arXiv subjects

Thomas Rauh

Publications and source records attributed to Thomas Rauh.

18 recordsLinked to original sources

arXiv2022

Two-loop anomalous dimension for the resummation of non-global observables

The soft radiation emitted in jet cross sections can resolve the directions and colors of individual hard partons, leading to a complicated pattern of logarithmically enhanced terms in the perturbative series. Starting from a factorization theorem and solving the renormalization group equations for its ingredients, these large logarithms can be resummed. In this paper, we extract the two-loop anomalous dimension governing the resummation of subleading logarithms in jet cross sections and other non-global observables. This anomalous dimension can be obtained by considering soft limits of hard amplitudes, but the presence of collinear singularities in intermediate expressions makes its extraction delicate. As a consistency check, we use our results to predict the known subleading non-global logarithms in the two-jet cross section.

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arXiv2021

$SU(3)$ breaking effects in $B$ and $D$ meson lifetimes

In the heavy quark expansion (HQE) of the total decay rates of $B_s$ and $D_s^+$ mesons non-perturbative matrix elements of four quark operators are arising as phase space enhanced contributions. We present the first determination of $m_s$ effects to the dimension six matrix elements of these four quark operators via a heavy quark effective theory (HQET) sum rule analysis. In addition we calculate for the first time eye contractions of the four quark operators as well as matrix elements of penguin operators. For the perturbative part we solve the 3-loop contribution to the sum rule and we evaluate condensate contributions. In this study we work in the strict HQET limit and our results can also be used to estimate the size of the matrix element of the Darwin operator via equations of motion.

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arXiv2021

Revisiting Inclusive Decay Widths of Charmed Mesons

Determining for the first time the Darwin operator contribution for the non-leptonic charm-quark decays and using new non-perturbative results for the matrix elements of $ΔC=0$ four-quark operators, including eye-contractions, we present a comprehensive study of the lifetimes of charmed mesons and inclusive semileptonic decay rates as well as the ratios, within the framework of the Heavy Quark Expansion (HQE). We find good agreement with experiment for the ratio $τ(D^+)/τ(D^0)$, for the total $D_s^+$-meson decay rate, for the semileptonic rates of all three mesons $D^0$, $D^+$ and $D_s^+$, and for the semileptonic ratio $Γ_{sl}^{D^+}/Γ_{sl}^{D^0}$. The total decay rates of the $D^0$ and $D^+$ mesons are underestimated in our HQE approach and we suspect that this is due to missing higher-order QCD corrections to the free charm quark decay and the Pauli interference contribution. For the $SU(3)_F$ breaking ratios $τ(D_s^+) / τ(D^0) $ and $Γ_{sl}^{D_s^+}/Γ_{sl}^{D^0} $ our predictions lie closer to one than experiment. This might originate from the poor knowledge of the non-perturbative parameters $μ_G^2$, $μ_π^2$ and $ρ_D^3$ in the $D^0$ and $D_s^+$ systems. These parameters could be determined by experimental studies of the moments of inclusive semileptonic $D$ meson decays.

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arXiv2020

Top quark mass dependence of the Higgs-gluon form factor at three loops

We compute three-loop corrections to the Higgs-gluon form factor, incorporating the top quark mass dependence. Our method is based on the combination of expansions around the top threshold and for large top quark mass, using conformal mapping and Padé approximation to describe the form factor over the full kinematic range.

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arXiv2020

Padé approach to top-quark mass effects in gluon fusion amplitudes

Gluon fusion processes like single and double Higgs production exhibit slow convergence and pose severe computational challenges. We show how the top-quark mass dependence of the virtual amplitudes can be reconstructed with a conformal mapping and Padé approximants based on the expansion in the inverse top-quark mass and the non-analytic terms in the expansion around the top threshold. The method is then applied at two- and three-loop order.

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arXiv2020

$|V_{cb}|$ and $γ$ from $B$-mixing -- Addendum to "$B_s$ mixing observables and $|V_{td}/V_{ts}|$ from sum rules"

In this addendum to "$B_s$ mixing observables and $|V_{td}/V_{ts}|$ from sum rules" \cite{King:2019lal} we study the impact of the recent improvements in the theoretical precision of $B$ meson mixing onto CKM unitarity fits. Our key results are the most precise determination of the angle $γ= \left(63.4\pm0.9\right)^\circ$ in the unitarity triangle and a new value for the CKM element $|V_{cb}|=(41.6\pm0.7)\cdot10^{-3}$.

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arXiv2019

$ΔM_s$ theory precision confronts flavour anomalies

Based on recent HQET sum rule and lattice calculations we present updated Standard Model predictions for the mass differences of neutral $B$ mesons: $ΔM_s^{\rm SM} = \left(18.4^{+0.7}_{-1.2} \right) \mbox{ps}^{-1}$ and $ΔM_d^{\rm SM} = \left(0.533^{+0.022}_{-0.036} \right) \mbox{ps}^{-1}$ and study their impact on new physics models that address the present hints of anomalous data in $b \to s \ell \ell$ transitions. We also examine future prospects of further reducing the theory uncertainties and discuss the implications of a 2025 scenario with $ΔM_s^\text{SM 2025} = \left(18.4 \pm 0.5\right) \mbox{ps}^{-1}$. In particular, the latter yields upper bounds $M_{Z'}\lesssim 9~\text{TeV}$ and $M_{S_3}\lesssim 30~\text{TeV}$ for the minimal $Z'$ and $S_3$ lepto-quark explanations of the $b \to s \ell \ell$ anomalies, respectively.

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arXiv2019

Top quark mass effects in $gg\to ZZ$ at two loops and off-shell Higgs interference

We consider top-quark mass effects in the Higgs-interference contribution to $Z$-boson pair production in gluon fusion. While this production mechanism is formally of next-to-next-to leading order, its contribution is numerically important above the top threshold $M_{ZZ}^2=4m_t^2$. This region is essential to constrain the width of the Higgs boson and good control over the top-quark mass dependence is crucial. We determine the form factors that are relevant for the interference contribution at two-loop order using a method based on a conformal mapping and Padé approximants constructed from the expansions of the amplitude for large top mass and around the top threshold.

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arXiv2019

Bs mixing observables and Vtd/Vts from sum rules

We consider the effects of a non-vanishing strange-quark mass in the determination of the full basis of dimension six matrix elements for $B_{s}$ mixing, in particular we get for the ratio of the $V-A$ Bag parameter in the $B_s$ and $B_d$ system: $\overline{B}^s_{Q_1} / \overline{B}^d_{Q_1} = 0.987^{+0.007}_{-0.009}$. Combining these results with the most recent lattice values for the ratio of decay constants $f_{B_s} / f_{B_d}$ we obtain the most precise determination of the ratio $ξ= f_{B_s} \sqrt{\overline{B}^s_{Q_1}}/ f_{B_d} \sqrt{\overline{B}^d_{Q_1}} = 1.2014^{+0.0065}_{-0.0072}$ in agreement with recent lattice determinations. We find $ΔM_s=(18.5_{-1.5}^{+1.2})\text{ps}^{-1}$ and $ΔM_d=(0.547_{-0.046}^{+0.035})\text{ps}^{-1}$ to be consistent with experiments at below one sigma. Assuming the validity of the SM, our calculation can be used to directly determine the ratio of CKM elements $|V_{td} / V_{ts} | = 0.2045^{+0.0012}_{-0.0013}$, which is compatible with the results from the CKM fitting groups, but again more precise.

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arXiv2018

Reconstruction of top-quark mass effects in Higgs pair production and other gluon-fusion processes

We propose a novel method for the treatment of top-quark mass effects in the production of $H^{(*)}$, $HH$, $HZ$ and $ZZ$ final states in gluon fusion. We show that it is possible to reconstruct the full top-quark mass dependence of the virtual amplitudes from the corresponding large-$m_t$ expansion and the non-analytic part of the amplitude near the top-quark threshold $\hat{s}=4m_t^2$ with a Padé ansatz. The reliability of our method is clearly demonstrated by a comparison with the recent NLO result for Higgs pair production with full top-quark mass dependence.

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arXiv2018

Non-resonant and electroweak NNLO correction to the $e^+ e^-$ top anti-top threshold

We determine the NNLO electroweak correction to the $e^+ e^-\to b\bar{b}W^+W^- X$ production cross section near the top-pair production threshold. The calculation includes non-resonant production of the final state as well as electroweak effects in resonant top anti-top pair production with non-relativistic resummation, and elevates the theoretical prediction to NNNLO QCD plus NNLO electroweak accuracy. We then study the impact of the new contributions on the top-pair threshold scan at a future lepton collider.

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arXiv2017

Electroweak and non-resonant corrections to top-pair production near threshold at NNLO

The top-quark mass can be determined with very high precision from a scan of the total $e^+e^-\to b\bar{b}W^+W^-X$ cross section near the top-pair production threshold. We present the full calculation of electroweak and non-resonant corrections to this process at NNLO. We discuss the size of the new contributions and estimate the theory uncertainty on the top-quark mass in the PS mass scheme.

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arXiv2016

NNNLO determination of the bottom-quark mass from non-relativistic sum rules

The mass of the bottom quark can be determined with high precision from moments of the pair-production cross section sigma(e+ e- -> b bbar) near threshold. We present the first complete NNNLO determination from non-relativistic sum rules, obtaining a bottom-quark mass of mb^PS(2 GeV) = (4.532 +0.013 -0.039) GeV in the potential-subtracted scheme. For the mass in the MSbar scheme we find mb^MS(mb^MS) = (4.203 +0.016 -0.034) GeV using the recently computed four-loop correction to the scheme conversion.

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arXiv2015

Non-QCD contributions to top-pair production near threshold

The threshold scan of top pair production at a future lepton collider allows to determine several Standard Model parameters with very high precision. The recent completion of the third-order QCD corrections to the inclusive top-pair production cross section demonstrated that strong dynamics are under control. We investigate effects from P-wave production and Higgs contributions at third order and from QED and the nonresonant production of the physical $W^+W^-b\bar{b}$ final state at first order. We discuss the sensitivity of the cross section to the top mass, width and Yukawa coupling as well as to the strong coupling.

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arXiv2015

Higgs effects in top anti-top production near threshold in e+ e- annihilation

The completion of the third-order QCD corrections to the inclusive top-pair production cross section near threshold demonstrates that the strong dynamics is under control at the few percent level. In this paper we consider the effects of the Higgs boson on the cross section and, for the first time, combine the third-order QCD result with the third-order P-wave, the leading QED and the leading non-resonant contributions. We study the size of the different effects and investigate the sensitivity of the cross section to variations of the top-quark Yukawa coupling due to possible new physics effects.

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arXiv2013

D-meson lifetimes within the heavy quark expansion

Even if new data indicate that direct CP violation in D-meson decays is compatible with the standard model expectation, it has triggered a lot of interest, and charm phenomenology will remain an essential part of new physics searches due to its unique role as a probe for flavor-changing neutral currents among up-type quarks. Charm physics poses considerable theoretical challenges, because the charm mass is neither light nor truly heavy. The heavy quark expansion (HQE) provides a perturbative expansion in the inverse heavy quark mass for inclusive rates. It has proved to be very successful in the B sector, yet its validity for charm decays has often been questioned. We present results of a HQE study of D-meson lifetimes including NLO QCD and subleading 1/m_c corrections. We find good agreement with experimental data, but with huge hadronic uncertainties due to missing lattice input for hadronic matrix elements.

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arXiv2013

The inclusive decay b to ccs revisited

The inclusive decay rate b to ccs is enhanced considerably due to perturbative QCD corrections. We recalculate the dominant part of the NLO-QCD corrections, because they cannot be reconstructed from the literature and we give the full expressions in this paper. Further we include some previously neglected corrections originating from penguin diagrams. Combined with the impressive progress in the accurate determination of input parameters like charm quark mass, bottom quark mass and CKM parameters, this enables us to make a very precise prediction of the corresponding branching ratio Br (b to ccs) = (23 pm 2)%. This result is an essential ingredient for a model and even decay channel independent search for new physics effects in B decays.

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arXiv2013

Short distance D-Dbar mixing

We review the status of Standard Model predictions for lifetimes and mixing rates of charmed mesons. It is shown that the short distance approach is able to reproduce tau(D^+)/tau(D^0) at leading order in the 1/m_c expansion. SU(3) violating effects from interactions with the soft hadronic background are identified as the dominant contribution to the D-Dbar mixing rate. We discuss the contribution from operators of dimension nine, which is able to enhance the neutral charm width splitting by a factor of order ten and comment on possible CP violation in mixing.

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