Théorie

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.

Selecting Horndeski theories without apparent symmetries and their black hole solutions

Since the no-scalar-hair theorems of the 1970s, it has long been thought that four-dimensional, asymptotically flat black holes cannot support any kind of non-minimally coupled real scalar hair, if not for the controversial Bocharova-Bronnikov-Melnikov-Bekenstein (BBMB) black hole. However, the 2010s have seen renewed interest in the healthy, higher-order scalar-tensor theories which were described by Horndeski in 1974, and easily escape the assumptions of the no-hair arguments.

From the tabletop to the Big Bang: Quantum simulators of false vacuum decay

False vacuum decay (FVD) plays a vital role in many models of the early Universe, with important implications for inflation, the multiverse, and gravitational waves. However, we still lack a satisfying theoretical understanding of this process, with existing approaches working only in imaginary (Euclidean) time, and relying on numerous assumptions that have yet to be empirically tested. An exciting route forward is to use laboratory experiments which undergo transitions analogous to FVD, allowing nature to simulate all of the non-perturbative quantum effects for us.

Primordial Magnetic Fields in Cosmic Web and Galaxy Clusters

Magnetic fields are ubiquitous on astrophysical and cosmological scales: from planets and stars to galaxies and galaxy clusters. Different observational methods infer a field strength of the order of microGauss and coherence scales reaching a few tens of kiloparsecs in galaxy clusters. Despite their ubiquity, the origin of these fields still remains unknown. It is commonly assumed that the observed fields are originated from either astrophysical or cosmological (primordial) weak seed magnetic fields that undergo efficient growth during structure formation.

Relativistic superfluids, and the connection between finite density and spontaneous symmetry breaking for interacting scalar fields

We study the low-energy effective action for relativistic superfluids obtained by integrating out the heavy fields of a UV theory. A careful renormalization procedure is required if one is interested in deriving the effective theory to all orders in the light fields (but still to fixed order in the derivative expansion). The result suggests a general relation between finite density and spontaneous symmetry breaking for QFTs of interacting scalars with an internal global symmetry.

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