The Standard model as a low-energy effective theory: what is triggering the Higgs mechanism?

by Prof. Fred Jegerlehner (DESY Zeuthen)

Wednesday 26 Jun 2013, 15:00 → 17:00 Europe/Rome

Aula Seminari (LNF INFN)

 The discovery of the Higgs by ATLAS and CMS at the LHC not only provided the last missing building block of the electroweak Standard Model, the mass of the Higgs has been found to have a very peculiar value about 125 GeV, which is such that vacuum stability is extending up to the Planck scale. This may have much deeper drawback than anticipated so far. The impact on the running of the SM gauge, Yukawa and Higgs couplings up to the Planck scale has been discussed in several articles recently. Here we consider the impact on the running masses and we discuss the role of quadratic divergences within the Standard Model. The change of sign of the coefficient of the quadratically divergent terms showing up at about mu_0 ~ 7 x 10^16 GeV may be understood as a first order phase transition restoring the symmetric phase, while its large negative values at lower scales triggers the Higgs mechanism, running parameters evolve in such a way that the symmetry is restored two orders of magnitude before the Planck scale. Thus, the electroweak phase transition takes place at the scale mu_0 and not at the electroweak scale v ~ 250 GeV. The SM Higgs system and its phase transition could play a key role for the inflation of the early universe. Also baryogenesis has to be reconsidered under the aspect that perturbative arguments surprisingly work up to the Planck scale.