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the “goldstino” superfield $^{3}$. 

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The scalar component x of X becomes a goldstino bilinear. Its fermionic component is the goldstino fermion G , and F is the auxiliary field that gets the vacuum expectation value. A major part in the anal- ysis in [27] is based on this novel nonlinear constraint satisfied by the superfield X in the IR. As shown there, the correct normalization of the goldstino su- perfield to derive all relevant low-energy theorems of broken supersymmetry is X$_{NL}$ = 3 8 $_{f}$X . 

• Finally, X generalizes the usual spurion couplings ap- pearing in the description of low-energy supersymmet- ric lagrangians. If m$_{soft}$ describes the soft supersym- metry breaking masses at low energies, the standard spurion in the lagrangian is replaced by m$_{soft}$ f X$_{NL}$ . This allows one to write the leading low-energy cou- plings of the goldtino to other matter fields. 

Since we are going to consider goldstino couplings, we will work with a field whose expectation values are well below the Planck scale. 

Our proposal is to identify in the UV the inflaton field with the scalar component of the superfield X . Since X is defined uniquely (up to the ambiguity mentioned in foot- note one) in the UV, this provides a well defined prescrip- tion. Furthermore, we will identify the inflationary period precisely with the flow of X from the UV to the IR i.e. X → X$_{NL}$ . Note that by making this assumption we do not need to think of the inflaton as any extra fundamental field. In fact, independently of how SUSY is broken, and 

what is the underlying fundamental theory we can always identify the X − superfield as well as its scalar component x . More importantly, by making this assumption we are identifying the vacuum energy driven inflation with the actual SUSY breaking order parameter. 

In the supergravity context, once we have the K¨ ahler potential K ( X, ¯ X ) and the superpotential W ( X ), the full scalar potential is given by [30]: 

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with 

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M is the high energy scale below which we can write the ef- fective action describing the dynamics of the X -superfield. It could be the Planck scale, or a GUT scale depending on the microscopic theory. We will work well below the scale M , and for simplicity take M = M$_{pl}$ In equation (4) we can see one of the basic problems in supergravity infla- tion [24]. As we will see later on, to satisfy the slow roll conditions, a necessary condition is that the η -parameter, defined by: 

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be much smaller than one. If we choose a K¨ ahler potential K ( X, ¯ X ) with R-symmetry, for instance the canonical one K ( X, ¯ X ) = X ¯ X + ... , where the ... represents a function of X ¯ X , it is easy to see that from the exponent of (4) we always get a contribution to η equal to 1: η = 1 + ... , no matter which component of X is taken as the inflaton field. This of course violates the slow roll conditions. Since we are considering a situation with supersymmetry breaking and gravity (early universe), we cannot exclude supergrav- ity from the picture, and this leads to the η -problem in these theories. 

The simplest way out of this problem without unreason- able fine tuning, is to have explicit R-symmetry breaking 

