Cosmic structure formation distinguishes holographic dark energy models

A new study has demonstrated that observations of large-scale structure formation in the universe, such as galaxies and galaxy clusters, can be a key tool to differentiate between various holographic dark energy models. Researchers utilized a combination of cosmological datasets, including Pantheon+ SN Ia, OHD, DESI DR2 baryonic acoustic oscillation data, and CMB distance prior measurements, to constrain the parameters of three specific models: HDE (Holographic Dark Energy), THDE (Thermal Holographic Dark Energy), and BHDE (Black Hole Holographic Dark Energy). The analysis focused on the evolution of two crucial cosmological parameters: fσ₈(z) and S₈(z), which describe the growth of structures and the amplitude of matter density fluctuations, respectively. The results showed that the evolutionary curves of both fσ₈(z) and S₈(z) for the HDE and BHDE models were nearly indistinguishable. However, the curves corresponding to the THDE model consistently lay lowest. Additionally, the χ² statistic indicated that the THDE model yielded the lowest value for both fσ₈ and S₈ measurements, suggesting a better fit to observational data. To visualize these differences, the authors constructed a diagnostic (fσ₈, S₈) plane and analyzed the trajectories of the models. In this plane, the trajectory of the THDE model was able to reach the current (fσ₈, S₈) data region, which was not the case for the other models. These findings confirm that cosmic structure formation offers a robust method to distinguish the THDE model from the HDE and BHDE models, and suggest that this approach can be extended to evaluate the viability of other holographic dark energy scenarios.

Exceptional Points Identified in Black Hole Ringdowns

Researchers have developed a procedure to identify Exceptional Points (EPs) in the ringdown phase of black holes. This phase, which follows the merger of two black holes or the perturbation of a single one, is characterized by the emission of gravitational waves that act as a "fingerprint" of the resulting object. Ringdown spectroscopy is a crucial tool for probing black hole dynamics, and the detection of EPs could reveal fundamental underlying degrees of freedom in the theory of gravity or in the structure of spacetime near these objects. The proposed method relies on the use of a time-weighted Jordan term and a splitting bound. For a relative Jordan excitation proportional to separation, the researchers derived a sixth-order squared distance between split and EP waveforms after fitting the resonance center. Incorporating independent constraints on these quantities can improve the precision to fourth order. These EPs are points in the parameter space of a system where two or more eigenmodes (or eigenvalues) coalesce, becoming indistinguishable and exhibiting non-Hermitian behavior, which can have profound implications for understanding black hole physics. The study also highlights that omitting ordinary responses in complete waveforms can strengthen the evidence for EPs and, paradoxically, spuriously tighten splitting bounds. This finding underscores the importance of careful analysis of gravitational wave data to avoid misinterpretations. The ability to identify and characterize these Exceptional Points could open new avenues for testing general relativity in extreme regimes and searching for deviations that suggest new physics beyond the Standard Model or Einstein's theory of gravity.