Familia representaciones

We denote the eighteen relevant generators by Ta_{, with a = 1, . . . ,18, which have been}

explicitly listed in Eq. (D.1). Furthermore, we assumeg _≡ gC =gRaround the GUT scale.

Thus, the D-flatness conditions from Eq. (9.3) give the more specific conditions in the PS case

Rc_i†_Ta∗Rc_i = ¯Rc†_TaR¯c, (9.4) where the sum over all generations i has to be taken into account in each of the eighteen equations. During inflation, our D-flat trajectory is thus constrained by the conditions in Eq. (9.4) which have to be imposed on the F-term scalar potential.

Using Eq. (9.4) it can be shown that several flat directions exist in this model. All these directions can in principle be valid trajectories for inflation to occur. During inflation Rci

and ¯Rc _{acquire VEVs along one of these directions and break the PS symmetry. The gauge}

fields coupled to this particular direction in field space become massive. This direction is classically flat and lifted only by radiative corrections such that it is suitable for inflation. On the other hand, other flat directions in field space along which the gauge symmetry is not broken and the gauge fields are still massless, acquire large two-loop mass corrections as will be clarified in Sec. 9.4.2. Such large mass contributions essentially lift these other flat directions strongly and drive their VEVs to zero. After inflation, the breaking ofGPSis realized by the VEVs ofHc _{and ¯H}c_{. In the next section we will explicitly consider inflation}

along the right-handed sneutrino directionsνc _{and ¯ν}c_{, which is one possible D-flat direction}

in field space. We show explicitly that in this case the waterfall is triggered in such a way that generically the VEVs ofHc_{and ¯H}c _{are aligned in the right-handed sneutrino direction}

as well. Thus an example model of sneutrino inflation is realized with the inflaton being in a non-singlet rep of GPS. It is important to emphasize that although the inflaton belongs to a non-singlet rep, it effectively behaves like a singlet since the gauge groupGPSis broken toGSMduring inflation. As already mentioned, this proves to be important w.r.t. quantum corrections to the inflaton potential.

9.3

Explicit Example: Sneutrino Inflation

As we have mentioned in the last section, the model has several tree-level flat directions in the Rc

i,R¯c field space and in principle inflation can proceed along any of them. In this

section we would like to discuss the inflationary scenario in which the inflaton fields acquire VEVs along the sneutrino direction. In this context we also study the waterfall mechanism in more detail. It turns out to be an interesting feature of this particular flat direction that, at the end of inflation, and for generic choices of parameters, the waterfall fields Hc _and

¯

9.3 Explicit Example: Sneutrino Inflation 109 νc

H and ¯νHc as well. This preferred waterfall direction helps to avoid the production of

topologically stable monopoles after inflation.

As an explicit example inflaton trajectory we consider a simple case where only one of the Rc _≡Rc

1 6= 0 is slowly rolling while all the others remain at zeroRci6=1 = 0. In addition, we want to realize inflation along the sneutrino direction, i.e.

Rc = 0 0 0 νc 0 0 0 0 , R¯c = 0 0 0 ¯νc 0 0 0 0 . (9.5)

This reduces our inflationary superpotential in Eq. (9.2) to the effective form

Winf =κ S HcH¯c −M2

+λ(νcν¯_Hc )2 +γ(¯νcν_Hc )2+ξ(νcν¯c)ν_Hc ν¯_Hc +ζ(νcν¯c)HcH¯c, (9.6)

where we have absorbed_hX_iand Λ into the definition of the parameters. Due to the VEVs in Eq. (9.5), GPS is already broken to GSM during inflation. If we can also ensure that the waterfall is forced into the νc

H and ¯νHc directions in field space, no monopoles will be

produced after inflation.

Since Rc _{and ¯R}c _{point in the right-handed sneutrino direction, the D-term potential}

projects out only the part proportional to the generators T15 _{and T}18 _{of G}

PS. Hence, the global SUSY D-term potential reads

VD = 5 16g

2

|νc_|2_{− |}ν¯c_|22 . (9.7)

This potential obviously has a flat direction _|νc_{| = |ν¯}c_{|. From now on, we assume that}

inflation occurs in this D-flat valley. Therefore the scalar potential during inflation has to be calculated in the inflationary trajectoryS=Hc _{= ¯H}c _{= 0 with the D-flatness condition}

|νc_|=|ν¯c_{| imposed.}

For the D-flat direction _hνc_{i = hν¯}c_{i, assuming real VEVs, the field combination}1 Re(δν¯c _−δνc_{) having mass 5g}2_hνc_i2

/2 is orthogonal to the flat direction Re(δν¯c _+δνc₎

which remains massless. On the other hand, for the other D-flat direction hνc_{i = −hν¯}c_i,

the field combination Re(δν¯c+δνc) acquires a mass of 5g2hνci2/2 and is orthogonal to the flat direction Re(δν¯c_−δνc_{). The complete mass spectrum of the inflaton sector is listed in}

Tab. 9.2.

Now we discuss how the waterfall mechanism works in our particular example. We decompose all complex scalar fields into canonically normalized real and imaginary com- ponents as νc H = (Re(˜νHc ) + i Im(˜νHc ))/ √ 2 and ¯νc H = (Re(˜¯νHc ) + i Im(˜¯νHc ))/ √ 2 and analo- gous for all the other waterfall fields. Here and in the following, a tilde denotes canonically normalized fields and we define the sneutrino inflaton fieldsνc _=|ν˜c_|/√_{2 and ¯ν}c _=|ν˜c_|/√_2.

1_{Where the quantum field is expanded about the background VEV asφ}

The full F-term potential calculated with the use of Eq. (3.38) is given by VF =κ HcH¯c−M22+2λ(νc)2ν¯_Hc +ξ(νcν¯c)ν_Hc +ζ(νcν¯c)ν_Hc 2 +κ SH¯c+ζ(νcν¯c) ¯Hc2+2γ(¯νc)2ν_Hc +ξ(νcν¯c) ¯ν_Hc +ζ(νcν¯c) ¯ν_Hc 2 +|κ S Hc+ζ(νcν¯c)Hc|2+2γν¯c(ν_Hc )2+ξ νc(ν_Hc ν¯_Hc ) +ζ νc(HcH¯c)2 +2λ νc(¯ν_Hc )2+ξν¯c(ν_Hc ν¯_Hc ) +ζν¯c(HcH¯c)2 , (9.8)

where terms containing single Hc _{and ¯H}c _{superfields have to be summed over all compo-}

nents of the PS multiplet. In terms like (Hc_H¯c_{) all gauge indices are contracted.}

Due to large F-term contributions to their masses from the VEVs of the inflaton fields, cf. Eq. (9.8), the waterfall fields get fixed at zero during inflation. As the inflaton fields slowly roll to smaller values, the masses of the waterfall fields decrease and finally one or more directions in field space become tachyonic. The Hc_,H¯c _{fields now quickly “fall” to}

their true minima and inflation ends by the waterfall. We now discuss into which direction in field space the waterfall gets triggered, i.e., which direction becomes tachyonic first.

Both scalar as well as pseudoscalar squared mass matrices are block-diagonal with universal sub-blocks for the (uc

H,u¯cH), (dcH,d¯cH) and (ecH,e¯cH) parts respectively coming

from the couplings κ and ζ. The scalar and pseudoscalar squared mass matrices are given by M2 Re(uc H,u¯cH)= ₁ 4|ζ|2|ν˜c|4 −|κ|2M2 −|κ_|2_M2 1 4|ζ| 2_|ν˜c_|4 , M2Im(uc H,u¯cH)= ₁ 4|ζ| 2_|ν˜c_|4 _|κ|2_M2 |κ|2_M2 1 4|ζ|2|ν˜c|4 , (9.9)

with two eigenvalues each. For example, the normalized field directions Re(uc

H + ¯ucH) and

Im(¯uc

H −ucH) have unstable squared masses m2_u,1 = 1

4|ζ|

2_|ν˜c_|4_{− |κ|}2_M2_{, (9.10)}

whereas the stable directions Re(¯uc

H −ucH) and Im(¯ucH +ucH) have squared masses m2_u,2 = 1

4|ζ|

2_|ν˜c_|4_+|κ|2_M2_{. (9.11)}

Exactly the same mass spectra hold for the equivalent combinations of (dc

H,d¯cH) and

(ec H,e¯cH).

Due to the additional contributions from the non-universal couplings λ, γ and ξ, the SM-singlet directions (νc

H,ν¯Hc ) obtain different mass matrices for the real scalar components

M2R = ₁ 4(|ζ+ξ| 2_{+ 4|γ|}2_)|ν˜c_|4 1 2Re ((γ+λ)∗(ζ+ξ)) |ν˜ c_|4_{− |κ|}2_M2 1 2Re ((γ+λ)∗(ζ+ξ)) |ν˜c|4− |κ|2M2 1 4(|ζ+ξ|2+ 4|λ|2)|ν˜c|4 , (9.12)

9.3 Explicit Example: Sneutrino Inflation 111

and for the pseudoscalar components

M2P= ₁ 4(|ζ+ξ| 2_{+ 4|γ|}2_)|ν˜c_|4 1 2Re ((γ+λ)∗(ζ+ξ))|ν˜ c_|4_+|κ|2_M2 1 2Re ((γ+λ)∗(ζ+ξ)) |ν˜c|4+|κ|2M2 1 4(|ζ+ξ|2+ 4|λ|2)|ν˜c|4 . (9.13) Setting γ =λ, we obtain the following mass eigenvalues for the real scalar parts

m2_Re(ν),1 = |ζ+ξ+ 2γ| 2 4 |ν˜ c |4− |κ_|2M2, m2_Re(ν),2 = |ζ+ξ−2γ| 2 4 |ν˜ c_|4_+|κ|2_M2_. (9.14)

For the pseudoscalar parts, we obtain the mass eigenvalues

m2_Im(ν),1 = |ζ+ξ−2γ| 2 4 |ν˜ c |4− |κ_|2M2, m2_Im(ν),2 = |ζ+ξ+ 2γ| 2 4 |ν˜ c |4+_|κ_|2M2. (9.15)

In Eqs. (9.14) and (9.15), the first one can give rise to an instability in both cases and corresponds to the directions Re(¯νc

H −νHc ), Im(¯νHc −νHc ), respectively. The second, stable

eigenvalues correspond to Re(¯νc

H +νHc ) and Im(¯νHc +νHc ). All these masses are listed in

Tab. 9.3 with the complete waterfall mass spectrum.

The critical values at which the system gets destabilized can be calculated by setting the dynamical masses to zero. For the Re(uc_H+ ¯uc_H)-, Im(¯uc_H−uc_H)-, . . . directions we find

|ν˜_critc _|=

s

2_|κ_|M

|ζ_| , (9.16)

and for the Re(¯νc

H −νHc )- and Im(¯νHc −νHc )-directions we find the real, positive solutions

|ν˜_critc |= s 2_|κ_|M |ζ+ξ+ 2γ|, |ν˜ c crit|= s 2_|κ_|M |ζ+ξ−2γ|. (9.17)

For generic non-zero values of γ and, e.g., small ξ, either the Re(¯νc

H −νHc )- or the

Im(¯νc

H−νHc )-direction will become tachyonic for larger values of the inflaton VEV than the

Re(uc

H+ ¯ucH)-, . . . directions. Consequently, it destabilizes first and the waterfall occurs in

the corresponding direction in field space.

We note that with the effective operators in Eq. (9.2) included in this discussion, there is still the possibility of domain wall formation associated with the Z2 symmetry νc

H → −νHc

and ¯νHc → −ν¯Hc . However, additional higher dimensional effective operators that contain

odd powers of Hc _{and ¯H}c _{(in particular terms linear in H}c _{and ¯H}c_{) can efficiently lift this}

degeneracy and force the waterfall to take place in one unique direction. An example for such a deformed inflaton potential is shown in Fig. 8.1. For different possibilities to evade the cosmological domain wall problem, the reader is referred to [141].

In summary, since the gauge symmetry is already broken by the inflaton VEVs during inflation, higher dimensional operators allow to force the waterfall to occur in one single direction in field space such that a particular vacuum is chosen everywhere in space and the production of topological defects such as monopoles can be avoided.