Théorie

Positivity Constraints on Lorentz-breaking EFTs

The coefficients of the operators of an effective field theory (EFT) are constrained to satisfy certain inequalities, under the (mild) assumption that the UV completion satisfies general requirements of causality and unitarity. We begin the extension of these ideas to theories where the Lorentz symmetry is spontaneously broken, as it happens in cosmology and condensed matter physics. Constraints are derived using dispersive arguments for the 2-point function of conserved currents and of the stress-energy tensor.

Quantum effects on the inner (Cauchy) horizon of rotating black holes

All black holes in the Universe are believed to be rotating. This poses interesting questions, since rotating black hole solutions of Einstein’s equations of General Relativity possess a so-called Cauchy horizon in their interior, which threatens the predictability of Einstein’s theory. However, these exact solutions may not model sufficiently accurately black holes in Nature, which have classical matter in their neighbourhood and, furthermore, are inevitably surrounded by a quantum vacuum (which is responsible for Hawking radiation).

Unveiling Positrons in Galactic Cosmic Rays

The spectrum of positrons in cosmic rays is currently measured with unprecedented precision by AMS-02 up to TeV energies, and represents an unique probe for the local properties of our Galaxy. Currently, its interpretation is still debated, especially for the excess above 10 GeV which suggests the presence of a local, primary source.
Recently, the observation of extended gamma-ray halos around Galactic pulsars has opened a new window to constrain the acceleration and propagation of positrons in our Galaxy.

Quantum orientations in the plane: Malus’ law (1808) and Stokes parameters (1852) for polarisation of light viewed as a quantum measurement

Two aspects of Positive Operator Valued Measures (POVM) on the Euclidean plane (a basic Hilbert space!) are presented, namely their status as quantum observables and their role as quantizers in the integral quantization procedure. The compatibility of POVMs in the ensuing quantum formalism is discussed, and a Naimark dilation is found for the quantum operators. The relation with Toeplitz quantization is explained. Within this framework, we describe the linear polarization of the light with the use of Stokes parameters and its interaction with a polariser as a quantum measurement (Malus’ law).

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