# M. Muhlleitner's research while affiliated with Karlsruhe Institute of Technology and other places

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## Publications (103)

The study of the Higgs boson properties offers compelling perspectives for testing the effects of physics beyond the Standard Model and has deep implications for the LHC program and future colliders. Accurate determinations of the Higgs boson properties can provide us with a distinctively precise picture of the Higgs sector, set tight bounds and pr...

We present a comprehensive study on Higgs pair production in various archetypical extended Higgs sectors such as the real and the complex 2-Higgs-Doublet Model, the 2-Higgs-Doublet Model augmented by a real singlet field and the Next-to-Minimal Supersymmetric extension of the Standard Model. Taking into account all relevant theoretical and experime...

We present the full next-to-leading order (NLO) supersymmetric (SUSY) electroweak and SUSY-QCD corrections to the decay widths of the charged Higgs boson decays into on-shell final states in the framework of the CP-conserving and CP-violating Next-to-Minimal Supersymmetric Model (NMSSM). The newly calculated corrections have been implemented in the...

The Higgs invisible decay width may soon become a powerful tool to probe extensions of the Standard Model with dark matter candidates at the Large Hadron Collider. In this work, we calculate the next-to-leading order (NLO) electroweak corrections to the 125 GeV Higgs decay width into two dark matter particles. The model is the next-to-minimal 2-Hig...

We evaluate the full next-to-leading order supersymmetric (SUSY) electroweak and SUSY-QCD corrections to the on-shell two-body decays of the charged Higgs bosons in the framework of the CP-conserving and CP-violating Next-to-Minimal Supersymmetric extension of the Standard Model (NMSSM). Our corrections are implemented in the code NMSSMCALCEW in or...

We present the C++ code BSMPT v2 which is an extension of the previous code BSMPT for the calculation of the strength of the electroweak phase transition in extended Higgs sectors. The new version BSMPT v2 includes the features of BSMPT and extends the already implemented models (the 2-Higgs-Doublet model (2HDM) in its CP-conserving and CP-violatin...

Higgs-pair production via gluon fusion is the dominant production mechanism of Higgs-boson pairs at hadron colliders. In this work, we present details of our numerical determination of the full next-to-leading-order (NLO) QCD corrections to the leading top-quark loops. Since gluon fusion is a loop-induced process at leading order, the NLO calculati...

In this paper we compute the electroweak corrections to the charged Higgs boson decay into a $W$ boson and a neutral Higgs boson in the CP-conserving NMSSM. We calculate the process in a general $R_\xi$ gauge and investigate the dependence of the loop-corrected decay width on the gauge parameter $\xi$. The gauge dependence arises from the mixing of...

Since no direct signs of new physics have been observed so far indirect searches in the Higgs sector have become increasingly important. With the discovered Higgs boson behaving very Standard Model (SM)-like, however, indirect new physics manifestations are in general expected to be small. On the theory side, this makes precision predictions for th...

We present the program package 2HDECAY for the calculation of the partial decay widths and branching ratios of the Higgs bosons of a general CP-conserving 2-Higgs doublet model (2HDM). The tool includes the full electroweak one-loop corrections to all two-body on-shell Higgs decays in the 2HDM that are not loop-induced. It combines them with the st...

We provide the C++ tool BSMPT for calculating the strength of the electroweak phase transition in extended Higgs sectors. This relies on the loop-corrected effective potential at finite temperature including daisy resummation of the bosonic masses. The program allows to compute the vacuum expectation value (VEV) $v$ of the potential as a function o...

Checking that a scalar potential is bounded from below (BFB) is an ubiquitous and notoriously difficult task in many models with extended scalar sectors. Exact analytic BFB conditions are known only in simple cases. In this work, we present a novel approach to algorithmically establish the BFB conditions for any polynomial scalar potential. The met...

The Next-to-Minimal 2-Higgs-Doublet Model (N2HDM) is an interesting benchmark model for a Higgs sector consisting of two complex doublet and one real singlet fields. Like the Next-to-Minimal Supersymmetric extension (NMSSM) it features light Higgs bosons that could have escaped discovery due to their singlet admixture. Thereby, the model allows for...

Higgs pair production through gluon fusion is an important process at the LHC to test the dynamics underlying electroweak symmetry breaking. Higgs sectors beyond the Standard Model (SM) can substantially modify this cross section through novel couplings not present in the SM or the on-shell production of new heavy Higgs bosons that subsequently dec...

Beyond the Standard Model (SM) extensions usually include extended Higgs sectors. Models with singlet or doublet fields are the simplest ones that are compatible with the $\rho$ parameter constraint. The discovery of new non-SM Higgs bosons and the identification of the underlying model requires dedicated Higgs properties analyses. In this paper, w...

The discovery of the Higgs boson by the LHC experiments ATLAS and CMS has marked a milestone for particle physics. Yet, there are still many open questions that cannot be answered within the Standard Model (SM). For example, the generation of the observed matter-antimatter asymmetry in the universe through baryogenesis can only be explained qualita...

The N2HDM is based on the CP-conserving 2HDM extended by a real scalar singlet field. Its enlarged parameter space and its fewer symmetry conditions as compared to supersymmetric models allow for an interesting phenomenology compatible with current experimental constraints, while adding to the 2HDM sector the possibility of Higgs-to-Higgs decays wi...

The detailed investigation of the Higgs sector at present and future colliders necessitates from the theory side as precise predictions as possible, including higher order corrections. An important ingredient for the computation of higher order corrections is the renormalization of the model parameters and fields. In this paper we complete the reno...

The 2-Higgs-Doublet Model (2HDM) belongs to the simplest extensions of the Standard Model (SM) Higgs sector that are in accordance with theoretical and experimental constraints. In order to be able to properly investigate the experimental Higgs data and, in the long term to distinguish between possible models beyond the SM, precise predictions for...

In composite Higgs models the Higgs boson arises as a pseudo-Goldstone boson from a strongly-interacting sector. Fermion mass generation is possible through partial compositeness accompanied by the appearance of new heavy fermionic resonances. The Higgs couplings to the Standard Model (SM) particles and between the Higgs bosons themselves are modif...

We study the decays of the lightest CP-even Higgs boson into a pair of pseudoscalar Higgs states within U(1)_N extensions of the MSSM.

The Next-to-Minimal Supersymmetric extension of the Standard Model (NMSSM)
features extra new sources for CP violation. In contrast to the MSSM CP
violation can already occur at tree level in the Higgs sector. We investigate
the range of possible allowed CP-violating phases by taking into account the
constraints arising from the measurements of the...

A consistent interpretation of the Higgs data requires the same precision in
the Higgs boson masses and in the trilinear Higgs self-couplings, which are
related through their common origin from the Higgs potential. In this work we
provide the two-loop corrections at order ${\cal O}(\alpha_t \alpha_s)$ in the
approximation of vanishing external mome...

We compute the full next-to-leading order supersymmetric (SUSY) electroweak
(EW) and SUSY-QCD corrections to the decays of CP-odd NMSSM Higgs bosons into
stop pairs. In our numerical analysis we also present the decay of the heavier
stop into the lighter stop and an NMSSM CP-odd Higgs boson. Both the EW and the
SUSY-QCD corrections are found to be...

New Physics that becomes relevant at some high scale $\Lambda$ beyond the
experimental reach, can be described in the effective theory approach by adding
higher-dimensional operators to the Standard Model (SM) Lagrangian. In Higgs
pair production through gluon fusion, which gives access to the trilinear Higgs
self-coupling, this leads not only to m...

A comprehensive review of physics at an e+e- Linear Collider in the energy
range of sqrt{s}=92 GeV--3 TeV is presented in view of recent and expected LHC
results, experiments from low energy as well as astroparticle physics.The
report focuses in particular on Higgs boson, Top quark and electroweak
precision physics, but also discusses several model...

We investigate the decays of the light stop in scenarios with the lightest
neutralino $\tilde{\chi}_1^0$ being the lightest supersymmetric particle,
including flavour-violating (FV) effects. We analyse the region where the
three-body decay $\tilde{t}_1\to W b \tilde{\chi}_1^0$ is kinematically allowed
and provide a proper description of the transit...

We review recent results on higher-order calculations to squark and gluino
production and decay at the LHC, as obtained within the Collaborative Research
Centre / Transregio 9 "Computational Particle Physics". In particular, we
discuss inclusive cross sections, including the summation of threshold
corrections, higher-order calculations for specific...

We discuss the interpretation of the LHC Higgs data and the test of the Higgs
mechanism. This is done in a more model-independent approach relying on an
effective Lagrangian, as well as in specific models like composite Higgs models
and supersymmetric extensions of the Standard Model. The proper interpretation
of the data requires the inclusion of...

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 ${\cal O} (\alpha_t \alpha_s)$. The adopted renormalization scheme
is a mixture between $\overline{\text{DR}}$ and on-shell conditions.
Additionally, the renormalization of the top/stop sec...

In U(1) extensions of the Minimal Supersymmetric extension of the Standard
Model there is a simple mechanism that leads to a heavy Z' boson with a mass
which is substantially larger than the supersymmetry breaking scale. This
mechanism may also result in a pseudoscalar state that is light enough for
decays of the 125 GeV Standard Model-like Higgs b...

Higgs physics beyond the Standard Model (SM) is presented in the context of
an underlying strong dynamics of electroweak symmetry breaking (EWSB) as given
by composite Higgs models. Subsequently, the study of New Physics (NP) effects
in a more model-independent way through the effective Lagrangian approach is
briefly sketched before moving on to th...

We investigate the flavour-changing neutral current decay of the lightest
stop into a charm quark and the lightest neutralino and its four-body decay
into the lightest neutralino, a down-type quark and a fermion pair. These are
the relevant stop search channels in the low-mass region. The SUSY-QCD
corrections to the two-body decay have been calcula...

We investigate the discovery prospects for NMSSM Higgs bosons during the
13~TeV run of the LHC. While one of the neutral Higgs bosons is demanded to
have a mass around 125~GeV and Standard Model (SM)-like properties, there can
be substantially lighter, nearby or heavier Higgs bosons, that have not been
excluded yet by LEP, Tevatron or the 8~TeV run...

The measured properties of the recently discovered Higgs boson are in good
agreement with predictions from the Standard Model. However, small deviations
in the Higgs couplings may manifest themselves once the currently large
uncertainties will be improved as part of the LHC program and at a future Higgs
factory. We review typical new physics scenar...

We present eHDECAY, a modified version of the program HDECAY which includes
the full list of leading bosonic operators of the Higgs effective Lagrangian
with a linear or non-linear realization of the electroweak symmetry and
implements two benchmark composite Higgs models.

We present the program package NMSSMCALC for the calculation of the
loop-corrected NMSSM Higgs boson masses and decay widths in the CP-conserving
and CP-violating NMSSM. The full one-loop corrections to the Higgs boson masses
are evaluated in a mixed renormalisation scheme of on-shell and
$\overline{\mbox{DR}}$ conditions. The Higgs decay widths in...

Like many other models, Composite Higgs Models feature the existence of heavy
vector-like quarks. Mixing effects between the Standard Model fields and the
heavy states, which can be quite large in case of the top quark, imply
deviations from the SM. In this work we investigate the possibility of heavy
bottom partners. We show that they can have a s...

This Report summarizes the results of the activities in 2012 and the first
half of 2013 of the LHC Higgs Cross Section Working Group. The main goal of the
working group was to present the state of the art of Higgs Physics at the LHC,
integrating all new results that have appeared in the last few years. This
report follows the first working group re...

After the discovery of a Higgs-like boson by the LHC experiments ATLAS and
CMS, it is of crucial importance to determine its properties in order to not
only identify it as the boson responsible for electroweak symmetry breaking but
also to clarify the question if it is a Standard Model (SM) Higgs boson or the
Higgs particle of some extension beyond...

Now that the Higgs boson has been observed by the ATLAS and CMS experiments
at the LHC, the next important step would be to measure accurately its
properties to establish the details of the electroweak symmetry breaking
mechanism. Among the measurements which need to be performed, the determination
of the Higgs self-coupling in processes where the...

A bstract
We reconsider the effective Lagrangian that describes a light Higgs-like boson and better clarify a few issues which were not exhaustively addressed in the previous literature. In particular we highlight the strategy to determine whether the dynamics responsible for the electroweak symmetry breaking is weakly or strongly interacting. We a...

We chart the theoretical basis of radiative decays of the Higgs boson, H→γγH→γγ and Zγ, for measuring the spin of the Higgs particle. These decay channels are complementary to other rare modes such as real/virtual Z-boson pair decays. In systematic helicity analyses the angular distribution for zero-spin is confronted with hypothetical spin-2±2± an...

We study the phenomenology of Higgs bosons close to 126 GeV within the scale
invariant unconstrained next-to-minimal supersymmetric Standard Model (NMSSM),
focusing on the regions of parameter space favoured by low fine-tuning
considerations, namely stop masses of order 400 GeV to 1 TeV and an effective
$\mu$ parameter between 100-200 GeV, with lar...

We chart the theoretical basis of radiative decays of the Higgs boson, $H \to
\gamma\gamma$ and $Z\gamma$, for measuring the spin of the Higgs particle.
These decay channels are complementary to other rare modes such as real/virtual
$Z$-boson pair-decays. In systematic helicity analyses the angular distribution
for zero-spin is confronted with hypo...

The 8 TeV LHC Higgs search data just released indicates the existence of a
scalar resonance with mass ~ 125 GeV. We examine the implications of the data
reported by ATLAS, CMS and the Tevatron collaborations on understanding the
properties of this scalar by performing joint fits on its couplings to other
Standard Model particles. We discuss and cha...

The Higgs low-energy theorem gives a simple and elegant way to estimate the
couplings of the Higgs boson to massless gluons and photons induced by loops of
heavy particles. We extend this theorem to take into account possible nonlinear
Higgs interactions resulting from a strong dynamics at the origin of the
breaking of the electroweak symmetry. We...

The Next-to-Minimal Supersymmetric Extension of the Standard Model (NMSSM) with a Higgs sector containing five neutral and two charged Higgs bosons allows for a rich phenomenology. In addition, the plethora of parameters provides many sources of CP violation. In contrast to the Minimal Supersymmetric Extension, CP violation in the Higgs sector is a...

We demonstrate by performing a global fit on Higgs signal strength data that large invisible branching ratios (Brinv) for a Standard Model (SM) Higgs particle are currently consistent with the experimental hints of a scalar resonance with mass m
h
~ 124 GeV. For this mass, we find Brinv< 0.64 (95% CL) from a global fit to individual channel signal...

For a reliable prediction of the NMSSM Higgs boson signatures at present and future high-energy colliders and a proper distinction of the NMSSM and MSSM Higgs sector the precise knowledge of the Higgs boson masses including higher-order corrections is indispensable. In this paper, the one-loop corrections to the neutral NMSSM Higgs boson masses and...

We present the activities of the "New Physics" working group for the "Physics
at TeV Colliders" workshop (Les Houches, France, 30 May-17 June, 2011). Our
report includes new agreements on formats for interfaces between computational
tools, new tool developments, important signatures for searches at the LHC,
recommendations for presentation of LHC s...

We outline a method for characterizing deviations from the properties of a Standard Model (SM) Higgs boson. We apply it to current data in order to characterize up to which degree the SM Higgs boson interpretation is consistent with experiment. We find that the SM Higgs boson is consistent with the current data set at the 82 % confidence level, bas...

This Report summarises the results of the second year's activities of the LHC
Higgs Cross Section Working Group. The main goal of the working group was to
present the state of the art of Higgs Physics at the LHC, integrating all new
results that have appeared in the last few years. The first working group
report Handbook of LHC Higgs Cross Sections...

The recent LHC indications of a SM-like Higgs boson near 125 GeV are
consistent not only with the Standard Model (SM) but also with Supersymmetry
(SUSY). However naturalness arguments disfavour the Minimal Supersymmetric
Standard Model (MSSM). We consider the Next-to-Minimal Supersymmetric Standard
Model (NMSSM) with a SM-like Higgs boson near 125...

In this paper we investigate methods to study the $t\bar{t}$ Higgs coupling.
The spin and CP properties of a Higgs boson are analysed in a model-independent
way in its associated production with a $t\bar{t}$ pair in high-energy $e^+e^-$
collisions. We study the prospects of establishing the CP quantum numbers of
the Higgs boson in the CP-conserving...

We present the Flavour Les Houches Accord (FLHA) which specifies a unique set
of conventions for flavour-related parameters and observables. The FLHA uses
the generic SUSY Les Houches Accord (SLHA) file structure. It defines the
relevant Standard Model masses, Wilson coefficients, decay constants, bag
parameters, flavour observables, etc. The accor...

This is the summary and introduction to the proceedings contributions for the Les Houches 2009 "Tools and Monte Carlo" working group. Comment: 144 Pages. Workshop site http://wwwlapp.in2p3.fr/conferences/LesHouches/Houches2009/ . Conveners were Butterworth, Maltoni, Moortgat, Richardson, Schumann and Skands

This is the summary and introduction to the proceedings contributions
for the Les Houches 2009 "Tools and Monte Carlo" working group.

In the MSSM scalar h,H production is mediated by heavy quark and squark loops. The higher order QCD corrections have been obtained some time ago and turned out to be large. The full SUSY QCD corrections have been obained recently including the full mass dependence of the loop particles. We describe our calculation and present first numerical result...

The discovery of the Standard Model (SM) or supersymmetric (SUSY) Higgs bosons belongs to the main endeavors of the Large Hadron Collider (LHC). In this article the status of the signal and background calculations for Higgs boson production at the LHC is reviewed.

Report of the Working Group on Higgs Bosons for the Workshop, ``Physics at
TeV Colliders'', Les Houches, France, 11-29 June, 2007.

One of the main endeavors at future high-energy colliders is the search for the Higgs boson(s) and, once found, the probe of the fundamental properties. In particular, the charge conjugation and parity (CP) quantum numbers have to be determined. We show that these are unambiguously accessible at future e +e- colliders through the measurement of the...

ILC Global Design Effort and World Wide Study

We present the program package SUSY-HIT for the computation of supersymmetric
particle decays within the framework of the Minimal Supersymmetric extension of
the Standard Model. The code is based on two existing programs HDECAY and
SDECAY for the calculation of the decay widths and branching ratios of,
respectively, the MSSM Higgs bosons and the SU...

There are many possibilities for new physics beyond the Standard Model that feature non-standard Higgs sectors. These may introduce new sources of CP violation, and there may be mixing between multiple Higgs bosons or other new scalar bosons. Alternatively, the Higgs may be a composite state, or there may even be no Higgs at all. These non-standard...

There are many possibilities for new physics beyond the Standard Model
that feature non-standard Higgs sectors. These may introduce new sources
of CP violation, and there may be mixing between multiple Higgs bosons
or other new scalar bosons. Alternatively, the Higgs may be a composite
state, or there may even be no Higgs at all. These non-standard...

Physics at the Large Hadron Collider (LHC) and the International e+e- Linear Collider (ILC) will be complementary in many respects, as has been demonstrated at previous generations of hadron and lepton colliders. This report addresses the possible interplay between the LHC and ILC in testing the Standard Model and in discovering and determining the...

The work contained herein constitutes a report of the "Beyond the Standard Model'' working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005. We present reviews of current topics as well as original research carried out for the workshop. Supersymmetric and non-supersymmetric models are studied, as well as comput...

High-precision analyses of supersymmetry parameters aim at reconstructing the fundamental supersymmetric theory and its breaking mechanism. A well defined theoretical framework is needed when higher-order corrections are included. We propose such a scheme, Supersymmetry Parameter Analysis SPA, based on a consistent set of conventions and input para...

The various search modes for the Higgs bosons of the Standard Model (SM) and its Minimal Supersymmetric Extension (MSSM) at the International Linear Collider (ILC) will be summarized briefly. In particular, as a unique discovery mode the production of heavy neutral MSSM Higgs bosons for medium values of $\tan\beta$ in photon collisions will be pres...