## NATIONAL SEMINAR THEORETICAL HIGH ENERGY PHYSICS (November 2019)

- Date:
15 November 2019

- Abstract:
**Vitor Cardoso (IST Lisbon, Nikhef colloquium speaker)**

**Black holes as a physics laboratory**The LIGO/Virgo gravitational wave detections, the imaging of a black hole shadow by long-baseline radio interferometry, and ever more precise observations across all electromagnetic wavelengths have opened an unprecedented window onto gravity at its strongest. Black holes are the simplest, most compact, and physically elusive macroscopic objects in the Universe and play a central role in this new era in physics and astronomy. In this talk, I will describe how black holes can be used to understand foundational questions: are gravitons massless? Are black holes the simplest possible macroscopic objects? do event horizons and black holes really exist, or is their formation halted by some as-yet unknown mechanism? Do singularities arise in our universe as the outcome of violent collisions? Can black holes inform us about the nature of the elusive dark matter?

**Oliver Schlotterer (Uppsala University)**

**The unity of scattering amplitudes in field and string theories**In a variety of recent developments, scattering amplitudes hint at new symmetries of and unexpected connections between physical theories which are otherwise invisible in their conventional description via Feynman diagrams or Lagrangians. Yet, many of these hidden structures are conveniently accessible to string theory where gauge interactions and gravity arise as the low-energy excitations of open and closed strings. In this talk, I will give an intuitive picture of gravity as a double copy of gauge interactions and extend the web of relations to scalar field theories including chiral Lagrangians for Goldstone bosons. Moreover, many of the string corrections to gauge and gravity amplitudes beyond their point-particle limit nicely resonate with the field-theoretic double-copy structures. The resulting higher-derivative interactions are accompanied by multiple zeta values whose number-theoretic properties pinpoint the double-copy pairing of higher-mass-dimension operators.

**Melissa van Beekveld (Radboud University of Nijmegen)**

**Anticipating the punch: The universal structure of large logarithms**Cross-sections in perturbative QCD are plagued by large corrections from soft and collinear radiation. The most singular terms are known to be universal, which allows their resummation to all orders in the coupling, hereby curing the cross-section of the large uncertainties. In this talk, I will explain how the large corrections come about, and review how resummation solves the issue.

**Gui Pimentel (UvA)**

**The Cosmological Bootstrap**In flat space, four point scattering amplitudes at weak coupling can be fully determined from Lorentz symmetry, unitarity and causality. The resulting scattering amplitude depends on model details only through coupling constants and the particle content of the theory. I will show how the analogous story works in the case of inflationary fluctuations. I will present explicit expressions for weakly coupled inflationary three and four-point functions, whose shapes depend on the field content of the theory, and do not depend on the specific inflationary model, as long as the fluctuations minimally break de Sitter symmetry. This “cosmological bootstrap” is a first step towards classifying all possible shapes of primordial non-gaussianity, which can be searched for in experimental data. I will also present results for cosmological correlation functions of spinning fields, where consistency forces us to rediscover many beautiful, universal results about gauge theory and gravity.