Sneutrino Tribrid Inflation, Metastable Cosmic Strings and Gravitational Waves

TL;DR

This paper develops a sneutrino-based inflation model within a gauged $U(1)_{B-L}$ extension of the MSSM, linking neutrino masses, leptogenesis, cosmic strings, and gravitational waves, with predictions compatible with current cosmological data.

Contribution

It introduces a novel sneutrino tribrid inflation model that simultaneously explains neutrino masses, reheating, leptogenesis, and predicts metastable cosmic strings and gravitational wave signals.

Findings

Predicted tensor-to-scalar ratio range: $3 imes 10^{-11}$ to $7 imes 10^{-4}$.

B-L breaking scale estimated between $3 imes 10^{14}$ and $2 imes 10^{16}$ GeV.

Cosmic string tension and gravitational wave background compatible with NANOGrav data.

Abstract

We present a successful realization of sneutrino tribrid inflation model based on a gauged $U(1)_{B-L}$ extension of Minimal Supersymmetric Standard Model (MSSM). A single interaction term involving the $B-L$ Higgs field and the right-handed neutrinos serves multiple purposes. These include the generation of heavy Majorana masses for the right-handed neutrinos to provide an explanation for the tiny neutrino masses via the seesaw mechanism, a realistic scenario for reheating and non-thermal leptogenesis with a reheat temperature as low as $10^6$ GeV, and a successful realization of inflation with right-handed sneutrino as the inflaton. The matter parity which helps avoid rapid proton decay survives as a $Z_{2}$ subgroup of a $U(1)$ $R$-symmetry. Depending on the choice of model parameters yields the following predicted range of the tensor to scalar ratio, $3 \times 10^{-11}\lesssim r\lesssim 7\times 10^{-4}$ ($ 6 \times 10^{-7} \lesssim r \lesssim 0.01 $), and the running of the scalar spectral index, $-0.00022 \lesssim dn_s/d\ln k \lesssim -0.0026$ ($-0.00014 \lesssim dn_s/d\ln k \lesssim 0.005$), along with the $B-L$ breaking scale, $ 3 \times 10^{14}\lesssim M/ \text{GeV}\lesssim 5 \times 10^{15}$ ($ 6 \times 10^{15}\lesssim M/ \text{GeV}\lesssim 2 \times 10^{16}$), calculated at the central value of the scalar spectral index, $n_s =0.966$, reported by Planck 2018. The possibility of realizing metastable cosmic strings in a grand unified theory setup is briefly discussed. The metastable cosmic string network admits string tension values in the range $10^{-8} \lesssim G\mu_s \lesssim 10^{-6}$, and predicts a stochastic gravitational wave background lying within the 2-$\sigma$ bounds of the recent NANOGrav 12.5-yr data.