Conveners
Theoretical Developments
- Riccardo Penco (Carnegie Mellon University)
The scattering amplitude for massive spin-2 particles at high energies suffers from growth proportional to energy to the tenth power. In this talk we discuss the origin of this bad high-energy behavior, how it must necessarily be mitigated in the case where the massive modes arise from a compactified theory of gravity, and we outline how the cancellations necessary to reduce this growth to...
We report the results of computations of the scattering amplitudes for massive spin-2 Kaluza-Klein particles in compactified five-dimensional theories of gravity. We demonstrate that different classes of diagrams individually grow as energy to the tenth power as expected, but that intricate cancellations among different diagrams reduce this growth to energy-squared. We show that these...
Infrared divergences have long been heralded to cancel in sufficiently inclusive cross sections, according to the famous Kinoshita-Lee-Nauenberg (KLN) theorem. The theorem states that summing over all initial and final states with energies in some compact energy window around a reference energy $E_0$ guarantees finiteness. While well-motivated, this theorem is much weaker than necessary: for...
We propose to construct effective field theory in terms of on-shell scattering amplitudes, rather than operators consisting of quantum fields. Using the methods like recursion relation and unitarity cut, most of the physical observables can be computed based on a set of on-shell amplitudes that we call the amplitude basis. We establish the correspondence between the amplitude basis and the...
Soft-Collinear Effective Theory (SCET) for gravity has recently been developed at leading and next-to-leading powers of a small parameter, $\lambda$. Being an effective theory, SCET for gravity is halfway between full theory of gravity (below Planck scale) and gravity scattering amplitudes. This reveals many interesting properties of gravity amplitudes which are obscure in full theory and...
The calculation of particle decay rates typically proceeds by an S-matrix approach in Minkowski spacetime. While such an approach is often highly effective, it fails, in general, when performing calculations in dynamic spacetimes since the S-matrix necessitates global energy conservation which is not present in an expanding universe, like ours. I will describe how the decay law of scalar...
The evidence for dark matter is overwhelming, but its nature is unknown. Dark matter may be the magnetic monopoles of a hidden sector, which acquire small coupling to the visible photon through kinetic mixing. When the hidden sector U(1) is broken, the monopoles confine, connected by a tube of magnetic flux. These flux tubes give rise to phase shifts in Aharanov-Bohm experiments. I show the...
Recent studies show that there is tension between the de Sitter swampland conjectures proposed by Obeid, et al. and inflationary cosmology. In this paper, we consider an alternative to inflation, `tachyacoustic' cosmology, in light of swampland conjectures. In tachyacoustic models, primordial perturbations are generated by a period of superluminal sound speed instead of accelerating expansion....
