arXiv subjects

Dominik Stöckinger

Publications and source records attributed to Dominik Stöckinger.

At least 55 records · Page 3Linked to original sources

arXiv2018

FlexibleSUSY 2.0: Extensions to investigate the phenomenology of SUSY and non-SUSY models

We document major new features and improvements of FlexibleSUSY, a Mathematica and C++ package with a dependency on the external package SARAH, that generates fast and precise spectrum generators. The extensions presented here significantly increase the generality and capabilities of the FlexibleSUSY package, which already works with a wide class of models, while maintaining an elegant structure and easy to use interfaces. The FlexibleBSM extension makes it possible to also create spectrum generators for non-supersymmetric extensions of the Standard Model. The FlexibleCPV extension adds the option of complex parameters to the spectrum generators, allowing the study of many interesting models with new sources of $CP$ violation. FlexibleMW computes the decay of the muon for the generated model and thereby allows FlexibleSUSY to predict the mass of the $W$ boson from the input parameters by using the more precise electroweak input of $\{ G_F, M_Z, α_{\text{em}} \}$ instead of $\{ M_W, M_Z, α_{\text{em}} \}$. The FlexibleAMU extension provides a calculator of the anomalous magnetic moment of the muon in any model FlexibleSUSY can generate a spectrum for. FlexibleSAS introduces a new solver for the boundary value problem which makes use of semi-analytic expressions for dimensionful parameters to find solutions in models where the classic two-scale solver will not work such as the constrained E$_6$SSM. FlexibleEFTHiggs is a hybrid calculation of the Higgs mass which combines the virtues of both effective field theory calculations and fixed-order calculations. All of these extensions are included in FlexibleSUSY 2.0, which is released simultaneously with this manual.

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arXiv2018

Muon g-2 in the 2HDM: maximum results and detailed phenomenology

We present a comprehensive analysis of the muon magnetic moment $a_μ$ in the flavour-aligned two-Higgs doublet model (2HDM) and parameter constraints relevant for $a_μ$. We employ a recent full two-loop computation of $a_μ$ and take into account experimental constraints from Higgs and flavour physics on the parameter space. Large $a_μ$ is possible for light pseudoscalar Higgs A with large Yukawa couplings to leptons, and it can be further increased by large A coupling to top quarks. We investigate in detail the maximum possible Yukawa couplings to leptons and quarks of a light A, finding values of around 50...100 (leptons) and O(0.5) (quarks). As a result we find that an overall maximum of $a_μ$ in the 2HDM of more than $45\times10^{-10}$ is possible in a very small parameter region around M_A=20 GeV. The parameter regions in which the currently observed deviation can be explained are characterized.

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arXiv2017

Squark production in R-symmetric SUSY with Dirac gluinos: NLO corrections

R-symmetry leads to a distinct realisation of SUSY with a significantly modified coloured sector featuring a Dirac gluino and a scalar colour octet (sgluon). We present the impact of R-symmetry on squark production at the 13 TeV LHC. We study the total cross sections and their NLO corrections from all strongly interacting states, their dependence on the Dirac gluino mass and sgluon mass as well as their systematics for selected benchmark points. We find that tree-level cross sections in the R-symmetric model are reduced compared to the MSSM but the NLO K-factors are generally larger in the order of ten to twenty per cent. In the course of this work we derive the required DREG $\to$ DRED transition counterterms and necessary on-shell renormalisation constants. The real corrections are treated using FKS subtraction, with results cross checked against an independent calculation employing the two cut phase space slicing method.

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arXiv2017

Precise Higgs mass calculations in (non-)minimal supersymmetry at both high and low scales

We present FlexibleEFTHiggs, a method for calculating the SM-like Higgs pole mass in SUSY (and even non-SUSY) models, which combines an effective field theory approach with a diagrammatic calculation. It thus achieves an all order resummation of leading logarithms together with the inclusion of all non-logarithmic 1-loop contributions. We implement this method into FlexibleSUSY and study its properties in the MSSM, NMSSM, E6SSM and MRSSM. In the MSSM, it correctly interpolates between the known results of effective field theory calculations in the literature for a high SUSY scale and fixed-order calculations in the full theory for a sub-TeV SUSY scale. We compare our MSSM results to those from public codes and identify the origin of the most significant deviations between the DR-bar programs. We then perform a similar comparison in the remaining three non-minimal models. For all four models we estimate the theoretical uncertainty of FlexibleEFTHiggs and the fixed-order DR-bar programs thereby finding that the former becomes more precise than the latter for a SUSY scale above a few TeV. Even for sub-TeV SUSY scales, FlexibleEFTHiggs maintains the uncertainty estimate around 2-3 GeV, remaining a competitive alternative to existing fixed-order computations.

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arXiv2015

Exploring the Higgs sector of the MRSSM with a light scalar

In a recent paper we showed that the Minimal R-symmetric Supersymmetric Standard Model (MRSSM) can accommodate the observed 125 GeV Higgs boson as the lightest scalar of the model in agreement with electroweak precision observables, in particular with the W boson mass and $T$ parameter. Here we explore a scenario with the light singlet (and bino-singlino) state in which the second-lightest scalar takes the role of the SM-like boson with mass close to 125 GeV. In such a case the second-lightest Higgs state gets pushed up via mixing already at tree-level and thereby reducing the required loop correction. Unlike in the NMSSM, the light singlet is necessarily connected with a light neutralino which naturally appears as a promising dark matter candidate. We show that dark matter and LHC searches place further bounds on this scenario and point out parameter regions, which are viable and of interest for LHC Run II and upcoming dark matter experiments.

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arXiv2015

GM2Calc: Precise MSSM prediction for $(g - 2)$ of the muon

We present GM2Calc, a public C++ program for the calculation of MSSM contributions to the anomalous magnetic moment of the muon, $(g-2)_μ$. The code computes $(g-2)_μ$ precisely, by taking into account the latest two-loop corrections and by performing the calculation in a physical on-shell renormalization scheme. In particular the program includes a $\tanβ$ resummation so that it is valid for arbitrarily high values of $\tanβ$, as well as fermion/sfermion-loop corrections which lead to non-decoupling effects from heavy squarks. GM2Calc can be run with a standard SLHA input file, internally converting the input into on-shell parameters. Alternatively, input parameters may be specified directly in this on-shell scheme. In both cases the input file allows one to switch on/off individual contributions to study their relative impact. This paper also provides typical usage examples not only in conjunction with spectrum generators and plotting programs but also as C++ subroutines linked to other programs.

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arXiv2015

Large muon $(g-2)$ from TeV-scale MSSM with infinite $\tanβ$

The muon anomalous magnetic moment $a_μ$ is studied in the infinite $\tanβ$ limit of the MSSM. Since the muon mass arises completely from loop effects, large corrections to $a_μ$ are expected in comparison to the usual case with moderately high $\tanβ$. Due to the qualitatively different parameter dependence, the gap between the experimental value and the Standard Model prediction can be filled only in parameter volumes in which a mass hierarchy suppresses the chargino loop in favour of the neutralino contribution. Two such possibilities are found to have either large Higgsino mass or large muon sneutrino mass. Supersymmetric particles even at the TeV scale can lead to the best fit of $a_μ$.

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arXiv2015

Large muon $(g-2)$ with TeV-scale SUSY masses for $\tanβ\to\infty$

The muon anomalous magnetic moment $a_μ$ is investigated in the MSSM for $\tanβ\to\infty$. This is an attractive example of radiative muon mass generation with completely different qualitative parameter dependence compared to the MSSM with the usual, finite $\tanβ$. The observed, positive difference between the experimental and Standard Model value can only be explained if there are mass splittings, such that bino contributions dominate over wino ones. The two most promising cases are characterized either by large Higgsino mass $μ$ or by large left-handed smuon mass $m_L$. The required mass splittings and the resulting $a_μ^\text{SUSY}$ are studied in detail. It is shown that the current discrepancy in $a_μ$ can be explained even in cases where all SUSY masses are at the TeV scale. The paper also presents useful analytical formulas, approximations for limiting cases, and benchmark points.

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arXiv2015

Two-loop correction to the Higgs boson mass in the MRSSM

We present the impact of two-loop corrections on the mass of the lightest Higgs boson in the Minimal R-symmetric Supersymmetric Standard Model (MRSSM). These shift the Higgs boson mass up by typically 5 GeV or more. The dominant corrections arise from strong interactions, from the gluon and its N=2 superpartners, the sgluon and Dirac gluino, and these corrections further increase with large Dirac gluino mass. The two-loop contributions governed purely by Yukawa couplings and the MRSSM $λ,Λ$ parameters are smaller. We also update an earlier analysis [Diessner:2014ksa], which showed that the MRSSM can accommodate the measured Higgs and W boson masses. Including the two-loop corrections increases the parameter space where the theory prediction agrees with the measurement.

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arXiv2015

FlexibleSUSY -- A spectrum generator generator for supersymmetric models

We introduce FlexibleSUSY, a Mathematica and C++ package, which generates a fast, precise C++ spectrum generator for any SUSY model specified by the user. The generated code is designed with both speed and modularity in mind, making it easy to adapt and extend with new features. The model is specified by supplying the superpotential, gauge structure and particle content in a SARAH model file; specific boundary conditions e.g. at the GUT, weak or intermediate scales are defined in a separate FlexibleSUSY model file. From these model files, FlexibleSUSY generates C++ code for self-energies, tadpole corrections, renormalization group equations (RGEs) and electroweak symmetry breaking (EWSB) conditions and combines them with numerical routines for solving the RGEs and EWSB conditions simultaneously. The resulting spectrum generator is then able to solve for the spectrum of the model, including loop-corrected pole masses, consistent with user specified boundary conditions. The modular structure of the generated code allows for individual components to be replaced with an alternative if available. FlexibleSUSY has been carefully designed to grow as alternative solvers and calculators are added. Predefined models include the MSSM, NMSSM, E$_6$SSM, USSM, R-symmetric models and models with right-handed neutrinos.

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arXiv2014

Higgs boson mass and electroweak observables in the MRSSM

R-symmetry is a fundamental symmetry which can solve the SUSY flavor problem and relax the search limits on SUSY masses. Here we provide a complete next-to-leading order computation and discussion of the lightest Higgs boson mass, the W boson mass and muon decay in the minimal R-symmetric SUSY model (MRSSM). This model contains non-MSSM particles including a Higgs triplet, Dirac gauginos and higgsinos, and leads to significant new tree-level and one-loop contributions to these observables. We show that the model can accommodate the measured values of the observables for interesting regions of parameter space with stop masses of order 1 TeV in spite of the absence of stop mixing. We characterize these regions and provide typical benchmark points, which are also checked against further experimental constraints. A detailed exposition of the model, its mass matrices and its Feynman rules relevant for computations in this paper is also provided.

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arXiv2014

FlexibleSUSY - a meta spectrum generator for supersymmetric models

FlexibleSUSY is a software package that takes as input descriptions of (non-)minimal supersymmetric models written in Wolfram/Mathematica and generates a set of spectrum generator libraries and executables, with the aid of SARAH. The design goals are precision, reliability, modularity, speed, and readability of the code. The boundary conditions are independent C++ objects that are plugged into the boundary value problem solver together with the model objects. This clean separation makes it easy to adapt the generated code for individual projects. The current status of the interface and implementation is sketched.

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arXiv2014

Understanding the correlation between $(g-2)_μ$ and $μ\rightarrow e γ$ in the MSSM

The supersymmetric contributions to the muon anomalous magnetic moment $a_μ$ and to the decay $μ\to eγ$ are given by very similar Feynman diagrams. Previous works reported correlations in specific scenarios, in particular if $a_μ$ is dominated by a single diagram. In this work we give an extensive survey of the possible correlations. We discuss examples of single-diagram domination with particularly strong correlations, and provide corresponding benchmark parameter points. We show how the correlations are weakened by significant cancellations between diagrams in large parts of the MSSM parameter space. Nevertheless, the order of magnitude of $\text{BR}(μ\to e γ)$ for a fixed flavor-violating parameter can often be predicted. We summarize the behavior by plotting the correlations as well as resulting bounds on the flavor-violating parameters under various assumptions on the MSSM spectrum.

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arXiv2014

Two-loop corrections to $(g-2)_μ$ in the SM and the MSSM

Recent results of two-loop contributions to the muon (g-2) in the Standard Model and its supersymmetric extension are presented. In the SM the EW contributions are fixed according to the Higgs boson mass measured at LHC. In the MSSM we present the recent result of fermion/sfermion two-loop contributions. The fermion/sfermion contributions are logarithmically enhanced for large sfermion masses and can yield the largest corrections compared to all previously known MSSM two-loop contributions. Numerical results in scenarios which are compatible with LHC data are also presented. We find up to 15\% (30\%) corrections for sfermion masses in the 20 TeV (1000 TeV) range.

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arXiv2014

Two-loop results on the renormalization of vacuum expectation values and infrared divergences in the FDH scheme

Recent progress in the understanding of vacuum expectation values and of infrared divergences in different regularization schemes is reviewed. Vacuum expectation values are gauge and renormalization-scheme dependent quantities. Using a method based on Slavnov-Taylor identities, the renormalization properties could be better understood. The practical outcome is the computation of the beta functions for vacuum expectation values in general gauge theories. The infrared structure of gauge theory amplitudes depends on the regularization scheme. The well-known prediction of the infrared structure in CDR can be generalized to the FDH and DRED schemes and is in agreement with explicit computations of the quark and gluon form factors. We discuss particularly the correct renormalization procedure and the distinction between MSbar and DRbar renormalization. An important practical outcome are transition rules between CDR and FDH amplitudes.

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arXiv2014

Two-Loop Corrections to the Muon Magnetic Moment from Fermion/Sfermion Loops in the MSSM: Detailed Results

Recently, first results were presented for two-loop corrections to the muon (g-2) from fermion/sfermion loops in the MSSM. These corrections were shown to be generally large and even logarithmically enhanced for heavy sfermions. Here, full details of the calculation and analytical results are presented. Also, a very compact formula is provided which can be easily implemented and serves as a good approximation of the full result as a function of the fourteen most important input parameters. Finally, a thorough discussion of the numerical behaviour of the fermion/sfermion-loop corrections to (g-2)_μ is given. The discussion includes the case of very heavy SUSY masses as well as experimentally allowed scenarios with very light SUSY masses.

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arXiv2014

The Infrared Structure of QCD Amplitudes and $H\to g g$ in FDH and DRED

We consider variants of dimensional regularization, including the four-dimensional helicity scheme (FDH) and dimensional reduction (DRED), and present the gluon and quark form factors in the FDH scheme at next-to-next-to-leading order. We also discuss the generalization of the infrared factorization formula to FDH and DRED. This allows us to extract the cusp anomalous dimension as well as the quark and gluon anomalous dimensions at next-to-next-to-leading order in the FDH and DRED scheme, using $\overline{\text{MS}}$ and $\overline{\text{DR}}$ renormalization. To obtain these results we also present the renormalization procedure in these schemes.

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arXiv2014

LHC explores what LEP hinted at: CP-violating type-I 2HDM

The Large Hadron Collider is shown to have great scope for a light charged Higgs discovery, in the context of the CP-violating type-I two Higgs doublet model. This scenario with similar masses of $H^\pm$ and W was suggested by the puzzling departure from charged current lepton universality found in the LEP data. With the lightest neutral Higgs mass set to 125 GeV, the charged-neutral Higgs associated production mechanism can cause a significant excess in the $τνb \bar{b}$ events over a vast range of tan beta as long as the Higgs mixing pattern avoids a few limiting cases. Thanks to the low $H^\pm$ mass, the charged Higgs loop can play a striking role in neutral Higgs decays into $γγ$, thereby compensating for a suppressed gluon-gluon fusion rate. The effect of scalar-pseudo-scalar mixing on loop-induced Higgs signals is also discussed.

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