Primordial inflation with flat supergravity potentials

A new class of primordial inflation models (PRIMO) is presented, based upon the possibility of getting naturally flat potentials in N = 1 supergravity. These models may be considered as the natural cosmological extension of some recently proposed no-scale particle physics models, where all mass scales are derived from the Planck mass (M_p). PRIMO seem to satisfy all presently known cosmological constraints and they are guaranteed (a) to be void of SUSY minima with negative cosmological constant, (b) of a stable (around the origin) potential form against finite temperature effects.     

Natural chaotic inflation in supergravity

We propose a chaotic inflation model in supergravity. In the model the Kahler potential has a Nambu-Goldstone-type shift symmetry of the inflaton chiral multiplet which ensures the flatness of the inflaton potential beyond the Planck scale. We show that chaotic inflation naturally takes place by introducing a small breaking term of the shift symmetry in the superpotential. This may open a new branch of model building for inflationary cosmology in the framework of supergravity.     

Induced-gravity GUT-scale Higgs inflation in supergravity

Models of induced-gravity inflation are formulated within Supergravity employing as inflaton the Higgs field which leads to a spontaneous breaking of a \(U(1)_{B-L}\) symmetry at \(M_\mathrm{GUT}=2\cdot 10^{16}~{\mathrm{GeV}}\). We use a renormalizable superpotential, fixed by a U(1) R symmetry, and Kähler potentials which exhibit a quadratic non-minimal coupling to gravity with or without an independent kinetic mixing in the inflaton sector. In both cases we find inflationary solutions of Starobinsky type whereas in the latter case, others (more marginal) which resemble those of linear inflation arise too. In all cases the inflaton mass is predicted to be of the order of \(10^{13}~{\mathrm{GeV}}\). Extending the superpotential of the model with suitable terms, we show how the MSSM \(\mu \) parameter can be generated. Also, non-thermal leptogenesis can be successfully realized, provided that the gravitino is heavier than about \(10~{\mathrm{TeV}}\).     

Chaotic inflation

We investigate the conditions under which the chaotic inflationary model can provide sufficient inflation to solve the usual cosmological problems. We use a mixture of analytic and numerical techniques to examine the success of the model in cases where spatial curvatures of the background metric are large and when the scalar field lagrangian includes contributions from velocity terms and spatial gradients. Using the simplest natural measure on the space of initial conditions, we calculate the probability of obtaining sufficient inflation given random initial conditions when velocity terms and curvature terms are included. We find this probability to be large in all cases considered. We also derive conditions under which scalar field inhomogeneities will not affect the viability of inflation.     

Chaotic inflation with constrained fields

The eternal chaotic inflation scenario is considered. It is shown that this scenario can be naturally realized in realistic theories containing scalar fields φ_i with sufficiently large masses and/or coupling constants, even if the values of all fields are, for some reasons, constrained to be smaller than φ=O(5M_p).     

Gauge internal symmetry in extended supergravity

Extended supergravity theories with global O(2) and SO(3) internal symmetry have recently been constructed, and a mechanism which implements local O(2) and SO(3) gauge invariance is given here. The introduction of a minimal gauge coupling automatically leads to a $\text{spin}\text{-}\text{3}\text{2}$ mass and a cosmological term in order to preserve local supersymmetry. Local internal symmetry for a $\text{spin}\text{-}\text{3}\text{2}$ field is related to spontaneous breakdown of global supersymmetry. Perturbation theory results which confirm the physical consistency of the system are given.     

Superconformal supergravity and internal symmetry

The Weyl-like gauging of Wess-Zumino superconformal symmetry and of its internal symmetric generalizations SU(2,2|N) are treated. The prolification of gauge fields is much more modest than in super-Riemannian theories. Unlike supergravity, a field theory of this type is still a unified theory that provides its own sources.     

Universal singlets,supergravity and inflation

In supersymmetric theories, the occurrence of universal singlets is a delicate issue, because they usually induce tadpoles that destabilize the hierarchy. We study the effects of these tadpoles in supersymmetric hybrid inflation models. The resulting scenario is generically modified, but it is still possible to achieve inflation in a natural way. It is argued that singlets, despite the problems associated with their presence, can lead to interesting cosmological consequences.     

SUGRA hybrid inflation with shift symmetry

We propose a solution to the η  -problem in supergravity (SUGRA) hybrid inflation using a Nambu–Goldstone-like shift symmetry within a new class of models. The flatness of the tree-level inflaton potential is ensured by shift symmetry invariance of the Kähler potential, while a small symmetry breaking term in the superpotential gives rise to a slope of the potential at loop-level. In the proposed class of inflation models, potentially dangerous couplings between the inflaton and the moduli sector are avoided. We also discuss under which conditions the predicted spectral index can be in agreement with the best-fit-value of the latest WMAP observation ns∼0.96$n_{\mathrm{s}}\sim 0.96$, corresponding to a hilltop-type inflaton potential at loop-level.     

Linear inflation from running kinetic term in supergravity

We propose a new class of inflation models in which the coefficient of the inflaton kinetic term rapidly changes with energy scale. This naturally occurs especially if the inflaton moves over a long distance during inflation as in the case of large-scale inflation. The peculiar behavior of the kinetic term opens up a new way to construct an inflation model. As a concrete example we construct a linear inflation model in supergravity. It is straightforward to build a chaotic inflation model with a fractional power along the same line. Interestingly, the potential takes a different form after inflation because of the running kinetic term.     

Gravity-induced weak symmetry breaking and supergravity

We give here a review of the recent developments of grand unified theories based onN=1 supergravity. We start with a brief introduction of supersymmetry and supergravity multiplets, and then discuss the construction of an invariant Lagrangian. The phenomena of gravity-induced weak symmetry breaking via the super Higgs effect at the tree level, corresponding to the conventional SU(5) gauge group, are then considered. We then extend this idea to the larger group SO(10), showing two possible breaking chains given as (i) SO(10)×susy→SU(2) _L ×U(1) _R ×U(1) _B-L ×SU(3) _C (≡ G₂₁₁₃)×susy→U(1)_em×SU(3) _C (G _LE ) predicting a secondZ-boson having mass lower than 1 TeV, and (ii) SO(10)×susy→SU(2) _L ×SU(2) _R ×SU(4)→(≡G₂₂₄)×susy→ SU(2) _L ×U(1) _Y ×SU(3) _C (≡ G₂₁₃)×susy→U(1)_em×SU(3) _C . We also consider the radiative breaking of weak symmetry via renormalisation group effects, which predicts the top quark mass. Some experimental signatures of the supersymmetric particles are investigated and possible future outlook is discussed. Invited talk presented at the International Symposium on Theoretical Physics, Bangalore, November 1984.     

Surface integrals as symmetry generators in supergravity theory

It is shown that in asymptotically flat space the weakly vanishing Hamiltonian of supergravity theory has to be modified by adding to it certain surface integrals. The numerical value of the surface integrals yields the total energy-momentum, angular momentum and supercharge of the system. The surface integrals have well defined (Dirac) brackets only after the coordinates and supergauge are fixed. In that case they close according to the flat space supersymmetry algebra. If an internal symmetry is included, new surface integrals appear corresponding to the additional gauge charges.     

Infinite symmetry algebras of extended supergravity theories

When extended supergravity theories with noncompact symmetry groups are written in a physical gauge, the noncompact symmetries join with the supersymmetries to generate an infinite-dimensional algebra. The details are worked out explicitly for a two-dimensional theory with an SU(1, 1) internal symmetry. Our analysis confirms the observation of Ellis et al. that the infinite rigid superalgebra should be obtained from the finite-dimensional local superalgebra by replacing scalar fields with their asymptotic values at infinity. The infinite algebra is described by extending the super-Poincaré generators to functions on the coset space defined by the scalar fields at infinity. While mathematically nontrivial, this result is, in a certain sense, trivial from a physical point of view.     

Massive supergravity from spontaneously breaking orthosymplectic gauge symmetry

We construct a Lagrangian density which is manifestly invariant under the orthosymplectic gauge group OSP(1; 4) and under general coordinate transformations. This is done by the use of two multiplets, the symmetric and antisymmetric representations of OSP(1; 4). We present the general features of OSP(m; 2n) and, in particular, its irreducible representations. The absence of OSP(1; 4) symmetry from the ground state indicates that one of the scalar fields, which is an element of the symmetric multiplet, has a nonvanishing vacuum expectation value. A shift in the fields reveals the physical spectrum of our Lagrangian. Two Goldstone fields are present, a vector and a spinor, corresponding to the breakdown of OSP(1; 4) to the Lorentzian group. The full Lagrangian contains a graviton, a massive $\text{spin}\text{-}\text{3}\text{2}$ field, and two massive scalar fields. The generalization to OSP(2; 4) is immediate.