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.

Primordial black holes from supercooled first-order phase transition

Cosmological first-order phase transitions are said to be strongly supercooled when the nucleation temperature is much smaller than the critical temperature. They are typical of potentials which feature nearly scale-invariance, for which the bounce action decreases only logarithmically with time. The phase transition takes place slowly and the probability distribution of bubble nucleation time is maximally spread. Hubble patches which get percolated later than the average are hotter than the background after reheating and potentially collapse into black holes.

Soft theorems for boosts and other time symmetries

I will derive new classes of soft theorems for theories in which time symmetries (i.e., symmetries that involve the transformation of time, an example of which are Lorentz boosts) are spontaneously broken. The soft theorems involve unequal-time correlation functions with the insertion of a soft Goldstone in the far past. I will discuss explicit examples, which include the effective theory of a relativistic superfluid and inflationary cosmology.


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