In this article we propose an overview on the current theoretical and experimental limits on a Higgs singlet extension of the Standard Model (SM). We assume that the boson which has recently been observed by the LHC experiments is the lightest Higgs boson of such a model, while for the second Higgs boson we consider a mass range of 600 GeV m H 1 TeV, where our model directly corresponds to a benchmark scenario of the heavy Higgs working group. In this light, we study the impact of perturbative unitarity limits, renormalization group equations analysis, and experimental constraints (electroweak precision tests, measurements of the observed light Higgs coupling strength at the Large Hadron Collider). We show that, in the case of no additional hidden sector contributions, the largest constraints for higher Higgs masses stem from the assumption of perturbativity as well as vacuum stability for scales of the order of the SM metastability scale, and that the allowed mixing range is severely restricted. We discuss implications for current LHC searches in the singlet extension, especially the expected suppression factors for SM-like decays of the heavy Higgs. We present these results in terms of a global scaling factor as well as the total width À of the new scalar.

In this article, a complete analysis of the three muonic lepton-flavour violating processes µ → eγ, µ → 3e and coherent nuclear µ → e conversion is performed in the framework of an effective theory with dimension six operators defined below the electroweak symmetry breaking scale m W . The renormalisation-group evolution of the Wilson coefficients between m W and the experimental scale is fully taken into account at the leading order in QCD and QED, and explicit analytic and numerical evolution matrices are given. As a result, muonic decay and conversion rates are interpreted as functions of the Wilson coefficients at any scale up to m W . Taking the experimental limits on these processes as input, the phenomenology of the mixing effects is investigated. It is found that a considerable set of Wilson coefficients unbounded in the simplistic tree-level approach are instead severely constrained. In addition, correlations among operators are studied both in the light of current data and future experimental prospects.

We present the complete set of Renormalisation Group Equations (RGEs) at one loop for the non-exotic minimal U (1) extension of the Standard Model (SM). It includes all models that are anomaly-free with the SM fermion content augmented by one Right-Handed (RH) neutrino per generation. We then pursue the numerical study of the pure B − L model, deriving the triviality and vacuum stability bounds on an enlarged scalar sector comprising one additional Higgs singlet field with respect to the SM.

The goal of this report is to summarize the current situation and discuss possible search strategies for charged scalars, in non-supersymmetric extensions of the Standard Model at the LHC. Such scalars appear in Multi-HiggsDoublet models, in particular in the popular Two-HiggsDoublet model, allowing for charged and additional neutral Higgs bosons. These models have the attractive property that electroweak precision observables are automatically in agreement with the Standard Model at the tree level. For the most popular version of this framework, Model II, a discovery of a charged Higgs boson remains challenging, since the parameter space is becoming very constrained, and the QCD background is very high. We also briefly comment on models with dark matter which constrain the corresponding charged a e-mail: Maria.Krawczyk@fuw.edu.pl b e-mail: Per.Osland@uib.no scalars that occur in these models. The stakes of a possible discovery of an extended scalar sector are very high, and these searches should be pursued in all conceivable channels, at the LHC and at future colliders.

We give an introduction to several regularization schemes that deal with ultraviolet and infrared singularities appearing in higher-order computations in quantum field theories. Comparing the computation of simple quantities in the various schemes, we point out similarities and differences between them.

We implement a systematic effective field theory approach to the benchmark process µ → eγ, performing automated one-loop computations including dimension 6 operators and studying their anomalous dimensions. We obtain limits on Wilson coefficients of a relevant subset of lepton-flavour violating operators that contribute to the branching ratio µ → eγ at one-loop. In addition, we illustrate a method to extract further constraints induced by the mixing of operators under renormalisation-group evolution. This results in limits on the corresponding Wilson coefficients directly at the high scale. The procedure can be applied to other processes as well and, as an example, we consider also lepton-flavour violating decays of the τ .

We present the Large Hadron Collider (LHC) discovery potential in the Z ′ sector of a U (1) B−L enlarged Standard Model (that also includes three heavy Majorana neutrinos and an additional Higgs boson) for √ s = 7, 10 and 14 TeV centre-of-mass (CM) energies, considering both theThe comparison of the (irreducible) backgrounds with the expected backgrounds for the DØ experiment at the Tevatron validates our simulation. We propose an alternative analysis that has the potential to improve the DØ sensitivity. Electrons provide a higher sensitivity to smaller couplings at small Z ′ B−L boson masses than do muons. The resolutions achievable may allow the Z ′ B−L boson width to be measured at smaller masses in the case of electrons in the final state. The run of the LHC at √ s = 7 TeV, assuming at most L ∼ 1 fb −1 , will be able to give similar results to those that will be available soon at the Tevatron in the lower mass region, and to extend them for a heavier M Z ′ .

We investigate the phenomenology of the Higgs sector of the minimal B − L extension of the Standard Model at a future e + e − Linear Collider. We consider the discovery potential of both a sub-TeV and a multi-TeV machine. We show that, within such a theoretical scenario, several novel production and decay channels involving the two physical Higgs states, precluded at the LHC, could experimentally be accessed at such machines. Amongst these, several Higgs signatures have very distinctive features with respect to those of other models with enlarged Higgs sector, as they involve interactions of Higgs bosons between themselves, with Z ′ bosons as well as with heavy neutrinos. In particular, we present the scope of the Z ′ strahlung process for single and double Higgs production, the only suitable mechanism enabling one to access an almost decoupled heavy scalar state (therefore outside the LHC range).