Théorie

Analysing arrival directions of ultra-high-energy cosmic rays with convolutional neural networks

The problem of identification of ultra-high-energy cosmic ray (UHECR) sources is greatly complicated by the fact that even the highest energy cosmic rays may be deflected by tens of degrees in the galactic magnetic fields. We show that arrival directions of UHECRs from several nearest active galaxies form specific patterns in the sky, which can be effectively recognized by convolutional neural networks.

Cosmological Phonon Collider

The expansion of the universe spontaneously breaks time translation by selecting a preferred reference frame. As a consequence, very much like a superfluid at zero temperature, the low-energy description of single field inflation can be organised in terms of the associated Goldstone mode of the broken symmetry (aka the phonon). Similar to particle colliders, if we were to scatter sound waves, the presence of additional heavy fields coupled to the medium would manifest as distinct peaks in the cross-section of the phonons.

High-Energy Multimesssenger Emission from Supermassive Black Holes

Supermassive black holes power accretion flows and outflows, and resulting radiation is observed at different wavelengths. A significant energy fraction of these flows may be carried by cosmic rays and associated high-energy non-thermal radiations. Recently, associations of high-energy neutrinos with galaxies hosting supermassive black holes, active galactic nuclei and tidal disruption events, have been reported. We review the implications of the multimessenger data for theoretical models and discuss their challenges.

Searching for Internal Absorption Signatures and Probing EBL Using Gamma-Rays from High-Redshift Blazars

 Blazars are a special type of AGN, with jets that happen to
point very close to the direction towards Earth. The powerful
gamma-ray beam from distant blazars represents a unique tool to
explore the environment along its path, and allows us to probe opacity
both inside the source and in the intergalactic medium. Internally,
gamma-rays experience attenuation due to photon-photon absorption, a
result of interactions with AGN-generated photon fields. This
interaction introduces distinct features in gamma-ray spectra. Upon

Curvature on Curvature: Gravitational Lensing of Gravitational Waves.

 Gravitational lensing phenomena are widespread in electromagnetic astrophysics, and in principle may also be uncovered with gravitational waves. We examine gravitational-wave events in the limit of Geometric Optics, where we expect to see multiple signals from the same event with different arrival times and amplitudes, and Wave Optics, where we expect to see effects such as interference and diffraction.

Multimessenger probes of superheavy dark matter decay and annihilation

We revisit constraints on decaying very heavy dark matter (VHDM) using the latest ultrahigh-energy cosmic-ray (UHECR; E >1e18 eV) data and ultrahigh-energy (UHE) gamma-ray flux upper limits, measured by the Pierre Auger Observatory. We present updated limits on the VHDM lifetime for masses up to ∼ 1e15 GeV, considering decay into quarks, leptons, and massive bosons. In particular, we consider not only the UHECR spectrum but their composition data that favors heavier nuclei. Such a combined analysis improves the limits at <1e12 GeV because VHDM decay does not produce UHECR nuclei.

Chaotic behavior in field and string theory

My talk will be divided into two parts: In the first I will present a novel
measure of chaotic scattering amplitudes.  For chaotic scattering the distribution function is given
by the β-ensemble of random matrix theory (RMT). We show that amplitudes of one highly
excited string (HES) state with two or three scalars in open bosonic string theory admit
this behavior. Quite remarkably this measure applies also to the distributin of non-trivial
zeros of the  Riemann zeta function.

High Scale Leptogenesis and Low Energy CP Violation

Aspects of non-resonant high scale leptogenesis (LG) associated with type I seesaw mechanism  will be discussed.
The questions of
i) how low can be the LG scale in the case of three right-handed neutrinos,
ii) how low/high can be the LG scale when the  CP violation is provided by the Dirac or Majorana phases in the PMNS neutrino mixing matrix,
iii)   how the transitions between the different flavour regimes take place, and

Euclidean Wormholes and Holography

In this talk I will review the physics of Euclidean wormholes in a holographic context. By studying the properties of various observables on these Euclidean backgrounds holographically, we found the common behaviour that there are interactions between the quantum field theories that live on each of the wormholes' boundaries. These interactions are very weak in the UV and become strong in the IR.

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