用原初核合成与重子生成约束倾斜偶极宇宙学
Constraining the Tilted Dipole Cosmology with Primordial Nucleosynthesis and Baryogenesis
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中文总结 AI 辅助
该研究用BBN和GB分析倾斜偶极宇宙学，约束辐射倾斜参数βᵣ，BBN给出|βᵣ|的2σ上限，GB则给出更严格的|βᵣ^BBN|≲10⁻⁸，且锂-7问题相关βᵣ值被排除。
中文摘要 AI 辅助
倾斜偶极宇宙学通过引入优选空间方向以及物质与辐射各自的整体速度，扩展了标准模型，为观测到的大尺度整体流和CMB偶极提供了潜在解释。我们利用大爆炸核合成（BBN）和引力重子生成（GB）对该各向异性框架开展全面分析，以对辐射倾斜参数βᵣ施加严格约束，该参数量化了辐射整体流的大小。通过推导修正后的膨胀速率H(T)及其对轻元素丰度的影响，我们发现，结合原初氦-4与氘的BBN给出的2σ约束，在最大剪切（最紧边界）下为|βᵣ|≲0.03，在最小剪切（最松边界）下为|βᵣ|≲0.2。这些约束与从有效中微子种类数|ΔNₑff|≲0.4推断出的约束一致，但更为严格。重要的是，两种约束均为上限；βᵣ=0始终符合BBN约束。锂-7问题依然存在，因为解决该问题所需的βᵣ值被氦-4数据排除。此外，GB在退耦温度T_D≳10¹²GeV下按βᵣ∝T的标度运行，给出了严苛得多的约束，对此类高能标重子生成场景限制|βᵣ^BBN|≲10⁻⁸。
英文摘要
The tilted dipole cosmology extends the standard model by incorporating a preferred spatial direction and separate bulk velocities for matter and radiation, offering a potential explanation for observed large-scale bulk flows and the CMB dipole. We conduct a comprehensive analysis of this anisotropic framework using Big Bang Nucleosynthesis (BBN) and Gravitational Baryogenesis (GB) to impose stringent constraints on the radiation tilt parameter $β_r$, which quantifies the magnitude of the radiation bulk flow. By deriving the modified expansion rate $H(T)$ and its impact on light element abundances, we find that the combined $2σ$ BBN limits from primordial helium-4 and deuterium are $|β_r| \lesssim 0.03$ for maximal shear (tightest bound) and $|β_r| \lesssim 0.2$ for minimal shear (weakest bound). These bounds are consistent with, but tighter than, those inferred from the effective neutrino species count $|ΔN_{\mathrm{eff}}| \lesssim 0.4$. Importantly, both bounds are upper limits; $β_r = 0$ is always allowed by the BBN constraints. The lithium-7 problem persists, as the $β_r$ values required to resolve it are excluded by helium-4 data. Furthermore, GB -- operating at decoupling temperatures $T_D \gtrsim 10^{12}$ GeV under the scaling $β_r \propto T$ -- yields far more severe constraints, limiting $|β_r^{\mathrm{BBN}}| \lesssim 10^{-8}$ for such high-scale baryogenesis scenarios.
