#### Chiral-scale perturbation theory and the renormalization group

- Event time: 2:00pm
- Event date: 30th November 2016
- Speaker: Lewis Tunstall (University Bern)
- Location: Higgs Centre Seminar Room, James Clerk Maxwell Building (JCMB) James Clerk Maxwell Building Peter Guthrie Tait Road Edinburgh EH9 3FD GB

### Event details

At an infrared fixed point (IRFP) of the QCD renormalization group, scale invariance can be realised in two possible ways: the Wigner-Weyl (WW) or Nambu-Goldstone (NG) modes. For a large number of fermion flavours 8 < Nf \leq 16, there is good theoretical evidence that the theory flows to an IRFP of the WW type, where Green’s functions exhibit power-law behaviour, and all particle masses go to zero.

In this talk, I will discuss the alternative possibility that for small Nf, the strong coupling runs non-perturbatively to an IRFP with scale non-invariant vacua, i.e. in NG mode. I will consider an explicit proposal for Nf = 3, where the quark condensate signals the breaking of scale invariance by the vacuum and produces 9 NG bosons: a 0^{++} dilaton sigma [f0(500) in the real world] as well as pi, K, eta. The enlarged symmetry group leads to chiral-scale perturbation theory (ChPT_sigma), which replaces 3-flavour ChPT to account for approximate scale invariance. The construction of this new effective field theory and its applications to hadron phenomenology will be discussed.

The Particle Physics Theory seminar is a weekly series of talks reflecting the diverse interests of the group. Topics include analytic and numerical calculations based on the Standard Model of elementary particle physics, theories exploring new physics, as well as more formal developments in gauge theories and gravity..