69 research outputs found
Precise determination of the Higgs mass in supersymmetric models with vectorlike tops and the impact on naturalness in minimal GMSB
We present a precise analysis of the Higgs mass corrections stemming from
vectorlike top partners in supersymmetric models. We reduce the theoretical
uncertainty compared to previous studies in the following aspects: (i)
including the one-loop threshold corrections to SM gauge and Yukawa couplings
due to the presence of the new states to obtain the
parameters entering all loop calculations, (ii) including the full momentum
dependence at one-loop, and (iii) including all two-loop corrections but the
ones involving and . We find that the additional threshold
corrections are very important and can give the largest effect on the Higgs
mass. However, we identify also parameter regions where the new two-loop
effects can be more important than the ones of the MSSM and change the Higgs
mass prediction by up to 10 GeV. This is for instance the case in the low
, small regime. We use these results to calculate the
electroweak fine-tuning of an UV complete variant of this model. For this
purpose, we add a complete and representation
of to the MSSM particle content. We embed this model in minimal Gauge
Mediated Supersymmetry Breaking and calculate the electroweak fine-tuning with
respect to all important parameters. It turns out that the limit on the gluino
mass becomes more important for the fine-tuning than the Higgs mass
measurements which is easily to satisfy in this setup.Comment: 64 pages, 17 figure
On the two-loop corrections to the Higgs masses in the NMSSM
We discuss the impact of the two-loop corrections to the Higgs mass in the
NMSSM beyond . For this purpose we use the
combination of the public tools SARAH and SPheno to include all contributions
stemming from superpotential parameters. We show that the corrections in the
case of a heavy singlet are often MSSM-like and reduce the predicted mass of
the SM-like state by about 1 GeV as long as is moderately large. For
larger values of the additional corrections can increase the SM-like
Higgs mass. If a light singlet is present the additional corrections become
more important even for smaller values of and can even dominate the
ones involving the strong interaction. In this context we point out that
important effects are not reproduced quantitatively when only including
corrections known from the MSSM.Comment: 23 pages, 11 figure
The Higgs Mass in the MSSM at two-loop order beyond minimal flavour violation
Soft supersymmetry-breaking terms provide a wealth of new potential sources
of flavour violation, which are tightly constrained by precision experiments.
This has posed a challenge to construct flavour models which both explain the
structure of the Standard Model Yukawa couplings and also predict soft-breaking
patterns that are compatible with these constraints. While such models have
been studied in great detail, the impact of flavour violating soft terms on the
Higgs mass at the two-loop level has been assumed to be small or negligible. In
this letter, we show that large flavour violation in the up-squark sector can
give a positive or negative mass shift to the SM-like Higgs of several GeV,
without being in conflict with other observations. We investigate in which
regions of the parameter space these effects can be expected.Comment: 8 pages, 9 figure
Precision Calculations in Supersymmetric Models using Phenomenological Tools
We present a Higgs mass calculation at two-loop level based on the effective potential approach, which has been made available in the public computer codes SARAH and SPheno. The approach is based on generic formulae for the two-loop effective potential available from literature and can be applied to a large number of renormalisable supersymmetric models in a highly automated way. Three equivalent algorithms are presented, which are completely independent of one another. The code enables the study of the neutral Higgs boson masses at two loops in models beyond the MSSM with a similar precision as has been widely available in MSSM spectrum generators before the Higgs discovery in 2012. Details about the implementation, validation and limitations of the code are presented. This precision calculation is applied to four supersymmetric models, including the MSSM with large flavour violation, the MSSM with R-parity violation and the NMSSM, where we found throughout that the two-loop corrections give rise to significant contributions. An additional model, namely the MSSM extended by vectorlike quarks, is also studied. Here we do not focus only on the two-loop Higgs mass but also on the fine-tuning in the context of gauge mediated supersymmetry breaking. Finally, we present a collider study examining the production of exotic long-lived neutral particles at the LHC, assuming that these particles escape the detector. By applying analyses from the ATLAS and CMS collaborations that focus on a large missing transverse energy signature, we obtain upper cross section limits for arbitrary lifetimes. We found this method to be a complementary approach compared to traditional displaced vertex searches
Hunting for neutral, long-lived exotica at the LHC using a missing transverse energy signature
Searches at the Large Hadron Collider (LHC) for neutral, long-lived particles
have historically relied on the detection of displaced particles produced by
their decay the detector volume. In this paper we study the
potential of the complementary signature comprising of the missing transverse
energy () signal, traditionally used to look for dark matter, e.g.,
the lightest supersymmetric particle (LSP), to extend the LHC coverage to
models with long-lived (LL) particles when they decay the
detector. Using CMS and ATLAS analyses at the 8 TeV LHC, we set an upper limit
at the 95% confidence level (CL) on the production cross sections for two
specific scenarios: (i) a model with a heavy non-standard model Higgs boson
decaying to a LL scalar and (ii) an R-parity violating RPV SUSY model with a LL
neutralino.
We show that this method can significantly extend the LHC sensitivity to
neutral, LL particles with arbitrary large lifetimes and that the limits
obtained from a signal are comparable to those from displaced
particle searches for decay distances above a few meters. Results obtained in
this study do not not depend on the specific decay channel of the LL particle
and therefore are model-independent in this sense. We provide limits for the
whole two-dimensional plane in terms of the mass of the LL particle and the
mass of the mediator up to masses of 2 TeV including particular benchmarks
studied in the original experimental papers. We have made these limits
available in the form of a grid which can be used for the interpretation of
various other new physics models.Comment: 28 page
On the two-loop corrections to the Higgs mass in trilinear R-parity violation
We study the impact of large trilinear R-parity violating couplings on the
lightest CP-even Higgs boson mass in supersymmetric models. We use the publicly
available computer codes SARAH and SPheno to compute the leading two-loop
corrections. We use the effective potential approach. For not too heavy third
generation squarks (< 1 TeV) and couplings close to the unitarity bound we find
positive corrections up to a few GeV in the Higgs mass.Comment: 6 pages, 5 figure
Lead-free, luminescent perovskite nanocrystals obtained through ambient condition synthesis
Heterovalent substitution of toxic lead is an increasingly popular design
strategy to obtain environmentally sustainable variants of the exciting
material class of halide perovskites. Perovskite nanocrystals (NCs) obtained
through solution-based methods exhibit exceedingly high optical quality.
Unfortunately, most of these synthesis routes still require reaction under
inert gas and at very high temperatures. Herein we present a novel synthesis
routine for lead-free double perovskite NCs. We combine hot injection and
ligand-assisted reprecipitation (LARP) methods to achieve a low-temperature and
ambient atmosphere-based synthesis for manganese-doped Cs_{2}NaBiCl_{6} NCs. Mn
incorporation is critical for the otherwise non-emissive material, with a 9:1
Bi:Mn precursor ratio maximizing the bright orange photoluminescence (PL) and
quantum yield (QY). Higher temperatures slightly increased the material's
performance, yet NCs synthesized at room temperature were still emissive,
highlighting the versatility of the synthetic approach. Furthermore, the NCs
show excellent long-term stability in ambient conditions, facilitating
additional investigations and energy-related applications
Precision tools and models to narrow in on the 750 GeV diphoton resonance
The hints for a new resonance at 750 GeV from ATLAS and CMS have triggered a
significant amount of attention. Since the simplest extensions of the standard
model cannot accommodate the observation, many alternatives have been
considered to explain the excess. Here we focus on several proposed
renormalisable weakly-coupled models and revisit results given in the
literature. We point out that physically important subtleties are often missed
or neglected. To facilitate the study of the excess we have created a
collection of 40 model files, selected from recent literature, for the
Mathematica package SARAH. With SARAH one can generate files to perform
numerical studies using the tailor-made spectrum generators FlexibleSUSY and
SPheno. These have been extended to automatically include crucial higher order
corrections to the diphoton and digluon decay rates for both CP-even and CP-odd
scalars. Additionally, we have extended the UFO and CalcHep interfaces of
SARAH, to pass the precise information about the effective vertices from the
spectrum generator to a Monte-Carlo tool. Finally, as an example to demonstrate
the power of the entire setup, we present a new supersymmetric model that
accommodates the diphoton excess, explicitly demonstrating how a large width
can be obtained. We explicitly show several steps in detail to elucidate the
use of these public tools in the precision study of this model.Comment: 184 pages, 24 figures; model files available at
http://sarah.hepforge.org/Diphoton_Models.tar.gz; v2: added a few
clarifications and reference
FineâTuning BlueâEmitting Halide Perovskite Nanocrystals
Lead halide perovskite nanocrystals (NCs) with narrow, bright emission in the visible range are promising candidates for light-emitting applications. Near-unity quantum yields have been realized for green and red-emitting perovskites, but efficient, stable blue-emitting perovskite materials are scarce. Current methods to synthesize quantum-confined CsPbBr3 NCs with blue emission are limited to specific wavelength ranges and still suffer from inhomogeneously broadened emission profiles. Herein, anisotropic blue-green emitting CsPbBr3 NCs are synthesized in ambient atmosphere using a spontaneous crystallization method. Optical spectroscopy reveals a gradual, asymptotic photoluminescence (PL) redshift of pristine colloidal NCs after synthesis. During this process, the emission quality improves notably as the PL spectra become narrower and more symmetric, accompanied by a PL intensity increase. Electron microscopy indicates that the gradual redshift stems from an isotropic growth of the CsPbBr3 NCs in at least two dimensions, likely due to residual precursor ions in the dispersion. Most importantly, the growth process can be halted at any point by injecting an enhancement solution containing PbBr2 and organic capping ligands. Thus, excellent control over NC size is achieved, allowing for nanometer-precise tunability of the respective emission wavelength in the range between 475 and 500 nm, enhancing the functionality of these already impressive NCs
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