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arXiv 1401.5488astro-ph.COhep-phnucl-exnucl-th
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轻WIMP、等效中微子、BBN和CMB

Light WIMPs, Equivalent Neutrinos, BBN, and the CMB

Gary Steigman, Kenneth M. Nollett

摘要:

将最近对氦和氘原始丰度的观测测定结果的更新与BBN的预测进行比较,以推断重子与光子的普适比(或目前的宇宙重子质量密度参数Omega_B h^2),并限制中微子的有效数(N_eff)和等效中微子数(Δ N_nu)。这些BBN的结果进行比较,来自独立的普朗克CMB数据。在没有轻WIMP(chi)的情况下,N_eff = 3.05(1 + Delta N_nu/3)。在这种情况下,BBN和CMB之间有很好的一致性,但联合拟合发现Δ N_nu = 0.40 +/- 0.17,不利于2.4 σ的标准大爆炸核合成(SBBN:Δ N_nu = 0),以及3.5 σ的无菌中微子(Δ N_nu = 1)。在存在轻WIMP的情况下,N_eff和Delta N_nu之间的关系取决于WIMP质量,导致N_eff、Delta N_nu和m_chi之间的简并。互补和独立的BBN和CMB数据可以打破这些简并。根据光WIMP(马约拉纳或狄拉克费米子,实标量或复标量)的性质,联合BBN + CMB分析将m_chi的下限设定在0.5至5 MeV的范围内,并且它们确定了m_chi在5至10 MeV范围内的最佳拟合值。BBN + CMB的联合分析发现了等效中微子数的最佳拟合值,Δ N_nu = 0.65,几乎与WIMP的性质无关。最佳拟合仍然不支持不存在暗辐射(在95%的置信度下,Δ N_nu = 0),同时允许存在无菌中微子(在小于1 sigma时,Δ N_nu = 1)。对于这里考虑的所有情况,锂问题仍然存在。这些结果在2013年巴黎天文台会议- ESO研讨会上发表,基于Nollett & Steigman 2013(arXiv:1312.5725 [astro-ph.CO])。

英文摘要:

Recent updates to the observational determinations of the primordial abundances of helium and deuterium are compared to the predictions of BBN to infer the universal ratio of baryons to photons (or, the present Universe baryon mass density parameter Omega_B h^2), as well as to constrain the effective number of neutrinos (N_eff) and the number of equivalent neutrinos (Delta N_nu). These BBN results are compared to those derived independently from the Planck CMB data. In the absence of a light WIMP (chi), N_eff = 3.05(1 + Delta N_nu/3). In this case, there is excellent agreement between BBN and the CMB, but the joint fit finds that Delta N_nu = 0.40 +/- 0.17, disfavoring standard big bang nucleosynthesis (SBBN: Delta N_nu = 0) at 2.4 sigma, as well as a sterile neutrino (Delta N_nu = 1) at 3.5 sigma. In the presence of a light WIMP, the relation between N_eff and Delta N_nu depends on the WIMP mass, leading to degeneracies among N_eff, Delta N_nu, and m_chi. The complementary and independent BBN and CMB data can break some of these degeneracies. Depending on the nature of the light WIMP (Majorana or Dirac fermion, real or complex scalar) the joint BBN + CMB analyses set a lower bound to m_chi in the range from 0.5 to 5 MeV, and they identify best fit values for m_chi in the range from 5 to 10 MeV. The joint BBN + CMB analyses find a best fit value for the number of equivalent neutrinos, Delta N_nu = 0.65, nearly independent of the nature of the WIMP. The best fit still disfavors the absence of dark radiation (Delta N_nu = 0 at 95% confidence), while allowing for the presence of a sterile neutrino (Delta N_nu = 1 at less than 1 sigma). For all cases considered here, the lithium problem persists. These results, presented at the 2013 Rencontres de l'Observatoire de Paris - ESO Workshop, are based on Nollett & Steigman 2013 (arXiv:1312.5725 [astro-ph.CO]).

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