[Paper Review] Antimatter regions in the baryon-dominated Universe

Maxim Khlopov, Sergei G. Rubin+1 more|ArXiv.org|Oct 1, 2002

Cosmology and Gravitation Theories1 references3 citations

TL;DR

This paper proposes that quantum fluctuations of a baryonic charged scalar field during inflation can generate isolated antimatter regions in a globally baryon-dominated Universe. These regions, surviving annihilation if larger than 8h² kpc, may evolve into anti-star globular clusters; the key observational signature is detectable fluxes of $\overline{^4\text{He}}$ and $\overline{^3\text{He}}$ nuclei, accessible to the AMS–02 experiment.

ABSTRACT

Quantum fluctuations of a complex, baryonic charged scalar field caused by inflation can generate large domains, which convert later into antimatter regions. As a result the Universe can become globally matter-dominated, with minor contribution of antimatter regions. The distribution and evolution of such antimatter regions could cause every galaxy to be a harbour of an anti-star globular cluster. At the same time, the scenario does not lead to large-scale isocuvature perturbations, which would disturb observable CMB anisotropy. The existence of one of such antistar globular cluster in our Galaxy does not contradict the observed $γ$-ray background, but the expected fluxes of $\bar{ m ^4He}$ and $\bar{ m ^3He}$ from such an antimatter object are definitely accessible to the sensitivity of the coming AMS--02 experiment.

Motivation & Objective

• To explain the global matter-antimatter asymmetry without large-scale isocurvature perturbations.
• To explore the formation of antimatter domains via spontaneous baryogenesis during inflation.
• To assess the viability of anti-star globular clusters as astrophysical remnants of such antimatter regions.
• To identify observable signatures of antimatter regions in cosmic-ray antinuclei fluxes.

Proposed method

• Modeling the baryonic charged scalar field $\chi$ with a pseudo-Nambu–Goldstone potential $V(\theta) = \Lambda^4(1 - \cos\theta)$.
• Using the phase $\theta$ of the scalar field to generate baryon/antibaryon asymmetry via out-of-equilibrium decay $\mathcal{L} = g\chi\bar{Q}L + \text{h.c.}$.
• Simulating the evolution of quantum fluctuations in de Sitter space during inflation, with effective dispersion $\delta\theta_{\text{eff}} = H_{\text{infl}}/(2\pi f_{\text{eff}})$.
• Calculating the critical survival size $L_c = 8h^2$ kpc to determine which antimatter domains avoid annihilation.
• Assessing the gravitational collapse of high-density antimatter progenitors into anti-star globular clusters.
• Estimating cosmic-ray fluxes of $\overline{^4\text{He}}$ and $\overline{^3\text{He}}$ from such clusters and comparing with AMS–02 sensitivity.

Experimental results

Research questions

• RQ1 Can quantum fluctuations of a baryonic scalar field during inflation generate isolated antimatter regions in a matter-dominated Universe?
• RQ2 Do such antimatter domains survive annihilation if they exceed a critical size of $8h^2$ kpc?
• RQ3 Can high-density antimatter regions evolve into anti-star globular clusters?
• RQ4 Can the resulting antinuclei fluxes be detected by current or upcoming space-based experiments like AMS–02?
• RQ5 Is the scenario consistent with observed CMB anisotropy and the diffuse gamma-ray background?

Key findings

• Antimatter regions with physical size exceeding $L_c = 8h^2$ kpc survive annihilation with surrounding matter, enabling long-lived antimatter domains.
• The model generates antimatter domains with a volume fraction less than $10^{-4}$ of the total Universe, preserving global baryon dominance.
• The effective phase dispersion $\delta\theta_{\text{eff}} = H_{\text{infl}}/(2\pi f_{\text{eff}})$ grows during inflation and peaks at the $N_c$-th e-fold, enabling critical-size progenitors.
• Anti-star globular clusters in our Galaxy could have masses between $10^3M_\odot$ and $10^5M_\odot$, consistent with gamma-ray background constraints.
• Expected fluxes of $\overline{^4\text{He}}$ and $\overline{^3\text{He}}$ from such clusters are within the sensitivity range of the AMS–02 experiment.
• The scenario avoids large-scale isocurvature perturbations that would disrupt CMB anisotropy, as the phase dispersion is constrained to $\delta\theta \leq 10^{-3}$ at large scales.