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Évolution des génomes et développement (chaire internationale): [résumé des cours et travaux : 2021-2022]
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Palatini Gauss-Bonnet theory
No full textInternational audienceWe consider a class of models in even spacetime dimensions which share many similarities with Chern-Simons theories in odd spacetime dimensions . The independent dynamical variables of these models are a -connection and a metric in internal space. The action is a polynomial of degree in the curvature of the connection, with indices saturated by means of the metric and the Levi-Civita tensor. We show that the theory has no local degree of freedom in spacetime dimensions (), where it can be reformulated as a constrained model, but that its dynamics is more intrincate in higher dimensions (n>1), where local degrees of freedom are present. We treat in detail the cases of and spacetime dimensions
Black Hole Spectroscopy and Tests of General Relativity with GW250114
No full textInternational audienceThe binary black hole signal GW250114, the loudest gravitational wave detected to date, offers a unique opportunity to test Einstein’s general relativity (GR) in the high-velocity, strong-gravity regime and probe whether the remnant conforms to the Kerr metric. Upon perturbation, black holes emit a spectrum of damped sinusoids with specific, complex frequencies. Our analysis of the postmerger signal shows that at least two quasinormal modes are required to explain the data, with the most damped remaining statistically significant for about one cycle. We probe the remnant’s Kerr nature by constraining the spectroscopic pattern of the dominant quadrupolar (ℓ=m=2) mode and its first overtone to match the Kerr prediction to tens of percent at multiple postpeak times. The measured mode amplitudes and phases agree with a numerical-relativity simulation having parameters close to GW250114. By fitting a parametrized waveform that incorporates the full inspiral-merger-ringdown sequence, we constrain the fundamental (ℓ=m=4) mode to tens of percent and bound the quadrupolar frequency to within a few percent of the GR prediction. We perform a suite of tests—spanning inspiral, merger, and ringdown—finding constraints that are comparable to, and in some cases 2–3 times more stringent than those obtained by combining dozens of events in the fourth Gravitational-Wave Transient Catalog. These results constitute the most stringent single-event verification of GR and the Kerr nature of black holes to date, and outline the power of black-hole spectroscopy for future gravitational-wave observations
Light-Induced Regioselective 6-Endo versus 5-Exo Cycloisomerization of o-Alkynylbenzoic Acids
No full textInternational audienceRegioselectivity of the gold(I)-catalyzed cycloisomerization of o-alkynyl benzoic acids is significantly influenced by blue LEDs irradiation. In particular, the reaction exhibits higher selectivity toward the 6-endo regioisomer when irradiated with blue light, whereas the 5-exo product is obtained as the major product in the absence of light. These findings prompted mechanistic inquiries that we sought to address through running the reactions in diverse conditions and also by studying the reactivity of the vinylgold(I) complexes that are formed as intermediates
Shake-up and shake-off spectra in the electron capture decay of atomic Be
No full textInternational audienceThe most stringent laboratory-based experimental limits on the existence of sub-MeV sterile neutrinos are currently set by decay spectroscopy of radioactive Be embedded into superconducting sensors. The systematic uncertainties are dominated by the modeling of the electron shake-up and shake-off spectra that are not based on state-of-the-art atomic theory and do not include electron correlations or relativistic effects. We have used the multiconfiguration Dirac-Fock formalism to obtain correlated wavefunctions ab initio and compute all single and double shake processes in the electron capture decay of atomic Be. The simulations can explain some but not all of the observed spectral features, likely because the wave functions are modified by the Ta sensor material that the Be is embedded into. The new models also show that the L/K electron capture ratio of Be in Ta has previously been slightly underestimated revising the previous value of 0.070(7) to a new value of 0.0756(20)
Documenter le fait rituel pour appréhender les histoires locales. Le cas des monuments sacrés de Mongolie-Intérieure
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Catastrophic disruption of asteroid 2023 CX1 and implications for planetary defence
No full textInternational audienceMitigation of the threat from airbursting asteroids requires an understanding of the potential risk they pose for the ground. How asteroids release their kinetic energy in the atmosphere is not well understood due to the rarity of large impacts. Here we present a comprehensive, space-to-laboratory characterization of an impact of an L chondrite, which represents a common type of Earth-impacting asteroid. Small asteroid 2023 CX1 was detected in space and predicted to impact over Normandy, France, on 13 February 2023. Observations from several independent sensors and reduction techniques revealed an unusual but potentially high-risk fragmentation behaviour. The nearly spherical 650 +/- 160 kg (72 +/- 6 cm diameter) asteroid catastrophically fragmented at a dynamic pressure of 4 MPa around 28 km altitude, releasing 98% of its total energy in a concentrated region of the atmosphere. The resulting shock wave was spherical, not cylindrical, and released more energy closer to the ground. This type of fragmentation increases the risk of substantial damage at ground level. These results warrant consideration for a planetary defence strategy for cases where a >3-4 MPa dynamic pressure is expected, including planning for evacuation of areas beneath anticipated disruption locations