Primordial perturbations from multifield inflation with nonminimal couplings

Abstract

Realistic models of particle physics include many scalar fields. These fields generically have nonminimal couplings to the Ricci curvature scalar, either as part of a generalized Einstein theory or as necessary counterterms for renormalization in curved background spacetimes. We develop a gauge-invariant formalism for calculating primordial perturbations in models with multiple nonminimally coupled fields.We work in the Jordan frame (in which the nonminimal couplings remain explicit) and identify two distinct sources of entropy perturbations for such models. One set of entropy perturbations arises from interactions among the multiple fields. The second set arises from the presence of nonminimal couplings. Neither of these varieties of entropy perturbations will necessarily be suppressed in the long-wavelength limit, and hence they can amplify the curvature perturbation, ζ, even for modes that have crossed outside the Hubble radius. Models that overproduce long-wavelength entropy perturbations endanger the close fit between predicted inflationary spectra and empirical observations. PACS numbers: 04.62+v; 98.80.Cq. Preprint MIT-CTP 4143Published as Phys. Rev. D81, 124037 (2010). *

MSSM-inspired multifield inflation

“…Recent analyses [41][42][43][44][45][46][47][48] of multifield models showed that unlike the single-field models they generically provide density (entropy) perturbations which can induce the curvature perturbation to evolve beyond the cosmological horizon in the process of inflation [49]. Evolution of density perturbations in multifield models should be studied in order to analyze new features in the observables such as non-Gaussianities [50] which are absent in the single-field inflationary models.…”

Stabilizing the Planck mass shortly after inflation

“…We have investigated numerically the effects of this coupling on the power spectrum of primordial fluctuations. It has previously been shown that a non-minimally coupled scalar field can induce changes in the curvature perturbation on superhorizon scales via the introduction of terms proportional to f,ḟ andf in the non-adiabatic pressure perturbation, δP nad [11]. Here, we have quantified this effect.…”

“…Models with non-minimally coupled scalar fields, on the other hand, will produce a distinct source of entropy perturbations, arising due to the coupling of the scalars. In the model we present above, it is expected that, after inflation has ended and during the reheating phase, these entropy perturbations can become sizeable due to the fact thatḟ andf no longer need to remain small [11]. It is these non-adiabatic pressure perturbations, and the resulting amplification of the power spectrum, that we will investigate in the remainder of the paper.…”

“…For more complexity, the scalar field could have a non-minimal coupling to gravity, such as in the newest version of the Higgs inflation model [10] (however, for the majority of cases, this can be treated as a field with a minimal coupling by moving to the Einstein frame and modifying the potential). Finally, the most complex inflationary models contain multiple scalar fields non-minimally coupled to gravity, and with non-standard kinetic terms [11,12]. By comparing each model's predictions with observational data, we can rule out regions of model space, with the ultimate goal to obtain a single inflationary model which best fits the data.…”

Cosmological sigma model with non-minimal coupling to the target space

“…There are at least two ways to solve the problem of late-time acceleration, namely modification of the gravitational theory orthe introduction of some exotic source of gravity, which is commonly called Dark Energy (DE). As the models of dark energy are customarily used not only canonical fields with the modified potential of self-interaction or the combination of fields with some physically or phenomenologically founded types of interaction between the components [5][6][7][8]. Among a great number of approaches for solving the problem of dark energy, we can mention the field theory with non-canonical kinetic term in cos-mology [9][10][11][12][13][14][15][16].…”