Engineering topics

Lerner, Rose N.

Publications and source records attributed to Lerner, Rose N..

7 records

DOE OSTI2014

Quantifying the 'naturalness' of the curvaton model

We investigate the probability of obtaining an observable curvature perturbation, using as an example the minimal curvaton-higgs (MCH) model. We determine ''probably observable'' and ''probably excluded'' regions of parameter space assuming generic initial conditions and applying a stochastic approach for the curvaton's evolution during inflation. Inflation is assumed to last longer than the N{sub obs} ≅ 55 observable e-folds, and the total number of e-folds of inflation determines the particular ranges of parameters that are probable. For the MCH model, these ''probably observable'' regions always lie within the range 8 × 10{sup 4} GeV ≤ m{sub σ} ≤ 2 × 10{sup 7} GeV, where m{sub σ} is the curvaton mass, and the Hubble scale at horizon exit is chosen as H{sub *} = 10{sup 10} GeV. Because the ''probably observable'' region depends on the total duration of inflation, information on parameters in the Lagrangian from particle physics and from precision CMB observations can therefore provide information about the total duration of inflation, not just the last N{sub obs} e-folds. This method could also be applied to any model that contains additional scalar fields to determine the probability that these scalar fields contribute to the curvature perturbation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2014

The minimal curvaton-higgs model

We present the first full study of the minimal curvaton-higgs (MCH) model, which is a minimal interpretation of the curvaton scenario with one real scalar coupled to the standard model Higgs boson. The standard model coupling allows the dynamics of the model to be determined in detail, including effects from the thermal background and from radiative corrections to the potential. The relevant mechanisms for curvaton decay are incomplete non-perturbative decay (delayed by thermal blocking), followed by decay via a dimension-5 non-renormalisable operator. To avoid spoiling the predictions of big bang nucleosynthesis, we find the ''bare'' curvaton mass to be m{sub σ} ≥ 8 × 10{sup 4}GeV. To match observational data from Planck there is an upper limit on the curvaton-higgs coupling g, between 10{sup −3} and 10{sup −2}, depending on the mass. This is due to interactions with the thermal background. We find that typically non-Gaussianities are small but that if f{sub NL} is observed in the near future then m{sub σ}∼<5 × 10{sup 9}GeV, depending on Hubble scale during inflation. In a thermal dark matter model, the lower bound on m{sub σ} can increase substantially. The parameter space may also be affected once the baryogenesis mechanism is specified.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

Reheating dynamics affects non-perturbative decay of spectator fields

The behaviour of oscillating scalar spectator fields after inflation depends on the thermal background produced by inflaton decay. Resonant decay of the spectator is often blocked by large induced thermal masses. We account for the finite decay width of the inflaton and the protracted build-up of the thermal bath to determine the early evolution of a homogeneous spectator field σ coupled to the Higgs Boson Φ through the term g{sup 2}σ{sup 2}Φ{sup 2}, the only renormalisable coupling of a new scalar to the Standard Model. We find that for very large higgs-spectator coupling g∼>10{sup −3}, the resonance is not always blocked as was previously suggested. As a consequence, the oscillating spectator can decay quickly. For other parameter values, we find that although qualitative features of the thermal blocking still hold, the dynamics are altered compared to the instant decay case. These findings are important for curvaton models, where the oscillating field must be relatively long lived in order to produce the curvature perturbation. They are also relevant for other spectator fields, which must decay sufficiently early to avoid spoiling the predictions of baryogenesis and nucleosynthesis.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2012

Unitarity-violation in generalized Higgs inflation models

Unitarity-violation presents a challenge for non-minimally coupled models of inflation based on weak-scale particle physics. We examine the energy scale of tree-level unitarity-violation in scattering processes for generalized models with multiple scalar fields where the inflaton is either a singlet scalar or the Higgs. In the limit that the non-minimal couplings are all equal (e.g. in the case of Higgs or other complex inflaton), the scale of tree-level unitarity-violation matches the existing result. However if the inflaton is a singlet, and if it has a larger non-minimal coupling than other scalars in the model, then this hierarchy increases the scale of tree-level unitarity-violation. A sufficiently strong hierarchy pushes the scale of tree-level unitarity-violation above the Planck scale. We also discuss models which attempt to resolve the issue of unitarity-violation in Higgs Inflation.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

Electrically charged curvaton

We consider the possibility that the primordial curvature perturbation was generated through the curvaton mechanism from a scalar field with an electric charge, or precisely the Standard Model U(1) weak hypercharge. This links the dynamics of the very early universe concretely to the Standard Model of particle physics, and because the coupling strength is known, it reduces the number of free parameters in the curvaton model. The gauge coupling also introduces several new physical effects. Charge fluctuations are generated during inflation, but they are screened by electron-positron pairs therefore do not violate observational constraints. After inflation, the curvaton interacts with thermal radiation which destroys the curvaton condensate and prevents the generation of curvature perturbations, unless the inflaton dynamics satisfy strong constraints. The curvaton also experiences a period of parametric resonance with the U(1) gauge field. Using the standard perturbative approach, we find that the model can generate the observed density perturbation for Hubble rate H{sub *}∼>10{sup 8}GeV and curvaton mass m∼>10{sup −2}H{sub *}, but with a level of non-Gaussianity (f{sub NL}∼>130) that violates observational constraints. However, previous studies have shown that the parametric resonance changes the predicted perturbations significantly, and therefore fully non-linear numerical field theory simulations are required.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

Spectator field dynamics in de Sitter and curvaton initial conditions

We investigate the stochastic behaviour of long wavelength modes of light spectator scalar fields during inflation. When starting from a classical field value, the probability distribution for the spectator both spreads out and moves towards an equilibrium distribution. We study the timescales for a mixed quadratic and quartic potential. The timescale of equilibration depends on the parameters of the model, and can be surprisingly large, more than thousands of e-folds for the majority of light spectators. These results imply that the initial conditions for spectator fields are not automatically erased during inflation. These general results can be used to determine the probability of the value of the zero-mode inside a Universe-sized patch, which is relevant for observations. As an example, we apply the results to the curvaton model to calculate the probability distribution of the curvature perturbation and discuss 'typical' Universes.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

Curvaton model completed

In an inflationary cosmology, the observed primordial density perturbation could come from the quantum fluctuations of another light ''curvaton'' field, rather than the inflaton. In this case, it is essential that the curvaton decays, converting its perturbation to an adiabatic perturbation. For the first time, we consistently account for this decay in the simplest curvaton model V(σ) = 1/2m{sup 2}σ{sup 2}, where the curvaton decays perturbatively. We point out that this decay gives rise to an important logarithmic correction to the potential. Moreover, the potential will also receive a correction from the thermal bath. As a consequence, the dynamics of the curvaton are substantially altered compared to the original model in the majority of the parameter space. It will therefore be necessary to re-calculate all the predictions of the original model.

79 ASTRONOMY AND ASTROPHYSICS↗