# Higgs mechanism and cosmological constant in \(N=1\) supergravity with inflaton in a vector multiplet

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## Abstract

The \(N=1\) supergravity models of cosmological inflation with an inflaton belonging to a massive vector multiplet and spontaneous SUSY breaking after inflation are reformulated as the supersymmetric *U*(1) gauge theories of a massless vector superfield interacting with the Higgs and Polonyi chiral superfields, all coupled to supergravity. The *U*(1) gauge sector is identified with the *U*(1) gauge fields of the super-GUT coupled to supergravity, whose gauge group has a *U*(1) factor. A positive cosmological constant (dark energy) is included. The scalar potential is calculated, and its de Sitter vacuum solution is found to be stable.

## Keywords

Dark Energy Cosmic Microwave Background Scalar Potential Vector Multiplet SUSY Breaking## 1 Introduction

PLANCK observations [1, 2, 3] of the Cosmic Microwave Background (CMB) radiation favor chaotic slow-roll inflation in its single-field realization, i.e. the large-field inflation driven by a single scalar called *inflaton* with an approximately flat scalar potential.

Embedding inflationary models into \(N=1\) four-dimensional supergravity is needed to connect them to particle physics theory beyond the Standard Model of elementary particles and to quantum gravity. Most of the literature about inflation in supergravity is based on an assumption that the inflaton belongs to a chiral (scalar) multiplet – see e.g., the reviews [4, 5]. However, the inflaton can also be assigned to a massive \(N=1\) *vector* multiplet. It has some theoretical advantages because there is only one real scalar in an \(N=1\) massive vector multiplet. The \(\eta \)-problem does not arise because the scalar potential of a vector multiplet in supergravity is of the *D*-type instead of the *F*-type. The minimal inflationary models with the inflaton belonging to a massive vector multiplet were constructed in Ref. [6] by exploiting the non-minimal self-coupling of a vector multiplet to supergravity [7]. The supergravity inflationary models [6] have the single-field scalar potential given by an arbitrary real function squared. Those scalar potentials are always bounded from below and allow any desired values of the CMB observables \(n_s\) and *r*. However, the minima of the scalar potentials of [6] have a vanishing cosmological constant and a vanishing Vacuum Expectation Value (VEV) of the auxiliary field *D*, so that they allow only Minkowski vacua where supersymmetry is restored after inflation.

A simple extension of the inflationary models [6] was proposed in Ref. [8] by adding a *Polonyi* (chiral) multiplet [9] with a linear superpotential. The inflationary models [8] also accommodate arbitrary values of \(n_s\) and *r*, and have a Minkowski vacuum after inflation, but *with* spontaneously broken supersymmetry (SUSY). In this paper we further extend the models of Ref. [8] by allowing them to have a *positive* cosmological constant, i.e. a *de Sitter* vacuum after inflation.

Yet another motivation comes from an exposition of the super-Higgs effect in supergravity by presenting the new *U*(1) gauge-invariant form of the class of inflationary models under investigation. This paves the way toward embedding our models into the superymmetric Grand Unification Theories (sGUT) coupled to supergravity, when they have a spontaneously broken *U*(1) factor in the sGUT gauge group. The physical scale of cosmological inflation can be identified with the Hubble (curvature) scale \(H\approx 10^{14}\) GeV or the inflaton mass \(m_\mathrm{inf}\approx 10^{13}\) GeV. The inflationary scale is thus less (though not much less!) than the sGUT scale of \(10^{16}\) GeV. The simple sGUT groups *SU*(5), *SO*(10) and \(E_6\) are well motivated in the Calabi–Yau compactified heterotic strings, however, they usually come with at least one extra “undesired” *U*(1) factor in the gauge group. The well-known examples include the gauge symmetry breaking \(E_6\rightarrow SO(10)\times U(1)\), \(SO(10)\rightarrow SU(5)\times U(1)\), and the “flipped” \(SU(5)\times U_X(1)\) sGUT originating from heterotic strings. Exploiting the Higgs mechanism in supergravity allows us to propose an identification of the *U*(1) gauge vector multiplet of those sGUT models with the inflaton vector multiplet we consider, thus unifying inflation with those sGUT in supergravity. Besides the sGUT gauge unification, related proton decay and baryon number violation, having the *U*(1) factor in the sGUT gauge group allows one to get rid of monopoles, because the gauge group is not semi-simple [10]. Having a positive cosmological constant takes into account dark energy too.

Our paper is organized as follows. In Sect. 2 we briefly review the supergravity models [8]. In Sect. 3 we present their *U*(1) gauge-invariant formulation and the Higgs mechanism. A positive cosmological constant is added in Sect. 4. The scalar potential and it stability are studied in Sect. 5. Our conclusion is given by Sect. 6.

## 2 Scalar potential and SUSY breaking with a massive vector multiplet in the absence of a cosmological constant

^{1}

*V*described by a real function \(J=J(V)\) and having the superfield strength \(W_\alpha \equiv -\frac{1}{4}(\overline{\mathcal {D}}\overline{\mathcal {D}} -8\mathcal {R})\mathcal {D}_\alpha V\). We have also introduced the chiral density superfield \(2\mathcal {E}\) and the chiral scalar curvature superfield \(\mathcal {R}\) [11].

*R*, the complex scalars \(A_i\) as physical components of \(\Phi _i\); the real scalar

*C*and the real vector \(B_m\), with the corresponding field strength \(F_{mn}=\mathcal {D}_mB_n-\mathcal {D}_nB_m\), as physical components of

*V*. The functions

*K*,

*J*and \(\mathcal {W}\) now represent the lowest components (\(A_i\) and

*C*) of the corresponding superfields. As regards their derivatives, we use the notation \(K_i\equiv \frac{\partial K}{\partial A_i}\), \(K_{i^*}\equiv \frac{\partial K}{\partial \overline{A}_i}\), \(K_{ij^*}\equiv \frac{\partial ^2K}{\partial A_i\partial \overline{A}_j}\), \(J'\equiv \frac{\partial J}{\partial C}\), \(\mathcal {W}_i\equiv \frac{\partial \mathcal {W}}{\partial A_i}\), \(\overline{\mathcal {W}}_i\equiv \frac{\partial \overline{\mathcal {W}}}{\partial \overline{A}_i}\). As is clear from Eq. (2), the absence of ghosts requires \(J''(C)>0\), where the primes denote differentiations with respect to the given argument.

^{2}

*Polonyi model*[9]:

*A*is the lowest component of the Polonyi chiral superfield \(\Phi \).

*stable*Minkowski vacuum with spontaneous SUSY breaking at an arbitrary scale \(\langle F\rangle =\mu \). The related gravitino mass (at the minimum having \(J'=0\)) is given by \(m_{3/2}=\mu e^{2-\sqrt{3}}\). There is also a massive scalar of mass \(2m_{3/2}\) and a massless fermion in the physical spectrum.

As a result, the Polonyi field does not affect the inflation driven by the inflaton scalar *C* belonging to the massive vector multiplet and having the *D*-type scalar potential \(V(C)=\frac{1}{2}{J'}^2\) with a real *J*-function. Of course, the true inflaton field should be canonically normalized via the proper field redefinition of *C*.

## 3 Massless vector multiplet and super-Higgs mechanism

The matter-coupled supergravity model (1) can also be considered as a supersymmetric (Abelian, non-minimal) gauge theory (coupled to supergravity and a Higgs superfield) in the (supersymmetric) gauge where the Higgs superfield is gauged away (say, equal to 1). When the gauge *U*(1) symmetry is restored by introducing back the Higgs (chiral) superfield, the vector superfield *V* becomes the gauge superfield of a spontaneously broken *U*(1) gauge group. In this Section we restore the gauge symmetry in the way consistent with local supersymmetry, and then compare our results with those of the previous Section.

*i*,

*j*,

*k*refer to the chiral (matter) superfields,

*excluding*the Higgs chiral superfield, which we denote \(H,\overline{H}\). Now, in contrast to the previous section, the real function

*J*also depends on the Higgs superfield as \(J=J(He^{2V}\overline{H})\), while the vector superfield

*V*is

*massless*. The Lagrangian (9) is invariant under the supersymmetric

*U*(1) gauge transformations

*Z*itself is a chiral superfield. The Lagrangian (1) of Sect. 2 is recovered from Eq. (9) in the gauge \(H=1\), after the redefinition \(J_\mathrm{new}(e^{2V})=J_\mathrm{old}(V)\).

*U*(1) gauge symmetry of the Lagrangian (9) allows us to choose a different (

*Wess–Zumino*) supersymmetric gauge by “gauging away” the chiral and anti-chiral parts of the general superfield

*V*via the appropriate choice of the superfield parameters

*Z*and \(\overline{Z}\),

*h*, \(\bar{h}\) are the Higgs field and its conjugate. We use the notation \(J_{h\bar{h}}\equiv \frac{\partial ^2J}{\partial h\partial \bar{h}}|\), \(J_{Vh}\equiv \frac{\partial ^2J}{\partial h\partial V}|\) and \(J_{V^2}\equiv \frac{\partial ^2J}{\partial V^2}|\). As regards the scalar potential, we get

*I*,

*J*collectively denote all chiral superfields (as well as their lowest field components) including the Higgs superfield.

*U*(1) Higgs mechanism setting appears after employing the canonical function \(J=\frac{1}{2}he^{2V}\bar{h}\). As regards the Higgs sector, it leads to

*h*and \(\bar{h}\) as

*Z*and \(i(Z-\overline{Z})\) as

*Z*| and \(\overline{Z}|\) cancels the Goldstone mode of (15). Similarly, applying the derivatives \(\overline{\mathcal {D}}_{\dot{\alpha }}\) and \(\mathcal {D}_{\alpha }\) to (11) and taking their lowest components (recalling then \(\overline{\mathcal {D}}_{\dot{\alpha }}\mathcal {D}_{\alpha }V|=\sigma ^m_{\alpha \dot{\alpha }}B_m\)), we conclude that the vector field “eats up” the Goldstone mode indeed, as

## 4 Adding a cosmological constant

A cosmological constant (or dark energy) can be introduced into our framework without breaking any symmetries, via a simple modification of the Polonyi sector and its parameters \(\alpha \) and \(\beta \) introduced in Sect. 2.^{3}

*de Sitter*vacuum with the spontaneously broken SUSY after inflation.

## 5 Scalar potential and vacuum stability

## 6 Conclusion

Our new results are given in Sects. 3, 4 and 5. The new gauge-invariant formulation of our models can be used for unification of inflation with super-GUT in the context of supergravity, and it has a single inflaton scalar field having a positive definite scalar potential, a spontaneous SUSY breaking and a de Sitter vacuum after inflation. Our approach does not preserve the *R*-symmetry.

Our upgrade of the earlier results in Ref. [8] is not limited to the generalized matter couplings in supergravity, given by Eqs. (12) and (13). The standard approach to inflation in supergravity is based on the assumption that the inflaton belongs to a chiral (scalar) multiplet. It leads to the well-known problems such as the so-called \(\eta \)-problem, stabilization of other scalars, getting SUSY breaking and a dS vacuum after inflation, etc. Though some solutions to these problems exist in the literature, they are rather complicated and include the additional “hand-made” input such as extra (stabilizing) matter superfields, extra (shift) symmetries or extra (nilpotency) conditions. We advocate another approach where inflaton is assumed to belong to a massive vector multiplet, while SUSY breaking and a dS vacuum are achieved with the help of a Polonyi superfield. It is much simpler and more flexible than the standard approach.

Physical applications of our approach to super-GUT and reheating are crucially dependent upon the way how the fields present in our models interact with the super-GUT fields. Consistency of sGUT with inflation may lead to some new constraints on both. For instance, inflaton couplings to other matter have to be smaller than \(10^{-3}\), in order to preserve flatness of the inflaton scalar potential and match the observed spectrum of CMB density perturbations. In particular, Yukawa couplings of inflaton to right-handed (sterile) neutrino are crucial in addressing leptogenesis via inflaton decay and the subsequent reheating via decays of the right-handed neutrino into visible particles of the Standard Model. Unfortunately, all this appears to be highly model-dependent at present. A derivation of our supergravity models from superstrings, if any, is desirable because it would simultaneously fix those (unknown) interactions and thus provide specific tools for a computation of reheating temperature, matter abundance, etc. after inflation, together with the low-energy predictions via gravity- or gauge-mediated SUSY breaking to the electro-weak scale – see e.g., Ref. [14] for the previous studies along these lines.

Our models can be further extended in the gauge sector to the Born–Infeld-type gauge theory coupled to supergravity and other matter, along the lines of Refs. [15, 16], thus providing further support toward their possible origin in superstring (flux-) compactification.

## Footnotes

- 1.
- 2.
- 3.
A similar idea was used in Ref. [13], though in the different context, where the Polonyi potential was needed to prevent the real part of the stabilizer field from vanishing at the minimum by imposing the condition \(m_{gravitino}\ll m_{inflaton}\). In our approach, there is no stabilizer field, while the inflation comes from the D-type potential.

## Notes

### Acknowledgements

Y.A. is supported by a scholarship from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) in Japan. S.V.K. is supported by a Grant-in-Aid of the Japanese Society for Promotion of Science (JSPS) under No. 26400252, a TMU President Grant of Tokyo Metropolitan University in Japan, the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan, and the Competitiveness Enhancement Program of Tomsk Polytechnic University in Russia. The authors are grateful to the referees for their critical comments.

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