Alessandro Georgoudis

A bstract: We introduce a new approach for the computation of the class of Feynman integrals whose integrands vanish in strictly four-dimensions, so-called “pseudo-evanescent” integrals. We argue that, up to 𝒪( ϵ ) corrections, local subtraction techniques can be used to express pseudo-evanescent integrals in terms of contributions from infrared and ultraviolet regions of loop-momentum space. We study two-loop pseudo-evanescent and show that singly-infrared singular cases can be reduced to either products of one-loop integrals or one-fold integrals thereof. As a demonstration of the power of our approach, we use it to recompute the two-loop all-plus five-point amplitude. We find that, up to scheme-dependent logarithms, all contributions from soft and collinear regions cancel exactly against known infrared structure and that the finite remainder is entirely given by contributions from ultraviolet regions.

We present the first computation of the nonlinear gravitational memory waveform for the scattering of two compact objects in general relativity at leading order in the post-Minkowskian expansion. We use the scattering-amplitude-based representation of the gravitational waveform, which naturally expresses the nonlinear memory as the contribution of soft gravitons emitted by the gravitational waves themselves. We perform the calculation by applying a multipolar decomposition to the waveform and using the reverse unitarity method to obtain explicit exact-in-velocity predictions. We validate the results by calculating the corresponding velocity-expanded post-Newtonian multipoles, finding perfect agreement. Our results complete the knowledge of the gauge-invariant nonanalytic-in-frequency part of the O ( G 3 ) multipolar waveform, thus providing a useful benchmark for future calculations of this quantity.

A bstract: We study the structure constants of two conformal primary operators and one spinning operator in planar 𝒩 = 4 Super-Yang-Mills theory using the hexagon formalism. By analytically continuing in the spin, we derive a formula for computing these structure constants at any coupling in the small-spin limit, up to a normalization factor. This formula allows us to explore their analytical properties at strong coupling. In this regime, using classical string calculations and a suitable ansatz, we extend our analysis to finite-spin operators, verifying recent two-loop results for structure constants in string theory and generalizing them to operators with arbitrary R-charges.

We consider the frequency-domain leading order and next-to-leading order post-Minkowskian waveforms obtained from the tree-level and one-loop amplitudes describing the scattering of two massive scalar objects and the emission of one graviton. We explicitly calculate their post-Newtonian (PN) limit obtaining an expansion up to the third subleading PN order in all ingredients: the tree-level amplitude, the odd and even parts of the real one-loop kernel, and the Compton or “rescattering” cuts, thus reaching 3PN precision for the latter. We provide explicit expressions for the multipole decomposition of these results in the center-of-mass frame and compare them with the results obtained from the classical multipolar post-Minkowskian method. We find perfect agreement between the two, once the Bondi-Metzner-Sachs supertranslation frame is properly adjusted and the infrared divergences due to rescattering are suitably subtracted in dimensional regularization. This shows that the approach proposed in Georgoudis et al. [An eikonal-inspired approach to the gravitational scattering waveform, J. High Energy Phys. 03 (2024) 089] can be applied beyond the soft-regime ensuring the agreement between amplitude-based and multipolar post-Minkowskian results for generic frequencies.

We revisit the space of gapped quantum field theories with a global O(N) symmetry in two spacetime dimensions. Previous works using S-matrix bootstrap revealed a rich space in which integrable theories such as the non-linear sigma model appear at special points on the boundary, along with an abundance of unknown models hinting at a non conventional UV behaviour. We extend the S-matrix set-up by including into the bootstrap form factors and spectral functions for the stress-energy tensor and conserved O(N) currents. Sum rules allow us to put bounds on the central charges of the conformal field theory (CFT) in the UV. We find that a big portion of the boundary can only flow from CFTs with infinite central charges. We track this result down to a particular behaviour of the amplitudes in physical kinematics and discuss its physical implications.