Browsing by Subject "EINSTEIN"

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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.
  • Räsänen, Syksy; Tomberg, Eemeli (2019)
    We study the production of primordial black hole (PBH) dark matter in the case when the Standard Model Higgs coupled non-minimally to gravity is the inflaton. PBHs can be produced if the Higgs potential has a near-critical point due to quantum corrections. In this case the slow-roll approximation may be broken, so we calculate the power spectrum numerically. We consider both the metric and the Palatini formulation of general relativity. Combining observational constraints on PBHs and on the CMB spectrum we find that PBHs can constitute all of the dark matter only if they evaporate early and leave behind Planck mass relics. This requires the potential to have a shallow local minimum, not just a critical point. The initial PBH mass is then below 10(6) g, and predictions for the CMB observables are the same as in tree-level Higgs inflation, n(s) = 0.96 and r = 5 x 10(-3) (metric) or r = 4 x 10(-8) ... 2 x 10(-7) (Palatini).