The renormalisation of chiral gauge theories such as the electroweak Standard Model inevitably leads to the well-known $\gamma_{5}$-problem. A mathematically rigorous approach is provided by the Breitenlohner-Maison/'t Hooft-Veltman (BMHV) scheme within dimen-sional regularisation (DReg), where full anti-commutativity of $\gamma_5$ is abandoned. This scheme, however, explicitly breaks gauge...
We discuss the full two-loop renormalization of a chiral gauge theory for non-anticommuting $\gamma_5$ at the example of a Non-Abelian toy model. We employ the BMHV scheme which trades the computational comfort of DReg calculations for consistency at arbitrary order. Crucially, BRST symmetry is spuriously broken and must be restored. We carry through the renormalization despite such...
Through tree-level mixing, vector-like leptons (VLL) can have a significant impact on the SM lepton mass generation, Higgs couplings and flavor (violating) observables. Precise predictions of these observables however require calculations beyond leading order, which necessitates the definition of a renormalization scheme.
In this talk, I present such a scheme, implementing on-shell...
We integrate out the heavy scalar mass eigenstate in a real Higgs singlet extension of the Standard Model (SM) at one-loop order, taking into account full mixing between the BSM singlet and the SM-like Higgs fields. We highlight subtleties in the renormalization of the effective theory. We discuss the choice of a proper decoupling limit and whether the resulting effective Lagrangian is of...
In theories with extended scalar sectors, e.g. when including a scalar mediator to a dark sector, the lightest new scalar degree of freedom might be accessible at colliders. Going beyond simplified models, such a theory can be described in a gauge-invariant way via an EFT with a non-linearly realised electroweak symmetry. In this generalised HEFT, depending on the SU(2) nature of the new...
An effective Lagrangian is composed of all higher dimensional operators that are Lorentz singlets and invariant under the gauge symmetries of the theory, suppressed by powers of the cutoff. A challenging problem is the construction of the EFT operators, since the number of possibilities grows extremely fast. Furthermore, many of these operators are linearly dependent or can even be discarded,...
The individual fermion generations of the Standard Model fit neatly into a representation of a simple Grand Unified Theory gauge algebra. If Grand Unification is not realized in nature, this would appear to be a coincidence. We attempt to quantify this coincidence.
We find that only a small fraction of consistent fermion representations similar to the Standard Model are unifiable when the...
Extra-dimensions are a very interesting tool to address various missing parts of the Standard Model of particle physics. When one extra-dimension is added, a compactification based on a orbifold is required to ensure a chiral spectrum for the fermions. It also allows mechanisms to consistently break the bulk gauge group. Symmetry breaking on orbifolds can be understood in two different ways:...
The idea of supplementing the number of spacetime dimensions has long been deemed as one of the potential extension of the Standard Model, as it provides powerful tools to explain some of its shortcomings. One example of higher-dimensional formulations are asymptotic grand unified theories (aGUTs), for which the couplings do not meet at a high scale, but instead flow together towards a fixed...
