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Quasinormal modes of rotating black holes beyond general relativity in the WKB approximation
No full textInternational audienceExploring gravitational theories beyond general relativity (GR) with black hole (BH) spectroscopy requires accurate and flexible methods for computing their quasinormal mode (QNM) spectrum. A popular method of choice is the higher-order Wentzel-Kramers-Brillouin (WKB) approximation, mostly applied to nonrotating BHs. While previous studies demonstrated that the higher-order WKB method can also be used for Kerr BHs in GR, there has been little work on rotating BHs in modified theories of gravity. In this work, we revive the idea by extending WKB calculations of the Kerr QNM spectrum to higher order and assessing its accuracy against continued-fraction tabulated data. We then apply the WKB approximation beyond GR, comparing it against both linearized and continued fraction calculations in the parametrized beyond-Teukolsky formalism and in higher-derivative gravity (HDG) theories. We find that the frequencies computed by the WKB method in theories beyond GR have better accuracy than the measurement errors for GW250114, the event with the highest ringdown signal-to-noise ratio observed to date
Cygnus X-3: A variable petaelectronvolt gamma-ray source
No full textInternational audienceWe report the discovery of variable -rays up to petaelectronvolt from Cygnus X-3, an iconic X-ray binary. The -ray signal was detected with a statistical significance of approximately 10 by the Large High Altitude Air Shower Observatory (LHAASO). Its intrinsic spectral energy distribution (SED), extending from 0.06 to 3.7 PeV, shows a pronounced rise toward 1 PeV after accounting for absorption by the cosmic microwave background radiation. The detected month-scale variability,together with a 3.2 evidence for orbital modulation, suggests that the PeV -rays originate within, or in close proximity to, the binary system itself. The observed energy spectrum and temporal modulation can be naturally explained by -ray production through photomeson processes in the innermost region of the relativistic jet, where protons need to be accelerated to tens of PeV energies
Cosmic Lockdown: When Decoherence Saves the Universe from Tunneling
No full textInternational audienceWe investigate how quantum decoherence influences the tunneling dynamics of quantum fields in cosmological spacetimes. Specifically, we study a scalar field in an asymmetric double well potential during inflation, coupled to environmental degrees of freedom provided either by heavy spectator fields or by short-wavelength modes as they cross out the Hubble scale. This setup enables a systematic derivation of both Markovian and non-Markovian master equations, along with their stochastic unravelings, which we solve numerically. We find that, while decoherence is essential for suppressing quantum interference between vacua, its impact on the relative vacuum populations is limited. Fields heavier than the Hubble scale relax adiabatically toward the true vacuum with high probability, while lighter fields exhibit non-adiabatic enhancements of false-vacuum occupation. Once the system has decohered, quantum tunneling between vacua becomes strongly suppressed, effectively locking the system into the stochastically selected local minimum. This ``cosmic lockdown'' mechanism is a manifestation of the quantum Zeno effect: environmental monitoring stabilizes enhanced false-vacuum occupation for light fields by preventing them from tunneling
Reading the Future of Oil: A Noncausal Approach to Supply News Shocks
No full textThis paper proposes a new strategy to identify oil supply news shocks by combining a Bayesian noncausal structural VAR with a Max-Share approach. The framework jointly resolves the problems of non-fundamentalness and recoverability that undermine standard (proxy) SVAR methods. Exploiting non-Gaussianity in a multivariate Student−t specification, we recover structural shocks from a two sided moving average representation and isolate the expectation driven component of oil supply innovations without external instruments. Applied to global oil market data, the model supports a non fundamental representation and detects anticipatory price and inventory movements consistent with rational expectations storage behavior. The identified shocks explain a substantial fraction of real oil price fluctuations, notably in the late 1970s–1980s and during the 2014–15 collapse, while the COVID-19 episode is predominantly demand driven. Decomposing global supply shows that these shocks are primarily OPEC-driven and generate stagflationary responses in output and inflation, underscoring the central role of expectations in oil market dynamics
Marble Wall Revetment in Roman Times: Materials and Techniques
No full textInternational audienceMaking marble wall revetment in Roman times required real know-how. Surprisingly,ancient sources are silent on the installation methods of revetment. The archaeologicalliterature is also sparse, but there are two schools of thought: one assumes that a plaster layer was applied before the marble slabs, while the other assumes that mortar was poured behind the slabs held in place by metal clamps. All point out the presence of shims on the plaster, although there has been no consensus as to their function. The recent discovery of an organic material (based on pitch and beeswax) helps us understand how these shims were laid: they were placed behind the slabs, before the slabs were installed, to hold them in place when the mortar set. Above all, it provides a clear understanding of how the Romans went about installing their marble revetment: choosing one or other of the two supposed variant methods as required. This synthesis also gives us the opportunity to present a typology of metal clamps and to discuss several adaptations of the technique, such as the practice at Pompeii of preparing the wall surface with a toothed chisel
A reversed latitudinal ocean oxygen gradient in the Proterozoic
No full textInternational audienceMajor changes in the oxygenation of the atmosphere and ocean have been suggested to trigger the taxonomic diversification and ecological expansion of complex life, including animals, during the Neoproterozoic–Palaeozoic transition. However, testing this hypothesis is hampered by the paucity of quantitative constraints on the oceanic oxygen availability at that time. Here we show how the spatial pattern of I/Ca ratios in marine carbonates—a proxy for dissolved oxygen in the local upper ocean—provides a fingerprint of the oxygenation state of Earth’s surface. Spatial analyses on published I/Ca ratios spanning the past 2,000 million years show that the latitudinal gradient of oxygen concentrations in the upper ocean was reversed in the Proterozoic eon relative to the modern pattern of decreasing oxygen concentrations from the mid-latitudes to the Equator. Using an Earth system model, we identify that the Proterozoic I/Ca latitudinal pattern is associated with a biosphere-controlled distribution of oxygen in the upper ocean at a low atmospheric oxygen level, and the transition to a modern pattern in the I/Ca proxy may correspond to a threshold of around 1% of today’s atmospheric oxygen concentration
Formes automorphes (chaire internationale): [résumé des cours et travaux : 2021-2022]
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Water permanence and connectivity are key drivers of high-mountain pond communities along altitudinal gradients in the French Alps and Pyrenees
No full textInternational audienceHigh-mountain species are particularly vulnerable to the effects of climate change, such as warming, drying, and isolation. While the role of temperature and hydroperiod in structuring communities along an altitudinal and connectivity gradients has been demonstrated in high-mountain lakes or rivers, very few studies have been conducted in high-mountain ponds, and the role of hydroperiod and network connectivity remains actively debated. To understand which environmental factors structure high-mountain pond communities, we investigated the relationship between three biotic groups (Odonata, Amphibia, and macrophytes) and their environment in 500 ponds in the French Alps and Pyrenees. As predicted, most communities varied along an altitudinal gradient, though not uniformly across all the alpine biogeographic regions studied. We also showed that water permanence is a key determinant of community variation in high-mountain ponds common to all the geographic zones studied. Finally, we demonstrated that connectivity between ponds should be maintained to conserve high-mountain Odonata specialist communities and mediate the effects of temperature and water permanence in the context of climate change. In order to design effective conservation measures for high-mountain pond communities, further research is needed on the drought resistance of non-permanent pond communities and on their dispersal potential between high-mountain ponds
Certified to Stay ? Long-Run Experimental Evidence on Land Formalization and Widows’ Tenure Security in Benin
No full textIn settings where women's land rights are informal, the death of a husband can severely limit a widow's access to land and her ability to remain in her home -- especially in the absence of a male heir. This paper examines whether large-scale land formalization programs can improve widows' land access. Using data from a randomized controlled trial in rural Benin, the analysis finds that widows in villages with land formalization are more likely to stay in their homes four years after the program, with the strongest effects among those without a male heir. The paper identifies two key mechanisms: enhanced community recognition of women's land rights and greater decision-making power over land resources. These findings highlight the potential of land formalization to strengthen women's tenure security and promote their long-term economic stability in similar settings