Polarized primordial gravitational waves in spatial covariant gravities
Polarized primordial gravitational waves in spatial covariant gravities
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DOI：
10.1103/physrevd.107.024031
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发表时间：
2022-10
影响因子：
5
通讯作者：
Tao Zhu;Wen Zhao;Anzhong Wang
中科院分区：
文献类型：
--
作者：
Tao Zhu;Wen Zhao;Anzhong Wang
空间协变引力提供了一种在引力作用中加入奇数阶空间导数项的自然方式，这打破了引力扇区的宇称对称性。通过施加么正规范，许多违反宇称的标量张量理论可以映射到空间协变框架。这为我们研究原始引力波中的宇称破坏效应提供了一个一般的框架。本文的主要目的是研究空间协变引力中的PGW的极化及其可能的观测效应。为此，我们首先利用一致渐近近似构造了慢滚膨胀过程中光波导模函数的近似解析解。利用该近似解，我们解析地计算了光子晶体波的功率谱和相应的圆极化。结果表明，空间协变引力对功率谱的新贡献包括两部分，一部分来自保持宇称项，另一部分来自违反宇称项。保持宇称项只能影响光子晶体的总振幅，而破坏宇称的项则会引起光子晶体的非零圆极化，即光子晶体的左右两个极化模式具有不同的振幅。文中还简要讨论了这种非零圆偏振的观测意义。
The spatial covariant gravities provide a natural way to including odd-order spatial derivative terms into the gravitational action, which breaks the parity symmetry at gravitational sector. A lot of parity-violating scalar-tensor theories can be mapped to the spatial covariant framework by imposing the unitary gauge. This provides us with a general framework for exploring the parity-violating effects in primordial gravitational waves (PGWs). The main purpose of this paper is to investigate the polarization of PGWs in the spatial covariant gravities and their possible observational effects. To this end, we first construct the approximate analytical solution to the mode function of the PGWs during the slow-roll inflation by using the uniform asymptotic approximation. With the approximate solution, we calculate explicitly the power spectrum and the corresponding circular polarization of the PGWs analytically. It is shown that the new contributions to power spectrum from spatial covariant gravities contain two parts, one from the parity-preserving terms and the other from the parity-violating terms. While the parity-preserving terms can only affect the overall amplitudes of PGWs, the parity-violating terms induce nonzero circular polarization of PGWs, i.e., the left-hand and right-hand polarization modes of GWs have different amplitudes. The observational implications of this nonzero circular polarization is also briefly discussed.