arXiv subjects

Dominik Stöckinger

Publications and source records attributed to Dominik Stöckinger.

At least 37 records · Page 2Linked to original sources

arXiv2022

Charged lepton flavor violating processes in the Grimus-Neufeld model

Charged Lepton Flavour Violating (cLFV) decays constrain the relationship between the neutrino and the scalar sectors of the Grimus-Neufeld model (GNM), an appealing minimal model of neutrino masses. It turns out, that in the scenario, where the seesaw scale is lower than the electroweak one, cLFV is completely defined by the new Yukawa interactions between the additional single heavy Majorana neutrino, the second Higgs doublet and the lepton doublets. Therefore, we derive a useful parameterization for the Yukawa couplings which reproduces by construction the correct PMNS matrix and the correct neutrino masses for both Normal and Inverted ordering at one-loop level. We embed this scenario in the $\texttt{FlexibleSUSY}$ spectrum-generator generator to perform parameter scans. Focusing on the tiny seesaw scale, we show that current $μ\to eγ$ limits provide significant constraints on the scalar sector, and we evaluate the impact of future cLFV $τ$-decay searches for the cases of discovery or non-discovery. The tiny seesaw scale makes the neutrino sector and the cLFV processes in the GNM similar to the scotogenic and the scoto-seesaw models, so we provide constraints for these models as well.

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arXiv2022

FlexibleDecay: An automated calculator of scalar decay widths

We present FlexibleDecay, a tool to calculate decays of scalars in a broad class of BSM models. The tool aims for high precision particularly in the case of Higgs boson decays. In the case of scalar and pseudoscalar Higgs boson decays the known higher order SM QED, QCD and EW effects are taken into account where possible. The program works in a modified $\bar{\text{MS}}$ scheme that exhibits a decoupling property with respect to heavy BSM physics, with BSM parameters themselves treated in the $\bar{\text{MS}}/\bar{\text{DR}}$-scheme allowing for an easy connection to high scale tests for, e.g., perturbativity and vacuum stability, and the many observable calculations readily available in $\bar{\text{MS}}/\bar{\text{DR}}$ programs. Pure BSM effects are taken into account at the leading order, including all one-loop contributions to loop-induced processes. The program is implemented as an extension to FlexibleSUSY, which determines the mass spectrum for arbitrary BSM models, and does not require any extra configuration from the user. We compare our predictions for Higgs decays in the SM, singlet extended SM, type II THDM, CMSSM and MRSSM, as well as for squark decays in the CMSSM against a selection of publicly available tools. The numerical differences between our and other programs are explained. The release of FlexibleDecay officially deprecates the old effective couplings routines in FlexibleSUSY.

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arXiv2022

Precise calculation of the W boson pole mass beyond the Standard Model with FlexibleSUSY

We present an updated calculation of the W boson pole mass in models beyond the Standard Model with FlexibleSUSY. The calculation has a decoupling behaviour and allows for a precise W pole mass prediction up to large new physics scales. We apply the calculation to several Standard Model extensions, including the MRSSM where we show that it can be compatible with large corrections to the W boson mass that would be needed to fit the recent 2022 CDF measurement.

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arXiv2022

$γ_5$ in dimensional regularization -- a no-compromise approach using the BMHV scheme

$γ_5$ is notoriously difficult to define in $D$ dimensions. The traditional BMHV scheme employs a non-anticommuting $γ_5$. Its key advantage is mathematical consistency and the existence of all-order proofs. Its disadvantage is the spurious breaking of gauge invariance in chiral gauge theories like the electroweak standard model. Our research programme aims to determine the special finite counterterms which are necessary to restore gauge invariance, to allow more straightforward applications of the BMHV scheme and to cross-check alternative schemes. In these proceedings we present the key concepts and methods, and we outline the calculational procedure and present results for an abelian gauge theory at the 2-loop level. An important observation is the simplicity of the results -- three types of symmetry-restoring counterterms are sufficient at the 2-loop level.

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arXiv2022

GM2Calc-2 for the 2HDM

GM2Calc is a leading tool for calculating precise contributions to $a_μ$ in the Minimal Supersymmetric Standard Model. In this proceeding we detail GM2Calc version 2 where it is extended so it can calculate two-loop contributions to $a_μ$ in the Two-Higgs Doublet Model (2HDM), based on the work in Ref. [1]. The 2HDM is a simple model, yet it is one of the few single field extensions of the Standard Model which is able to explain the muon $g-2$ anomaly. We demonstrate the powerful and flexible 2HDM capabilities of GM2Calc2, which include the most precise contributions in the literature and allow the user to work in their favourite type of the 2HDM as well as use complex and lepton flavour violating couplings. With its multiple interfaces and input flexibility, GM2Calc2 is a powerful tool both as a standalone code and as part of a larger code toolchain.

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arXiv2022

NPointFunctions: a calculator of amplitudes and observables in FlexibleSUSY

We present $\texttt{NPointFunctions}$, a package to incorporate desired amplitudes and observables for an arbitrary BSM model in $\texttt{FlexibleSUSY}$. The package relies on the $\texttt{SARAH}$-generated output used with $\texttt{FeynArts}/\texttt{FormCalc}$, embedded in an appropriate way, thus allowing calculations up to one-loop level. The resulting tool is an extension to $\texttt{FlexibleSUSY}$, a generator of spectrum generator programs. $\texttt{NPointFunctions}$ was designed to be customizable, modular and extensible with additional process- or amplitude- dependent contributions. We explain, how these goals are achieved, and discuss modifications to the default $\texttt{FlexibleSUSY}$ workflow.

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arXiv2022

Two-loop Prediction of the Anomalous Magnetic Moment of the Muon in the Two-Higgs Doublet Model with GM2Calc 2

We present an extension of the GM2Calc software to calculate the muon anomalous magnetic moment ($a_μ^{\text{BSM}}$) in the Two-Higgs Doublet Model. The Two-Higgs Doublet Model is one of the simplest and most popular extensions of the Standard Model. It is one of the few single field extensions that can give large contributions to $a_μ^{\text{BSM}}$. It is essential to include two-loop corrections to explain the long standing discrepancy between the Standard Model prediction and the experimental measurement in the Two-Higgs Doublet Model. The new version GM2Calc 2 implements the state of the art two-loop calculation for the general, flavour violating Two-Higgs Doublet Model as well as for the flavour aligned Two-Higgs Doublet Model and the type I, II, X and Y flavour conserving variants. Input parameters can be provided in either the gauge basis or the mass basis, and we provide an easy to use SLHA-like command-line interface to specify these. Using this interface users may also select between Two-Higgs Doublet Model types and choose which contributions to apply. In addition, GM2Calc 2 also provides interfaces in C++, C, Python and Mathematica, to make it easy to interface with other codes.

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arXiv2021

The muon magnetic moment in the 2HDM: complete two-loop result

We study the ${\text{2HDM}}$ contribution to the muon anomalous magnetic moment $a_μ$ and present the complete two-loop result, particularly for the bosonic contribution. We focus on the Aligned ${\text{2HDM}}$, which has general Yukawa couplings and contains the type I, II, X, Y models as special cases. The result is expressed with physical parameters: three Higgs boson masses, Yukawa couplings, two mixing angles, and one quartic potential parameter. We show that the result can be split into several parts, each of which has a simple parameter dependence, and we document their general behavior. Taking into account constraints on parameters, we find that the full ${\text{2HDM}}$ contribution to $a_μ$ can accommodate the current experimental value, and the complete two-loop bosonic contribution can amount to $(2\cdots 4)\times 10^{-10}$, more than the future experimental uncertainty.

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arXiv2021

Two-loop application of the Breitenlohner-Maison/'t Hooft-Veltman scheme with non-anticommuting $γ_5$: Full renormalization and symmetry-restoring counterterms in an abelian chiral gauge theory

We apply the BMHV scheme for non-anticommuting $γ_5$ to an abelian chiral gauge theory at the two-loop level. As our main result, we determine the full structure of symmetry-restoring counterterms up to the two-loop level. These counterterms turn out to have the same structure as at the one-loop level and a simple interpretation in terms of restoration of well-known Ward identities. In addition, we show that the ultraviolet divergences cannot be canceled completely by counterterms generated by field and parameter renormalization, and we determine needed UV divergent evanescent counterterms. The paper establishes the two-loop methodology based on the quantum action principle and direct computations of Slavnov-Taylor identity breakings. The same method will be applicable to nonabelian gauge theories.

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arXiv2021

Simple BSM explanations of $a_μ$ in light of the FNAL muon $g-2$ measurement

Now that the Fermilab muon $g-2$ experiment has released the results of its Run-1 data, which agrees with the results of the Brookhaven experiment, one can examine the potential of simple extensions to explain the combined $4.2σ$ discrepancy between the SM prediction and experiment. This proceeding examines a single-, two-, and three-field extension of the standard model and examines their ability to explain the muon $g-2$ anomaly, and where possible, produce a dark matter candidate particle with the observed relic density. This is based on work carried out for Ref. [1]. It is found that one can only explain the $a_μ$ discrepancy whilst avoiding dark matter and collider constraints when the contributions from BSM fields benefit from a chirality flip enhancement. However, in general without small couplings and/or large masses, these models can be heavily constrained by collider and dark matter experiments.

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arXiv2021

New physics explanations of $a_μ$ in light of the FNAL muon $g-2$ measurement

The Fermilab Muon $g-2$ experiment recently reported its first measurement of the anomalous magnetic moment $a_μ^{\textrm{FNAL}}$, which is in full agreement with the previous BNL measurement and pushes the world average deviation $Δa_μ^{2021}$ from the Standard Model to a significance of $4.2σ$. Here we provide an extensive survey of its impact on beyond the Standard Model physics. We use state-of-the-art calculations and a sophisticated set of tools to make predictions for $a_μ$, dark matter and LHC searches in a wide range of simple models with up to three new fields, that represent some of the few ways that large $Δa_μ$ can be explained. In addition for the particularly well motivated Minimal Supersymmetric Standard Model, we exhaustively cover the scenarios where large $Δa_μ$ can be explained while simultaneously satisfying all relevant data from other experiments. Generally, the $Δa_μ$ result can only be explained by rather small masses and/or large couplings and enhanced chirality flips, which can lead to conflicts with limits from LHC and dark matter experiments. Our results show that the new measurement excludes a large number of models and provides crucial constraints on others. Two-Higgs doublet and leptoquark models provide viable explanations of $a_μ$ only in specific versions and in specific parameter ranges. Among all models with up to three fields, only models with chirality enhancements can accommodate $a_μ$ and dark matter simultaneously. The MSSM can simultaneously explain $a_μ$ and dark matter for Bino-like LSP in several coannihilation regions. Allowing under abundance of the dark matter relic density, the Higgsino- and particularly Wino-like LSP scenarios become promising explanations of the $a_μ$ result.

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arXiv2021

Two Real Scalar WIMP Model in the Assisted Freeze-Out Scenario

We study a simple dark matter model given by two interacting real singlet scalars, with only one of them coupled to the Higgs. The model therefore presents a minimal assisted-freeze-out framework: both scalars contribute to the dark matter relic density, but only one of them takes part in the elastic scattering with nuclei. This reduces the expected interaction rate in direct detection experiments in such a way that the model in some regions of the parameter space may evade XENON1T constraints. We explore the model under theoretical (perturbativity, stability potential and unitarity) and experimental constraints (Higgs to invisible, relic density, direct detection), with the use of the narrow-width-approximation near the Higgs resonance to calculate the average annihilation cross section. We show that the model is viable in the Higgs resonance region and for scalar singlets masses of hundreds of GeV, although the model becomes highly constrained at high energies.

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arXiv2021

Resummation of terms enhanced by trilinear squark-Higgs couplings in the MSSM

We analyze the appearance of the trilinear squark-Higgs couplings $x_q$ in Green functions in the Higgs sector of the MSSM and in threshold corrections to the SM. The results are constraints on maximal powers of $x_q$ in QCD-related loop corrections. In practice these often imply all-order resummations of leading or subleading $x_q$ contributions in SM-parametrized expressions. We present a variety of all-order resummation relations for $Δλ$ which include such $x_q$-enhanced terms and different orders in Yukawa and gauge couplings. We contrast which terms cannot be resummed.

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arXiv2020

Dimensional Regularization and Breitenlohner-Maison / 't Hooft-Veltman Scheme for $γ_5$ applied to Chiral YM Theories: Full One-Loop Counterterm and RGE Structure

We study the application of the Breitenlohner-Maison-'t Hooft-Veltman (BMHV) scheme of Dimensional Regularization to the renormalization of chiral gauge theories, focusing on the specific counterterm structure required by the non-anticommuting Dirac $γ_5$ matrix and the breaking of the BRST invariance. Calculations are performed at the one-loop level in a massless chiral Yang-Mills theory with chiral fermions and real scalar fields. We discuss the setup and properties of the regularized theory in detail. Our central results are the full counterterm structures needed for the correct renormalization: the singular UV-divergent counterterms, including evanescent counterterms that have to be kept for consistency of higher-loop calculations. We find that the required singular, evanescent counterterms associated with vector and scalar fields are uniquely determined but are not gauge invariant. Furthermore, using the framework of algebraic renormalization, we determine the symmetry-restoring finite counterterms, that are required to restore the BRST invariance, central to the consistency of the theory. These are the necessary building blocks in one-loop and higher-order calculations. Finally, renormalization group equations are derived within this framework, and the derivation is compared with the more customary calculation in the context of symmetry-invariant regularizations. We explain why, at one-loop level, the extra BMHV-specific counterterms do not change the results for the RGE. The results we find complete those that have been obtained previously in the literature in the absence of scalar fields.

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arXiv2019

Confronting the coloured sector of the MRSSM with LHC data

R-symmetry leads to a distinct low energy realisation of SUSY with a significantly modified colour-charged sector featuring a Dirac gluino and scalar colour octets (sgluons). In the present work we recast results from LHC BSM searches to discuss the impact of R-symmetry on the squark and gluino mass limits. We work in the framework of the Minimal R-symmetric Supersymmetric Standard Model and take into account the NLO corrections to the squark production cross sections in the MRSSM that have become available recently. We find substantially weaker limits on squark masses compared to the MSSM: for simple scenarios with heavy gluinos and degenerate squarks, the MRSSM mass limit is $m_{\tilde q} > 1.7$ TeV, approximately 600 GeV lower than in the MSSM.

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arXiv2019

Low-energy lepton physics in the MRSSM: $(g-2)_μ$, $μ\to eγ$ and $μ\to e$ conversion

Low-energy lepton observables are discussed in the Minimal R-symmetric Supersymmetric Standard Model. We present comprehensive numerical analyses and the analytic one-loop results for $(g-2)_μ$, $μ\to e γ$, and $μ\to e$ conversion. The interplay between the three observables is investigated as well as the parameter regions with large $g-2$. A striking difference to the MSSM is the absence of $\tanβ$ enhancements; however we find smaller enhancements governed by MRSSM-specific R-Higgsino couplings $λ_d$ and $Λ_d$. As a result we find significant contributions to $g-2$ only in a small parameter space with several SUSY masses below $200$ GeV, compressed spectra and large $λ_d$, $Λ_d$. In this parameter space there is a correlation between all three considered observables. In the parameter region with small $(g-2)_μ$ the SUSY masses can be larger and the correlation between $μ\to eγ$ and $μ\to e$ conversion is weak. Therefore already COMET Phase 1 has a promising sensitivity to the MRSSM.

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arXiv2018

FlexibleSUSY: Precise automated calculations in any BSM theory

FlexibleSUSY is a software package for various calculations in any model of physics beyond the standard model (not just any supersymmetric model). FlexibleSUSY can solve boundary value problems and uses this to find $\overline{DR}/\overline{MS}$ parameters and calculate the Higgs and BSM particle masses, as well as other observables. FlexibleSUSY is designed to be adaptable, fast, precise and reliable. We describe FlexibleSUSY with particular emphasis on recent developments and the state of the art Higgs mass calculations it can perform. We also show some applications to illustrate how it can be used to obtain interesting physics results with the highest precision possible and with remarkable speed.

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arXiv2018

Three-loop MSSM Higgs-Boson Mass Predictions and Regularization by Dimensional Reduction

The evaluation of three-loop contributions to the MSSM Higgs-boson mass is considered at the orders enhanced by the strong gauge coupling and top or bottom Yukawa couplings, i.e. at the orders $O(α_{t,b}α_s^2,α_{t,b}^2α_s,α_{t,b}^3)$. We prove that regularization by dimensional reduction preserves supersymmetry at the required level. Thus generating counterterms by multiplicative renormalization is correct. Technically, we extend a previous two-loop analysis to the three-loop level. The extension covers not only the genuine three-loop Higgs potential counterterms but also a large sector of two-loop counterterms, required for subrenormalization.

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