Conditions and possible mechanism of condensation of e-h pairs in bulk GaAs at room temperature

A mechanism of the condensation of e-h pairs in bulk GaAs at room temperature, which has been observed earlier, is proposed. The point is that the photon assisted pairing happens in a system of electrons and holes that occupy energy levels at the very bottoms of the bands. Due to a very high e-h density, the destruction of the pairs and loss of coherency does not occur because almost all energy levels inside a 30-60 meV band from the bottom of the conduction band prove to be occupied. As a result, a coherent ensemble of composite bosons (paired electrons and holes) with the minimum possible energy appears. The lifetime of this strongly non-equilibrium coherent e-h BCS-like state is as short as a few hundred of femtosecondsComment: 10 pages, 8 figure

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 $d$-dimensional $\beta$-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

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 $U(1)$ $\times$ $U(1)$ and $SU(M)$ $\times$ $SU(M)$ at $O(1/N^2)$ in a $1/N$ expansion.Comment: 9 latex pages, 4 figures (available on request from the author), LTH-308, (2 eqns corrected

Electron Mass Anomalous Dimension at O(1/N^2_f) in Quantum Electrodynamics

The critical exponent corresponding to the renormalization of the composite operator $\bar{\psi}\psi$ is computed in quantum electrodynamics at O(1/\Nf^2) in arbitrary dimensions and covariant gauge at the non-trivial zero of the $\beta$-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 $\epsilon$ $=$ $2$ $-$ $d/2$ 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

The simple scheme for the calculation of the anomalous dimensions of composite operators in the 1/N expansion

The simple method for the calculating of the anomalous dimensions of the composite operators up to 1/N^2 order is developed. We demonstrate the effectiveness of this approach by computing the critical exponents of the $(\otimes\vec\Phi)^{s}$ and $\vec\Phi\otimes(\otimes\vec\partial)^{n}\vec\Phi$ operators in the 1/N^2 order in the nonlinear sigma model. The special simplifications due to the conformal invariance of the model are discussed.Comment: 20 pages, Latex, uses Feynman.st