[Show abstract][Hide abstract] ABSTRACT: Different mechanisms operate in various regions of the MSSM parameter space
to bring the relic density of the lightest neutralino, neutralino_1, assumed
here to be the LSP and thus the Dark Matter (DM) particle, into the range
allowed by astrophysics and cosmology. These mechanisms include coannihilation
with some nearly-degenerate next-to-lightest supersymmetric particle (NLSP)
such as the lighter stau (stau_1), stop (stop_1) or chargino (chargino_1),
resonant annihilation via direct-channel heavy Higgs bosons H/A, the light
Higgs boson h or the Z boson, and enhanced annihilation via a larger Higgsino
component of the LSP in the focus-point region. These mechanisms typically
select lower-dimensional subspaces in MSSM scenarios such as the CMSSM, NUHM1,
NUHM2 and pMSSM10. We analyze how future LHC and direct DM searches can
complement each other in the exploration of the different DM mechanisms within
these scenarios. We find that the stau_1 coannihilation regions of the CMSSM,
NUHM1, NUHM2 can largely be explored at the LHC via searches for missing E_T
events and long-lived charged particles, whereas their H/A funnel, focus-point
and chargino_1 coannihilation regions can largely be explored by the LZ and
Darwin DM direct detection experiments. We find that the dominant DM mechanism
in our pMSSM10 analysis is chargino_1 coannihilation: {parts of its parameter
space can be explored by the LHC, and a larger portion by future direct DM
searches.
[Show abstract][Hide abstract] ABSTRACT: LHC searches for non-standard Higgs bosons decaying into tau lepton pairs
constitute a sensitive experimental probe for physics beyond the Standard Model
(BSM), such as Supersymmetry (SUSY). Recently, the limits obtained from these
searches have been presented by the CMS collaboration in a nearly
model-independent fashion - as a narrow resonance model - based on the full 8
TeV dataset. In addition to publishing a 95% C.L. exclusion limit, the full
likelihood information for the narrow resonance model has been released. This
provides valuable information that can be incorporated into global BSM fits. We
present a simple algorithm that maps an arbitrary model with multiple neutral
Higgs bosons onto the narrow resonance model and derives the corresponding
value for the exclusion likelihood from the CMS search. This procedure has been
implemented into the public computer code HiggsBounds (version 4.2.0 and
higher). We validate our implementation by cross-checking against the official
CMS exclusion contours in three Higgs benchmark scenarios in the Minimal
Supersymmetric Standard Model (MSSM), and find very good agreement. Going
beyond validation, we discuss the combined constraints of the tau tau search
and the rate measurements of the SM-like Higgs at 125 GeV in a recently
proposed MSSM benchmark scenario, where the lightest Higgs boson obtains
SM-like couplings independently of the decoupling of the heavier Higgs states.
Technical details for how to access the likelihood information within
HiggsBounds are given in the appendix. The program is available at
http://higgsbounds.hepforge.org.
European Physical Journal C 07/2015; 75(9). DOI:10.1140/epjc/s10052-015-3650-z · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Electroweak precision observables, being highly sensitive to loop
contributions of new physics, provide a powerful tool to test the theory and to
discriminate between different models of the underlying physics. In that
context, the $W$ boson mass, $M_W$, plays a crucial role. The accuracy of the
$M_W$ measurement has been significantly improved over the last years, and
further improvement of the experimental accuracy is expected from future LHC
measurements. In order to fully exploit the precise experimental determination,
an accurate theoretical prediction for $M_W$ in the Standard Model (SM) and
extensions of it is of central importance. We present the currently most
accurate prediction for the $W$ boson mass in the Next-to-Minimal
Supersymmetric extension of the Standard Model (NMSSM), including the full
one-loop result and all available higher-order corrections of SM and SUSY type.
The evaluation of $M_W$ is performed in a flexible framework, which facilitates
the extension to other models beyond the SM. We show numerical results for the
$W$ boson mass in the NMSSM, focussing on phenomenologically interesting
scenarios, in which the Higgs signal can be interpreted as the lightest or
second lightest CP-even Higgs boson of the NMSSM. We find that, for both Higgs
signal interpretations, the NMSSM $M_W$ prediction is well compatible with the
measurement. We study the SUSY contributions to $M_W$ in detail and investigate
in particular the genuine NMSSM effects from the Higgs and neutralino sectors.
Journal of High Energy Physics 06/2015; 2015(9). DOI:10.1007/JHEP09(2015)158 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a frequentist analysis of the parameter space of the pMSSM10, in
which the following 10 soft SUSY-breaking parameters are specified
independently at the mean scalar top mass scale Msusy = Sqrt[M_stop1 M_stop2]:
the gaugino masses M_{1,2,3}, the 1st-and 2nd-generation squark masses M_squ1 =
M_squ2, the third-generation squark mass M_squ3, a common slepton mass M_slep
and a common trilinear mixing parameter A, the Higgs mixing parameter mu, the
pseudoscalar Higgs mass M_A and tan beta. We use the MultiNest sampling
algorithm with 1.2 x 10^9 points to sample the pMSSM10 parameter space. A
dedicated study shows that the sensitivities to strongly-interacting SUSY
masses of ATLAS and CMS searches for jets, leptons + MET signals depend only
weakly on many of the other pMSSM10 parameters. With the aid of the Atom and
Scorpion codes, we also implement the LHC searches for EW-interacting
sparticles and light stops, so as to confront the pMSSM10 parameter space with
all relevant SUSY searches. In addition, our analysis includes Higgs mass and
rate measurements using the HiggsSignals code, SUSY Higgs exclusion bounds, the
measurements B-physics observables, EW precision observables, the CDM density
and searches for spin-independent DM scattering. We show that the pMSSM10 is
able to provide a SUSY interpretation of (g-2)_mu, unlike the CMSSM, NUHM1 and
NUHM2. As a result, we find (omitting Higgs rates) that the minimum chi^2/dof =
20.5/18 in the pMSSM10, corresponding to a chi^2 probability of 30.8 %, to be
compared with chi^2/dof = 32.8/24 (31.1/23) (30.3/22) in the CMSSM (NUHM1)
(NUHM2). We display 1-dimensional likelihood functions for SUSY masses, and
show that they may be significantly lighter in the pMSSM10 than in the CMSSM,
NUHM1 and NUHM2. We discuss the discovery potential of future LHC runs, e+e-
colliders and direct detection experiments.
European Physical Journal C 04/2015; 75(9). DOI:10.1140/epjc/s10052-015-3599-y · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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 models of beyond the Standard
Model physics such as Supersymmetry, little Higgs models and extra gauge
bosons. The connection to cosmology has been analyzed as well.
[Show abstract][Hide abstract] ABSTRACT: The importance of off-shell contributions is discussed for $H\to VV^{(*)}$
with $V\in\{Z,W\}$ for large invariant masses $m_{VV}$ involving a standard
model (SM)-like Higgs boson with $m_H=125$GeV at a linear collider (LC). Both
dominant production processes $e^+e^-\to ZH\to ZVV^{(*)}$ and
$e^+e^-\to\nu\bar\nu H\to\nu\bar\nu VV^{(*)}$ are taken into account, and the
signal processes are compared with background yielding the same final state.
The relative size of the off-shell contributions is strongly dependent on the
centre-of-mass energy. These contributions can have an important impact on the
determination of cross sections and branching ratios. However, the combination
of on- and off-shell contributions can also be utilised to lift degeneracies
allowing to test higher-dimensional operators, unitarity and light and heavy
Higgs interferences in extended Higgs sectors. The latter is demonstrated in
the context of a 2-Higgs-Doublet model. Where relevant, the impact of these
aspects for physics at the Large Hadron Collider (LHC) is discussed. The
importance of a precise measurement of the Higgs mass for on-shell
contributions in $H\to VV^{(*)}$ is emphasized. A particular focus is put on
methods for extracting the Higgs width at a LC. Off-shell contributions are
shown to have a negligible impact on the width determination at low $\sqrt{s}$
when applying the $Z$ recoil method to extract branching ratios in combination
with an appropriate determination of a partial width. On the other hand,
off-shell contributions can be exploited to constrain the Higgs width in a
similar fashion as in recent analyses at the LHC. It is demonstrated that this
approach, besides relying heavily on theoretical assumptions, is affected by
the negative interference of Higgs and background contributions that may limit
the sensitivity that is achievable with the highest foreseeable statistics at
the LHC and a LC.
Journal of High Energy Physics 02/2015; 2015(6). DOI:10.1007/JHEP06(2015)093 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A generalisation of the narrow-width approximation (NWA) is formulated which
allows for a consistent treatment of interference effects between nearly
mass-degenerate particles in the factorisation of a more complicated process
into production and decay parts. It is demonstrated that interference effects
of this kind arising in BSM models can be very large, leading to drastic
modifications of predictions based on the standard NWA. The application of the
generalised NWA is demonstrated both at tree level and at one-loop order for an
example process where the neutral Higgs bosons $h$ and $H$ of the MSSM are
produced in the decay of a heavy neutralino and subsequently decay into a
fermion pair. The generalised NWA, based on on-shell matrix elements or their
approximations leading to simple weight factors, is shown to produce UV- and
IR-finite results which are numerically close to the result of the full process
at tree level and at one-loop order, where an agreement of better than $1\%$ is
found for the considered process. The most accurate prediction for this process
based on the generalised NWA, taking into account also corrections that are
formally of higher orders, is briefly discussed.
European Physical Journal C 11/2014; 75(6). DOI:10.1140/epjc/s10052-015-3472-z · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We make a frequentist analysis of the parameter space of the NUHM2, in which
the soft supersymmetry (SUSY)-breaking contributions to the masses of the two
Higgs multiplets, $m^2_{H_{u,d}}$, vary independently from the universal soft
SUSY-breaking contributions $m^2_0$ to the masses of squarks and sleptons. Our
analysis uses the MultiNest sampling algorithm with over $4 \times 10^8$ points
to sample the NUHM2 parameter space. It includes the ATLAS and CMS Higgs mass
measurements as well as their searches for supersymmetric jets + MET signals
using the full LHC Run~1 data, the measurements of $B_s \to \mu^+ \mu^-$ by
LHCb and CMS together with other B-physics observables, electroweak precision
observables and the XENON100 and LUX searches for spin-independent dark matter
scattering. We find that the preferred regions of the NUHM2 parameter space
have negative SUSY-breaking scalar masses squared for squarks and sleptons,
$m_0^2 < 0$, as well as $m^2_{H_u} < m^2_{H_d} < 0$. The tension present in the
CMSSM and NUHM1 between the supersymmetric interpretation of $g_\mu - 2$ and
the absence to date of SUSY at the LHC is not significantly alleviated in the
NUHM2. We find that the minimum $\chi^2 = 32.5$ with 21 degrees of freedom
(dof) in the NUHM2, to be compared with $\chi^2/{\rm dof} = 35.0/23$ in the
CMSSM, and $\chi^2/{\rm dof} = 32.7/22$ in the NUHM1. We find that the
one-dimensional likelihood functions for sparticle masses and other observables
are similar to those found previously in the CMSSM and NUHM1.
European Physical Journal C 08/2014; 74(12). DOI:10.1140/epjc/s10052-014-3212-9 · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: For the interpretation of the signal discovered in the Higgs searches at the LHC it will be crucial in particular to discriminate between the minimal Higgs sector realized in the standard model (SM) and its most commonly studied extension, the minimal supersymmetric standard model (MSSM). The measured mass value, having already reached the level of a precision observable with an experimental accuracy of about 500 MeV, plays an important role in this context. In the MSSM the mass of the light CP-even Higgs boson, Mh, can directly be predicted from the other parameters of the model. The accuracy of this prediction should at least match the one of the experimental result. The relatively high mass value of about 126 GeV has led to many investigations where the scalar top quarks are in the multi-TeV range. We improve the prediction for Mh in the MSSM by combining the existing fixed-order result, comprising the full one-loop and leading and subleading two-loop corrections, with a resummation of the leading and subleading logarithmic contributions from the scalar top sector to all orders. In this way for the first time a high-precision prediction for the mass of the light CP-even Higgs boson in the MSSM is possible all the way up to the multi-TeV region of the relevant supersymmetric particles. The results are included in the code FeynHiggs.
[Show abstract][Hide abstract] ABSTRACT: The signal discovered in the Higgs searches at the LHC can be interpreted as
the Higgs boson of the Standard Model as well as the light CP-even Higgs boson
of the Minimal Supersymmetric Standard Model (MSSM). In this context the
measured mass value, having already reached the level of a precision observable
with an experimental accuracy of about 500 MeV, plays an important role. This
precision can be improved substantially below the level of about 50 MeV at the
future International Linear Collider (ILC). Within the MSSM the mass of the
light CP-even Higgs boson, M_h, can directly be predicted from the other
parameters of the model. The accuracy of this prediction should match the one
of the experimental measurements. The relatively high experimentally observed
value of the mass of about 125.6 GeV has led to many investigations where the
supersymmetric (SUSY) partners of the top quark have masses in the multi-TeV
range. We review the recent improvements for the prediction for M_h in the MSSM
for large scalar top masses. They were obtained by combining the existing
fixed-order result, comprising the full one-loop and leading and subleading
two-loop corrections, with a resummation of the leading and subleading
logarithmic contributions from the scalar top sector to all orders. In this way
for the first time a high-precision prediction for the mass of the light
CP-even Higgs boson in the MSSM is possible all the way up to the multi-TeV
region of the relevant supersymmetric particles. However, substantial further
improvements will be needed to reach the ILC precision. The newly obtained
corrections to M_h are included into the code FeynHiggs.
[Show abstract][Hide abstract] ABSTRACT: We explore the room for possible deviations from the Standard Model (SM)
Higgs boson coupling structure in a systematic study of Higgs coupling scale
factor benchmark scenarios using the latest signal rate measurements from the
Tevatron and LHC experiments. We employ a profile likelihood method based on a
chi-squared test performed with HiggsSignals, which takes into account detailed
information on signal efficiencies and major correlations of theoretical and
experimental uncertainties. All considered scenarios allow for additional
non-standard Higgs boson decay modes, and various assumptions for constraining
the total decay width are discussed. No significant deviations from the SM
Higgs boson coupling structure are found in any of the investigated benchmark
scenarios. We derive upper limits on an additional (undetectable) Higgs decay
mode under the assumption that the Higgs couplings to weak gauge bosons do not
exceed the SM prediction. We furthermore discuss the capabilities of future
facilities for probing deviations from the SM Higgs couplings, comparing the
high luminosity upgrade of the LHC with a future International Linear Collider
(ILC), where for the latter various energy and luminosity scenarios are
considered. At the ILC model-independent measurements of the coupling structure
can be performed, and we provide estimates of the precision that can be
achieved.
Journal of High Energy Physics 03/2014; 2014(11). DOI:10.1007/JHEP11(2014)039 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We discuss the allowed parameter spaces of supersymmetric scenarios in light
of improved Higgs mass predictions provided by FeynHiggs 2.10.0. The Higgs mass
predictions combine Feynman-diagrammatic results with a resummation of leading
and subleading logarithmic corrections from the stop/top sector, which yield a
significant improvement in the region of large stop masses. Scans in the pMSSM
parameter space show that, for given values of the soft supersymmetry-breaking
parameters, the new logarithmic contributions beyond the two-loop order
implemented in FeynHiggs tend to give larger values of the light CP-even Higgs
mass, M_h, in the region of large stop masses than previous predictions that
were based on a fixed-order Feynman-diagrammatic result, though the differences
are generally consistent with the previous estimates of theoretical
uncertainties. We re-analyze the parameter spaces of the CMSSM, NUHM1 and
NUHM2, taking into account also the constraints from CMS and LHCb measurements
of B_s to \mu+\mu- and ATLAS searches for MET events using 20/fb of LHC data at
8 TeV. Within the CMSSM, the Higgs mass constraint disfavours tan beta lesssim
10, though not in the NUHM1 or NUHM2.
European Physical Journal C 12/2013; 74(3). DOI:10.1140/epjc/s10052-014-2809-3 · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We analyze the impact of data from the full Run 1 of the LHC at 7 and 8 TeV
on the CMSSM with mu > 0 and < 0 and the NUHM1 with mu > 0, incorporating the
constraints imposed by other experiments such as precision electroweak
measurements, flavour measurements, the cosmological density of cold dark
matter and the direct search for the scattering of dark matter particles in the
LUX experiment. We use the following results from the LHC experiments: ATLAS
searches for events with MET accompanied by jets with the full 7 and 8 TeV
data, the ATLAS and CMS measurements of the mass of the Higgs boson, the CMS
searches for heavy neutral Higgs bosons and a combination of the LHCb and CMS
measurements of B_s to mu+mu- and B_d to mu+mu-. Our results are based on
samplings of the parameter spaces of the CMSSM for both mu>0 and mu<0 and of
the NUHM1 for mu > 0 with 6.8 x 10^6, 6.2 x 10^6 and 1.6 x 10^7 points,
respectively, obtained using the MultiNest tool. The impact of the Higgs mass
constraint is assessed using FeynHiggs 2.10.0, which provides an improved
prediction for the masses of the MSSM Higgs bosons in the region of heavy
squark masses. It yields in general larger values of M_h than previous versions
of FeynHiggs, reducing the pressure on the CMSSM and NUHM1. We find that the
global chi^2 functions for the supersymmetric models vary slowly over most of
the parameter spaces allowed by the Higgs mass and the MET searches, with
best-fit values that are comparable to the chi^2/dof for the best Standard
Model fit. We provide 95% CL lower limits on the masses of various sparticles
and assess the prospects for observing them during Run 2 of the LHC.
European Physical Journal C 12/2013; 74(6). DOI:10.1140/epjc/s10052-014-2922-3 · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present the currently most precise W boson mass (M_W) prediction in the
Minimal Supersymmetric Standard Model (MSSM) and discuss how it is affected by
recent results from the LHC. The evaluation includes the full one-loop result
and all known higher order corrections of SM and SUSY type. We show the MSSM
prediction in the M_W-m_t plane, taking into account constraints from Higgs and
SUSY searches. We point out that even if stops and sbottoms are heavy,
relatively large SUSY contributions to M_W are possible if either charginos,
neutralinos or sleptons are light. In particular we analyze the effect on the
M_W prediction of the Higgs signal at about 125.6 GeV, which within the MSSM
can in principle be interpreted as the light or the heavy CP-even Higgs boson.
For both interpretations the predicted MSSM region for M_W is in good agreement
with the experimental measurement. We furthermore discuss the impact of
possible future LHC results in the stop sector on the M_W prediction,
considering both the cases of improved limits and of the detection of a scalar
top quark.
Journal of High Energy Physics 11/2013; 2013(12). DOI:10.1007/JHEP12(2013)084 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We describe the new developments in version 4 of the public computer code
HiggsBounds. HiggsBounds is a tool to test models with arbitrary Higgs sectors,
containing both neutral and charged Higgs bosons, against the published
exclusion bounds from Higgs searches at the LEP, Tevatron and LHC experiments.
From the model predictions for the Higgs masses, branching ratios, production
cross sections and total decay widths - which are specified by the user in the
input for the program - the code calculates the predicted signal rates for the
search channels considered in the experimental data. The signal rates are
compared to the expected and observed cross section limits from the Higgs
searches to determine whether a point in the model parameter space is excluded
at 95% confidence level. In this document we present a modification of the
HiggsBounds main algorithm that extends the exclusion test in order to ensure
that it provides useful results in the presence of one or more significant
excesses in the data, corresponding to potential Higgs signals. We also
describe a new method to test whether the limits from an experimental search
performed under certain model assumptions can be applied to a different
theoretical model. Further developments discussed here include a framework to
take into account theoretical uncertainties on the Higgs mass predictions, and
the possibility to obtain the $\chi^2$ likelihood of Higgs exclusion limits
from LEP. Extensions to the user subroutines from earlier versions of
HiggsBounds are described. The new features are demonstrated by additional
example programs.
European Physical Journal C 10/2013; 74(3). DOI:10.1140/epjc/s10052-013-2693-2 · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: With the discovery of the Higgs boson, the spectrum of particles in the
Standard Model (SM) is complete. It is more important than ever to perform
precision measurements and to test for deviations from SM predictions in the
electroweak sector. In this report, we investigate two themes in the arena of
precision electroweak measurements: the electroweak precision observables
(EWPOs) that test the particle content and couplings in the SM and the minimal
supersymmetric SM, and the measurements involving multiple gauge bosons in the
final state which provide unique probes of the basic tenets of electroweak
symmetry breaking. Among the important EWPOs we focus our discussion on M_W and
sin^2 theta_eff^l, and on anomalous quartic gauge couplings probed by triboson
production and vector boson scattering. We investigate the thresholds of
precision that need to be achieved in order to be sensitive to new physics. We
study the precision that can be achieved at various facilities on these
observables. We discuss the calculational tools needed to predict SM rates and
distributions in order to perform these measurements at the required precision.
This report summarizes the work of the Energy Frontier Precision Study of
Electroweak Interactions working group of the 2013 Community Summer Study
(Snowmass).
[Show abstract][Hide abstract] ABSTRACT: The ILC Higgs White Paper is a review of Higgs Boson theory and experiment at
the International Linear Collider (ILC). Theory topics include the Standard
Model Higgs, the two-Higgs doublet model, alternative approaches to electroweak
symmetry breaking, and precision goals for Higgs boson experiments.
Experimental topics include the measurement of the Higgs cross section times
branching ratio for various Higgs decay modes at ILC center of mass energies of
250, 500, and 1000 GeV, and the extraction of Higgs couplings and the total
Higgs width from these measurements. Luminosity scenarios based on the ILC TDR
machine design are used throughout. The gamma-gamma collider option at the ILC
is also discussed.
[Show abstract][Hide abstract] ABSTRACT: 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 report Handbook of LHC Higgs Cross
Sections: 1. Inclusive Observables (CERN-2011-002) and the second working group
report Handbook of LHC Higgs Cross Sections: 2. Differential Distributions
(CERN-2012-002). After the discovery of a Higgs boson at the LHC in mid-2012
this report focuses on refined prediction of Standard Model (SM) Higgs
phenomenology around the experimentally observed value of 125-126 GeV, refined
predictions for heavy SM-like Higgs bosons as well as predictions in the
Minimal Supersymmetric Standard Model and first steps to go beyond these
models. The other main focus is on the extraction of the characteristics and
properties of the newly discovered particle such as couplings to SM particles,
spin and CP-quantum numbers etc.
[Show abstract][Hide abstract] ABSTRACT: The interpretation of the Higgs signal at \sim 126 GeV within the Minimal
Supersymmetric Standard Model (MSSM) depends crucially on the predicted
properties of the other Higgs states of the model, as the mass of the charged
Higgs boson, MH+-. This mass is calculated in the Feynman-diagrammatic approach
within the MSSM with real parameters. The result includes the complete one-loop
contributions and the two-loop contributions of O(alpha_t alpha_s). The
one-loop contributions lead to sizable shifts in the MH+- prediction, reaching
up to \sim 8 GeV for relatively small values of M_A. Even larger effects can
occur depending on the sign and size of the mu parameter that enters the
corrections affecting the relation between the bottom-quark mass and the bottom
Yukawa coupling. The two-loop O(alpha_t alpha_s) terms can shift MH+- by more
than 2 GeV. The two-loop contributions amount to typically about 30% of the
one-loop corrections for the examples that we have studied. These effects can
be relevant for precision analyses of the charged MSSM Higgs boson.