[Paper Review] Twin Cogenesis

Wan-Zhe Feng, Jiang-Hao Yu|arXiv (Cornell University)|May 13, 2020

Particle physics theoretical and experimental studies44 references4 citations

TL;DR

This paper proposes a twin cogenesis mechanism in the twin Higgs framework that simultaneously explains dark matter, the cosmic coincidence of matter and dark matter densities, the little hierarchy problem, leptogenesis, and tiny neutrino masses. By introducing three heavy Majorana neutrinos—one in the Standard Model sector and two in the twin sector—the model generates lepton asymmetries in both sectors, with the lightest twin baryons as 5.5 GeV dark matter candidates naturally accounting for the observed dark matter abundance.

ABSTRACT

We investigate a cogenesis scenario within the twin Higgs setup which can naturally explain the nature of dark matter, the cosmic coincidence puzzle, little hierarchy problem, leptogenesis and the tiny neutrino masses. Three heavy Majorana neutrinos are introduced to the standard model sector and the twin sector respectively, which explain the tiny neutrino masses and generate the lepton asymmetry and the twin lepton asymmetry at the same time. The twin cogenesis scenario is general and applies to any viable twin Higgs model without hard $\mathbb{Z}_2$ breaking and evading the $\Delta N_{ m eff}$ constraint. We demonstrate twin cogenesis in two models: fraternal twin Higgs model, and neutrino-philic twin two Higgs doublet model, a newly proposed model to lift the twin neutrino masses with spontaneous $\mathbb{Z}_2$ breaking. The MeV scale dark photon ensures the energy in the twin sector as well as the symmetric component of twin sector particles can be depleted. The lightest twin baryons are the dark matter candidates with masses approximately 5.5~GeV, which explain naturally the amount of dark matter and visible matter in the Universe are of the same order.

Motivation & Objective

• To resolve the cosmic coincidence problem, where dark matter and visible matter densities are of the same order.
• To address the little hierarchy problem in the context of the twin Higgs mechanism.
• To explain the origin of tiny neutrino masses and the lepton asymmetry in both the visible and twin sectors.
• To unify dark matter, baryogenesis, and neutrino mass generation within a single framework compatible with twin Higgs models.

Proposed method

• Introduce three heavy Majorana neutrinos: one in the Standard Model sector and two in the twin sector to generate lepton asymmetries in both sectors.
• Utilize the twin cogenesis mechanism to simultaneously produce lepton asymmetries in the visible and twin sectors via decays of heavy Majorana neutrinos.
• Implement a MeV-scale dark photon to efficiently deplete energy and symmetric components in the twin sector.
• Employ the fraternal twin Higgs model and a newly proposed neutrino-philic twin two Higgs doublet model to realize the scenario with spontaneous Z₂ breaking.
• Ensure compatibility with the ΔN_eff constraint by avoiding explicit Z₂ breaking in the model.
• Identify the lightest twin baryons as stable dark matter candidates with a mass of approximately 5.5 GeV.

Experimental results

Research questions

• RQ1 Can a single mechanism simultaneously explain dark matter, baryogenesis, and tiny neutrino masses in a twin Higgs framework?
• RQ2 How can the observed coincidence in dark matter and visible matter densities be naturally explained within a twin sector model?
• RQ3 What role do heavy Majorana neutrinos play in generating lepton asymmetries in both the visible and twin sectors?
• RQ4 How can the twin cogenesis mechanism be realized in viable twin Higgs models without violating the ΔN_eff constraint?
• RQ5 What are the phenomenological implications of a 5.5 GeV twin baryon as a dark matter candidate?

Key findings

• The lightest twin baryons, with a mass of approximately 5.5 GeV, emerge as stable dark matter candidates that naturally account for the observed dark matter density.
• The twin cogenesis mechanism successfully generates both the visible and twin lepton asymmetries through the decay of heavy Majorana neutrinos in their respective sectors.
• The model explains the cosmic coincidence of matter and dark matter densities as a natural outcome of the symmetric twin sector and shared baryogenesis mechanism.
• The MeV-scale dark photon efficiently depletes energy and symmetric components in the twin sector, ensuring the stability and correct relic abundance of the twin baryons.
• The framework is realizable in both the fraternal twin Higgs model and a newly proposed neutrino-philic twin two Higgs doublet model with spontaneous Z₂ breaking.
• The scenario remains consistent with the ΔN_eff constraint, as it avoids explicit Z₂ breaking while still allowing for the necessary physics to emerge.