Supersymmetric Hybrid Inflation Models Research Articles

Gravitational waves and primordial black holes from supersymmetric hybrid inflation

We study the effect of supergravity corrections due to a linear and a bilinear term in the K\"ahler potential, in the context of a supersymmetric hybrid inflation model. By appropriate choice of the parameters associated to these terms, we are able to satisfy the main cosmological constraints for the spectral index $n_s$ and the tensor-to-scalar ratio $r$. In addition, this model predicts primordial black hole abundance enough to account for the whole dark matter of the Universe and gravitational wave spectra within the reach of future detection experiments. The predictions of the model can be made compatible to the NANOGrav reported signal, at the cost of significantly lower primordial black hole abundance.

Kähler potential braneworld inflation in supergravity after Planck 2015

We analyze the slow-roll mechanism in Randall–Sundrum II braneworld with a supersymmetric hybrid inflation model. We are interested in studying various inflationary spectrum perturbation parameters in two cases. The first is the minimal Kähler potential where the inflationary parameters depend on the number of [Formula: see text]-foldings [Formula: see text] as well as the brane tension [Formula: see text], such that we produce the central value of the spectral index [Formula: see text]. The second case concerns the nonminimal Kähler potential, where the inflationary parameters depend only on the brane tension. Also, the [Formula: see text]-problem is solved for natural coupling parameter values which is not realized in the standard case. In addition, for a suitable choice of brane tension value [Formula: see text], the perturbation spectrum is widely consistent with Planck data.

Inflation and cosmic (super)strings: implications of their intimate relation revisited

We briefly discuss constraints on supersymmetric hybrid inflation models and examine the consistency of brane inflation models. We then address the implications for inflationary scenarios resulting from the strong constraints on the cosmic (super)string tension imposed from the most recent cosmic microwave background temperature anisotropies data.

Smooth hybrid inflation on brane constrained by Planck data

It is shown that, in the supersymmetric smooth hybrid inflation model with the minimal Kähler potential, the spectral index ns is larger than 0.97 in the standard inflation. In this context, we study the smooth hybrid inflationary model in the framework of the Randall–Sundrum type-II braneworld model. We derive all known inflationary spectrum parameters which are widely consistent with Planck data for a particular choice of brane tension values λ especially for number of e-folds N = 50. We reproduce the central value of the scalar spectral index ns = 0.96 whereas the ratio r~(10-4-10-3). However, the running of the scalar spectral index [Formula: see text] is not excluded from the range given by the latest observational measurements.

Upper bound on the tensor-to-scalar ratio in GUT-scale supersymmetric hybrid inflation

We explore the upper bound on the tensor-to-scalar ratio r in supersymmetric (F-term) hybrid inflation models with the gauge symmetry breaking scale set equal to the value 2.86⋅1016 GeV, as dictated by the unification of the MSSM gauge couplings. We employ a unique renormalizable superpotential and a quasi-canonical Kähler potential, and the scalar spectral index ns is required to lie within the two-sigma interval from the central value found by the Planck satellite. In a sizable region of the parameter space the potential along the inflationary trajectory is a monotonically increasing function of the inflaton, and for this case, r≲2.9⋅10−4, while the spectral index running, |dns/dln⁡k|, can be as large as 0.01. Ignoring higher order terms which ensure the boundedness of the potential for large values of the inflaton, the upper bound on r is significantly larger, of order 0.01, for subplanckian values of the inflaton, and |dns/dln⁡k|≃0.006.

Supersymmetric hybrid inflation with a light scalar

Light scalar fields present during inflation can lead to interesting observable signatures, especially in models with nonequilibrium reheating dynamics. We study a supersymmetric hybrid inflation model with a third scalar whose lightness is protected by symmetry, using analytical and numerical techniques, and demonstrate that the amplitude, the spectral index and the non-Gaussianity parameter ${f}_{\mathrm{NL}}$ of the primordial curvature perturbation are within the Planck observational bounds for suitable parameter values.

Heavy gravitino in hybrid inflation

It is known that supersymmetric hybrid inflation model may require severe tunings on the initial condition for large gravitino mass of order 100 - 1000 TeV due to the constant term in the superpotential. We propose a modified hybrid inflation model, where the constant term is suppressed during inflation and generated after inflation by replacing a constant term with dynamical field. In this modified model, successful inflation consistent with large gravitino mass takes place without severe tunings on the initial condition. Constraint from cosmic strings is also relaxed.

Spectral index and non-Gaussianity in supersymmetric hybrid inflation

We consider a supersymmetric hybrid inflation model with two inflaton fields. The superpotential during inflation is dominated by W=(\kappa S+\kappa' S')M^2, where S, S' are inflatons carrying the same U(1)_R charge, \kappa, \kappa' are dimensionless couplings, and M (\sim 10^{15-16} GeV) is a dimensionful parameter associated with a symmetry breaking scale. One light mass eigenstate drives inflation, while the other heavier mass eigenstate is stuck to the origin. The smallness of the lighter inflaton mass for the scalar spectral index n_s\approx 0.96, which is the center value of WMAP7, can be controlled by the ratio \kappa'/\kappa through the supergravity corrections. We also discuss the possibility of the two field inflation and large non-Gaussianity in this setup.

Observable gravity waves from supersymmetric hybrid inflation. II.

It is shown that a tensor-to-scalar ratio close to $r=0.03$, which can be observed by Planck, is realized in supersymmetric hybrid inflation models with TeV-scale soft supersymmetry breaking terms. This extends our previous analysis, which also found $r\ensuremath{\lesssim}0.03$ but employed intermediate-scale soft terms. Other cosmological observables such as the scalar spectral index are in good agreement with the WMAP data.

Realistic Inflation Models and Primordial Gravity Waves

We consider a variety of realistic inflationary potentials and discuss their predictions for the tensor to scalar ratio r, a canonical measure of gravity waves generated during inflation. For a Standard Model gauge singlet inflaton with a Higgs-like potential, for example, we find that r ≳ 0.02, which may be observed by the Planck satellite. We also identify supersymmetric hybrid inflation models where r can be as high as 0.03, again within the reach of Planck. The scalar spectral index in these models lies within the WMAP one sigma bounds.

Supersymmetric hybrid inflation redux

We discuss the important role played during inflation by one of the soft supersymmetry breaking terms in the inflationary potential of supersymmetric hybrid inflation models. With minimal Kähler potential, the inclusion of this term allows the prediction for the scalar spectral index to agree with the value ns=0.963−0.015+0.014 found by WMAP5. In the absence of this soft term, and by taking into account only radiative and supergravity corrections, it is well known that ns⩾0.985. This same soft term has previously been shown to play a key role in resolving the MSSM μ problem. The tensor to scalar ratio r is quite small in these models, taking on values r⩽10−5 in the WMAP5 2σ range of ns.

Supersymmetric hybrid inflation with non-minimal Kähler potential

Minimal supersymmetric hybrid inflation based on a minimal Kähler potential predicts a spectral index ns≳0.98. On the other hand, WMAP three year data prefers a central value ns≈0.95. We propose a class of supersymmetric hybrid inflation models based on the same minimal superpotential but with a non-minimal Kähler potential. Including radiative corrections using the one-loop effective potential, we show that the prediction for the spectral index is sensitive to the small non-minimal corrections, and can lead to a significantly red-tilted spectrum, in agreement with WMAP.

Supersymmetric hybrid inflation with minimal and non-minimal Kähler potential

Minimal supersymmetric hybrid inflation based on a minimal Kähler potential predicts a spectral index ns ≳ 0.98. On the other hand, WMAP three-year data prefer a central value ns ≈ 0.95. We propose a class of supersymmetric hybrid inflation models based on the same minimal superpotential but with a non-minimal Kähler potential. Including radiative corrections using the one-loop effective potential, we show that the prediction for the spectral index is sensitive to the small non-minimal corrections, and can lead to a significantly red-tilted spectrum, in agreement with WMAP.

Constraints on supersymmetric hybrid inflation models

We point out that the inclusion of a string component contributing around 5% to the CMBpower spectrum amplitude on large scales can increase the preferred value of the spectral indexns of density fluctuations measured by CMB experiments. While this finding appliesto any cosmological scenario involving strings, we consider in particular modelsof supersymmetric hybrid inflation, which predict , in tension with the CMB data when strings are not included.Using MCMC analysis we constrain the parameter space allowed forF- andD-term inflation.For the F-term model, using minimal supergravity corrections, we find thatlogκ = −2.34 ± 0.38 and M = (0.518 ± 0.059) × 1016 GeV. The inclusion of non-minimal supergravity corrections canmodify these values somewhat. In the corresponding analysis forD-term inflation,we find logκ = −4.24 ± 0.19 and mFI = (0.245 ± 0.031) × 1016 GeV. Under the assumption that these models are correct, these results represent precisionmeasurements of important parameters of a grand unified theory. We consider the possibleuncertainties in our measurements and additional constraints on the scenario from the stochasticbackground of gravitational waves produced by the strings. The best fitting model predicts aB-modepolarization signal ≈0.3 μK rms peaking at . This is of comparable amplitude to the expected signal due to gravitational lensing of the adiabaticE-mode signal on these scales.

Simulations of the end of supersymmetric hybrid inflation and nontopological soliton formation

We present two- and three-dimensional simulations of the growth of quantum fluctuations of the scalar fields in supersymmetric hybrid inflation models. For a natural range of couplings, subhorizon quantum fluctuations undergo rapid growth due to scalar field dynamics, resulting in the formation of quasistable nontopological solitons (inflaton condensate lumps) which dominate the postinflation era.

Reheating and gravitino production in braneworld inflation

We consider the constraints that can be imposed on a wide class of Inflation models in modified gravity scenarios in which the Friedmann equation is modified by the inclusion of ${\ensuremath{\rho}}^{2}$ terms, where $\ensuremath{\rho}$ is the total energy density. In particular we obtain the reheating temperature and gravitino abundance associated with the end of inflation. Whereas models of chaotic inflation and natural inflation can easily avoid the conventional gravitino overproduction problem, we show that supersymmetric hybrid inflation models (driven by both $F$ and $D$ terms) do not work in the ${\ensuremath{\rho}}^{2}$ dominated era. We also study inflation driven by exponential potentials in this modified background and show that the gravitino production is suppressed enough to avoid there being a problem, although other conditions severely constrain these models.

Hybrid inflation, dark energy and dark matter

It has been suggested that the dark energy density ρv∼10−12 eV4 in the universe is associated with a metastable (false) vacuum, while the true vacuum has a vanishing cosmological constant. By including supergravity corrections we show how this is naturally realized in realistic supersymmetric hybrid inflation models. With a fundamental supersymmetry breaking scale ∼TeV, the LSP is not a suitable candidate for cold dark matter. We consider axion physics to overcome this and simultaneously provide a resolution of the MSSM μ problem.

Reheat temperature in supersymmetric hybrid inflation models

The allowed range of parameters for supersymmetric hybrid inflation and its extensions are investigated. The lower bound on the reheat temperature ${T}_{r}$ in these models with hierarchical right-handed neutrinos is found to be $3\ifmmode\times\else\texttimes\fi{}{10}^{7}\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$. (${T}_{r}$ as low as 100 GeV is possible for quasidegenerate right-handed neutrinos.) We also present revised estimates for the scalar spectral index and the symmetry breaking scale associated with inflation.

GUT phase transition and hybrid inflation

The supersymmetric model of hybrid inflation is interesting not only because of its naturalness but also because of another reason. Its energy scale determined by the COBE normalization is 1015–1016 GeV. It happens to be the energy scale of interest in particle physics, namely, the mass scale of right-handed neutrinos or the energy scale of the gauge-coupling unification. It is true that topological defects are produced after the hybrid inflation if it is related to a U(1)B−L or a GUT-symmetry breaking, and hence one cannot naively identify models of particle physics with that of inflation. But those defects are not necessarily found in modified models. We show in this Letter that quite a simple extension of the minimal supersymmetric hybrid inflation model is free from monopoles or cosmic strings. Moreover, it happens to be exactly the same as a well-motivated extension of SU(5)-unified theories. The vacuum energy is dominated by F-term. The η-problem is not necessarily serious when the model is realized by D-branes. Although it has been considered that a coupling constant has to be very small when the vacuum energy is dominated by F-term, this constraint is not applied either to the D-brane model. They are due to a particular form of the Kähler potential and interaction of the model. Reheating process is also discussed.

Two-fieldQ-ball solutions of supersymmetric hybrid inflation

We demonstrate the existence of two-field Q-ball solutions of the scalar field equations of supersymmetric D- and F-term hybrid inflation. The solutions consist of a complex inflaton field together with a real symmetry breaking field. Such inflatonic Q-balls may play a fundamental role in reheating and the post-inflation era of supersymmetric hybrid inflation models.