One-loop QCD contribution to the potential of Q(Q)

Without the non-relativistic approximation in one-loop function, the dominating one-loop con-tribution to the quark-antiquark potential is studied numerically in terms of perturbative Quantum Chromo Dynamics (QCD). For Coulomb-like potential, the ratio of the one-loop correction to the tree diagram con-tribution is presented, whose absolute value is about 20%. Our result is consistent with the analysis that the one-loop contribution should be suppressed by a factor αs/π to the leading order contribution. This work can deepen the comprehension of αs in Cornel potential.     

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.     

Effective Potential for the Reaction-Diffusion-Decay System

In previous work we have developed a general method for casting stochastic partial differential equations (SPDEs) into a functional integral formalism, and have derived the one-loop effective potential for these systems. In this paper we apply the same formalism to a specific field theory of considerable interest, the reaction-diffusion-decay system. When this field theory is subject to white noise we can calculate the one-loop effective potential (for arbitrary polynomial reaction kinetics) and show that it is one-loop ultraviolet renormalizable in 1, 2, and 3 space dimensions. For specific choices of interaction terms the one-loop renormalizability can be extended to higher dimensions. We also show how to include the effects of fluctuations in the study of pattern formation away from equilibrium, and conclude that noise affects the stability of the system in a way which is calculable.     

Non-renormalization of Yukawa couplings on orbifolds

We discuss the non-renormalization of Yukawa couplings in the orbifold compactification of the heterotic string, at the one-loop level. Special attention is paid to on-shell infrared divergences. The non-vanishing part of the one-loop quark-quark-quark scattering amplitude is identified with the one-loop correction of the external legs.     

A closed expression for the UV-divergent parts of one-loop tensor integrals in dimensional regularization

Starting from the general definition of a one-loop tensor N-point function, we use its Feynman parametrization to calculate the ultraviolet (UV-)divergent part of an arbitrary tensor coefficient in the framework of dimensional regularization. In contrast to existing recursion schemes, we are able to present a general analytic result in closed form that enables direct determination of the UV-divergent part of any one-loop tensor N-point coefficient independent from UV-divergent parts of other one-loop tensor N-point coefficients. Simplified formulas and explicit expressions are presented for A-, B-, C-, D-, E-, and F-functions.     

Automorphic functions on super Riemann surfaces and fermionic string

Using the theory of super Riemann surfaces, the light-cone gauge formulation of the fermionic string by Mandelstam is extended to the one-loop level. The one-loop N-massless vector particle amplitude is explicitly calculated. The higher-loop extension is also discussed. We also demonstrate the equivalence between the light-cone picture and the Polyakov picture at the one-loop level.     

Superstring loop corrections to σ-model ß-functions

We present an algorithm for string one-loop corrections to σ-model ß-functions in closed superstring theories, by identifying the massless poles in string one-loop amplitudes with the ultraviolet divergences in the corresponding two-dimensional σ-model. The string one-loop corrected ß-functions for the type-II superstring are given.     

Effective potential for the massless KPZ equation

In previous work we have developed a general method for casting a classical field theory subject to Gaussian noise (that is, a stochastic partial differential equation (SPDE)) into a functional integral formalism that exhibits many of the properties more commonly associated with quantum field theories (QFTs). In particular, we demonstrated how to derive the one-loop effective potential. In this paper we apply the formalism to a specific field theory of considerable interest, the massless KPZ equation (massless noisy Burgers equation), and analyze its behavior in the ultraviolet (short-distance) regime. When this field theory is subject to white noise we can calculate the one-loop effective potential and show that it is one-loop ultraviolet renormalizable in 1, 2, and 3 space dimensions, and fails to be ultraviolet renormalizable in higher dimensions. We show that the one-loop effective potential for the massless KPZ equation is closely related to that for λφ⁴ QFT. In particular, we prove that the massless KPZ equation exhibits one-loop dynamical symmetry breaking (via an analog of the Coleman–Weinberg mechanism) in 1 and 2 space dimensions, and that this behavior does not persist in 3 space dimensions.     

Supersymmetry in Anti-de Sitter Space

We review the renormalization of the ground state solution of extended supergravity and super-symmetric Kaluza-Klein theories. The computation of an adiabatic expansion of the effective action to the one-loop order yields the result that a linear superfield insertion in the superpotential is needed, in order to renormalize the nonvanishing one-particle-irreducible one-point functions, whereas supersymmetry is preserved at each extremum of the effective potential. The calculation of the one-particle-irreducible two-and three-point functions shows that neither the mass nor the interaction lagrangians get renormalized to the one-loop order. We conclude that the one-loop effects proportional to the contraction parameter of the curved background space force a violation of the no-renormalization theorem.     

Holonomies of gauge fields in twistor space 4: Functional MHV rules and one-loop amplitudes

We consider generalization of the Cachazo-Svrcek-Witten (CSW) rules to one-loop amplitudes of N=4 super Yang-Mills theory in a recently developed holonomy formalism in twistor space. We first reconsider off-shell continuation of the Lorentz-invariant Nair measure for the incorporation of loop integrals. We then formulate an S-matrix functional for general amplitudes such that it implements the CSW rules at quantum level. For one-loop MHV amplitudes, the S-matrix functional correctly reproduces the analytic expressions obtained in the Brandhuber-Spence-Travaglini (BST) method. Motivated by this result, we propose a novel regularization scheme by use of an iterated-integral representation of polylogarithms and obtain a set of new analytic expressions for one-loop NMHV and N²MHV amplitudes in a conjectural form. We also briefly sketch how the extension to one-loop non-MHV amplitudes in general can be carried out.     

On the computation of one-loop amplitudes with external fermions in 4D heterotic superstrings

We present the technical tools needed to compute any one-loop amplitude involving external spacetime fermions in a four-dimensional heterotic string model à la Kawai-Lewellen-Tye. As an example, we compute the one-loop three-point amplitude with one “photon” and two external massive fermions (“electrons”). As a check of our computation, we verify that the one-loop contribution to the Anomalous Magnetic Moment vanishes if the model has spacetime supersymmetry, as required by the supersymmetric sum rules.     

Explicit counteraction algorithms in higher dimensions

Using the background field method we construct algorithms for the one-loop counterterms of a field theory in a space-time of dimension 2, 4, 6, 8 or 10. From the d = 6 algorithm we demonstrate the one-loop finiteness of N = 2 supersymmetric Yang-Mills theories and also N = 1 Yang-Mills theory. All other N = 1 Yang-Mills theories + N = 1 matter theories in d = 6 are shown to have a divergent one-loop S-matrix.

We also present partial results for two- and three-loop algorithms in d = 6 and d = 4 respectively.     

Restoration of Lorentz invariance in the lattice O(3) model with improved actions

Symanzik one-loop and block-spin renormalization group improved actions are studied by Monte Carlo simulation. Scaling sets in at small correlation length for the considered actions. The approach to the continuum relativistic energy-momentum dispersion is best for Symanzik one-loop improved action.     

Quantum gravity stability of isotropy in homogeneous cosmology

It has been shown that anisotropy of homogeneous spacetime described by the general Kasner metric can be damped by quantum fluctuations coming from perturbative quantum gravity in one-loop approximation. Also, a formal argument, not limited to one-loop approximation, is put forward in favor of stability of isotropy in the exactly isotropic case.     

Self-energy and vertex radiative corrections in LQG

We consider the elementary radiative-correction terms in loop quantum gravity. These are a two-vertex “elementary bubble” and a five-vertex “ball”; they correspond to the one-loop self-energy and the one-loop vertex correction of ordinary quantum field theory. We compute their naive degree of (infrared) divergence.     

Dispersion Relation of σ Meson and Pion at Finite Nuclear Density in Chiral σ Model

The propagators of pion and sigma meson at a finite nuclear density and zero temperature are studied in chiral σ model. Their dispersion relations are calculated numerically in one-loop approximation. In order to avoid the so-called tachyon pole appearing in the one-loop propagators of pion and sigma meson, we regard the mass of sigma meson m_σ as a free parameter and adjust it to fit the nuclear saturation properties. For m_σ equal to 3075 MeV, the tachyon pole does not appear at the normal nuclear density. Thus the dispersion relation can be calculated in chiral σ model in one-loop level for the first time.     

A convergent series for the QED effective action

The one-loop effective action of QED obtained by Heisenberg and Euler and by Schwinger has been expressed by an asymptotic perturbative series which is divergent. In this Letter we present a nonperturbative but convergent series of the effective action. With the convergent series we establish the existence of the manifest electric-magnetic duality in the one-loop effective action of QED.     

Octet and decuplet magnetic and axial couplings from one-loop self-consistent perturbation theory

Octet and decuplet wave functions, obtained in a recent precision fit to the spectrum using one-loop self-consistent perturbation theory of mesons and gluons interacting with bagged relativistic quarks, are used to evaluate axial couplings and magnetic moments. Results are fully competitive with other models and provide further support to one-loop self-consistent perturbation theory as a useful model of baryon structure.     

Quantum gravity in 2 + ε dimensions

We examine quantum gravity in 2 + ε dimensions, where the theory is formally renormalizable. Paying due attention to surface integrals (which prove crucial), we calculate the one-loop counterterms and establish a criterion for asymptotic freedom. We find, incidentally, that the β function vanishes to one-loop order for all models which are supersymmetric in two dimensions.     

Unnaturalness in the higgs-Fermion sector

The Higgs-fermion-antifermion coupling is examined at one-loop level. It is shown that for a process like e⁺e⁻ → Hγ the one-loop radiative corrections can be several orders of magnitude larger than the Born approximation provided that the photon is sufficiently hard.