gauge fixing is constructed in eight dimensions. The renormalization group functions are computed at one loop with the special cases of $N_{\! c}$ $=$ $2$ and $3$ treated separately. By computing the critical exponents derived from these in the large $N_{\! f}$ expansion at the Wilson-Fisher fixed point it is shown that the Lagrangian is in the same universality class as the two dimensional non-abelian Thirring model and Quantum Chromodynamics (QCD). As the eight dimensional Lagrangian contains new quartic gluon operators not present in four dimensional QCD, we compute in parallel the mixing matrix of four dimensional dimension $8$ operators in pure Yang-Mills theory.Comment: 31 latex pages, anc directory now added which contains txt file of all renormalization group function

beta-functions in higher dimensional field theories

We review recent activity in the construction of the renormalization group functions for O(N) scalar and gauge theories in six and higher dimensions. The theories lie in their respective universality classes at the Wilson-Fisher fixed point. The critical exponents at this fixed point in the various dimensions are all in agreement with the known exponents determined in the large Nexpansion

Asymptotic freedom from the two-loop term of the beta function in a cubic theory

We renormalize a six dimensional cubic theory to four loops in the MSbar scheme where the scalar is in a bi-adjoint representation. The underlying model was originally derived in a problem relating to gravity being a double copy of Yang-Mills theory. As a field theory in its own right we find that it has a curious property in that while unexpectedly there is no one loop contribution to the $\beta$-function the two loop coefficient is negative. It therefore represents an example where asymptotic freedom is determined by the two loop term of the $\beta$-function. We also examine a multi-adjoint cubic theory in order to see whether this is a more universal property of these models.Comment: 17 latex page

Vertex functions in QCD - preparation for beyond two loops

We summarize the algorithm to determine the two loop off-shell 3-point vertexfunctions of QCD before outlining the steps required to extend the results tothree and higher loops

Quark mass anomalous dimension at O(1/N_f^2) in QCD

We compute the d-dimensional critical exponents corresponding to the wave function and mass renormalization of the quark in QCD in the Landau gauge at a new order, O(1/N_f^2), in the large N_f expansion. The computations are simplified by the establishment in d-dimensions of the critical point equivalence of QCD and the non-abelian Thirring model beyond leading order. The form of the O(1/N_f^2) coefficients in the MSbar quark mass anomalous dimension at five loops is deduced and compared with the numerical asymptotic Pade approximant prediction.Comment: 13 latex pages, 3 eps figure

Higher dimensional higher derivative φ⁴ theory

We construct several towers of scalar quantum field theories with an $O(N)$ symmetry which have higher derivative kinetic terms. The Lagrangians in each tower are connected by lying in the same universality class at the $d$-dimensional Wilson-Fisher fixed point. Moreover the universal theory is studied using the large $N$ expansion and we determine $d$-dimensional critical exponents to $O(1/N^2)$. We show that these new universality classes emerge naturally as solutions to the linear relation of the dimensions of the fields deduced from the underlying force-matter interaction of the universal critical theory. To substantiate the equivalence of the Lagrangians in each tower we renormalize each to several loop orders and show that the renormalization group functions are consistent with the large $N$ critical exponents. While we focus on the first two new towers of theories and renormalize the respective Lagrangians to $16$ and $18$ dimensions there are an infinite number of such towers. We also briefly discuss the conformal windows and the extension of the ideas to theories with spin-$\frac{1}{2}$ and spin-$1$ fields as well as the idea of lower dimension completeness.Comment: 30 latex pages, minor typos correcte

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We apply the Local Composite Operator method to construct the three loop effective potential for the dimension two operator $\frac{1}{2} { A_\mu^a }^2$ in the Landau gauge in Quantum Chromodynamics. For $SU(3)$ we show that the three loop value of the effective mass of the gluon is similar to the two loop estimates when the number of massless quarks is strictly less than five for $SU(3)$.Comment: 29 latex pages, 5 figures, 11 tables, minor text change