will not allow couplings of type; φ 2 ∑ χ 2 $_{i}$, or some non-renormalizable couplings to other fields (belonging to other hidden sectors) such as ∼ φ $^{n}$χ$^{m}$/M n + m − 4 P for n, m > 2. There may be some discrete symmetries which will forbid some terms or some com- binations, but it cannot render all the couplings to be vanishing. Any such light field other than the inflaton would introduce isocurvature perturbations during inflation, which at the classical level leaves such models vulnerable to quantum predictions of the CMB fluctuations. A simple calculation assuming adiabatic nature of density perturbations will not suffice in such cases. 

Furthermore, the same couplings can dump almost all the inflaton energy density into some other non-SM degrees of freedom (or hidden sectors) upon reheating or preheat- ing. One must assume that SM degress of freedom are excited, but such assumptions are always hard to justify if the particle contents are unknown. 

• Quantum stability of the potential: 

The inflaton cannot be considered free from matter couplings, any coupling of the inflaton to fermions and gauge bosons would introduce loop corrections at the pertur- bative level [360]. This will spoil the classical flatness of the inflaton potential even when the scale of inflation is far below the scale of gravity [290, 354, 357] $^{55}$. Be- yond destabilizing or modifying the shape of the potential, radiative corrections can substantially alter the CMB predictions of the models. 

SUSY helps stabilizing the classical potential, as the leading quantum corrections are logarithmic in nature. The another classic example is the pseudo Nambu Goldstone Boson (pNGB) as an inflaton, where the potential explicitly breaks the global sym- metry with small couplings [361, 504, 581, 582]. In Ref. [582], it was observed that if the global symmetry is explicitly broken by a combination of couplings, then loop contributions to pNGB masses must involve all of the couplings, and therefore one-loop contribution cannot be quadratically divergent . This is due to collective or non-local symmetry breaking as discussed in Ref. [583]. 

