Cosmic Collider Gravitational Waves sourced by Right-handed Neutrino production from Bubbles: Testing Seesaw, Leptogenesis and Dark Matter

Abstract

We study a minimal type-I seesaw framework in which a first-order phase transition (FOPT), driven by a singlet scalar, produces right-handed neutrinos (RHNs) through bubble collisions, realizing a cosmic-scale collider that probes ultra-high energy scales. The resulting RHN distribution sources novel low-frequency gravitational-waves (GWs) in addition to the standard bubble-collision contribution. A stable lightest RHN can account for the observed dark matter (DM) relic abundance for masses as low as $M_1\equiv m_{\mathrm{DM}}\gtrsim 10^6\mathrm{GeV}$, with the associated novel GW signal accessible in LISA, ET and upcoming LVK detectors. If the RHNs are unstable, their CP-violating decays generate the observed baryon asymmetry via leptogenesis for $M_1\gtrsim 10^{11}\mathrm{GeV}$ and phase transition temperatures $T_{\ast }\gtrsim 10^6\mathrm{GeV}$, for which the novel GW spectrum is detectable in ET, BBO and upcoming LVK. If RHN decays also populate a dark-sector fermion with mass $m_{\chi }\in [10^{-4},10^4],\mathrm{GeV}$, successful co-genesis of baryons and asymmetric dark matter occurs for $T_{\ast }\gtrsim 10^7\mathrm{GeV}$ and $M_1\gtrsim 10^9\mathrm{GeV}$, naturally explaining ${\Omega }_{\mathrm{DM}}\simeq 5{\Omega }_{\mathrm{B}}$. The corresponding GW signals are testable with LISA, ET, and BBO. Finally, we analyze a UV-complete multi-Majoron model, based on a global $U(1{)}_N\times U(1{)}_{\mathrm{B}-\mathrm{L}}$ extension, motivated from the hierarchy of lepton masses, which we dub as Mojaron collider. The corresponding FOPT in this model leaves a distinctive GW signature arising from RHN production during $U(1{)}_N$ symmetry breaking detectable by BBO, ET and upcoming LVK. Successful leptogenesis is realized for heaviest RHN mass $M_3\sim 10^{10}\mathrm{GeV}$ and a $U(1{)}_N$ breaking vev $v_2\sim \mathcal{O}(\mathrm{TeV})$, which sets the seesaw scale.

Comments: 55 pages, 16 figures + appendix + references. Version accepted for publication in PRD