Sunny Vagnozzi

Cosmologically coupled black holes (CCBHs), whose masses evolve in response to the cosmological expansion, have recently attracted significant theoretical and observational interest. Existing studies have treated CCBHs as purely classical objects, neglecting the effect of Hawking radiation (HR), which competes with the cosmological coupling (CC) mechanism. We take a first step toward studying evaporating CCBHs, adopting a quasiadiabatic approximation in which the HR rate is evaluated at the instantaneous CCBH mass, and modeling the CC mechanism through the phenomenological scaling of the mass with the scale factor, M ∝ a k . We show that, depending on the coupling strength k , even late-time CC activation can significantly delay Hawking evaporation, or lead to asymptotic CC-dominated mass growth, with important implications. We set limits on the abundance of primordial CCBHs from γ -ray observations, finding limits which are weaker than their uncoupled counterparts, as CCBHs are kept farther from the endpoint of evaporation for a longer time. Unlike standard primordial black holes, the CCBH formation and present-day masses no longer approximately coincide, even for formation masses M form ≳ 10 15 g . Therefore, the same population of primordial CCBHs may be subject to evaporation limits through its past emission history, as well as to other limits (such as microlensing) through its present-day mass.

Single-field ultra-slow-roll (USR) inflation is among the most studied mechanisms for primordial black hole (PBH) formation. When a nonstationary inflection point close to cosmic microwave background (CMB) scales is present, these models predict a negative spectral running ( α s < 0 ), whose magnitude increases with the PBH mass. This is in tension with recent hints for positive running from Atacama Cosmology Telescope (ACT) CMB data. However, inflationary parameters inferred from CMB data are sensitive to the assumed prerecombination expansion history, which is precisely where new physics motivated by the Hubble tension should operate. Focusing on axionlike early dark energy (EDE) as a benchmark, we investigate the effect of such prerecombination new physics on α s , and hence on the viability of USR PBH models, in light of state-of-the-art CMB data from , ACT, and the South Pole Telescope, together with baryon acoustic oscillation data from the Dark Energy Spectroscopic Instrument Data Release 2. Our analysis, therefore, provides an updated set of constraints on α s and the running of the running β s . For most dataset combinations, moving from Λ cold dark matter to EDE increases the inferred α s : once the acoustic angular scale θ s is fixed, EDE increases the diffusion-to-acoustic angular scale ratio θ d / θ s , and the shift in α s compensates this extra damping by increasing small-scale power. In this sense, tension calls for tension: taking the Hubble tension seriously as an indication for new physics strengthens the challenges faced by USR PBH models. More broadly, our analysis stresses that inflationary model selection using CMB-inferred inflationary parameters such as n s and α s may be premature, especially until the Hubble tension, and more generally the prerecombination expansion history, is understood.

We reassess prospects for direct detection of solar chameleons, in light of recent progress in modeling their production, and the availability of new XENONnT data. We show that the contribution from Primakoff production in the electric fields of electrons and ions dominates the electron recoil event rate, which is enhanced compared to earlier estimates based on magnetic conversion in the tachocline alone. We argue that the signal is governed by the effective coupling β eff ≡ β γ M e − 4 , which encodes the combined effects of production and detection, where β γ and M e are the chameleon-photon (conformal) coupling and chameleon-electron disformal coupling scale, respectively. Setting the height of the chameleon potential to the dark energy (DE) scale Λ ≃ 2.4 meV , we show that XENONnT electron recoil data set the upper limit log 10 β eff < − 6.9 . This limit is independent of the conformal matter coupling β m and index n , and applies to the whole class of inverse power-law chameleons, well beyond the n = 1 case usually studied. We comment on how future multitarget experiments and lower-threshold analyses could distinguish solar chameleons from other light (pseudo)scalar particles such as axions. Our work demonstrates that existing dark matter direct detection experiments can probe regions of parameter space relevant to screened DE models, providing complementary tests to astrophysical and fifth-force searches at no additional experimental cost.

Baryon acoustic oscillation (BAO) measurements play a key role in ruling out postrecombination solutions to the Hubble tension. However, because the data compression leading to these measurements assumes a fiducial Λ CDM cosmology, their reliability in testing late-time modifications to Λ CDM has at times been called into question. We play devil’s advocate and posit that fiducial cosmology assumptions do indeed affect BAO measurements in such a way that low-redshift acoustic angular scales (proportional to the Hubble constant H 0 ) are biased low and test whether such a rescaling can rescue postrecombination solutions. The answer is no. First, strong constraints on the shape of the z ≲ 2 expansion history from unanchored Type Ia Supernovae (SNeIa) prevent large deviations from Λ CDM . In addition, unless Ω m is significantly lower than 0.3, the rescaled BAO measurements would be in strong tension with geometrical information from the cosmic microwave background. We demonstrate this explicitly on several dark energy (DE) models ( w CDM , CPL DE, phenomenologically emergent DE, holographic DE, Λ s CDM , and the negative cosmological constant model), finding that none can address the Hubble tension once unanchored SNeIa are included. We argue that the Λ s CDM sign-switching cosmological constant model possesses interesting features which make it the least unpromising one among those tested. Our results demonstrate that possible fiducial cosmology-induced BAO biases cannot be invoked as loopholes to the Hubble tension “no-go theorem”, and highlight the extremely important but so far underappreciated role of unanchored SNeIa in ruling out postrecombination solutions.