Impact of high-scale Seesaw and Leptogenesis on inflationary tensor perturbations as detectable gravitational waves

Abstract

We discuss the damping of inflationary gravitational waves (GW) that reenter the horizon before or during an epoch, where the energy budget of the universe is dominated by an unstable right handed neutrino (RHN), whose out of equilibrium decay releases entropy. Starting from the minimal Standard Model extension, motivated by the observed neutrino mass scale, with nothing more than 3 RHN for the Seesaw mechanism, we discuss the conditions for high scale leptogenesis assuming a thermal initial population of RHN. We further address the associated production of potentially light non-thermal dark matter and a potential component of dark radiation from the same RHN decay. One of our main findings is that the frequency, above which the damping of the tensor modes is potentially observable, is completely determined by successful leptogenesis and a Davidson-Ibarra type bound to be at around 0.1 Hz. To quantify the detection prospects of this GW background for various proposed interferometers such as AEDGE, BBO, DECIGO, Einstein Telescope or LISA we compute the signal-to-noise ratio (SNR). This allows us to investigate the viable parameter space of our model, spanned by the mass of the decaying RHN M 1 2.4 × 10 8 GeV • 2 × 10 −7 eV/ m1 (for leptogenesis) and the effective neutrino mass parameterizing its decay width m1 < 2.9 × 10 −7 eV (for RHN matter domination). Thus gravitational wave astronomy is a novel way to probe both the Seesaw and the leptogenesis scale, which are completely inaccessible to laboratory experiments in high scale scenarios.

An Étude on the regularization and renormalization of divergences in primordial observables

“…Before delving into the substance of this section, it is informative to contrast the results obtained in the previous section to analogous expressions typically found in the literature in the context of gravitational waves (see e.g., [70][71][72][73][74][75][76][77][78][79][80][81][82][83]), where imposing hard cutoffs on the energy density of gravitational waves results in expressions of the form:…”

Measuring inflaton couplings via dark radiation as $ΔN_{\rm eff}$ in CMB

“…In this work, we assume that a relativistic non-thermal non-self-interacting BSM particle contributes to ρ γ which is produced from the inflaton during reheating era. [45].…”

Primordial gravitational waves assisted by cosmological scalar perturbations

“…Efforts have been made to detect primordial tensor perturbations on small scales, which are detectable by spaceborne and ground-based gravitational-wave interferometers a e-mail: wangsai@ihep.ac.cn (corresponding author) [16][17][18][19][20][21][22]. However, models of canonical single-field slow-roll inflation predict a red-tilted tensor spectrum, with the spectral index exhibiting a consistency relation of n t = −r/8 [23].…”