Low-energy probes of the small cosmic microwave background amplitude in models of the radiative Higgs mechanism

Abstract

The small cosmic microwave background (CMB) amplitude As similar or equal to 10(-9) (or small temperature fluctuation delta T/T similar or equal to 10(-5)) typically requires an unnaturally small effective coupling of an inflaton lambda(phi) similar to 10(-14). In models with non-minimal coupling xi, extra suppression of the amplitude, e.g. by the inflaton's large field values, usually allows lambda(phi) to be much larger, but at the price of xi >> 1. Although the difficulties have not been strictly quantified, models with lambda(phi )<< 1 or xi >> 1 are harder to build. We show that the absence of new physics signals at TeV scale can suggest a relatively small xi less than or similar to O(1-100) with lambda(phi) less than or similar to O(10(-4)-10(-8)), while constraining larger xi with larger lambda(phi) more strongly. Above all, this is possible by a connection between low- and high-energy physics that can be made in scenarios where the U(1)(X) Higgs is an inflaton at a high scale while its renormalization running also induces the Coleman-Weinberg mechanism for the electroweak symmetry breaking at a low scale. The best TeV-scale signals are Z' resonances and Higgs signal strengths. We further find the connection particularly useful since the Z' mass is upper bounded in order to produce the correct A(s) and the weak scale simultaenously. Utilizing the intriguing upper bounds, we work out the prospects for LHC 13 and 100 TeV pp colliders probing the parameter space of the small CMB amplitude in such a model.