Refinements of the Bottom and Strange MSSM Higgs Yukawa Couplings at NNLO

We extend the already existing two-loop calculation of the effective bottom-Yukawa coupling in the MSSM. In addition to the resummation of the dominant corrections for large values of tg$\beta$, we include the subleading terms related to the trilinear Higgs coupling $A_b$ and contributions induced by the electroweak gauge couplings. This calculation has been extended to the NNLO corrections to the MSSM strange-Yukawa coupling. Our analysis leads to residual theoretical uncertainties of the effective Yukawa couplings at the per-cent level.Comment: 23 pages, 9 figures, extension of the work described in arxiv:1001.1935 and arxiv:0808.0087, reference added, substantial upgrade to the full Delta_b results at NNL

Electroweak corrections to dark matter direct detection in the dark singlet phase of the N2HDM

Direct detection experiments are the only way to obtain indisputable evidence of the existence of dark matter (DM) in the form of a particle. These experiments have been used to probe many extensions of the Standard Model (SM) that provide DM candidates. Experimental results like the latest ones from XENON1T lead to severe constraints in the parameter space of many of the proposed models. In a simple extension of the SM, the addition of a complex singlet to the SM content, one-loop corrections need to be taken into account because the tree-level cross section is proportional to the DM velocity, and therefore negligible. In this work we study the case of a DM particle with origin in a singlet but in a larger framework of an extension by an extra doublet together with the extra singlet providing the DM candidate. We show that in the region of interest of the present and future direct detection experiments, electroweak corrections are quite stable with a K-factor very close to one

Electroweak corrections in a pseudo Nambu-Goldstone Dark Matter model revisited

Having so far only indirect evidence for the existence of Dark Matter a plethora of experiments aims at direct detection of Dark Matter through the scattering of Dark Matter particles off atomic nuclei. For the correct interpretation and identification of the underlying nature of the Dark Matter constituents higher-order corrections to the cross section of Dark Matter-nucleon scattering are important, in particular in models where the tree-level cross section is negligibly small. In this work we revisit the electroweak corrections to the dark matter-nucleon scattering cross section in a model with a pseudo Nambu-Goldstone boson as the Dark Matter candidate. Two calculations that already exist in the literature, apply different approaches resulting in different final results for the cross section in some regions of the parameter space leading us to redo the calculation and analyse the two approaches to clarify the situation. We furthermore update the experimental constraints and examine the regions of the parameter space where the cross section is above the neutrino floor but which can only be probed in the far future

Gluon fusion into Higgs pairs at NLO QCD and the top mass scheme

We present the calculation of the full next-to-leading order (NLO) QCD corrections to Higgs boson pair production via gluon fusion at the LHC, including the exact top-mass dependence in the two-loop virtual and one-loop real corrections. This is the first independent cross-check of the NLO QCD corrections presented in the literature before. Our calculation relies on numerical integrations of Feynman integrals, stabilised with integration-by-parts and a Richardson extrapolation to the narrow width approximation. We present results for the total cross section as well as for the invariant Higgs-pair-mass distribution at the LHC, including for the first time a study of the uncertainty due to the scheme and scale choice for the top mass in the loops.Comment: 8 pages double column, 2 figures. V2: identical to published versio

NLO QCD corrections to Higgs boson pair production

In this contribution the next-to-leading (NLO) QCD corrections to Higgs boson pair production are discussed. A brief sketch of the calculation is given. The differential cross section as a function of the invariant Higgs pair mass and the total hadronic cross section are presented. Furthermore, the uncertainties not only from the renormalisation and factorisation scales but also the uncertainties due to the scheme-and-scale choice of the top mass are shown. In addition, the effects of varying the Higgs self-coupling strength on the cross section are investigated

Full NLO QCD corrections to Higgs-pair production in the Standard Model and beyond

Higgs-pair production is one of the targets of the high-luminosity LHC and of future hadron colliders, as it allows for a direct probe of the trilinear Higgs coupling and hence of the mechanism behind electroweak symmetry breaking. This contribution focuses on the impact of the full next- to-leading order QCD corrections to Higgs-pair production via gluon fusion, the main production mechanism at hadron colliders, in the Standard Model and in Two-Higgs-Doublet models. The uncertainties due to the top-mass scale-and-scheme choice will be discussed

Electroweak corrections to dark matter direct detection in a vector dark matter model

Although many astrophysical and cosmological observations point towards the existence of Dark Matter (DM), the nature of the DM particle has not been clarified to date. In this paper, we investigate a minimal model with a vector DM (VDM) candidate. Within this model, we compute the cross section for the scattering of the VDM particle with a nucleon. We provide the next-to-leading order (NLO) cross section for the direct detection of the DM particle. Subsequently, we study the phenomenological implications of the NLO corrections, in particular with respect to the sensitivity of the direct detection DM experi- ments. We further investigate more theoretical questions such as the gauge dependence of the results and the remaining theoretical uncertainties due to the applied approximations.info:eu-repo/semantics/publishedVersio

Higgs Boson Pair Production via Gluon Fusion: Full NLO QCD Corrections

The measured properties of the particle detected six years ago at the LHC at CERN indicate that it is compatible with the Higgs boson predicted by the Standard Model. However, the theoretical and experimental uncertainties allow associations with extended models. Therefore it is of essential importance to investigate the properties of this particle in more detail. The determination of the Higgs potential is crucial to test whether this particle causes electroweak symmetry breaking. The self-coupling strength has to be determined to measure the Higgs potential. This can be achieved in a first step by measuring the trilinear self-coupling in Higgs pair production. At the LHC, the dominant process of Higgs pair production is the loop induced gluon fusion. Therefore the main goal of this thesis is the calculation of the next-to-leading order (NLO) QCD corrections considering the complete top-quark mass dependence in the framework of the Standard Model. The relevant two-loop integrals cannot be calculated analytically with the currently known methods. Instead a numerical integration is required. The main challenge is the extraction of the ultraviolet, the infrared and the collinear divergences from the amplitudes. For this purpose, a modified end-point subtraction has been developed for the extraction of the IR-singularities. Publicly available programs have been used for the real corrections. The differential cross section has been obtained as a distribution in the invariant Higgs pair mass. It shows that the main contributions to the cross section emerge from the invariant Higgs pair masses between 300 and 800 GeV and that the heavy-top limit is a reasonable approximation for invariant Higgs pair masses only up to about 600 GeV. Further, it can be observed that for an invariant Higgs pair mass up to 400-600 GeV the NLO QCD corrections can be reasonably approximated by the K-factor of the triangular contributions alone. The obtained hadronic cross section implies a negative contribution of about −15% from NLO mass effects compared to the previous known heavy-top limit results involving the full leading-order mass dependence