The small CMB amplitude $A_s simeq 10^{-9}$ (or, small temperature fluctuation $delta T/T simeq 10^{-5}$) typically requires an unnaturally small effective coupling of an inflaton $lambda_phi sim 10^{-14}$. In successful models, there usually is extra suppression of the amplitude, e.g. by large-field inflaton with non-minimal coupling $xi$, so that $lambda_phi$ can be much larger. But $lambda_phi$ and $xi$ cannot be $sim {cal O}(1)$ simultaneously; the naturalness burden is shared between them. We show that the absence of new physics signals at TeV scale may prefer a more natural size of $xi lesssim {cal O}(1-100)$ with $lambda_phi lesssim {cal O}(10^{-4}-10^{-8})$, constraining larger $xi$ with larger $lambda_phi$ more strongly. This intriguing connection between low- and high-energy physics is made in the scenarios with $U(1)_X$ where inflatons renormalization running also induces Coleman-Weinberg mechanism for the electroweak symmetry breaking. We particularly work out the prospects of LHC 13 and 100 TeV $pp$ colliders for probing the parameter space of the small CMB amplitude.
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