This epoch of inflation is expected to be driven by some scalar field called the inflaton. It is well known that a number of important cosmological problems, such as the flatness, isotropy and homogeneity of the Universe, can be solved simultaneously by the accelerated expansion of the Universe in the distant past. It has been shown that the form of the potential is not changed by perturbative higher order corrections, provided the mass of the Higgs boson obeys the requirement (see also ):ģ. Higgs boson, cosmological inflation and the hot Big Bang In particular, the physical effective potential (obtained by transforming the theory from the so-called Jordan frame to the Einstein frame) does not depend on the Higgs field, as depicted in figure 1. In the limit of large Higgs fields, physical observables do not depend on h, as in all dimensionless ratios the magnitude of h cancels out M W/ M eff P is one such example. In this regime, the Higgs field not only gives masses ∝ h to fermions and vector bosons, but also determines the gravity interaction strength, which is simply the inverse coefficient in front of the scalar curvature R. To elucidate the role of the non-minimal coupling ξ, let us consider large Higgs fields, ( h 2= H † H/2), which may have existed in the early Universe. As is the case with other couplings of the SM, the value of ξ cannot be fixed from within the model, but instead can be determined by specific experiments (cosmological observations in our case). Here R is the scalar curvature, g is the determinant of the metric, H is the Higgs field and ξ is a new dimensionless coupling constant of the SM. In addition, active neutrino masses and mixing are induced via Yukawa couplings of both HNLs and left-handed neutrinos to the Higgs field. Moreover, in the modest extension of the SM by three relatively light Majorana fermions-heavy neutral leptons (HNLs)-the Higgs field is important for baryogenesis, leading to the charge asymmetric Universe, and for dark matter production . As will be discussed in this paper, the Higgs field may also have had an important role in cosmology: it could have made the Universe flat, homogeneous and isotropic, it could have produced the fluctuations that led to structure formation and it could also have enabled the radiation-dominated epoch of the hot Big Bang to occur. It provides a mechanism for including weakly interacting massive vector bosons in the SM, and for ‘giving’ masses to quarks and leptons.
The Higgs boson is a very special particle in the SM. Nevertheless, since the assumption that the SM is valid up to the Planck scale is the most conservative option available to us, it has more predictive power than any other approach. Of course, this does not mean that the Standard Model (SM) is a correct theory of Nature up to these energies, as this would be an enormous extrapolation of known physics into a region that is not accessible to present experiments.
A Higgs boson-like particle with mass ≃126 GeV has recently been discovered at CERN, and thus we now have a theory of the strong, weak, electromagnetic and gravitational interactions that may be a self-consistent effective field theory all the way up to the Planck scale E∼ M P≃2.44×10 18 GeV see a recent discussion in.
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