Particle 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.

Cosmological surveys can reveal new particles through signals hidden among astrophysical foregrounds. This talk examines axion conversion of microwave photons in magnetized galactic halos, using Planck, unWISE and ACT observations with improved component separation. It then turns to inflationary particle signatures in galaxy clustering, including a constraint on the primordial four-point amplitude from DESI galaxies and quasars. The discussion highlights both the reach of these measurements and the systematic challenges of analysing extremely large scales.

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.

Some protected operators exist only at particular gauge-group ranks, a phenomenon connected conjecturally to black-hole microstates. This talk studies such fortuitous operators in ABJM theory at large Chern–Simons level. Harmonic representatives make the operators explicit, while analytic continuation of the two-loop Hamiltonian tracks them from finite rank toward the large-rank limit. Selected operator-product coefficients complement the trajectory analysis.

This talk tests asymptotic safety using perturbative methods that retain gauge invariance and allow Lorentzian calculations. Unlike mass-independent prescriptions, the proposed schemes preserve power-law sensitivity through modified dimensional regularization or gradient-flow techniques. Heavy-quark decoupling in QCD supplies a demonstration. Applying the approach to gravity yields a one-loop ultraviolet fixed point with indications of perturbative accessibility, which is compared with functional-renormalization-group evidence.