Higgs mass implications on the stability of the electroweak vacuum

We update instability and metastability bounds of the Standard Model electroweak vacuum in view of the recent ATLAS and CMS Higgs results. For a Higgs mass in the range 124–126 GeV, and for the current central values of the top mass and strong coupling constant, the Higgs potential develops an instability around 10¹¹ GeV, with a lifetime much longer than the age of the Universe. However, taking into account theoretical and experimental errors, stability up to the Planck scale cannot be excluded. Stability at finite temperature implies an upper bound on the reheat temperature after inflation, which depends critically on the precise values of the Higgs and top masses. A Higgs mass in the range 124–126 GeV is compatible with very high values of the reheating temperature, without conflict with mechanisms of baryogenesis such as leptogenesis. We derive an upper bound on the mass of heavy right-handed neutrinos by requiring that their Yukawa couplings do not destabilize the Higgs potential.     

Quark see-saw,Higgs mass and vacuum stability

The issue of vacuum stability of standard model (SM) is discussed by embedding it within the TeV scale left–right quark see-saw model. The Higgs potential in this case has only two coupling parameters (λ₁, λ₂) and two mass parameters. There are only two physical neutral Higgs bosons (h,H), the lighter one being identified with the 126 GeV Higgs boson. We explore the range of values for (λ₁, λ₂) for which the vacuum is stable for all values of the Higgs fields till 10¹⁶ GeV. Combining with the further requirement that the scalar self-couplings remain perturbative till 10¹⁶ GeV, we find (i) an upper and lower limit on the second Higgs (H) mass to be within the range: 0.4 ≤ (M_H/v_R) ≤ 0.7, where v_R is the parity breaking scale and (ii) the masses of heavy vector-like top, bottom and τ partner fermions (P₃, N₃,E₃) have an upper bound ≤ v_R. These predictions can be tested at LHC and future higher energy colliders.     

The fate of the mixmaster behaviour in vacuum inhomogeneous Kaluza-Klein cosmological models

The generic behaviour of vacuum inhomogeneous Kaluza-Klein cosmologies is studied in the vicinity of the cosmological singularity. The collision law for the Kasner exponents is calculated in any number of spatial dimensions d. Its properties are investigated both theoretically and numerically. It is argued that the chaotic oscillatory behaviour disappears for d ⩾ 10. This regime is replaced by the monotonic Kasner behaviour found previously.     

Charge confinement and vacuum structure in the 1 + 1 dimensional Higgs model

We demonstrate that the 1 + 1 dimensional Higgs model is equivalent to the massive sine-Gordon model, and hence to the massive Schwinger model in a special case. We do this by deriving a dual Lagrangian which embodies instanton effects. Based on this equivalence, we discuss charge confinement and vacuum structure in the Lagrangian formalism.     

The Higgs Factor

A Europhysics News section devoted to the undiscovered Higgs boson, the search for which costs Europe billions of Ecus a year, but the discovery of which should finally settle where particles get their mass     

The private Higgs

We introduce Higgs democracy in the Yukawa sector by constructing a model with a private Higgs and a dark scalar for each fermion thus addressing the large hierarchy among fermion masses. The model has interesting implications for the LHC, while the Standard Model phenomenology is recovered at low energies. We discuss some phenomenological implications such as FCNC, new Higgses at the TeV scale and dark matter candidates.     

Higgs boson production at CLIC in SUSY models with hierarchy of the vacuum expectation values

Many theoretical schemes predict the existence of unconventional quarks and leptons not fitting the standard pattern of fermion families. We consider two possible kinds of non-standard fermions, mirror fermions and exceptional fermions. Mirror fermions arise in a variety of models ranging from family unification to extended supersymmetry and Kaluza-Klein theories; exceptional fermions come along with the groupE ₆ which is believed to be the low energy gauge symmetry of the superstring theory. We discuss some physical properties of these non-standard particles relevant for the LEP     

The Higgs mass beyond the CMSSM

The recent discovery of a new boson at the LHC, which resembles a SM-like Higgs boson with m _h =125 GeV, is starting to provide strong guidelines into SUSY model building. For instance, the identification of such a state with the lightest CP-even Higgs boson of the MSSM (h ⁰), requires large values of tanβ and/or heavy sfermions. One outcome of this result is the possibility to solve the SUSY flavor and CP problems by decoupling, which points towards some realization of Split-inspired SUSY scenarios, in which scalars are much heavier than gauginos and higgsinos. However, we argue here that the remaining Higgs bosons of the MSSM (H ⁰, A ⁰, H ^±) do not have to be as heavy as the sfermions, and having them with masses near the EW scale does not pose any conflict with current MSSM constraints. We discuss then some SUSY scenarios with heavy sfermions, from a bottom-up approach, which contain the full Higgs sector, as well as a possible dark matter candidate, with masses near the EW scale, and identify distinctive signals from these scenarios that could be searched at the LHC.     

The Higgs boson of the Standard Model

An introduction is made to the key concepts of gauge invariance and spontaneous symmetry breaking which are the foundations of the Standard Model of particle physics. A new scalar field corresponding to a spin-0 particle, the Higgs boson, is a necessary consequence of this model. Properties of the Higgs boson are constrained; however, its mass is not. Searches using LEP have been both unique, intense, and also efficient: the Standard Model Higgs boson must be heavier than 114 GeV$/{\mathrm{c}}^2$. A hint of a signal was obtained at 115 GeV$/{\mathrm{c}}^2$, but will have to be confirmed (or falsified) by forthcoming experiments at the Tevatron and LHC. To cite this article: M. Davier, C. R. Physique 8 (2007).     

The holographic composite Higgs

Theories where the Higgs boson is a composite particle elegantly solve the hierarchy problem. This idea has been recently investigated in the framework of 5-dimensional warped models that, according to the AdS/CFT correspondence, have a 4-dimensional holographic interpretation in terms of strongly coupled field theories. We present a minimal model in which the Higgs arises as a pseudo-Goldstone boson and the electroweak symmetry is dynamically broken. This model can successfully solve the flavor problem and pass all the electroweak precision tests. To cite this article: R. Contino, A. Pomarol, C. R. Physique 8 (2007).     

Higgs mechanism without Higgs particle

Until now there has been no empirical evidence for the existence of the Higgs particle, although the Higgs mechanism of symmetry breaking is very successful. We propose a scalar-tensor theory of gravity with the Higgs field of theSU(3)×SU(2)×U(1) standard model of the elementary particles as scalar field, which results finally in Einstein's gravity and in theSU(3)×SU(2)×U(1) standard model without any influence of the excited Higgs field.