arXiv subjects

Robert V. Harlander

Publications and source records attributed to Robert V. Harlander.

At least 37 records · Page 2Linked to original sources

arXiv2019

Results and techniques for higher order calculations within the gradient-flow formalism

We describe in detail the implementation of a systematic perturbative approach to observables in the QCD gradient-flow formalism. This includes a collection of all relevant Feynman rules of the five-dimensional field theory and the composite operators considered in this paper. Tools from standard perturbative calculations are used to obtain Green's functions at finite flow time $t$ at higher orders in perturbation theory. The three-loop results for the quark condensate at finite $t$ and the conversion factor for the "ringed" quark fields to the $\overline{\mbox{MS}}$ scheme are presented as applications. We also re-evaluate an earlier result for the three-loop gluon condensate, improving on its accuracy.

hep-lat↗

arXiv2017

Higgs mass prediction in the MSSM at three-loop level in a pure $\overline{\text{DR}}$ context

The impact of the three-loop effects of order $α_tα_s^2$ on the mass of the light CP-even Higgs boson in the MSSM is studied in a pure $\overline{\text{DR}}$ context. For this purpose, we implement the results of Kant et al. into the C++ module Himalaya and link it to FlexibleSUSY, a Mathematica and C++ package to create spectrum generators for BSM models. The three-loop result is compared to the fixed-order two-loop calculations of the original FlexibleSUSY and of FeynHiggs, as well as to the result based on an EFT approach. Aside from the expected reduction of the renormalization scale dependence with respect to the lower order results, we find that the three-loop contributions significantly reduce the difference from the EFT prediction in the TeV-region of the SUSY scale $M_S$. Himalaya can be linked also to other two-loop $\overline{\text{DR}}$ codes, thus allowing for the elevation of these codes to the three-loop level.

hep-ph↗

arXiv2016

SusHi Bento: Beyond NNLO and the heavy-top limit

Version 1.6.0 of the code SusHi is presented. Concerning inclusive CP-even Higgs production in gluon fusion, the following new features with respect to previous versions have been implemented: expansion of the partonic cross section in the soft limit, i.e. around $x=M_H^2/\hat{s}\to 1$; N$^3$LO QCD corrections in terms of the soft expansion; top-quark mass suppressed terms through NNLO; matching to the cross section at $x\to 0$ through N$^3$LO. For CP-even and -odd scalars, an efficient evaluation of the renormalization-scale dependence is included, and effects of dimension-5 operators can be studied, which we demonstrate for the SM Higgs boson and for a CP-even scalar with a mass of $750$ GeV. In addition, as a generalization of the previously available $b\bar{b}\to H$ cross section, SusHi 1.6.0 provides the cross section for charged and neutral Higgs production in the annihilation of arbitrary heavy quarks. At fixed order in perturbation theory, SusHi thus allows to obtain Higgs cross-section predictions in different models to the highest precision known today. For the SM Higgs boson of $M_H=125$ GeV, SusHi yields $48.28$ pb for the gluon-fusion cross section at the LHC at $13$ TeV. Simultaneously, SusHi provides the renormalization-scale uncertainty of $\pm 1.97$ pb.

hep-ph↗

arXiv2016

The perturbative QCD gradient flow to three loops

The gradient flow in QCD is treated perturbatively through next-to-next-to-leading order in the strong coupling constant. The evaluation of the relevant momentum and flow-time integrals is described, including various means of validation. For the vacuum expectation value of the action density, which turns out to be a useful quantity in lattice calculations, we find a very well-behaved perturbative series through NNLO. Quark mass effects are taken into account through NLO. The theoretical uncertainty due to renormalization scale variation is significantly reduced with respect to LO and NLO, as long as the flow time is smaller than about 0.1 fm.

hep-ph↗

arXiv2016

Higgs production in heavy quark annihilation through next-to-next-to-leading order QCD

The total inclusive cross section for charged and neutral Higgs production in heavy-quark annihilation is presented through NNLO QCD. It is shown that, aside from an overall factor, the partonic cross section is independent of the initial-state quark flavors, and that any interference terms involving two different Yukawa couplings vanish. A simple criterion for defining the central renormalization and factorization scale is proposed. Its application to the $b\bar bH$ process yields results which are compatible with the values usually adopted for this process. Remarkably, we find little variation in these values for the other initial-state quark flavors. Finally, we disentangle the impact of the different parton luminosities from genuine hard NNLO effects and find that, for the central scales, a naive rescaling by the parton luminosities approximates the full result remarkably well.

hep-ph↗

arXiv2015

Resummation ambiguities in the Higgs transverse-momentum spectrum in the Standard Model and beyond

We study the prediction for the Higgs transverse momentum distribution in gluon fusion and focus on the problem of matching fixed- and all-order perturbative results. The main sources of matching ambiguities on this distribution are investigated by means of a twofold comparison. On the one hand, we present a detailed qualitative and quantitative comparison of two recently introduced algorithms for determining the matching scale. On the other hand, we apply the results of both methods to three widely used approaches for the resummation of logarithmically enhanced contributions at small transverse momenta: the MC@NLO and POWHEG Monte Carlo approaches, and analytic resummation. While the three sets of results are largely compatible in the low-pT region, they exhibit sizable differences at large pT. We show that these differences can be significantly reduced by suitable modifications of formally subleading terms in the Monte Carlo implementations. We apply our study to the Standard Model Higgs boson and to the neutral Higgs bosons of the Two-Higgs-Doublet Model for representative scenarios of the parameter space, where the top- and bottom-quark diagrams enter the cross section at different strength.

hep-ph↗

arXiv2014

Philosophical perspectives on ad hoc hypotheses and the Higgs mechanism

We examine physicists' charge of ad hocness against the Higgs mechanism in the standard model of elementary particle physics. We argue that even though this charge never rested on a clear-cut and well-entrenched definition of "ad hoc", it is based on conceptual and methodological assumptions and principles that are well-founded elements of the scientific practice of high-energy particle physics. We further evaluate the implications of the recent discovery of a Higgs-like particle at the CERN's Large Hadron Collider for the charge of ad hocness against the Higgs mechanism.

physics.hist-ph↗

arXiv2014

Transverse momentum resummation for Higgs production via gluon fusion in the MSSM

The resummed transverse momentum distribution of supersymmetric Higgs bosons produced through gluon fusion at NLO+NLL is presented, including the exact quark and squark mass dependences. Considering various MSSM scenarios, we compare our results to previous ones within the POWHEG approach. We analyze the impact of the bottom loop which becomes the dominant contribution to the gluon fusion cross section for a wide range of the parameter space for the pseudo-scalar and heavy Higgs.

hep-ph↗

arXiv2014

Soft gluon resummation for gluon-induced Higgs Strahlung

We study the effect of soft gluon emission on the total cross section predictions for the $gg\to HZ$ associated Higgs production process at the LHC. To this end, we perform resummation of threshold corrections at the NLL accuracy in the absolute threshold production limit and in the threshold limit for production of a $ZH$ system with a given invariant mass. Analytical results and numerical predictions for various possible LHC collision energies are presented. The perturbative stability of the results is verified by including universal NNLL effects. We find that resummation significantly reduces the scale uncertainty of the $gg\to HZ$ contribution, which is the dominant source of perturbative uncertainty to $ZH$ production. We use our results to evaluate updated numbers for the total inclusive cross section of associated $pp \to ZH$ production at the LHC. The reduced scale uncertainty of the $gg\to HZ$ component translates into a decrease of the overall scale error by about a factor of two.

hep-ph↗

arXiv2014

Higgs production in bottom quark annihilation: Transverse momentum distribution at NNLO+NNLL

We present the inclusive transverse momentum distribution for Higgs bosons produced in bottom quark annihilation at the LHC. The results are obtained in the five-flavor scheme. The soft and collinear terms at small $p_T$ are resummed through NNLL accuracy and matched to the NNLO transverse momentum distribution at large $p_T$. We find that the theoretical uncertainty, derived from a variation of the unphysical scales entering the calculation, is significantly reduced with respect to lower orders.

hep-ph↗

arXiv2014

Higgs Strahlung at the Large Hadron Collider in the 2-Higgs-Doublet Model

We present a calculation of all relevant contributions to associated production of a Higgs boson with a weak gauge boson in the 2-Higgs-Doublet Model (2HDM) at the LHC, $pp \rightarrow Vϕ$, with $ϕ\in\{h,H^0,A\}$ and $V\in\{W,Z\}$. While for the $Wϕ$ mode, this mostly amounts to a simple rescaling of the Standard Model (SM) cross section, the $Zϕ$ cross section depends on several 2HDM parameters. The ratio $σ^{Wϕ}/σ^{Zϕ}$, for which we present the currently most complete SM prediction, therefore appears to be a sensitive probe of possible New Physics effects. We study its numerical dependence on the top and bottom Yukawa couplings, including their sign. Furthermore, we consider the $Wϕ/Zϕ$ ratio in exemplary 2HDM scenarios and briefly address the effects in the boosted regime. Analogous studies for other 2HDM scenarios will become possible with an upcoming version of the program vh@nnlo which incorporates the 2HDM effects.

hep-ph↗

arXiv2013

Probing the nature of the Higgs-gluon coupling

One and two-jet observables of dimension-7 Higgs-gluon coupling operators are studied as probes of possible deviations from the top-loop induced gluon-Higgs coupling. We discuss the case of both a scalar as well as a pseudo-scalar Higgs boson and show that higher order operators can give visible deviations from Standard Model distribution shapes.

hep-ph↗

arXiv2013

SusHi: A program for the calculation of Higgs production in gluon fusion and bottom-quark annihilation in the Standard Model and the MSSM

This article describes the code SusHi (for "Supersymmetric Higgs") which calculates the cross sections $pp/p\bar{p}\rightarrowϕ+X$ in gluon fusion and bottom-quark annihilation in the SM and the MSSM, where $ϕ$ is any of the neutral Higgs bosons within these models. Apart from inclusive cross sections up to NNLO QCD, differential cross sections with respect to the Higgs' transverse momentum $p_T$ and (pseudo-)rapidity $y(η)$ can be calculated through NLO QCD. In case of gluon fusion, SusHi contains NLO QCD contributions from the third family of quarks and squarks, NNLO corrections due to top-quarks, approximate NNLO corrections due to top-squarks, and electro-weak effects. It supports various renormalization schemes for the sbottom sector and the bottom Yukawa coupling, as well as resummation effects of higher order $\tanβ$-enhanced sbottom contributions. SusHi provides a link to FeynHiggs for the calculation of the Higgs masses.

hep-ph↗

arXiv2012

vh@nnlo - Higgs Strahlung at hadron colliders

A numerical program for the evaluation of the inclusive cross section for associated Higgs production with a massive weak gauge boson at hadron colliders is described, sigma(pp/pbar p -> HV), V=W,Z. The calculation is performed in the framework of the Standard Model and includes next-to-next-to-leading order QCD as well as next-to-leading order electro-weak effects.

hep-ph↗

arXiv2012

Gluon-induced Higgs-strahlung at next-to-leading order QCD

Gluon-induced contributions to the associated production of a Higgs and a Z-boson are calculated with NLO accuracy in QCD. They constitute a significant contribution to the cross section for this process. The perturbative correction factor (K-factor) is calculated in the limit of infinite top-quark and vanishing bottom-quark masses. The qualitative similarity of the results to the well-known ones for the gluon-fusion process $gg\to H$ allows to conclude that rescaling the LO prediction by this K-factor leads to a reliable NLO result and realistic error estimate due to missing higher-order perturbative effects. We consider the total inclusive cross section as well as a scenario with a boosted Higgs boson, where the Higgs boson's transverse momentum is restricted to values ptH>200GeV. In both cases, we find large correction factors $K\approx 2$ in most of the parameter space.

hep-ph↗

arXiv2012

Top-mass effects in differential Higgs production through gluon fusion at order α_s^4

Effects from a finite top quark mass on differential distributions in the Higgs+jet production cross section through gluon fusion are studied at next-to-leading order in the strong coupling, i.e. $O(α_s^4)$. Terms formally subleading in $1/m_t$ are calculated, and their influence on the transverse momentum and rapidity distribution of the Higgs boson are evaluated. We find that, for the differential K-factor, the heavy-top limit is valid at the 2-3% level as long as the transverse momentum of the Higgs remains below about 150 GeV.

hep-ph↗

arXiv2011

Supersymmetric Higgs production in gluon fusion

The cross section through gluon fusion is calculated for the production of the light neutral Higgs boson through next-to-leading order QCD within the Minimal Supersymmetric Standard Model. The quark-mediated contributions are taken into account exactly, while for the genuinely supersymmetric terms we use expressions obtained in the limit of large squark, gluino and top quark masses. We present numerical results for the total inclusive cross section as well as for kinematical distributions of the Higgs boson. We also consider the effect of an MSSM-like fourth generation on the total Higgs production cross section.

hep-ph↗

arXiv2010

Higgs plus jet production in bottom quark annihilation at next-to-leading order

The cross section for Higgs+jet production in bottom quark annihilation is calculated through NLO QCD. The five-flavour scheme is used to derive this contribution to the Higgs+jet production cross section which becomes numerically important in the MSSM for large values of tan(beta). We present numerical results for a proton collider with 14 TeV center-of-mass energy. The NLO matrix elements for d(sigma)/d(pT) are then combined with the total inclusive cross section in order to derive the integrated cross section with a maximum cut on pT at next-to-next-to-leading order.

hep-ph↗