D-term Hybrid Inflation Research Articles

Non-minimal D-term hybrid inflation in supergravity

Non-minimal D-term hybrid inflation in supergravity

Trans-Planckian censorship and inflation in grand unified theories

The recently proposed trans-Planckian censorship conjecture (TCC) amounts to the claim that inflation models with an inflationary energy scale larger than Λinfmax∼109GeV belong to the swampland, i.e., cannot be embedded into a consistent theory of quantum gravity. In this paper, we point out that this constraint can be readily satisfied in D-term hybrid inflation (DHI), which is a well-motivated inflation scenario in the context of supersymmetric grand unification. In DHI, the amplitude of the primordial scalar power spectrum originates from a Fayet–Iliopoulos term of the order of the unification scale, ξ∼1016GeV. At the same time, the TCC results in an upper bound on the corresponding gauge coupling constant of gmax∼10−14. We are able to show that this constraint translates into an upper bound on the gravitino mass of m3/2max∼10MeV, which opens the possibility that dark matter is accounted for by thermally produced gravitinos, if the reheating temperature is close to Treh∼100TeV. Interestingly enough, a somewhat similar gravitino mass range has recently been derived in a model that aims at explaining dark energy in terms of axion quintessence and resolving the Hubble tension by means of decaying gravitino dark matter.

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.

Superconformal subcritical hybrid inflation

We consider D-term hybrid inflation in the framework of superconformal supergravity. In part of the parameter space, inflation continues for subcritical inflaton field value. Consequently, a new type of inflation emerges, which gives predictions for the scalar spectral index and the tensor-to-scalar ratio that are consistent with the Planck 2015 results. The potential in the subcritical regime is found to have a similar structure to one in the simplest class of superconformal α attractors.

A viable D-term hybrid inflation model

We propose a new model of the D-term hybrid inflation in the framework of supergravity. Although our model introduces, analogously to the conventional D-term inflation, the inflaton and a pair of scalar fields charged under a U(1) gauge symmetry, we study the logarithmic and exponential dependence on the inflaton field, respectively, for the Kähler and superpotential. This results in a characteristic one-loop scalar potential consisting of linear and exponential terms, which realizes the small-field inflation dominated by the Fayet-Iliopoulos term. With the reasonable values for the coupling coefficients and, in particular, with the U(1) gauge coupling constant comparable to that of the Standard Model, our D-term inflation model can solve the notorious problems in the conventional D-term inflation, namely, the CMB constraints on the spectral index and the generation of cosmic strings.

Inflation with Fayet-Iliopoulos terms

Two of the most attractive realizations of inflation in supergravity are based upon the presence of a constant Fayet-Iliopoulos (FI) term. In D-term hybrid inflation it is the FI term itself which sets the energy scale of inflation. Alternatively, the breaking of a U(1) symmetry induced by the FI term can dynamically generate the quadratic potential of chaotic inflation. The purpose of this note is to study the possible UV embedding of these schemes in terms of the `field-dependent FI term' related to a string modulus field which is stabilized by a non-perturbative superpotential. We find that in settings where the FI term drives inflation, gauge invariance prevents a decoupling of the modulus from the inflationary dynamics. The resulting inflation models generically contain additional dynamical degrees of freedom compared to D-term hybrid inflation. However, the dynamical realization of chaotic inflation can be obtained in complete analogy to the case of a constant FI term. We present a simple string-inspired toy model of this type.

D7‐brane moduli space in axion monodromy and fluxbrane inflation

AbstractWe analyze the quantum‐corrected moduli space of D7‐brane position moduli with special emphasis on inflationary model building. D7‐brane deformation moduli are key players in two recently proposed inflationary scenarios: The first, D7‐brane chaotic inflation, is a variant of axion monodromy inflation which allows for an effective 4d supergravity description. The second, fluxbrane inflation, is a stringy version of D‐term hybrid inflation. Both proposals rely on the fact that D7‐brane coordinates enjoy a shift‐symmetric Kähler potential at large complex structure of the Calabi‐Yau threefold, making them naturally lighter than other fields. This shift symmetry is inherited from the mirror‐dual Type IIA Wilson line on a D6‐brane at large volume. The inflaton mass can be provided by a tree‐level term in the flux superpotential. It induces a monodromy and, if tuned to a sufficiently small value, can give rise to a large‐field model of inflation. Alternatively, by a sensible flux choice one can completely avoid a tree‐level mass term, in which case the inflaton potential is induced via loop corrections. The positive vacuum energy can then be provided by a D‐term, leading to a small‐field model of hybrid natural inflation. In the present paper, we continue to develop a detailed understanding of the D7‐brane moduli space focusing among others on shift‐symmetry‐preserving flux choices, flux‐induced superpotential in Type IIB/F‐theory language, and loop corrections. While the inflationary applications represent our main physics motivation, we expect that some of our findings will be useful for other phenomenological issues involving 7‐branes in Type IIB/F‐theory constructions.

No-scale D-term inflation with stabilized moduli

We study the consistency of hybrid inflation and moduli stabilization, using the Kallosh–Linde model as an example for the latter. We find that F-term hybrid inflation is not viable since inflationary trajectories are destabilized by tachyonic modes. On the other hand, D-term hybrid inflation is naturally compatible with moduli stabilization due to the absence of a large superpotential term during the inflationary phase. Our model turns out to be equivalent to superconformal D-term inflation and it therefore successfully accounts for the CMB data in the large-field regime. Supersymmetry breaking can be incorporated via an O'Raifeartaigh model. For GUT-scale inflation one obtains stringent bounds on the gravitino mass. A rough estimate yields 105 GeV≲m3/2≲1010 GeV, contrary to naive expectation.

Superconformal D-term inflation

We study models of hybrid inflation in the framework of supergravitywith superconformal matter. F-term hybrid inflation is not viable since the inflatonacquires a large tachyonic mass. On the contrary, D-term hybrid inflation can successfully account forthe amplitude of the primordial power spectrum.It is a two-field inflation model which, depending on parameters,yields values of the scalar spectral index down tons ≃ 0.96. Generically, there is a tension between a small spectralindex and the cosmic string bound albeit,within 2σ uncertainty, the current observational bounds can be simultaneously fulfilled.

Tight constraints onF- andD-term hybrid inflation scenarios

We use present cosmological data from the cosmic microwave background, large-scale structure and deuterium at high redshifts to constrain supersymmetric F- and D-term hybrid inflation scenarios including possible contributions to the CMB anisotropies from cosmic strings. Using two different realizations of the cosmic string spectrum, we find that the minimal version of the D-term model is ruled out at high significance. F-term models are also in tension with the data. We also discuss possible non-minimal variants of the models.

Super hilltop inflation

In this paper, we consider logarithmic radiative corrections and higher order terms to the supersymmetric hilltop F- and D-term hybrid inflation models. Conventional F- and D-term hybrid inflation only predicts ns⪆0.98. We show that via a positive quadratic and a negative quartic correction the spectral index can be reduced to ns = 0.96 suggested from latest WMAP result and also cosmic string problem appeared in SUSY hybrid inflation can be solved with mild tuning of the parameters if κ⪅0.01 for F-term inflation and g⪅0.05 for D-term inflation.

Supersymmetric inflation and baryogenesis via extra-flat directions of the minimalsupersymmetric standard model

One interpretation of proton stability is that it implies the existence of extra-flatdirections of the minimal supersymmetric standard model, in particularucucdcec and QQQL, where the operators lifting the potential are suppressed by a mass scaleΛ which is much larger than the Planck mass, . Using D-term hybrid inflation as an example, we show that such flat directions can serve as theinflaton in supersymmetric inflation models. The resulting model is a minimal version ofD-term inflation which requires the smallest number of additional fields. In the case whereQ-balls form from the extra-flat direction condensate after inflation, successful Affleck–Dinebaryogenesis is possible if the suppression mass scale is . In this case the reheating temperature fromQ-ball decay isin the range 3–100 GeV, while observable baryon isocurvature perturbations and non-thermaldark matter are possible. In the case of extra-flat directions with a larget squark component,there is no Q-ball formation and reheating is via conventional condensatedecay. In this case the reheating temperature is in the range1–100 TeV,naturally evading thermal gravitino overproduction while allowing sphaleron erasure of any largeB–L asymmetry.

Moduli corrections to D-term inflation

We present a D-term hybrid inflation model, embedded in supergravity with moduli stabilization.Its novel features allow us to overcome the serious challenges of combiningD-term inflation and moduli fields within the same string motivatedtheory. One salient point of the model is the positive definite upliftingD-term arising from the moduli stabilization sector. By coupling thisD-term to the inflationary sector, we generate an effective Fayet–Iliopoulos term. Moduli correctionsto the inflationary dynamics are also obtained. Successful inflation is achieved for a limitedrange of parameter values with spectral index compatible with the WMAP3 data. CosmicD-term strings are also formed at the end of inflation; these are no longerBogomol’nyi–Prasad–Sommerfeld (BPS) objects. The properties of the strings are studied.

Anatomy ofFD-term hybrid inflation

We analyze the cosmological implications of F-term hybrid inflation with a subdominant Fayet--Iliopoulos D-term whose presence explicitly breaks a D-parity in the inflaton-waterfall sector. This scenario of inflation, which is called F_D-term hybrid model for brevity, can naturally predict lepton number violation at the electroweak scale, by tying the mu-parameter of the MSSM to an SO(3)-symmetric Majorana mass m_N, via the vacuum expectation value of the inflaton field. We show how a negative Hubble-induced mass term in a next-to-minimal extension of supergravity helps to accommodate the present CMB data and considerably weaken the strict constraints on the theoretical parameters, resulting from cosmic string effects on the power spectrum P_R. The usual gravitino overabundance constraint may be significantly relaxed in this model, once the enormous entropy release from the late decays of the ultraheavy waterfall gauge particles is properly considered. As the Universe enters a second thermalization phase involving a very low reheat temperature, which might be as low as about 0.3 TeV, thermal electroweak-scale resonant leptogenesis provides a viable mechanism for successful baryogenesis, while thermal right-handed sneutrinos emerge as new possible candidates for solving the cold dark matter problem. In addition, we discuss grand unified theory realizations of F_D-term hybrid inflation devoid of cosmic strings and monopoles, based on the complete breaking of an SU(2) subgroup. The F_D-term hybrid model offers rich particle-physics phenomenology, which could be probed at high-energy colliders, as well as in low-energy experiments of lepton flavour or number violation.

Supergravity modification ofD-term hybrid inflation: Solving the cosmic string and spectral index problems via a right-handed sneutrino

Supergravity corrections due to the energy density of a right-handed sneutrino can generate a negative mass squared for the inflaton, flattening the inflaton potential and reducing the spectral index and inflaton energy density. For the case of D-term hybrid inflation, we show that the spectral index can be lowered from the conventional value n = 0.98 to a value within the range allowed by the latest WMAP analysis, n = 0.951^{+0.015}_{-0.019}. The modified energy density is consistent with non-observation of cosmic strings in the CMB if n < 0.946. The WMAP lower bound on the spectral index implies that the D-term cosmic string contribution may be very close present CMB limits, contributing at least 5% to the CMB multipoles.