Multifield Dynamics in Higgs-otic Inflation

TL;DR

Higgs-otic inflation is analyzed as a two-field model with non-canonical kinetics arising from D-brane dynamics in string theory. By incorporating adiabatic and isocurvature perturbations, the study shows that isocurvature modes couple to and transfer power into curvature perturbations, with end-of-inflation isocurvature strongly suppressed. Depending on the flux parameter $A$ and the flux density $oldsymbol{\hat{G}}$, turning in field space can enhance or suppress multifield effects, leading to predictions for $n_s$ and $r$ that lie within Planck/BICEP constraints, notably $r o 0.08$–$0.12$ for representative cases. The results reinforce the viability of Higgs-otic inflation in a stringy, two-field framework and outline how future refinements (e.g., reheating, moduli stabilization) could further test the scenario.

Abstract

In Higgs-otic inflation a complex neutral scalar combination of the $h^0$ and $H^0$ MSSM Higgs fields plays the role of inflaton in a chaotic fashion. The potential is protected from large trans-Planckian corrections at large inflaton if the system is embedded in string theory so that the Higgs fields parametrize a D-brane position. The inflaton potential is then given by a DBI+CS D-brane action yielding an approximate linear behaviour at large field. The inflaton scalar potential is a 2-field model with specific non-canonical kinetic terms. Previous computations of the cosmological parameters (i.e. scalar and tensor perturbations) did not take into account the full 2-field character of the model, ignoring in particular the presence of isocurvature perturbations and their coupling to the adiabatic modes. It is well known that for generic 2-field potentials such effects may significantly alter the observational signatures of a given model. We perform a full analysis of adiabatic and isocurvature perturbations in the Higgs-otic 2-field model. We show that the predictivity of the model is increased compared to the adiabatic approximation. Isocurvature perturbations moderately feed back into adiabatic fluctuations. However, the isocurvature component is exponentially damped by the end of inflation. The tensor to scalar ratio varies in a region $r=0.08-0.12$, consistent with combined Planck/BICEP results.

Figures (11)

• Figure 1: Energy scales in the Higgs-otic Inflation scenario higgsotic. Below $10^{13}$ GeV the light degrees of freedom in the Higgs sector are given by the $SU(2)$ doublet $H_L$. Above this scale $SU(2)$ is broken and they lie within the neutral components of $h$ and $H$.
• Figure 2: Scalar potential for three different values of $A$, $A=0.1$ (upper left), $A=0.5$ (upper right) and $A=0.9$ (below).
• Figure 3: Left: The last 68 efoldings for some representative inflationary trajectories. Red dots mark 10 efoldings intervals on each trajectory. Right: Evolution of $\eta_\perp$ for the different trajectories.
• Figure 4: Evolution of the curvature (blue) and isocurvature (red) two point functions for $k_{60}$ for the trajectories of Fig. \ref{['fig:BGGhat1']}. Curvature and isocurvature power are normalised to the single field estimate $P_0=\frac{H^2}{8 \pi^2 \epsilon}|_{*}$.
• Figure 5: Spectral index (left) and tensor to scalar ratio (right) for $\hat{G}=1$ and $A=0.83$ superimposed with the PLANCK 2015 constraints $n_s= 0.96688 \pm 0.0061$ and $r<0.114$ (grey band). The slightly transparent curve corresponds to the single field estimate while the one surrounded by the data points corresponds to the multi-field results. Circles: $N_e=60$, Squares: $N_e=50$.