Theoretical Physics seminars

The CHY scattering equations link particle interactions to geometric and statistical structures. This seminar studies what happens when Mandelstam invariants are restricted to a graph, identifies graph conditions under which the equations behave well, and connects associated varieties to maximum-likelihood degree. Bipartite graphs and bipyramids provide concrete examples and motivate a combinatorial conjecture.

The behaviour of massive scalar waves near black holes links spacetime geometry, stability and long-time evolution. After reviewing Klein-Gordon instabilities on rotating Kerr backgrounds, the seminar presents polynomial decay results for localized initial data on Schwarzschild spacetime despite stable trapping. The proof brings in analytic-number-theory bounds on exponential sums.

Simple matrix integrals have been proposed as descriptions of higher-dimensional geometries. This seminar reviews the polarized IKKT model and the proposed correspondence between its local minima and smooth dual geometries. Numerical work addresses the difficulty of separating holographic minima that are subdominant in the classical-gravity regime, with comparisons across related models.

Consistency requirements on scattering amplitudes can constrain quantum gravity without a perturbative expansion. This talk applies analyticity, crossing and unitarity to maximally supersymmetric gravitational theories in ten and eleven dimensions. It extends bounds from the leading correction to higher-order effective couplings, comparing the allowed regions with string-theory and M-theory predictions. A nearby kink in eleven dimensions suggests a possible route toward characterizing the M-theory scattering matrix through consistency alone.

A weak attractive interaction confined to dark matter can outweigh gravity over subgalactic distances. This talk studies its effects on collapse and stable bound structures when the force is screened beyond roughly kiloparsec scales. Delaying its onset until low cosmic density avoids early-Universe and galaxy-structure constraints. For fermionic matter, the additional attraction can support much lighter particles against degeneracy pressure; a density-triggered phase transition provides a concrete delayed-activation mechanism.

Can quantum uncertainty resolve cosmological singularities within the Wheeler–DeWitt description itself? Introducing an observer's proper time turns the problem into evolution resembling scattering in a central potential. The talk describes a smooth quantum bounce for a radiation-filled universe, with large scale-factor uncertainty, and explains why anisotropy introduces a critical attractive potential. That harder regime motivates extending the classical BKL account of singularities into quantum theory.