Leading QCD Corrections Research Articles

More accurate σGG→h,Γh→GGAAΨ¯Ψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sigma \\left(\\mathcal{GG}\ o h\\right),\\Gamma \\left(h\ o \\mathcal{GG},\\mathcal{AA},\\overline{\\Psi}\\Psi \\right) $$\\end{document} and Higgs width results via the geoSMEFT

We develop Standard Model Effective Field Theory (SMEFT) predictions of σ(GG\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{GG} $$\\end{document} → h), Γ(h → GG\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{GG} $$\\end{document}), Γ(h → AA\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{AA} $$\\end{document}) to incorporate full two loop Standard Model results at the amplitude level, in conjunction with dimension eight SMEFT corrections. We simultaneously report consistent Γ(h → Ψ¯Ψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\overline{\\Psi}\\Psi $$\\end{document}) results including leading QCD corrections and dimension eight SMEFT corrections. This extends the predictions of the former processes Γ, σ to a full set of corrections at Ov¯T2/Λ216π22\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O}\\left({\\overline{v}}_T^2/{\\varLambda}^2{\\left(16{\\pi}^2\\right)}^2\\right) $$\\end{document} and Ov¯T4/Λ4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O}\\left({\\overline{v}}_T^4/{\\Lambda}^4\\right) $$\\end{document}, where v¯T\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\overline{v}}_T $$\\end{document} is the electroweak scale vacuum expectation value and Λ is the cut off scale of the SMEFT. Throughout, cross consistency between the operator and loop expansions is maintained by the use of the geometric SMEFT formalism. For Γ(h → Ψ¯Ψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\overline{\\Psi}\\Psi $$\\end{document}), we include results at Ov¯T2/Λ216π2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O}\\left({\\overline{v}}_T^2/{\\Lambda}^2\\left(16{\\pi}^2\\right)\\right) $$\\end{document} in the limit where subleading mΨ → 0 corrections are neglected. We clarify how gauge invariant SMEFT renormalization counterterms combine with the Standard Model counter terms in higher order SMEFT calculations when the Background Field Method is used. We also update the prediction of the total Higgs width in the SMEFT to consistently include some of these higher order perturbative effects.

Two-loop master integrals for the leading QCD corrections to the Higgs coupling to a W pair and to the triple gauge couplings ZW W and \u03b3\u2217W W

We compute the two-loop master integrals required for the leading QCD corrections to the interaction vertex of a massive neutral boson X0, e.g. H, Z or γ∗, with a pair of W bosons, mediated by a SU(2)L quark doublet composed of one massive and one massless flavor. All the external legs are allowed to have arbitrary invariant masses. The Magnus exponential is employed to identify a set of master integrals that, around d = 4 space-time dimensions, obey a canonical system of differential equations. The canonical master integrals are given as a Taylor series in ϵ = (4 − d)/2, up to order four, with coefficients written as combination of Goncharov polylogarithms, respectively up to weight four. In the context of the Standard Model, our results are relevant for the mixed EW-QCD corrections to the Higgs decay to a W pair, as well as to the production channels obtained by crossing, and to the triple gauge boson vertices ZWW and γ∗WW.

Leading QCD corrections for indirect dark matter searches: A fresh look

The annihilation of non-relativistic dark matter particles at tree level can be strongly enhanced by the radiation of an additional gauge boson. This is particularly true for the helicity-suppressed annihilation of Majorana particles, like neutralinos, into fermion pairs. Surprisingly, and despite the potentially large effect due to the strong coupling, this has so far been studied in much less detail for the internal bremsstrahlung of gluons than for photons or electroweak gauge bosons. Here, we aim at bridging that gap by presenting a general analysis of neutralino annihilation into quark anti-quark pairs and a gluon, allowing e.g. for arbitrary neutralino compositions and keeping the leading quark mass dependence at all stages in the calculation. We find in some cases largely enhanced annihilation rates, especially for scenarios with squarks being close to degenerate in mass with the lightest neutralino, but also notable distortions in the associated antiproton and gamma-ray spectra. Both effects significantly impact limits from indirect searches for dark matter and are thus important to be taken into account in, e.g., global scans. For extensive scans, on the other hand, full calculations of QCD corrections are numerically typically too expensive to perform for each point in parameter space. We present here for the first time an efficient, numerically fast implementation of QCD corrections, extendable in a straight-forward way to non-supersymmetric models, which avoids computationally demanding full one-loop calculations or event generator runs and yet fully captures the leading effects relevant for indirect dark matter searches. In this context, we also present updated constraints on dark matter annihilation from cosmic-ray antiproton data. Finally, we comment on the impact of our results on relic density calculations.

Rare exclusive decays of theZboson revisited

The realization that first- and second-generation Yukawa couplings can be probed by decays of the Higgs boson to a meson in association with a photon has renewed interest in such rare exclusive decays. We present here a detailed study of the rare $Z$-boson processes $Z \to J/\psi+\gamma$, $Z \to \Upsilon+\gamma$, and $Z \to \phi+\gamma$ that can serve as benchmarks for the analogous Higgs-boson decays. We include both direct-production and fragmentation contributions to these decays, and consider the leading QCD corrections and the relativistic corrections to the $J/\psi$ and $\Upsilon$ processes. We present numerical predictions for the branching ratios that include a careful accounting of the theoretical uncertainties.

Radiative corrections to bino-stop co-annihilation

In co-annihilation scenarios, the weakly interacting dark matter particle (WIMP) is close in mass to another particle that can decay into the WIMP. As a result, the other particle does not freeze out before the WIMP in the early universe, and both contribute to the effective dark matter annihilation cross-section. Since the heavier particle does not need to be weakly interacting, the co-annihilation processes are in general subject to sizeable radiative corrections. Here this is analyzed for the example of neutralino–stop co-annihilation in supersymmetry. The leading QCD corrections are calculated and it is found that they have a large effect on the effective annihilation cross-section, reaching more than 50% in some regions of parameter space.

CPviolation in the inclusiveb→sgdecay in the framework of multi-Higgs-doublet models

We study the decay width and $\mathrm{CP}$ asymmetry of the inclusive process $\stackrel{\ensuremath{\rightarrow}}{b}\mathrm{sg}$ $(g$ denotes gluon) in the multi-Higgs-doublet models with complex Yukawa couplings, including next to leading QCD corrections. We analyze the dependences of the decay width and $\mathrm{CP}$ asymmetry on the scale \ensuremath{\mu} and $\mathrm{CP}$-violating parameter $\ensuremath{\theta}.$ We observe that there exists an enhancement in the decay width and $\mathrm{CP}$ asymmetry is at the order of ${10}^{\ensuremath{-}2}.$

QCD factorization for exclusive non-leptonic B-meson decays: general arguments and the case of heavy–light final states

We provide a rigorous basis for factorization for a large class of non-leptonic two-body $B$-meson decays in the heavy-quark limit. The factorization formula incorporates elements of the naive factorization approach and the hard-scattering approach, but allows us to compute systematically radiative (``non-factorizable'') corrections to naive factorization for decays such as $B\to D\pi$ and $B\to \pi \pi$. We discuss the factorization formula for a general final state from a general point of view. We then consider factorization for decays into heavy-light final states (such as $B\to D\pi$) in more detail, including a proof of the factorization formula at two-loop order. Explicit results for the leading QCD corrections to factorization are presented and compared to existing measurements of branching fractions and final-state interaction phases.

Formula omitted] decay in the two Higgs doublet model with flavor changing neutral currents

We study the decay width, forward–backward asymmetry and the longitudinal lepton polarization for the exclusive decay B→K ∗l +l − in the two Higgs doublet model with three level flavor changing neutral currents (model III) and analyse the dependencies of these quantities on the the selected parameters, ξ U, D , of model III including the next to leading QCD corrections. It is found that to look for charged Higgs effects, the measurements of the branching ratio, forward–backward asymmetry and the longitudinal lepton polarization for the decay B→K ∗l +l − are promising.

QCD corrections to flavor-changing neutral currents in the supersymmetric standard model

We compute the leading QCD corrections to K-Kbar mixing in the supersymmetric standard model with general soft supersymmetry-breaking parameters. We construct the \Delta S=2 effective Lagrangian for three hierarchies of supersymmetric particle masses, namely, when the gluino mass is comparable to, much greater than, or much less than the masses of the first two generation squarks. We find that the QCD corrections tighten the limits on squark mass splittings by more than a factor of two.

On the QCD corrections to b → sγ in supersymmetric models

We reinvestigate the leading QCD corrections to the radiative decay b → sγ for supersymmetric extensions of the Standard Model. Although the major contributions to the corrections originate from the running of the effective Lagrangian from the W scale down to the b scale, additional corrections are expected from large mass between the particles running in the loops, as well as from integrating out heavy particles at scales different from the W mass. The calculation is performed in the framework of effective field theories.

Electroweak supersymmetric quantum corrections to the top quark width

Within the framework of the MSSM, we compute the electroweak one-loop supersymmetric quantum corrections to the width Γ(t → W+b) of the canonical main decay of the top quark. The results are presented in two on-shell renormalization schemes parametrized either by α or GF. While in the Standard Model, and in the Higgs sector of the MSSM, the electroweak radiative corrections in the GF-scheme are rather insensitive to the top quark mass and are of order of 1% at most, the rest (“genuine” part) of the supersymmetric quantum effects in the MSSM amount to a non-negligible correction that could be about one order of magnitude larger, depending on the top quark mass and of the region of the supersymmetric parameter space. These new electroweak effects, therefore, could be of the same order (and go in the same direction) as the conventional leading QCD corrections.

QCD nonleading corrections to weak decays in the dimensional scheme.

We compute the next to leading QCD corrections to weak four fermion interactions introducing a scheme that does not require an explicit definition of $\gamma_5$ in $d$ dimensions. This scheme reduces greatly the difficulties in calculating the two loop anomalous dimensions; we recover the results obtained in the previous literature.

A study of the amplitude zero in W − → jet+jet+γ using the Lund model

The decay W − → jet+jet+γ is studied using the Lund string fragmentation scheme and including O(α s) leading QCD corrections. Even with fragmentation and full parton showers included, the radiation amplitude zero characteristic of the fundamental Yang-Mills WWγ coupling leaves a clear signal in the W center-of-mass frame.

Leading QCD corrections to W → jet + jet + γ

The O(α s) QCD corrections for the decay W − → jet + jet + γ are examined. The jets are defined by (δ, λ) cutoffs, and the leading corrections for δ, λ → 0 evaluated analytically. We find these corrections to be dominated by factorized leading logarithms, leaving a clear signal of the radiation zero present in lowest order.

Penguin effects inΔ S≠0B decays in a five flavourSU(2)×U(1) model

The leading QCD corrections to the tree level interaction density for the ΔS≠0, ΔB≠0 couplings in anSU(2)×U(1) five flavour model due to Gorn and Paschos are evaluated.