Classical diffusion in strong random media

We study classical diffusion of particles in random media. Although many of our results are general, we focus on the case of an ion in a three-dimensional medium with random, quenched charge centers obeying bulk charge neutrality. Within a functional-integral framework, we calculate the effective diffusion coefficients by first-order and second-order self-consistent perturbation theory (with a Gaussian reference in both cases). We also carry out a one-loop order momentum space renormalization group calculation. The self-consistent methods are complicated numerically and fail beyond intermediate disorder strengths. In contrast, the renormalization group calculation gives an analytical result that appears valid even to high disorder strengths. The methodology, generally applicable to a quantitative calculation of effective diffusion coefficients in disordered media, resolves deficiencies in self-consistent perturbation theory approaches to this class of problems.     

Comparing different hard-thermal-loop approaches to quark number susceptibilities

We compare our previously proposed hard-thermal-loop (HTL) resummed calculation of quark number susceptibilities using a self-consistent two-loop approximation to the quark density with a recent calculation of the same quantity at the one-loop level in a variant of HTL-screened perturbation theory. Besides pointing out conceptual problems with the latter approach, we show that it severely over-includes the leading-order interaction effects, while including none of the plasmon terms, which is the main reason for requiring improved resummation schemes. Received: 27 June 2002 / Revised version: 23 September 2002 / Published online: 31 January 2003     

QCD corrections to inclusive jet photoproduction via direct photons

The direct chiral perturbation theory (ChPT) one-loop prediction for the production of two pions from two photons is compared with the recent Crystal Ball experimental data. The one-loop computation does not fit data even close to threshold because unitarity effects are important even at very low energies. However, when the constraints coming from unitarity and analyticity are included in a suitable way, the range of application of one-loop ChPT can be largely extended in agreement with the experiment.     

The sigma-model with Wilson lattice fermions

The σ-model with Wilson fermions is considered in one-loop lattice perturbation theory and in the hopping-parameter expansion at large bare couplings. Chiral-symmetry restoration in the large cut-off limit of perturbation theory is only possible if asymmetric counterterms are added to the lattice action. In the hopping-parameter expansion at infinitely large bare Yukawa coupling, dynamical parity doubling of the fermion occurs.     

Spontaneous Compactification of Extra Dimensions in Eleven-Dimensional Quantum Gravity

The reduction of the eleven-dimensional pure gravity theory to a field theory to a field theory in the four-dimensional Minkowski space-time by means of the spontaneous compactification of the extra dimensions is investigated. The contribution of the quantum fluctuations of the eleven-dimensional second rank symmetric tensor field to the curvatures of the space-time and the compactified space of the extra dimensions are calculated in the one-loop approximations. It is shown that there exist the values of the cosmological constant such that the resulting four-dimensional theory is self-consistent.     

The Born-Infeld action from conformal invariance of the open superstring

We show that the one-loop approximation to sigma-model perturbation theory for the open-superstring leads to the low-energy effective action of Born-Infeld for the gauge field coupled to the ends of the string. Thus the bosonic part of the low-energy open superstring effective action is just that of the open bosinic string. We also that these results are exact to all loop orders of sigma-model perturbation theory.     

Absence of the anomalous magnetic moment in a supersymmetric abelian gauge theory

We give a general argument for the vanishing of the anomalous magnetic moment in a supersymmetric Abelian gauge theory recently constructed by Wess and Zumino, provided in such a model the appropriate Ward identities are consistent with renormalized perturbation theory. Our conclusion is in fact confirmed by explicit one-loop calculation, thus providing a new example of cancellation of Feynman graphs in supersymmetric theories.     

The superconformal anomaly in the 1 + 1 dimensional Wess-Zumino model

The superconformal trace anomaly is worked out to one-loop order in perturbation theory for the 1+1 dimensional Wess-Zumino model.     

One-Loop Calculation in Time-Dependent Non-Equilibrium Thermo Field Dynamics

This paper is a review on the structure of thermo field dynamics (TFD) in which the basic concepts such as the thermal doublets, the quasi-particles and the self-consistent renormalization are presented in detail. A strong emphasis is put on the computational scheme. A detailed structure of this scheme is illustrated by the one-loop calculation in a non-equilibrium time-dependent process. A detailed account of the one-loop calculation has never been reported anywhere. The role of the self-consistent renormalization is explained. The equilibrium TFD is obtained as the long-time limit of non-equilibrium TFD.     

Generalized parton distributions for the nucleon in chiral perturbation theory

We complete the analysis of twist-two generalized parton distributions of the nucleon in one-loop order of heavy-baryon chiral perturbation theory. Extending our previous study of the chiral-even isosinglet sector, we give results for chiral-even isotriplet distributions and for the chiral-odd sector. We also calculate the one-loop corrections for the chiral-odd generalized parton distributions of the pion.     

The super-heat-kernel expansion and the renormalization of the pion–nucleon interaction

A recently proposed super-heat-kernel technique is applied to heavy baryon chiral perturbation theory. A previous result for the one-loop divergences of the pion–nucleon system to is confirmed, giving at the same time an impressive demonstration of the efficiency of the new method. The cumbersome and tedious calculations of the conventional approach are now reduced to a few simple algebraic manipulations. The present computational scheme is not restricted to chiral perturbation theory, but can easily be applied or extended to any (in general non-renormalizable) theory with boson–fermion interactions. Received: 21 July 1998 / Published online: 5 October 1998     

One-loop diagrams in lattice QCD with Wilson fermions

A large number of one-loop integrals emerging in a gauge perturbation theory on a lattice with Wilson fermions at r = 1 are evaluated with the use of the Burgio-Caracciolo-Pelissetto algorithm and the FORMpackage. In the bosonic case, an explicit analytical form of the recursion relations is presented.     

Mass generation by self-interaction in non-minkowskian spacetimes

The one-loop contribution to the self-energy of a massless scalar particle with a λφ⁴ self-interaction is investigated in non-minkowskian spacetimes. It is found that the particle may acquire a mass in order λ in perturbation theory.     

Newtonian Kinetic Theory and the Ergodic-Nonergodic Transition

In a recent work we have discussed how kinetic theory, the statistics of classical particles obeying Newtonian dynamics, can be formulated as a field theory. The field theory can be organized to produce a self-consistent perturbation theory expansion in an effective interaction potential. In the present work we use this development for investigating ergodic-nonergodic (ENE) transitions in dense fluids. The theory is developed in terms of a core problem spanned by the variables ρ, the number density, and B, a response density. We set up the perturbation theory expansion for studying the self-consistent model which gives rise to a ENE transition. Our main result is that the low-frequency dynamics near the ENE transition is the same for Smoluchowski and Newtonian dynamics. This is true despite the fact that term by term in a density expansion the results for the two dynamics are fundamentally different.     

Analysis of the pion-kaon sigma term and related topics

We calculate the one-loop contributions to the difference between the isoscalar on-shell pion-kaon scattering amplitude at the Cheng-Dashen point and the scalar form factor in the framework of three flavor chiral perturbation theory. These corrections turn out to be small. This is further sharpened by treating the kaons as heavy fields (two flavor chiral perturbation theory). We also analyze the two-loop corrections to the kaon scalar form factor based on a dispersive technique. We find that these corrections are smaller than in the comparable case of the scalar form factor of the pion. This is related to the weaker final state interactions in the pion-kaon channel. Received: 21 March 2002 / Published online: 5 July 2002     

More comments on asymptotic freedom

The effective Coulomb interaction between sources with SU(2) color charge is reinvestigated at the one-loop order of perturbation theory. This quantity is shown to be formally identical with the effective Coulomb interaction between electric charges in the QED of massless, charged, vector fields with anomalous magnetic moments. This correspondence allows the one-loop Yang-Mills charge renormalization factor to be deduced from a knowledge of the size and origins of this quantity in massless scalar and spinor QED. Careful consideration of the analogy with QED suggests a mechanism for asymptotic freedom in the Feynman gauge.     

Mass terms and mass renormalization for Susskind fermions

We discuss the symmetry properties of a geometrically motivated mass term giving different masses to the four flavours of Susskind fermions. Using this mass term we calculate the fermion self-energy in weak coupling perturbation theory at the one-loop level as well as the relation between the fermion masses on the lattice and in the continuum.     

Quark-mass dependence of the rho and sigma mesons from dispersion relations and chiral perturbation theory

We use the one-loop chiral perturbation theory pipi-scattering amplitude and dispersion theory in the form of the inverse amplitude method to study the quark-mass dependence of the two lightest resonances of the strong interactions, the f(0)(600) (sigma) and the rho meson. As the main results, we find that the rhopipi coupling constant is almost quark mass independent and that the rho mass shows a smooth quark-mass dependence while that of the sigma shows a strong nonanalyticity. These findings are important for studies of the meson spectrum on the lattice.     

On the strong-CP problem in models with several Higgs multiplets and supersymmetry

We point out that the strong-CP problem becomes even more pressing in the context of weak models where CP violation originates in the Higgs sector. θ renormalization is numerically too large at the one-loop level and even divergent at the two-loop level. When supersymmetry (SUSY) is introduced, many more possible sources for CP violation open up. θ renormalization could stay finite in perturbation theory, however, we find that the one-loop result turns out to be too large by orders of magnitude unless SUSY fields like gauginos and higgsinos are highly degenerate in mass or SUSY breaking proceeds in a very special way, or a Peccei-Quinn symmetry holds leading to superlight axions.     

Renormalization group equations for effective field theories

We derive the renormalization group equations for a generic non-renormalizable theory. We show that the equations allow one to derive the structure of the leading divergences at any loop order in terms of one-loop diagrams only. In chiral perturbation theory, e.g., this means that one can obtain the series of leading chiral logs by calculating only one-loop diagrams. We discuss also the renormalization group equations for the subleading divergences, and the crucial role of counterterms that vanish at the equations of motion. Finally, we show that the renormalization group equations obtained here apply equally well also to renormalizable theories.Received: 5 September 2003, Published online: 20 November 2003