Constraints on inflation with an extended neutrino sector

Constraints on inflationary models typically assume only the standard models of cosmology and particle physics. By extending the neutrino sector to include a new interaction with a light scalar mediator ($m_{\varphi }\sim \mathrm{MeV}$), it is possible to relax these constraints, in particular via opening up regions of the parameter space of the spectral index $n_s$. These new interactions can be probed at IceCube via interactions of astrophysical neutrinos with the cosmic neutrino background for nearly all of the relevant parameter space.

Figure 1

2d posterior distributions of the parameters most affected by the effective neutrino coupling $G_{\mathrm{eff}}$. $G_{\mathrm{eff}}$ is given in units of ${\mathrm{MeV}}^{-2}$ and $H_0$ in $\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$.

Figure 2

Allowed parameter range for $G_{\mathrm{eff}}$ in the $(g,m_{\varphi })$-plane. The white region is allowed while the various shaded regions are excluded. The two disjoint white regions correspond to the two solutions allowed by CMB data: the smaller compact one is that with a new neutrino interaction and the larger one corresponds to the $\mathrm{\Lambda }\mathrm{CDM}$ mode.

Figure 3

Comparison of the predictions of natural inflation (green) and Coleman Weinberg inflation (red) with the 68% (dark blue) and 95% (light blue) confidence regions for the interacting neutrino mode (same data set as Fig. 1). Dashed lines mark the confidence regions obtained within the standard $\mathrm{\Lambda }\mathrm{CDM}$ framework assuming free-streaming neutrinos ($G_{\mathrm{eff}}=0$).

Figure 4

The resonant energy of each of the three $\mathrm{C}\nu \mathrm{B}$ mass eigenstates as a function of the lightest neutrino mass in the normal mass ordering. The upper three curves are for $m_{\varphi }=5\mathrm{MeV}$ and the lower three for $m_{\varphi }=0.2\mathrm{MeV}$. These curves are for the NO, the IO is generally the same without the middle, orange, $m_2$ curve. The blue band is the broadest range of energies that IceCube could possibly measure the astrophysical neutrino flux. The gray band indicates the temperature of the $\mathrm{C}\nu \mathrm{B}$ over $z\in [0,1]$; for $m_{\text{lightest}}$ below $T_{\mathrm{C}\nu \mathrm{B}}$, the resonant energy for $m_1$ levels off as it is relativistic. The red dashed line indicates the limit from cosmology at $\sum m_{\nu }<0.12\mathrm{eV}$ [15, 16].