Hybrid Inflation In Supergravity Research Articles

Non-minimal D-term hybrid inflation in supergravity

Non-minimal D-term hybrid inflation in supergravity

Axion isocurvature perturbations in low-scale models of hybrid inflation

The quantum chromodynamics (QCD) axion solves the strong $CP$ problem and represents an attractive particle candidate for cold dark matter (CDM). However, quantum fluctuations of the axion field during inflation easily result in large CDM isocurvature perturbations that are in conflict with observations of the cosmic microwave background. In this paper, we demonstrate how this problem can be solved in low-scale models of hybrid inflation that may emerge from supersymmetric grand unified theories. We consider both F-term hybrid inflation and D-term hybrid inflation in supergravity, explicitly taking into account the effect of hidden-sector supersymmetry breaking. We discuss the production of cosmic strings and show how the soft terms in the scalar potential readily allow us to achieve the correct scalar spectral index. In both cases, we are able to identify large regions in parameter space that are consistent with all constraints. In particular, we find that evading the CDM isocurvature constraint always requires a small Yukawa or gauge coupling of $\mathcal{O}({10}^{\ensuremath{-}3})$ or smaller. This translates into upper bounds on the gravitino mass of $\mathcal{O}({10}^{5})\text{ }\text{ }\mathrm{GeV}$ in F-term hybrid inflation and $\mathcal{O}({10}^{9})\text{ }\text{ }\mathrm{GeV}$ in D-term hybrid inflation. Our results point to interesting scenarios in well-motivated parameter regions that will be tested in future axion and cosmic microwave background experiments.

Dynamical supersymmetry breaking and late-timeRsymmetry breaking as the origin of cosmic inflation

Spontaneously broken supersymmetry (SUSY) and a vanishingly small cosmological constant imply that R symmetry must be spontaneously broken at low energies. Based on this observation, we suppose that, in the sector responsible for low-energy R symmetry breaking, a discrete R symmetry remains preserved at high energies and only becomes dynamically broken at relatively late times in the cosmological evolution, i.e., after the dynamical breaking of SUSY. Prior to R symmetry breaking, the Universe is then bound to be in a quasi-de Sitter phase---which offers a dynamical explanation for the occurrence of cosmic inflation. This scenario yields a new perspective on the interplay between SUSY breaking and inflation, which neatly fits into the paradigm of high-scale SUSY: inflation is driven by the SUSY-breaking vacuum energy density, while the chiral field responsible for SUSY breaking, the Polonyi field, serves as the inflaton. Because R symmetry is broken only after inflation, slow-roll inflation is not spoiled by otherwise dangerous gravitational corrections in supergravity. We illustrate our idea by means of a concrete example, in which both SUSY and R symmetry are broken by strong gauge dynamics and in which late-time R symmetry breaking is triggered by a small inflaton field value. In this model, the scales of inflation and SUSY breaking are unified; the inflationary predictions are similar to those of F-term hybrid inflation in supergravity; reheating proceeds via gravitino decay at temperatures consistent with thermal leptogenesis; and the sparticle mass spectrum follows from pure gravity mediation. Dark matter consists of thermally produced winos with a mass in the TeV range.

How thermal inflation can saveminimal hybrid inflation in supergravity

Minimal hybrid inflation in supergravity has been ruled out by the 2015 Planck observations because the spectral index of the produced curvature perturbation falls outside observational bounds. To resurrect the model, a number of modifications have been put forward but many of them spoil the accidental cancellation that resolves the η-problem and require complicated Kähler constructions to counterbalance the lost cancellation. In contrast, in this paper the model is rendered viable by supplementing the scenario with a brief period of thermal inflation, which follows the reheating of primordial inflation. The scalar field responsible for thermal inflation requires a large non-zero vacuum expectation value (VEV) and a flat potential. We investigate the VEV of such a flaton field and its subsequent effect on the inflationary observables. We find that, for large VEV, minimal hybrid inflation in supergravity produces a spectral index within the 1-σ Planck bound and a tensor-to-scalar ratio which may be observable in the near future. The mechanism is applicable to other inflationary models.

Chaotic hybrid inflation with a gauged [formula omitted

In this paper we present a novel formulation of chaotic hybrid inflation in supergravity. The model includes a waterfall field which spontaneously breaks a gauged U1(B–L) at a GUT scale. This allows for the possibility of future model building which includes the standard formulation of baryogenesis via leptogenesis with the waterfall field decaying into right-handed neutrinos. We have not considered the following issues in this short paper, i.e. supersymmetry breaking, dark matter or the gravitino or moduli problems. Our focus is on showing the compatibility of the present model with Planck, WMAP and Bicep2 data.

Eliminating the η-problem in SUGRA hybrid inflation with vector backreaction

It is shown that, when the inflaton field modulates the gauge kinetic functionof the gauge fields in supergravity realisations of inflation, the dynamicbackreaction leads to a new inflationary attractor solution, in which theinflaton's variation suffers additional impedance. As a result, slow-rollinflation can naturally occur along directions of the scalar potential whichwould be too steep and curved to support it otherwise. This provides a genericsolution to the infamous eta-problem of inflation in supergravity. Moreover,it is shown that, in the new inflationary attractor, the spectral index of thegenerated curvature perturbations is kept mildly red despite eta of orderunity. The above findings are applied to a model of hybrid inflation insupergravity with a generic Kähler potential. The spectral index of thegenerated curvature perturbations is found to be 0.97–0.98, in excellentagreement with observations. The gauge field can play the role of the vectorcurvaton after inflation but observable statistical anisotropy requiressubstantial tuning of the gauge coupling.

Aspects of Hybrid Inflation in Supergravity

Aspects of Hybrid Inflation in Supergravity

Coupling hybrid inflation to moduli

Hybrid inflation can be realized in low energy effective string theory, asdescribed using supergravity. We find that the coupling of moduli toF-term hybrid inflation in supergravity leads to a slope and a curvature for the inflaton potential. Theϵ and η parameters receive contributions at tree and one loop level which are not compatible withslow roll inflation. Furthermore the coupling to the moduli sector can even preventinflation from ending at all. We show that introducing shift symmetries in theinflationary sector and taking the moduli sector to be no-scale removes mostof these problems. If the moduli fields are fixed during inflation, as is usuallyassumed, it appears that viable slow roll inflation can then be obtained with just onefine-tuning of the moduli sector parameters. However, we show this is not a reasonableassumption, and that the small variation of the moduli fields during inflation gives asignificant contribution to the effective inflaton potential. This typically implies thatη≈−6, although it may be possible to obtain smaller values with heavy fine-tuning.

Confronting hybrid inflation in supergravity with CMB data

$F$-term GUT inflation coupled to N=1 Supergravity is confronted with CMB data. Corrections to the string mass-per-unit-length away from the Bogomolny limit are taken into account. We find that a superpotential coupling $10^{-7}/\mcN \lesssim \kappa \lesssim 10^{-2}/\mcN$, with $\mcN$ the dimension of the Higgs-representation, is still compatible with the data. The parameter space is enlarged in warm inflation, as well as in the curvaton and inhomogeneous reheat scenario. $F$-strings formed at the end of $P$-term inflation are also considered. Because these strings satisfy the Bogomolny bound the bounds are stronger: the gauge coupling is constrained to the range $10^{-7} < g <10^{-4}$.

Sneutrino hybrid inflation in supergravity

We propose a hybrid inflation scenario in which the singlet sneutrino, the superpartner of the right-handed neutrino, plays the role of the inflaton. We study a minimal model of sneutrino hybrid inflation in supergravity, where we find a spectral index ${n}_{\mathrm{s}}\ensuremath{\approx}1+2\ensuremath{\gamma}$ with $|\ensuremath{\gamma}|\ensuremath{\lesssim}0.02$, and predict a running spectral index $|\mathrm{d}{n}_{\mathrm{s}}/\mathrm{d}\mathrm{ln}k|\ensuremath{\ll}|\ensuremath{\gamma}|$ and a tensor-to-scalar ratio $r\ensuremath{\ll}{\ensuremath{\gamma}}^{2}$ for field values well below the Planck scale. In our scenario, the baryon asymmetry of our universe can be explained via nonthermal leptogenesis and a low reheat temperature ${T}_{\mathrm{RH}}\ensuremath{\approx}{10}^{6}$ GeV can be realized.

Realizations of hybrid inflation in supergravity with natural initial conditions

We present viable F-term realizations of the hybrid inflationary scenario in the context of supergravity addressing at the same time the well-known problems of the initial conditions and of the adequate suppression of the inflaton mass. An essential role in our construction is played by "decoupled" superheavy fields without superpotential acquiring large vevs due to D-terms associated with "anomalous" U(1) gauge symmetries. The naturalness of the initial conditions is achieved through a "chaotic" inflation starting at energies close to the Planck scale and driven by the "anomalous" D-terms. We discuss two distinct mechanisms leading to such an early "chaotic" D-term inflation which depend on the choice of the K\"ahler potential involving the superheavy fields. The one relies on a choice of the K\"ahler potential of the $SU(1,1)/U(1)$ K\"ahler manifold of the type encountered in no-scale supergravity whereas the other employs a more "conventional" choice for the K\"ahler potential of the $SU(1,1)/U(1)$ or $SU(2)/U(1)$ K\"ahler manifold but invokes rather specific valuesof the Fayet-Iliopoulos $\xi$ term.

Smooth hybrid inflation in supergravity with a running spectral index and early star formation

It is shown that in a smooth hybrid inflation model in supergravity adiabatic fluctuations with a running spectral index with ${n}_{s}&gt;1$ on a large scale and ${n}_{s}&lt;1$ on a smaller scale can be naturally generated, as favored by the first-year data of WMAP. It is due to the balance between the nonrenormalizable term in the superpotential and the supergravity effect. However, since smooth hybrid inflation does not last long enough to reproduce the central value of observation, we invoke new inflation after the first inflation. Its initial condition is set dynamically during smooth hybrid inflation and the spectrum of fluctuations generated in this regime can have an appropriate shape to realize early star formation as found by WMAP. Hence two new features of WMAP observations are theoretically explained in a unified manner.

Hybrid inflation in supergravity with ( SU(1,1)/ U(1)) m Kähler manifolds

In the presence of fields without superpotential but with large vevs through D-terms the mass-squared of the inflaton in the context of supergravity hybrid inflation receives positive contributions which could cancel the possibly negative Kähler potential ones. The mechanism is demonstrated using Kähler potentials associated with products of SU(1,1)/ U(1) Kähler manifolds. In a particularly simple model of this type all supergravity corrections to the F-term potential turn out to be proportional to the inflaton mass allowing even for an essentially completely flat inflationary potential. The model also allows for a detectable gravitational wave contribution to the microwave background anisotropy. Its initial conditions are quite natural largely due to a built in mechanism for a first stage of “chaotic” D-term inflation.

Hybrid inflation in supergravity

We propose a simple realization of hybrid inflation in supergravity, which does not require any unnaturally small parameters. Inflation in this scenario is relatively short, and inflationary density perturbations fall down on large scales, which corresponds to a blue spectrum with n > 1. Superheavy strings which are formed after inflation in this scenario produce density perturbations of comparable magnitude. In this mixed perturbation (MP) model one may have microwave anisotropy produced by strings and galaxy formation due to inflationary perturbations.