Energy conditions bounds and their confrontation with supernovae data
M. P. Lima, S. Vitenti, M. J. Reboucas
备注：
7 pages, 3 figures. V2: Version to appear in Phys.Rev.D, analyses extended to 1sigma, 2sigma and 3sigma confidence levels, references added, minors changes
The energy conditions play an important role in the understanding of several properties of the Universe, including the current accelerating expansion phase and the possible existence of the so-called phantom fields. We show that the integrated bounds provided by the energy conditions on cosmological observables such as the distance modulus $μ(z)$ and the lookback time $t_L(z)$ are not sufficient (nor necessary) to ensure the local fulfillment of the energy conditions, making explicit the limitation of these bounds in the confrontation with observational data. We recast the energy conditions as bounds on the deceleration and normalized Hubble parameters, obtaining new bounds which are necessary and sufficient for the local fulfillment of the energy conditions. A statistical confrontation, with $1σ-3σ$ confidence levels, between our bounds and supernovae data from the gold and combined samples is made for the recent past. Our analyses indicate, with $3σ$ confidence levels, the fulfillment of both the weak energy condition (WEC) and dominant energy condition (DEC) for $z \leq 1$ and $z \lesssim 0.8$, respectively. In addition, they suggest a possible recent violation of the null energy condition (NEC) with $3σ$, i.e. a very recent phase of super-acceleration. Our analyses also show the possibility of violation of the strong energy condition (\textbf{SEC}) with $3σ$ in the recent past ($z \leq 1$), but interestingly the $q(z)$-best-fit curve crosses the SEC-fulfillment divider at $z \simeq 0.67$, which is a value very close to the beginning of the epoch of cosmic acceleration predicted by the standard concordance flat $Λ$CDM scenario.
Supernovae type Ia data favour coupled phantom energy
我们估计的约束，最近的高红移样本的超新星Ia型把暗能量和暗物质之间的现象学相互作用。这种相互作用可以解释为由暗物质粒子质量随时间的变化引起的。我们发现耦合与状态方程相关：粗略地说，负耦合（在我们的符号约定中）意味着幻影能量（$w_ϕ<-1$），而正耦合意味着“普通”暗能量。从目前的超新星Ia哈勃图的约束有利于一个负耦合和状态方程$w_ϕ<-1$。实际上，在99% c.l.下不太可能出现零或正耦合。（假设状态方程恒定）;同时，非体模值（$w_ϕ>-1$）不太可能达到95%。我们还表明，通常的界限上的能量密度大大减弱时，耦合被引入：值大到$Ω_{m0}=0.7$成为可以接受的关注SNIa。我们发现暗物质粒子的质量$\dot{m}/m$的变化率在哈勃时间内被限制为$δ_{0}$，其中$-10<δ_{0}<-1$为95% c. l.。我们表明，一个大的正耦合可能在原则上避免未来的奇异性被称为“大撕裂”（发生$w_ϕ<-1$），但发生这种情况的参数区域几乎被排除的数据。我们还预测了可以从未来的实验中获得的约束，重点是超新星和重子振荡的深红移调查的功率谱。我们指出重子振荡方法是抑制耦合的最佳方法。
Probing the dark side: Constraints on the dark energy equation of state from CMB, large scale structure and Type Ia supernovae
本文用几组宇宙学数据重新分析了暗能量状态方程参数w_Q = P/ρ的约束条件，并放宽了通常的约束条件w_Q >-1。结合宇宙微波背景辐射、大尺度结构和Ia型超新星数据，我们发现了一个非平凡的w_Q下界。在95.4%的置信度下，我们发现，假设宇宙的几何形状是平坦的，-2.68 < w_Q-1的界限< -0.78 if w_Q is taken to be a completely free parameter. Reassuringly we also find that the constraint w_Q >不会显著地偏离w_Q的整体允许区域。当施加此约束时，95.4%置信界限为-1 < w_Q <-0.71。此外，一个纯宇宙学常数（w = -1）是所有可用数据的极好拟合。基于对未来普朗克CMB实验、SNAP和SNfactory超新星实验数据的模拟，我们估计在未来将w_Q限制在5%的水平是可能的。
