Rose N. Lerner

Gauge singlet scalar as inflaton and thermal relic dark matter

We show that, by adding a gauge singlet scalar S to the standard model which is nonminimally coupled to gravity, S can act both as the inflaton and as thermal relic dark matter. We obtain the allowed region of the (m_s, m_h) parameter space which gives a spectral index in agreement with observational bounds and also produces the observed dark matter density while not violating vacuum stability or nonperturbativity constraints. We show that, in contrast to the case of Higgs inflation, once quantum corrections are included the spectral index is significantly larger than the classical value (n = 0.966 for N = 60) for all allowed values of the Higgs mass m_h. The range of Higgs mass compatible with the constraints is 145 GeV SS, while future direct dark matter searches should be able to significantly constrain the model.

Higgs inflation and naturalness

Inflation based on scalar fields which are non-minimally coupled to gravity has been proposed as a way to unify inflation with weak-scale physics, with the inflaton being identified with the Higgs boson or other weak-scale scalar particle. These models require a large non-minimal coupling ξ ~ 104 to have agreement with the observed density perturbations. However, it has been suggested that such models are unnatural, due to an apparent breakdown of the calculation of Higgs-Higgs scattering via graviton exchange in the Jordan frame. Here we argue that Higgs inflation models are in fact natural and that the breakdown does not imply new physics due to strong-coupling effects or unitarity breakdown, but simply a failure of perturbation theory in the Jordan frame as a calculational method. This can be understood by noting that the model is completely consistent when analysed in the Einstein frame and that scattering rates in the two frames are equal by the Equivalence Theorem for non-linear field redefinitions.

A unitarity-conserving Higgs inflation model

Scalar field models of inflation based on a large nonminimal coupling to gravity

Distinguishing Higgs inflation and its variants

\ensuremath{\xi}

Curvaton decay by resonant production of the Standard Model higgs

, in particular, Higgs inflation, may violate unitarity at an energy scale

Unitarity-violation in generalized Higgs inflation models

\ensuremath{\Lambda}\ensuremath{\sim}{M}_{p}/\ensuremath{\xi}\ensuremath{\ll}{M}_{p}

Reheating dynamics affects non-perturbative decay of spectator fields

. In this case the model is incomplete at energy scales relevant to inflation. Here we propose a new unitarity-conserving model of Higgs inflation. The completion of the theory is achieved via additional interactions which are proportional to products of the derivatives of the Higgs doublet. The resulting model differs from the original version of Higgs inflation in its prediction for the spectral index, with a classical value

Space-dependent step features:transient breakdown of slow-roll, homogeneity, and isotropy during inflation

n=0.974

Electrically charged curvaton

. In the case of a nonsupersymmetric model, quantum corrections are likely to strongly modify the tree-level potential, suggesting that supersymmetry or a gauge singlet scalar inflaton is necessary for a completely successful model.

Thermal blocking of preheating

We consider how Higgs Inflation can be observationally distinguished from variants based on gauge singlet scalar extensions of the Standard Model, in particular where the inflaton is a non-minimally coupled gauge singlet scalar (S-inflation). We show that radiative corrections generally cause the spectral index n to decrease relative to the classical value as the Higgs mass is increased if the Higgs boson is the inflaton, whereas n increases with increasing Higgs mass if the inflaton is a gauge singlet scalar. The accuracy to which n can be calculated in these models depends on how precisely the reheating temperature can be determined. The number of Einstein frame e-foldings N is similar in both models, with N = 58-61 for singlet inflation compared with N = 57-60 for Higgs inflation. This allows the spectral index to be calculated to an accuracy \Delta n = 0.001. Provided the Higgs mass is above ~ 135 GeV, a combination of a Higgs mass measurement and a precise determination of n will enable Higgs Inflation and S-inflation to be distinguished.