Extranatural inflation redux

Abstract

The success of a given inflationary model crucially depends upon two features: its predictions for observables such as those of the Cosmic Microwave background (CMB) and its insensitivity to the unknown ultraviolet (UV) physics such as quantum gravitational effects. Extranatural inflation is a well motivated scenario which is insensitive to UV physics by construction. In this five dimensional model, the fifth dimension is compactified on a circle and the zero mode of the fifth component of a bulk U (1) gauge field acts as the inflaton. In this work, we study simple variations of the minimal extranatural inflation model in order to improve its CMB predictions while retaining its numerous merits. We find that it is possible to obtain CMB predictions identical to those of e.g. R + R 2 Starobinsky model of inflation and show that this can be done in the most minimal way by having two additional light fermionic species in the bulk, with the same U (1) charges. We then find the constraints that CMB observations impose on the parameters of the model.

Diphoton resonance at 750 GeV in the brokenR-symmetric MSSM

“…In addition, electroweak vacuum stability and inflation in the presence of this new resonance has been analysed in Refs. [24]. However, it is probably a fair statement to say that an explanation of the current results is rather difficult to obtain in any of the popular 'minimal' models which have hitherto been the mainstay of phenomenological studies of physics beyond the SM.…”

750 GeV diphoton resonance and inflation

“…This possible excess has already sparked numerous theoretical explorations [3][4][5][6][7]. To explain this potential new resonance, two prevailing ideas are as follows: (1) to stay within weakly coupled theories and introduce vectorlike SM charged fermions, or (2) to invoke strong dynamics as in composite Higgs models.…”

“…While we maintain our healthy skepticism towards the reality of this signal, we think it worthwhile to explore the cosmological implications of this potential new resonance while awaiting further data from the LHC to either confirm or falsify its existence. Though previous works [3][4][5][6][7] Inflation is the leading paradigm of early universe cosmology. An inflationary universe can be realized with a scalar or pseudoscalar (known as the inflaton) with a sufficiently flat potential.…”

“…We hope to address these issues elsewhere. Note added: While this work was being completed, other papers [5][6][7] on electroweak vacuum stabilization appeared on the arXiv. Our analysis concerns more general setups and the implications to inflation.…”

“…We also like to also point out that the Refs. [5,6] did not take into account the Landau pole of gauge couplings g Y and g 2 , which is appropriately taken into account in our analysis. See Table I.…”