Alexandre Payez

Revisiting the SN1987A gamma-ray limit on ultralight axion-like particles

We revise the bound from the supernova SN1987A on the coupling of ultralight axion-like particles (ALPs) to photons. In a core-collapse supernova, ALPs would be emitted via the Primakoff process, and eventually convert into gamma rays in the magnetic field of the Milky Way. The lack of a gamma-ray signal in the GRS instrument of the SMM satellite in coincidence with the observation of the neutrinos emitted from SN1987A therefore provides a strong bound on their coupling to photons. Due to the large uncertainty associated with the current bound, we revise this argument, based on state-of-the-art physical inputs both for the supernova models and for the Milky-Way magnetic field. Furthermore, we provide major amendments, such as the consistent treatment of nucleon-degeneracy effects and of the reduction of the nuclear masses in the hot and dense nuclear medium of the supernova. With these improvements, we obtain a new upper limit on the photon-ALP coupling: gaγ 5.3 × 10-12 GeV-1, for ma 4.4 × 10-10 eV, and we also give its dependence at larger ALP masses ma. Moreover, we discuss how much the Fermi-LAT satellite experiment could improve this bound, should a close-enough supernova explode in the near future.

Axions and polarisation of quasars

We present results showing that, thanks to axion‐photon mixing in external magnetic fields, it is actually possible to produce an effect similar to the one needed to explain the large‐scale coherent orientations of quasar polarisation vectors in visible light that have been observed in some regions of the sky.

New polarimetric constraints on axion-like particles

We show that the parameter space of axion-like particles can be severely constrained using high-precision measurements of quasar polarisations. Robust limits are derived from the measured bounds on optical circular polarisation and from the distribution of linear polarisations of quasars. As an outlook, this technique can be improved by the observation of objects located behind clusters of galaxies, using upcoming space-borne X-ray polarimeters.

Probing axions with the neutrino signal from the next galactic supernova

We study the impact of axion emission in simulations of massive star explosions, as an additional source of energy loss complementary to the standard neutrino emission. The inclusion of this channel shortens the cooling time of the nascent protoneutron star and hence the duration of the neutrino signal. We treat the axion-matter coupling strength as a free parameter to study its impact on the protoneutron star evolution as well as on the neutrino signal. We furthermore analyze the observability of the enhanced cooling in current and next-generation underground neutrino detectors, showing that values of the axion mass

Can axionlike particles explain the alignments of the polarizations of light from quasars

{m}_{a}\ensuremath{\gtrsim}8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }\mathrm{eV}

Cornering the axionlike particle explanation of quasar polarizations

can be probed. Therefore a galactic supernova neutrino observation would provide a valuable possibility to probe axion masses in a range within reach of the planned helioscope experiment, the International Axion Observatory.

On the circular polarisation of light from axion‐photon mixing

The standard axionlike particle explanation of the observed large-scale coherent orientations of quasar polarization vectors is ruled out by the recent measurements of vanishing circular polarization. We introduce a more general wave-packet formalism and show that, although decoherence effects between waves of different frequencies can reduce significantly the amount of circular polarization, the axionlike particle hypothesis is disfavored given the bandwidth with which part of the observations were performed. Finally, we show that a more sophisticated model of extragalactic fields does not lead to an alignment of polarizations.

Large-scale coherent orientations of quasar polarisation vectors: interpretation in terms of axion-like particles

In a series of paper, it has been shown that the distribution of polarisation position angles for visible light from quasars is not random in extremely large regions of the sky. As explained in a recent article, the measurement of vanishing circular polarisation for such quasars is an important problem for a mechanism involving the mixing with axion-like particles in external magnetic fields. In this note, we stress that a recent report of similar coherent orientations of polarisation in radiowaves further disfavours the need for such particles, as an effect at these wavelengths would be extremely suppressed or would directly contradict data.

Large-Scale Alignments of Quasar Polarization Vectors: Evidence at Cosmological Scales for Very Light Pseudoscalar Particles Mixing with Photons?

From the analysis of measurements of the linear polarisation of visible light coming from quasars, the existence of large‐scale coherent orientations of quasar polarisation vectors in some regions of the sky has been reported. Here, we show that this can be explained by the mixing of the incoming photons with nearly massless pseudoscalar (axion‐like) particles in extragalactic magnetic fields. We present a new treatment in terms of wave packets and discuss its implications for the circular polarisation.

Constraining ALPs with linear and circular Polarisation Measurements of Quasar Light

The observation of redshift‐dependent coherent orientations of quasar polarisation vectors over cosmological distances in some regions of the sky is reviewed. Based on a good‐quality sample of 355 measured quasars, this observation seems to infer the existence of a new effect acting on light propagation on such huge distances.A solution in terms of nearly massless axion‐like particles has been proposed in the literature and its current status is discussed.