Krzysztof Turzyński

Strongly Coupled Perturbations in Two-Field Inflationary Models

We study models of inflation with two scalar fields and non-canonical kinetic terms, focusing on the case in which the curvature and isocurvature perturbations are strongly coupled to each other. In the regime where a heavy mode can be identified and integrated out, we clarify the passage from the full two-field model to an effectively single-field description. However, the strong coupling sets a new scale in the system, and affects the evolution of the perturbations as well as the beginning of the regime of validity of the effective field theory. In particular, the predictions of the model are sensitive to the relative hierarchy between the coupling and the mass of the heavy mode. As a result, observables are not given unambiguously in terms of the parameters of an effectively single field model with non-trivial sound speed. Finally, the requirement that the sound horizon crossing occurs within the regime of validity of the effective theory leads to a lower bound on the sound speed. Our analysis is done in an extremely simple toy model of slow-roll inflation, which is chosen for its tractability, but is non-trivial enough to illustrate the richness of the dynamics in non-canonical multi-field models.

Decoupling survives inflation: a critical look at effective field theory violations during inflation

We investigate the validity of effective field theory methods and the decoupling of heavy fields during inflation. Considering models of inflation in which the inflaton is coupled to a heavy (super-Hubble) degree of freedom initially in its vacuum state, we find that violations of decoupling are absent unless there is a breakdown of the slow-roll conditions. Next we allow for a temporary departure from inflation resulting in a period of non-adiabaticity during which effective field theory methods are known to fail. We find that the locality of the event and energy conservation lead to a tight bound on the size of the effects of the heavy field. We discuss the implications for the power spectrum and non-gaussianity, and comment on the connection with recent studies of the dynamics of multi-field inflation models. Our results further motivate the use of effective field theory methods to characterize cosmic inflation, and focus the question of observability of additional degrees of freedom during inflation to near the Hubble scale or below — as anticipated from the Wilsonian notions of decoupling and naturalness.

Degenerate minimal see-saw and leptogenesis

We analyze the most general version of the supersymmetric minimal see-saw model with only two right-chiral neutrinos which are degenerate in masses at the scale of Grand Unification. We study the renormalization effects that give rise to non-zero CP asymmetries in the decays of these neutrinos and find that their resonant enhancement due to small mass splitting is partly compensated by other RG effects in the running of the neutrino Yukawa couplings. In spite of this compensation, the CP asymmetries can be large enough for successful thermal leptogenesis. Moreover, they depend very weakly on the right-chiral neutrino masses and the resulting leptogenesis can be successful for very low reheating temperature, thereby allowing to overcome the gravitino problem.

The importance of slow-roll corrections during multi-field inflation

We re-examine the importance of slow-roll corrections during the evolution of cosmological perturbations in models of multi-field inflation. We find that in many instances the presence of light degrees of freedom leads to situations in which next to leading order slow-roll corrections become significant. Examples where we expect such corrections to be crucial include models in which modes exit the Hubble radius while the inflationary trajectory undergoes an abrupt turn in field space, or during a phase transition. We illustrate this with several examples — hybrid inflation, double quadratic inflation and double quartic inflation. Utilizing both analytic estimates and full numerical results, we find that corrections can be as large as 20%. Our results have implications for many existing models in the literature, as these corrections must be included to obtain accurate observational predictions — particularly given the level of accuracy expected from CMB experiments such as Planck.

Patterns of lepton-flavour violation motivated by decoupling and sneutrino inflation

Abstract We present predictions for flavour-violating charged-lepton decays induced by the seesaw mechanism implemented within the constrained minimal supersymmetric standard model (CMSSM) with universal input soft supersymmetry breaking terms. We assume that one heavy singlet neutrino almost decouples from the seesaw mechanism, as suggested by the pattern of light neutrino masses and mixing angles. This is suggested independently by sneutrino inflation with a low reheating temperature, T RH ≲10 7 GeV , so as to avoid overproducing gravitinos. This requirement further fixes the mass of the weakly-coupled sneutrino, whose decays may lead to leptogenesis. We find that BR ( μ → eγ )≳10 −13 but BR ( τ → μγ )≲10 −9 in the bulk of the acceptable parameter space, apart from a few isolated points. The ratio BR ( μ → eγ )/ BR ( τ → eγ ) depends on only one complex parameter, and is particularly interesting to compare with experiment.

Noncanonical kinetic terms and the tilt of the power spectrum

We argue that in models of inflation with two scalar fields and noncanonical kinetic terms there is a possibility of obtaining a red tilt of the power spectrum of curvature perturbations from noncanonicality-induced interactions between the curvature and isocurvature perturbations. We describe an extremely simple model realizing this idea, study numerically its predictions for the perturbations, and discuss applications in realistic scenarios of inflation. We discuss to what extent in this model the scale of the inflationary potential can be decoupled from the amplitude of the density fluctuations.

Neutralino and gravitino dark matter with low reheating temperature

A bstractWe examine a scenario in which the reheating temperature TR after inflation is so low that it is comparable to, or lower than, the freeze out temperature of ordinary WIMPs. In this case the relic abundance of dark matter is reduced, thus relaxing the impact of the usually strong constraint coming from the requirement that the universe does not overclose. We first re-examine the dynamics of freezeout during reheating. Next we study the parameter space of the MSSM with ten free parameters, the Constrained MSSM and the singlino-dominated regions of the Next-to-MSSM. In each case we often find dramatic departures from the usually considered regime of high TR, with important implications for direct detection dark matter searches. In particular, in the MSSM we examine WIMP mass range up to about 5 TeV, and we find large regions of bino dark matter over the whole mass range, and of higgsino dark matter with mass over a similar range but starting from the ∼ 1 TeV value of the standard high TR scenario. We show that the prospects for bino detection strongly depend on TR, while the higgsino is for the most part detectable by future one-tonne detectors. The wino, which is excluded in the standard scenario, becomes allowed again if its mass is roughly above 3.5 TeV, and can also be partially detectable. In the CMSSM, the bino and higgsino mass ranges become much more constrained although detection prospects remain roughly similar. In the Next-to-MSSM we show that, at low enough TR wide ranges of singlino-dominated parameter space of the model become again cosmologically allowed, although detection prospects remain nearly hopeless. We also study the non-thermal contribution to the DM relic density from direct and cascade decays of the inflaton. Finally, in the framework of the MSSM we consider the case of a gravitino as dark matter. In this case we find strong bounds from overclosure and from Big Bang Nucleosynthesis, and derive lower limits on TR which depend on the gravitino mass and on the nature of the lightest ordinary superpartner.

Gravitino dark matter with constraints from Higgs boson mass and sneutrino decays

A bstractWe investigate gravitino dark matter produced thermally at high temperatures and in decays of a long-lived sneutrino. We consider the Non-Universal Higgs Model and a generalized gauge mediation model, and in each case identify sneutrino LOSP regions of the parameter space consistent with the mass of the Higgs-like boson observed at the LHC. We apply relevant collider and cosmological bounds, including constraints from Big Bang Nucleosynthesis and from warm dark matter on large scale structures. Generally, we find allowed values of the reheating temperature TR below 109 GeV, i.e. somewhat smaller than the values needed for thermal leptogenesis, even with a conservative lower bound of 122 GeV on the Higgs mass. Requiring mass values closer to 126 GeV implies TR below 107 GeV and the gravitino mass less than 10 GeV.

Supersymmetric mass spectra for gravitino dark matter with a high reheating temperature

Supersymmetric theories with gravitino dark matter generally do not allow the high reheating temperature required by thermal leptogenesis without running afoul of relic abundance or big bang nucleosynthesis constraints. We report on a search for parameter space that satisfies these requirements with neutralino as the next-to-lightest superpartner. The main implication is the near degeneracy of the gluino with the other neutralinos in the spectrum. The leading discovery channel at the LHC for this scenario is through monojet plus missing energy events.

On low-energy predictions of unification models inspired by F-theory

Abstract The aim of this Letter is to discuss phenomenological consequences of a particular unification model ( Z 3 model) inspired by F-theory. The most distinctive feature of this model is a variety of (cosmologically feasible) options for the NLSP and NNLSP, beyond the usually considered benchmark scenarios.