A Unified Theory of Matter Genesis: Asymmetric Freeze-In

TL;DR

The paper introduces a unified theory of matter genesis in which dark matter and the baryon asymmetry arise from thermal freeze-in with a feeble inter-sector mediator between the visible MSSM sector and a hidden $X$-sector, leveraging a difference in sector temperatures to provide the out-of-equilibrium condition. It presents minimal supersymmetric realizations, notably a renormalizable $LH_u X$ coupling and dimension-5 operators, that generate calculable, linked $B-L$ and $X$ asymmetries via CP-violating MSSM phases, yielding testable collider and precision measurements. A key result is a predictive dark matter mass $m_X$ determined by the visible-sector spectrum through sphaleron processing, with typical values in the GeV range and explicit dependencies on the MSSM content; the mechanism also yields distinctive experimental signatures such as long-lived LOSPs with displaced decays, potential baryon/lepton number violation at the LHC, EDM prospects, and X-sector phenomenology. The framework maps cosmic abundance coincidences to concrete particle-physics observables, offering a clear path for collider and precision tests to confirm or falsify the asymmetric freeze-in scenario.

Abstract

We propose a unified theory of dark matter (DM) genesis and baryogenesis. It explains the observed link between the DM density and the baryon density, and is fully testable by a combination of collider experiments and precision tests. Our theory utilises the "thermal freeze-in" mechanism of DM production, generating particle anti-particle asymmetries in decays from visible to hidden sectors. Calculable, linked, asymmetries in baryon number and DM number are produced by the feeble interaction mediating between the two sectors, while the out-of-equilibrium condition necessary for baryogenesis is provided by the different temperatures of the visible and hidden sectors. An illustrative model is presented where the visible sector is the MSSM, with the relevant CP violation arising from phases in the gaugino and Higgsino masses, and both asymmetries are generated at temperatures of order 100 GeV. Experimental signals of this mechanism can be spectacular, including: long-lived metastable states late decaying at the LHC; apparent baryon-number or lepton-number violating signatures associated with these highly displaced vertices; EDM signals correlated with the observed decay lifetimes and within reach of planned experiments; and a prediction for the mass of the dark matter particle that is sensitive to the spectrum of the visible sector and the nature of the electroweak phase transition.

Figures (6)

• Figure 1: From Ref.FIMP. Log-Log plot of the evolution of the relic yields for freeze-in via a Yukawa interaction (dashed coloured) and conventional freeze-out (solid coloured) as a function of $x=m/T$. Arrows indicate the effect of increasing coupling strength for the two processes, and the black solid line indicates yield if equilibrium is maintained. The freeze-in yield is dominated by the epoch $x\sim 2-5$, in contrast to freeze-out which only departs from equilibrium for $x\sim 20-30$.
• Figure 2: Schematic illustration of the three on-shell amplitudes necessary for generation of the linked $(B-L)$ and $X$ asymmetries. State $B_1$ of the visible thermal bath must be able to decay to two different final states $B_2B_3$ and $B_4X$ with differing $(B-L)$ and $X$ quantum numbers, with respective amplitudes ${\cal A}_1$ and ${\cal A}_2$. Moreover there must be an independent re-scattering process linking these differing final states, with amplitude denoted ${\cal A}_{12}$. The black dot indicates the feeble coupling linking the visible and hidden sectors, while all other vertices are ${\cal O}(1)$ visible sector couplings. The decay amplitude ${\cal A}_1$ implies that $B_1$ cannot be the lightest visible sector $Z_2$-odd particle.
• Figure 3: Examples of the diagrams that contribute to the asymmetry in the case of the decays of the heavier chargino ${\tilde{\chi}}_2^-$ of the MSSM. Dashed vertical lines indicate position of the cuts.
• Figure 4: Diagrams depicting the explicit mass insertions that encode the dependence of the asymmetry on the potentially CP-violating parameters in the gaugino-higgsino sector.
• Figure 5: Sub-leading contribution to neutralino LOSP decay allowing measurement of inter-sector coupling $\lambda$ in the case of $\lambda LHX$ interactions.