In the Minimal Supersymmetric Standard Model (MSSM), there are numerous sources of flavour-violation in addition to the usual Kobayashi-Maskawa mixing matrix of the Standard Model. We reexamine the renormalisation group equations (RGEs) with a view to investigating flavour effects in a supersymmetric theory with an arbitrary flavour structure at some high scale. To incorporate (two-loop sized) threshold effects in the one-loop RGEs, we calculate the beta-functions using a sequence of (non-supersymmetric) effective theories with heavy particles decoupled at the scale of their mass, keeping track of the fact that many couplings (such as gauge and gaugino couplings) which are equal in an exact supersymmetric theory may no longer be equal once the supersymmetry (SUSY) is broken. We find that this splitting, which is ignored in the literature, may be larger than two-loop terms that are included. In addition, gaugino couplings develop flavour structure that is absent without including decoupling effects. A program (to be incorporated into ISAJET) has been developed, which includes flavour-violating couplings of superparticles and solves the two-loop threshold RGEs subject to specified high scale inputs. The weak scale flavour structure derived in this way can be applied to the study of flavour-changing decays of SUSY particles. As an illustration, we revisit the branching ratio of the flavour-violating decay of the top squark. We find that, in the minimal supergravity (mSUGRA) class of models, previous estimates for the width of this decay have been too large by a factor 10-25. We also analyse the consequences of introducing non-universality in the high scale soft SUSY-breaking mass matrices and find that under these conditions the partial width can be altered by a large amount.
In recent years three-, four- and five-loop beta functions have been computed for various phenomenologically interesting models. However, most of these results have not been implemented in easy to use software packages. $\texttt{RGE++}$ bridges this gap by providing a flexible, template-based, $\texttt{C++}$ library to solve renormalisation group equations. Furthermore, we implement the available beta functions for the Standard Model, the minimal supersymmetric extension of the Standard Model and two-Higgs-doublet models, as well as right-handed neutrino extensions of the former two.
We present a comprehensive renormalisation group analysis of the Littlest Seesaw model involving two right-handed neutrinos and a very constrained Dirac neutrino Yukawa coupling matrix. We perform the first $χ^2$ analysis of the low energy masses and mixing angles, in the presence of renormalisation group corrections, for various right-handed neutrino masses and mass orderings, both with and without supersymmetry. We find that the atmospheric angle, which is predicted to be near maximal in the absence of renormalisation group corrections, may receive significant corrections for some non-supers…
Two-loop renormalisation and Higgs phenomenology in the five-dimensional MSSM
University of Hafr Al Batin（哈夫阿尔巴廷大学）；Sudan University of Science and Technology（苏丹科学与技术大学）；University of Johannesburg（约翰内斯堡大学）；De La Salle University（德拉萨大学）；Université Lyon 1（里昂第一大学）；CNRS（法国国家科学研究中心）；IP2I（里昂-罗讷-阿尔卑斯粒子物理研究所）；University of Khartoum（喀土穆大学）
We have completed the one-loop renormalisation of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) allowing for and comparing between different renormalisation schemes. A special attention is paid to on-shell schemes. We study a variety of these schemes based on alternative choices of the physical input parameters. In this paper we present our approach to the renormalisation of the NMSSM and report on our results for the neutralino-chargino and sfermion sectors. We will borrow some results from our study of the Higgs sector whose full discussion is left for a separate publication. We …
Resummation of tan-beta-enhanced supersymmetric loop corrections beyond the decoupling limit
本文研究了具有最小味破坏的最小超对称标准模型，其中tan β是大参数，超对称质量参数是任意值.我们推导出几个重申公式tan β增强环路校正，这是以前只知道在超对称质量远远高于电弱尺度的限制。首先研究底部汤川耦合的重正化公式的重正化方案依赖性，我们阐明了在超对称回路因子Delta_b中sbottom混合角的使用。作为一个新的功能，我们发现tan-β增强环诱导的味道变化中性电流（FCNC）耦合的胶子和中性子，这反过来又引起了新的影响，在重整化的Cabibbo-小林-Maskawa矩阵和FCNC过程中的B介子。对于色磁Wilson系数C_8，这些胶子-夸克环可以与已知的电荷-夸克贡献具有相同的大小。我们讨论了B_d-> phi K_S中混合诱导CP不对称性的唯象结果。我们进一步给出了B_s-> mu ^+ mu ^-和B_s-B_s棒混频在退耦极限以外的有效公式，并发现了影响B_s-B_s棒混频振幅相位的一个新贡献。我们的非线性tan-beta增强效应被转换为费曼规则，允许在自动计算中轻松实现。
We present a full one-loop renormalisation of the Higgs sector of the Next-to-Minimal- Supersymmetric-Standard-Model (NMSSM) and its implementation within SloopS, a code for the automated computations of one-loop processes in theories beyond the Stan- dard Model. The present work is the sequel to the study we performed on the renor- malisation of the sectors of the NMSSM comprising neutralinos, charginos and sfermions thereby completing the full one-loop renormalisation of the NMSSM. We have investi- gated several renormalisation schemes based on alternative choices (on-shell or DR) of the phy…
We compute the two-loop O(as*at) corrections to the Higgs boson masses in supersymmetric extensions of the Standard Model with Dirac gaugino masses. We rely on the effective-potential technique, allow for both Dirac and Majorana mass terms for the gluinos, and compute the corrections in both the DRbar and on-shell renormalisation schemes. We give detailed results for the MDGSSM and the MRSSM, and simple approximate formulae valid in the decoupling limit for all currently-studied variants of supersymmetric models with Dirac gluinos. These results represent the first explicit two-loop calculatio…
We discuss the possibility of unifying in a simple and economical manner the Yukawa couplings of third generation fermions in a non-supersymmetric SO(10) model with an intermediate symmetry breaking, focusing on two possible patterns with intermediate Pati-Salam and minimal left-right groups. assume a minimal Yukawa sector at high energy, starting with two Higgs bi-doublets at the intermediate scale which then simply reduce to a two Higgs doublet model at the electroweak scale. We first enforce gauge coupling unification at the two-loop level by including the threshold corrections in the renor…
We present our computation of the ${\cal O}((α_t+α_λ+α_κ)^2)$ two-loop corrections to the Higgs boson masses of the CP-violating Next-to-Minimal Supersymmetric Standard Model (NMSSM) using the Feynman-diagrammatic approach in the gaugeless limit at vanishing external momentum. We choose a mixed $\overline{\mbox{DR}}$-on-shell (OS) renormalisation scheme for the Higgs sector and apply both $\overline{\mbox{DR}}$ and OS renormalisation in the top/stop sector. For the treatment of the infrared divergences we apply and compare three different regularisation methods: the introduction of a regulator…
The Quantum Chromodynamics (QCD) coupling $α_s$ is a central parameter in the Standard Model of particle physics. However, it depends on theoretical conventions related to renormalisation and hence is not an observable quantity. In order to capture this dependence in a transparent way, a novel definition of the QCD coupling, denoted by $\hat a$, is introduced, whose running is explicitly renormalisation scheme invariant. The remaining renormalisation scheme dependence is related to transformations of the QCD scale $Λ$, and can be parametrised by a single parameter $C$. Hence, we call $\hat a$ …
