One-loop Form Factors Research Articles

One-loop expressions for h → l l̅γ in Higgs extensions of the Standard Model

Abstract A systematic study of one-loop contributions to the decay channels $h\rightarrow l\bar{l}\gamma$ with l = νe, μ, τ, e, μ, performed in Higgs extended versions of the Standard Model (SM), is presented in the ’t Hooft–Veltman gauge. Analytic formulas for one-loop form factors are expressed in terms of the logarithm and di-logarithmic functions. As a result, these form factors can be reduced to those relating to the loop-induced decay processes h → γγ, Zγ, confirming not only previous results using different approaches but also close relations between the three kinds of loop-induced Higgs decay rates. For phenomenological study, we focus on the two observables, namely the enhancement factors defined as ratios of the decay rates calculated between the Higgs extended versions and the SM, and the forward-backward asymmetries of fermions, which can be used to search for Higgs extensions of the SM. We show that direct effects of mixing between neutral Higgs bosons and indirect contributions of charged Higgs boson exchanges can be probed at future colliders.

One-loop formulas for H → Zν l ν l for l = e, µ, τ in 't Hooft-Veltman gauge* *This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under the grant number (103.01-2019.346)

In this paper, we present analytical results for one-loop contributions to the decay processes (for ). The calculations are performed within the Standard Model framework in the 't Hooft-Veltman gauge. One-loop form factors are then written in terms of scalar one-loop functions in the standard notations of . As a result, one-loop decay rates for the decay channels can be evaluated numerically by using the package. Furthermore, we analyze the signals of via the production processes , including the initial beam polarizations at future lepton colliders. The Standard Model backgrounds, such as the processes , are also examined in this study. Numerical results indicate that one-loop corrections make contributions of approximately 10% to the decay rates. These are sizeable contributions and should be taken into account at future colliders. We show that the signals are clearly visible at the center-of-mass energy GeV and are difficult to probe in higher-energy regions owing to the dominant backgrounds.

Gluonic evanescent operators: classification and one-loop renormalization

Evanescent operators are a special class of operators that vanish classically in four-dimensional spacetime, while in general dimensions they are non-zero and are expected to have non-trivial physical effects at the quantum loop level in dimensional regularization. In this paper we initiate the study of evanescent operators in pure Yang-Mills theory. We develop a systematic method for classifying and constructing the d-dimensional Lorentz invariant evanescent operators, which start to appear at mass dimension ten. We also compute one-loop form factors for the dimension-ten operators via the d-dimensional unitarity method and obtain their one-loop anomalous dimensions. These operators are necessary ingredients in the study of high dimensional operators in effective field theories involving a Yang-Mills sector.

One-loop Form Factors for \(H\rightarrow \gamma^*\gamma^*\) in \(R_{\xi}\) Gauge

In this paper, we present general one-loop form factors for \(H\rightarrow \gamma^* \gamma^*\) in \(R_{\xi}\) gauge, considering all cases of two on-shell, one on-shell and two off-shell for final photons. The calculations are performed in standard model and in arbitrary beyond the standard models which charged scalar particles may be exchanged in one-loop diagrams. Analytic results for the form factors are shown in general forms which are expressed in terms of the Passarino-Veltman functions. We also confirm the results in previous computations which are available for the case of two on-shell photons. The \(\xi\)-independent of the result is also discussed. We find that numerical results are good stability with varying \(\xi=0,1\) and \(\xi\rightarrow \infty\).

Hypergeometric presentation for one-loop contributing to H → Z γ

Abstract In this paper, new analytic formulas for one-loop contributing to Higgs decay channel $H \rightarrow Z\gamma$ are presented in terms of hypergeometric functions. The calculations are performed by following the technique for tensor one-loop reduction developed in [A. I. Davydychev, Phys. Lett. B 263 (1991) 107]. For the first time, one-loop form factors for the decay process are shown which are valid at arbitrary space–time dimension $d$.

Dual conformal invariance for form factors

Form factors of the stress-tensor multiplet operator in mathcal{N}=4 supersymmetric Yang-Mills reveal surprisingly simple structures similar to those appearing in scattering amplitudes. In this paper we show that, as for the case of amplitudes, they also enjoy dual conformal symmetry. We compute the dual conformal anomaly at one loop for an arbitrary number of particles and generic helicities, which matches the expression of the dual conformal anomaly of amplitudes, and perform explicit checks for MHV and NMHV one-loop form factors. In the NMHV case the realisation of dual conformal symmetry requires a delicate cancellation of offending terms arising from three-mass triangles, which we explicitly check in the case of the four-point NMHV form factor.

Form factors in $ \mathcal{N} = 4 $ super Yang-Mills and periodic Wilson loops

We calculate form factors of half-BPS operators in \( \mathcal{N} = 4 \) super Yang-Mills theory at tree level and one loop using novel applications of recursion relations and unitarity. In particular, we determine the expression of the one-loop form factors with two scalars and an arbitrary number of positive-helicity gluons. These quantities resemble closely the MHV scattering amplitudes, including holomorphicity of the tree-level form factor, and the expansion in terms of two-mass easy box functions of the one-loop result. Next, we compare our result for these form factors to the calculation of a particular periodic Wilson loop at one loop, finding agreement. This suggests a novel duality relating form factors to periodic Wilson loops.

Algebraic reduction of one-loop Feynman diagrams to scalar integrals. II

An extended scheme for the reduction of one-loop form factors occuring in a general gauged quantum field theory to scalar integrals is discussed and an alternative method that may be applied in the case when the scheme fails is indicated. The extensions are implemented in a new version of the package LERG-I, written in REDUCE.