arXiv subjects
Publications and source records attributed to J. A. Gracey.
We compute the $O(1/N^2)$ correction to the critical exponent $2λ$ $=$ $-$ $β^\prime(g_c)$ for the chiral Gross Neveu model in arbitrary dimensions by substituting the corrections to the asymptotic scaling forms of the propagators into the Schwinger Dyson equations and solving the resulting consistency equations.
The addition of $m$ singlet right-handed neutrinos to the Standard Model leads to radiatively generated mass corrections for the $SU(2)_L $ doublet neutrinos. For those neutrinos which are massless at the tree level after this addition, this implies a small mass generated at the two-loop level via $W^{\pm}$ exchange. We calculate these mass corrections exactly by obtaining an analytic form for the general case of $n$ doublets and $m$ singlets. As a phenomenological application, we consider the $m=1$ case and examine the masses and mixings of the doublet neutrinos which arise as a result of the two-loop correction in the light of experimental data from two sources which may shed light on the question of neutrino masses. These are(a) the neutrino detectors reporting a solar neutrino deficit (and its resolution via Mikheyev-Smirnov-Wolfenstein matter oscillations), and (b) the COBE satellite data on the non-zero angular variations of the cosmic microwave background temperature (and its possible implications for hot dark matter). Within the framework of the extension considered here, which leaves the gauge group structure of the Standard Model intact, we show that it is possible for neutrinos to acquire small masses naturally, with values which are compatible with current theoretical bias and experimental data.
We use the large N_f self consistency formalism to compute the $O(1/N_f)$ 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 $d$-dimensional expression in powers of $ε$ $=$ $(4-d)/2$ the coefficients of $ε$ agree with the known two loop structure of the corresponding renormalization group function and we deduce analytic expressions for all moments, $n$, at three and higher orders in perturbation theory in the $\overline{\mbox{MS}}$ scheme at $O(1/N_f)$.
We present a detailed evaluation of $η$, the critical exponent corresponding to the electron anomalous dimension, at $O(1/N^2_{\!f})$ in a large flavour expansion of QED in arbitrary dimensions in the Landau gauge. The method involves solving the skeleton Dyson equations with dressed propagators in the critical region of the theory. Various techniques to compute massless two loop Feynman diagrams, which are of independent interest, are also given.
By considering the scaling behaviour of various Feynman graphs at leading order in large $\Nf$ at the non-trivial fixed point of the $d$-dimensional $β$-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.
The critical exponent corresponding to the renormalization of the composite operator $\barψψ$ is computed in quantum electrodynamics at $O(1/\Nf^2)$ in arbitrary dimensions and covariant gauge at the non-trivial zero of the $β$-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 $ε$ $=$ $2$ $-$ $d/2$ we check it is consistent with the known three loop perturbative structure and determine the subsequent coefficients in the coupling constant
We present the formalism for computing the critical exponent corresponding to the $β$-function of the Nambu--Jona-Lasinio model with $SU(M)$ $\times$ $SU(M)$ continuous chiral symmetry at $O(1/N^2)$ in a large $N$ expansion, where $N$ is the number of fermions. We find that the equations can only be solved for the case $M$ $=$ $2$ and subsequently an analytic expression is then derived. This contrasting behaviour between the $M$ $=$ $2$ and $M$ $>$ $2$ cases, which appears first at $O(1/N^2)$, is related to the fact that the anomalous dimensions of the bosonic fields are only equivalent for $M$ $=$ $2$.
We solve the gauged Nambu--Jona-Lasinio model at leading order in the large $N$ expansion by computing the anomalous dimensions of all the fields of the model and other gauge independent critical exponents by examining the scaling behaviour of the Schwinger Dyson equation. We then restrict to the three dimensional model and include a Chern Simons term to discover the $θ$-dependence of the same exponents where $θ$ is the Chern Simons coupling.
By using the corrections to the asymptotic scaling forms of the fields of the $O(N)$ Gross Neveu model to solve the dressed skeleton Schwinger Dyson equations, we deduce the critical exponent corresponding to the $β$-function of the model at $O(1/N^2)$.
We solve the conformal bootstrap equations of the four fermi model or $O(N)$ Gross Neveu model to deduce the fermion anomalous dimension of the theory at $O(1/N^3)$ in arbitrary dimensions.
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 $U(1)$ $\times$ $U(1)$ and $SU(M)$ $\times$ $SU(M)$ at $O(1/N^2)$ in a $1/N$ expansion.
By considering corrections to the asymptotic scaling functions of the photon and electron in quantum electrodynamics with $\Nf$ flavours, we solve the skeleton Dyson equations at $O(1/\Nf)$ in the large $\Nf$ expansion at the $d$-dimensional critical point of the theory and deduce the critical exponent $β^\prime(g_c)$, in arbitrary dimensions, and subsequently present a method for computing higher order corrections to $β(g)$.
An arbitrary dimensional expression is given for the anomalous dimension of the fermion field in a model with a four point interaction and a $U(1)$ gauge field, at $O(1/N^2)$ within a large flavour expansion in the Landau gauge.
We apply the self consistency method for determining critical exponents to a model with a four fermi interaction coupled to QED and compute various gauge independent exponents in arbitrary dimensions in the large $N$ expansion at $O(1/N)$. The formalism is developed to include a Chern Simons term in three dimensions and the effect such a term has on the exponents is deduced.