We present detailed forecasts for the constraints on the characteristics of primordial magnetic fields (PMFs) generated prior to recombination that will be obtained with the LiteBIRD satellite. The constraints are driven by some of the main physical effects of PMFs on the CMB anisotropies: the gravitational effects of magnetically-induced perturbations; the effects on the thermal and ionization history of the Universe; the Faraday rotation imprint on the CMB polarization spectra; and the non-Gaussianities induced in polarization anisotropies. LiteBIRD represents a sensitive probe for PMFs. We explore different levels of complexity, for LiteBIRD data and PMF configurations, accounting for possible degeneracies with primordial gravitational waves from inflation. By exploiting all the physical effects, LiteBIRD will be able to improve the current limit on PMFs at intermediate and large scales coming from Planck. In particular, thanks to its accurate B-mode polarization measurement, LiteBIRD will improve the constraints on infrared configurations for the gravitational effect, giving B ^{n _B=-2.9} _{1 Mpc}< 0.8 nG at 95% C.L., potentially opening the possibility to detect nanogauss fields with high significance. We also observe a significant improvement in the limits when marginalized over the spectral index, B ^{n _Bmarg} _{1 Mpc}< 2.2 nG at 95 % C.L. From the thermal history effect, which relies mainly on E-mode polarization data, we obtain a significant improvement for all PMF configurations, with the marginalized case, √⟨B ²⟩^marg<0.50 nG at 95 % C.L. Faraday rotation constraints will take advantage of the wide frequency coverage of LiteBIRD and the high sensitivity in B modes, improving the limits by orders of magnitude with respect to current results, B ^{n _B=-2.9} _{1 Mpc} < 3.2 nG at 95 % C.L. Finally, non-Gaussianities of the B-mode polarization can probe PMFs at the level of 1 nG, again significantly improving the current bounds from Planck. Altogether our forecasts represent a broad collection of complementary probes based on widely tested methodologies, providing conservative limits on PMF characteristics that will be achieved with the LiteBIRD satellite.

中文翻译：

---

LiteBIRD 科学目标和预测：原始磁场


我们对复合之前产生的原始磁场（PMF）特性的约束进行了详细的预测，这些预测将通过莱特鸟卫星。这些约束是由 PMF 对 CMB 各向异性的一些主要物理效应驱动的：磁感应扰动的引力效应；对宇宙热和电离历史的影响； CMB 偏振光谱上的法拉第旋转印记；以及偏振各向异性引起的非高斯性。莱特鸟代表 PMF 的敏感探针。我们探索不同级别的复杂性，莱特鸟数据和 PMF 配置，解释了膨胀引起的原始引力波可能发生的简并。通过利用所有的物理效应，莱特鸟将能够改善中型和大型 PMF 的当前限制普朗克。特别是，由于其准确乙-模式偏振测量，莱特鸟将改善引力效应对红外构型的约束，给出乙^{n _B =-2.9} _{1 Mpc} < 0.8 nG (95% CL)，可能开启检测具有高度意义的纳高斯场的可能性。我们还观察到当光谱指数被边缘化时，极限有显着改善，乙^{n _B裕量}_{1 Mpc} < 2.2 nG（95 % CL） 从主要依赖于 E 模偏振数据的热历史效应来看，我们对所有 PMF 配置都获得了显着的改进，在边缘化情况下，√⟨乙² ⟩^玛格<0 id=142>LiteBIRD和高灵敏度乙模式，相对于当前结果将限制提高了几个数量级，乙^{n _B =-2.9} _{1 Mpc} < 3.2 nG at 95 % CL 最后，B 模式偏振的非高斯性可以探测 1 nG 水平的 PMF，再次显着提高了电流范围普朗克。总而言之，我们的预测代表了基于广泛测试的方法的一系列互补探针，对 PMF 特性提供了保守的限制，这些特性将通过莱特鸟卫星。