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Matthias Steinhauser

Publications and source records attributed to Matthias Steinhauser.

At least 109 records · Page 6Linked to original sources
arXiv2016

Electron contribution to the muon anomalous magnetic moment at four loops

We present results for the QED contributions to the anomalous magnetic moment of the muon containing closed electron loops. The main focus is on perturbative corrections at four-loop order where the external photon couples to the external muon. Furthermore, all four-loop contributions involving simultaneously a closed electron and tau loop are computed. In combination with our recent results on the light-by-light-type corrections (see Ref. \cite{Kurz:2015bia}) the complete four-loop electron-loop contribution to the anomalous magnetic moment of the muon has been obtained with an independent calculation. Our calculation is based on an asymptotic expansion in the ratio of the electron and the muon mass and shows the importance of higher order terms in this ratio. We perform a detailed comparison with results available in the literature and find good numerical agreement. As a by-product we present analytic results for the on-shell muon mass and wave function renormalization constants at three-loop order including massive closed electron and tau loops, which we also calculated using the method of asymptotic expansion.

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arXiv2016

Four-loop relation between the $\bar{\rm MS}$ and on-shell quark mass

In this contribution we discuss the four-loop relation between the on-shell and $\bar{\rm MS}$ definition of heavy quark masses which is applied to the top, bottom and charm case. We also present relations between the $\bar{\rm MS}$ quark mass and various threshold mass definitions and discuss the uncertainty at next-to-next-to-next-to-leading order.

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arXiv2015

$Gamma(H\to b\bar{b})$ to order $αα_s$

We compute the decay rate of the Standard Model Higgs boson to bottom quarks to order $αα_s$. We apply the optical theorem and calculate the imaginary part of three-loop corrections to the Higgs boson propagator using asymptotic expansions in appropriately chosen mass ratios. The corrections of order $αα_s$ are of the same order of magnitude as the ${\cal O}(α_s^3)$ QCD corrections but have the opposite sign.

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arXiv2015

Exact N$^3$LO results for $q q^\prime\to H +X$

We compute the contribution to the total cross section for the inclusive production of a Standard Model Higgs boson induced by two quarks with different flavour in the initial state. Our calculation is exact in the Higgs boson mass and the partonic center-of-mass energy. We describe the reduction to master integrals, the construction of a canonical basis, and the solution of the corresponding differential equations. Our analytic result contains both Harmonic Polylogarithms and iterated integrals with additional letters in the alphabet.

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arXiv2015

Higgs boson pair production: top quark mass effects at NLO and NNLO

We compute next-to-next-to-leading order QCD corrections to the gluon-induced production cross section of Higgs boson pairs in the large top quark mass limit using the soft-virtual approximation. In the limit of infinitely-heavy top quark we confirm the results in the literature. We add two more expansion terms in the inverse top quark mass to the $M_t\to\infty$ result. Since the $1/M_t$ expansion converges poorly, we try to improve on it by factorizing the exact leading order cross section. We discuss two ways of doing that and conclude that the finite top quark mass effects shift the cross section at most by about 10\% at next-to-leading order and by about 5\% at next-to-next-to-leading order.

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arXiv2015

Light-by-light-type corrections to the muon anomalous magnetic moment at four-loop order

The numerically dominant QED contributions to the anomalous magnetic moment of the muon stem from Feynman diagrams with internal electron loops. We consider such corrections and present a calculation of the four-loop light-by-light-type corrections where the external photon couples to a closed electron or muon loop. We perform an asymptotic expansion in the ratio of electron and muon mass and reduce the resulting integrals to master integrals which we evaluate using analytical and numerical methods. We confirm the results present in the literature which are based on different computational methods.

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arXiv2015

Decoupling of heavy quarks at four loops and effective Higgs-fermion coupling

We compute the decoupling constant $ζ_m$ relating light quark masses of effective $n_l$-flavour QCD to $(n_l+1)$-flavour QCD to four-loop order. Immediate applications are the evaluation of the $\overline{\rm MS}$ charm quark mass with five active flavours and the bottom quark mass at the scale of the top quark or even at GUT scales. With the help of a low-energy theorem $ζ_m$ can be used to obtain the effective coupling of a Higgs boson to light quarks with five-loop accuracy. We briefly discuss the influence on $Γ(H\to b\bar{b})$.

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arXiv2015

Non-relativistic high-energy physics: top production and dark matter annihilation

Non-relativistic physics is often associated with atomic physics and low-energy phenomena of the strong interactions between nuclei and quarks. In this review we cover three topics in contemporary high-energy physics at or close to the TeV scale, where non-relativistic dynamics plays an important if not defining role. We first discuss in detail the third-order corrections to top-quark pair production in electron-positron collisions in the threshold region, which plays a major role at a future high-energy e+ e- collider. Threshold effects are also relevant in the production of heavy particles in hadronic collisions, where in addition to the Coulomb force soft gluon radiation contributes to enhanced quantum corrections. We review the joint resummation of non-relativistic and soft gluon effects for pair production of top quarks and supersymmetric particles to next-to-next-to-leading logarithmic accuracy. The third topic deals with pair annihilation of dark matter particles within the framework of the Minimal Supersymmetric Standard Model. Here the electroweak Yukawa force generated by the exchange of gauge and Higgs bosons can cause large "Sommerfeld" enhancements of the annihilation cross section in some parameter regions.

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arXiv2015

Quark mass relations to four-loop order

We present results for the relation between a heavy quark mass defined in the on-shell and $\bar{\rm MS}$ scheme to four-loop order. The method to compute the four-loop on-shell integral is briefly described and the new results are used to establish relations between various short-distance masses and the $\bar{\rm MS}$ quark mass to next-to-next-to-next-to-leading order accuracy. These relations play an important role in the accurate determination of the $\bar{\rm MS}$ heavy quark masses.

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arXiv2015

Massive Tadpoles: Techniques and Applications

A brief discussion of massive tadpole diagrams and their phenomenological consequences is presented. This includes predictions of the $ρ$ parameter and, as a consequence, the mass of the $W$ boson, implications on the charm and bottom quark masses from the moments, i.e. the derivatives of the current correlators, and the Higgs boson decay rate. A fairly consistent picture emerges, with $m_c(3 {GeV})=0.986\pm0.013$ GeV and $m_b(m_b)=3.610\pm0.016$ GeV. Furthermore, fairly stringent predictions for the Higgs decay rate into photons and gluons are obtained, which will be interesting in increasingly precise experiments.

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arXiv2015

The (Q_7,Q_{1,2}) contribution to B -> X_s gamma at O(alpha_s^2)

Interference between the photonic dipole operator Q_7 and the current-current operators Q_{1,2} gives one of the most important QCD corrections to the B -> X_s gamma decay rate. So far, the O(alpha_s^2) part of this correction has been known in the heavy charm quark limit only (m_c >> m_b/2). Here, we evaluate this part at m_c=0, and use both limits in an updated phenomenological study. Our prediction for the CP- and isospin-averaged branching ratio in the Standard Model reads B^SM_{s gamma} = (3.36 +_ 0.23) * 10^-4 for E_gamma > 1.6 GeV.

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arXiv2015

Parallel versions of FORM and more

We review the status of the parallel versions of the computer algebra system FORM. In particular, we provide a brief overview about the historical developments, discuss the strengths of ParFORM and TFORM, and mention typical applications. Furthermore, we briefly discuss the programs FIRE and FIESTA, which have also been developed with the Collaborative Research Center/TR~9 (CRC/TR~9).

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arXiv2014

Virtual corrections to Higgs boson pair production in the large top quark mass limit

We calculate the three-loop matching coefficient $C_{HH}$, required for a consistent description of Higgs boson pair production in gluon fusion through next-to-next-to-leading order QCD in the heavy top quark approximation. We also compute the $gg \to HH$ amplitude in $m_t \to \infty$ approximation in the full theory and show its consistency with an earlier computation in heavy-top effective theory.

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arXiv2014

Higher-order hadronic and heavy-lepton contributions to the anomalous magnetic moment

We report about recent results obtained for the muon anomalous magnetic moment. Three-loop kernel functions have been computed to obtain the next-to-next-to-leading-order hadronic vacuum polarization contributions. The numerical result, $a_μ^{\rm{had,NNLO}}=1.24\pm 0.01 \times 10^{-10}$, is of the same order of magnitude as the current uncertainty from the hadronic contributions. For heavy-lepton corrections, analytical results are obtained at four-loop order and compared with the known results.

hep-ph↗
arXiv2014

$B_s\to μ^+μ^-$ and $\bar{B} \to X_s γ$ to NNLO

In this contribution, the recent calculation of next-to-next-to-leading order QCD and next-to-leading order electroweak corrections to the decay $B_s\to μ^+μ^-$ is reviewed, and a detailed discussion of the uncertainty of the theory prediction is provided. Furthermore, we discuss the status of the next-to-next-to-leading order QCD corrections to $\bar{B} \to X_s γ$.

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