arXiv subjects

Heidi Rzehak

Publications and source records attributed to Heidi Rzehak.

30 records · Page 2Linked to original sources

arXiv2016

A Review of Higgs Mass Calculations in Supersymmetric Models

The discovery of the Higgs boson is both a milestone achievement for the Standard Model and an exciting probe of new physics beyond the SM. One of the most important properties of the Higgs is its mass, a number that has proven to be highly constraining for models of new physics, particularly those related to the electroweak hierarchy problem. Perhaps the most extensively studied examples are supersymmetric models, which, while capable of producing a 125 GeV Higgs boson with SM-like properties, do so in non-generic parts of their parameter spaces. We review the computation of the Higgs mass in the Minimal Supersymmetric Standard Model, in particular the large radiative corrections required to lift $m_h$ to 125 GeV and their calculation via Feynman-diagrammatic and effective field theory techniques. This review is intended as an entry point for readers new to the field, and as a summary of the current status, including the existing analytic calculations and publicly-available computer codes.

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arXiv2014

Two-Loop Contributions of the Order $\mathcal{O}(α_tα_s)$ to the Masses of the Higgs Bosons in the CP-Violating NMSSM

We provide the two-loop corrections to the Higgs boson masses of the CP-violating NMSSM in the Feynman diagrammatic approach with vanishing external momentum at ${\cal O} (α_t α_s)$. The adopted renormalization scheme is a mixture between $\overline{\text{DR}}$ and on-shell conditions. Additionally, the renormalization of the top/stop sector is provided both for the $\overline{\text{DR}}$ and the on-shell scheme. The calculation is performed in the gaugeless limit. We find that the two-loop corrections compared to the one-loop corrections are of the order of 5-10\%, depending on the top/stop renormalization scheme. The theoretical error on the Higgs boson masses is reduced due to the inclusion of these higher order corrections.

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arXiv2014

Higher-Order Contributions in Higgs Sectors of Supersymmetric Models

In 2012, the discovery of a particle compatible with a Higgs boson of a mass of roughly 125 GeV was announced. This great success is now being followed by the identification of the nature of this particle and the particle's properties are being measured. One of these properties is the Higgs boson mass which is already known very precisely with an experimental uncertainty of below 1 GeV. In some extensions of the Standard Model, like in supersymmetric extensions, the Higgs boson mass can be predicted and hence, the measured mass constrains the parameters of the model. For a full exploitation of this constraint, a precise theoretical prediction is needed. The presented combination of the results obtained by the Feynman diagrammatic approach and the renormalization group equation approach improves the known Higgs mass prediction for larger mass scales of the superpartner particles.

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arXiv2013

Physics at the CLIC e+e- Linear Collider -- Input to the Snowmass process 2013

This paper summarizes the physics potential of the CLIC high-energy e+e- linear collider. It provides input to the Snowmass 2013 process for the energy-frontier working groups on The Higgs Boson (HE1), Precision Study of Electroweak Interactions (HE2), Fully Understanding the Top Quark (HE3), as well as The Path Beyond the Standard Model -- New Particles, Forces, and Dimensions (HE4). It is accompanied by a paper describing the CLIC accelerator study, submitted to the Frontier Capabilities group of the Snowmass process.

hep-ex↗

arXiv2013

SUSY Background to Neutral MSSM Higgs Boson Searches

Within the Minimal Supersymmetric Standard Model (MSSM) the production and decay of superpartners can give rise to backgrounds for Higgs boson searches. Here MSSM background processes to the vector boson fusion channel with the Higgs boson decaying into two tau leptons or two W-bosons are investigated, giving rise to dilepton plus missing transverse momentum signals of the Higgs boson. Starting from a scenario with relatively small masses of the supersymmetric (SUSY) particles, with concomitant large cross section of the background processes, one obtains a first conservative estimate of the background. Light chargino pair production plus two jets, lightest and next-to-lightest neutralino production plus two jets as well as slepton pair production plus two jets are identified as important contributions to the irreducible SUSY background. Light chargino and next-to-lightest neutralino production plus two jets and next-to-lightest neutralino pair production plus two jets give rise to reducible backgrounds, which can be larger than the irreducible ones in some scenarios. The relevant distributions are shown and additional cuts for MSSM background reduction are discussed. Extrapolation to larger squark masses is performed and shows that MSSM backgrounds are quite small for squark masses at the current exclusion limits.

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arXiv2013

How well do we need to measure the Higgs boson mass and self-coupling?

Much of the discussion regarding future measurements of the Higgs boson mass and self-coupling is focussed on how well various collider options can do. In this article we ask a physics-based question of how well do we need colliders to measure these quantities to have an impact on discovery of new physics or an impact in how we understand the role of the Higgs boson in nature. We address the question within the framework of the Standard Model and various beyond the Standard Model scenarios, including supersymmetry and theories of composite Higgs bosons. We conclude that the LHC's stated ability to measure the Higgs boson to better than 150 MeV will be as good as we will ever need to know the Higgs boson mass in the foreseeable future. On the other hand, we estimate that the self-coupling will likely need to be measured to better than 20 percent to see a deviation from the Standard Model expectation. This is a challenging target for future collider and upgrade scenarios.

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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.

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arXiv2012

New Physics backgrounds to the H -> WW search at the LHC?

The searches for H -> WW events at the LHC use data driven techniques for estimating the q qbar -> WW background, by normalizing the background cross section to data in a control region. We investigate the possibility that new physics sources which mainly contribute to the control region lead to an overestimate of Standard Model backgrounds to the Higgs boson signal and, thus, to an underestimate of the H -> WW signal. A supersymmetric scenario with heavy squarks and gluinos but charginos in the 200 to 300 GeV region and somewhat lighter sleptons can lead to such a situation.

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arXiv2012

How well do we need to measure Higgs boson couplings?

Most of the discussion regarding the Higgs boson couplings to Standard Model vector bosons and fermions is presented with respect to what present and future collider detectors will be able to measure. Here, we ask the more physics-based question of how well do we need to measure the Higgs boson couplings? We first present a reasonable definition of "need" and then investigate the answer in the context of various highly motivated new physics scenarios: supersymmetry, mixed-in hidden sector Higgs bosons, and a composite Higgs boson. We find the largest coupling deviations away from the SM Higgs couplings that are possible if no other state related to EWSB is directly accessible at the LHC. Depending on the physics scenario under consideration, we find targets that range from less than 1% to 10% for vector bosons, and from a few percent to tens of percent for couplings to fermions.

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arXiv2011

Higher order corrections to Higgs boson decays in the MSSM with complex parameters

We discuss Higgs boson decays in the CP-violating MSSM, and examine their phenomenological impact using cross section limits from the LEP Higgs searches. This includes a discussion of the full 1-loop results for the partial decay widths of neutral Higgs bosons into lighter neutral Higgs bosons (h_a -> h_b h_c) and of neutral Higgs bosons into fermions (h_a -> f fbar). In calculating the genuine vertex corrections, we take into account the full spectrum of supersymmetric particles and all complex phases of the supersymmetric parameters. These genuine vertex corrections are supplemented with Higgs propagator corrections incorporating the full one-loop and the dominant two-loop contributions, and we illustrate a method of consistently treating diagrams involving mixing with Goldstone and Z bosons. In particular, the genuine vertex corrections to the process h_a -> h_b h_c are found to be very large and, where this process is kinematically allowed, can have a significant effect on the regions of the CPX benchmark scenario which can be excluded by the results of the Higgs searches at LEP. However, there remains an unexcluded region of CPX parameter space at a lightest neutral Higgs boson mass of ~45 GeV. In the analysis, we pay particular attention to the conversion between parameters defined in different renormalisation schemes and are therefore able to make a comparison to the results found using renormalisation group improved/effective potential calculations.

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arXiv2010

Supersymmetric Higgs Production in Vector-Boson Fusion

We present a full calculation of the supersymmetric NLO corrections to Higgs boson production via vector-boson fusion. The supersymmetric QCD corrections turn out to be significantly smaller than the electroweak ones. These higher-order corrections are an important ingredient to a precision analysis of the Higgs sector at the LHC.

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arXiv2009

MSSM Higgs Boson Production via Gluon Fusion: The Large Gluino Mass Limit

Scalar MSSM Higgs boson production via gluon fusion gg -> h,H is mediated by heavy quark and squark loops. The higher order QCD corrections to these processes turn out to be large. The full supersymmetric QCD corrections have been calculated recently. In the limit of large SUSY masses a conceptual problem appears, i.e. the proper treatment of the large gluino mass limit. In this work we will describe the consistent decoupling of heavy gluino effects and derive the effective Lagrangian for decoupled gluinos.

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