Browsing by Subject "Renormalization Group"

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  • Enckell, Vera-Maria; Nurmi, Sami; Rasanen, Syksy; Tomberg, Eemeli (2021)
    We study Higgs inflation in the Palatini formulation with the renormalisation group improved potential in the case when loop corrections generate a feature similar to an inflection point. Assuming that there is a threshold correction for the Higgs quartic coupling lambda and the top Yukawa coupling y(t), we scan the three-dimensional parameter space formed by the two jumps and the non-minimal coupling xi .The spectral index n(s) can take any value in the observationally allowed range. The lower limit for the running is alpha (s)> -3.5 x 10(-3), and alpha (s) can be as large as the observational upper limit. Running of the running is small. The tensor-to-scalar ratio is 2.2x10(-17)< r < 2 x 10(-5). We find that slow-roll can be violated near the feature, and a possible period of ultra-slow-roll contributes to the widening of the range of CMB predictions. Nevertheless, for the simplest tree-level action, the Palatini formulation remains distinguishable from the metric formulation even when quantum corrections are taken into account, because of the small tensor-to-scalar ratio.
  • Ryttov, Thomas A.; Tuominen, Kimmo (2019)
    We consider a non-Abelian gauge theory with N-f fermions and discuss the possible existence of a non-trivial UV fixed point at large N-f . Specifically, we study the anomalous dimension of the (rescaled) glueball operator Tr F-2 to first order in 1/N-f by relating it to the derivative of the beta function at the fixed point. At the fixed point the anomalous dimension violates its unitarity bound and so the (rescaled) glueball operator is either decoupled or the fixed point does not exist. We also study the anomalous dimensions of the two spin-1/2 baryon operators to first order in 1/N-f for an SU(3) gauge theory with fundamental fermions and find them to be relatively small and well within their associated unitarity bounds.
  • Heikinheimo, Matti; Kannike, Kristjan; Lyonnet, Florian; Raidal, Martti; Tuominen, Kimmo; Veermäe, Hardi (2017)
    We calculate the vacuum stability conditions and renormalisation group equations for the extensions of standard model with a higher colour multiplet scalar up to the representation 1 5 0 that leaves the strong interaction asymptotically free. In order to find the vacuum stability conditions, we calculate the orbit spaces for the self-couplings of the higher multiplets, which for the representations 1 5 and 1 5 0 of SU(3)(c) are highly complicated. However, if the scalar potential is linear in orbit space variables, it is sufficient to know the convex hull of the orbit space. Knowledge of the orbit spaces also facilitates the minimisation of the potentials. In contrast to the self-couplings of other multiplets, we find that the scalar quartic couplings of the representations 3 and 8 walk rather than run, remaining nearly constant and perturbative over a vast energy range. We describe the conditions for walking couplings using a schematic model. With these technical results at hand we revise earlier results of generation of new scales with large SU(3) c scalar multiplets. Our results are easily extendable to models of new physics with additional SU(3) or SU(N) gauge symmetries.