Conformal symmetry: towards the link between the Fermi and the Planck scales. 
Mikhail Shaposhnikov, EPFL 
Event Type: HEP Seminar 

Time: 2:00 PM  3:30 PM 

Location: 726 Broadway, 940, CCPP Seminar 

Description: If the mass of the Higgs boson is put to zero, the classical Lagrangian of the Standard Model (SM) becomes conformally invariant (CI). Taking into account quantum nonperturbative QCD effects violating CI leads to electroweak symmetry breaking with the scale $v sim Lambda_{rm QCD}sim 100$ MeV which is three orders of magnitude less than it is observed experimentally. Depending on the mass of the top quark, the radiative corrections may lead to another minimum of the effective potential for the Higgs field with $v gtrsim M_P$, where $M_P$ is the Planck mass, at least $16$ orders of magnitude more than it is observed. We explore yet another source of CI breaking associated with gravity. We suggest a nonperturbative mechanism that can reproduce the observed hierarchy between the Fermi and the Planck scales, by constructing an instanton configuration contributing to the vacuum expectation value of the Higgs field. The crucial role in this effect is played by the nonminimal coupling of the Higgs field to the Ricci scalar and by the approximate Weyl invariance of the theory for large values of the Higgs field. 