Djuna Croon (TRIUMF): New Physics and the Black Hole Mass Gap | 9/30/20
In this talk I will demonstrate the potential of the black hole mass gap to probe new physics. The mass gap, in which no black holes can be formed, is a standard prediction of stellar structure theory. I will show that new physics that couples to the Standard Model can act as an additional source of energy loss in the cores of population-III stars, dramatically altering their evolution, resulting in large shifts of the gap. The gravitational wave observations by the LIGO/Virgo collaboration will bring the edges of the black hole mass gap in sight in the coming years, making this a promising novel probe of new physics.
Harikrishnan Ramani (Stanford): Detecting terrestrial dark matter traffic jams | 11/4/20
Subcomponent dark matter having large interactions with the standard model or with itself can accumulate terrestrially over the age of the earth leading to massive build-ups. This thermalized population is too cold to be visible in traditional direct detection. In this talk I outline a few detection strategies including accelerating this slow dark matter with metastable nuclear isomers or with electrostatic accelerators like LUNA. Intriguingly such a terrestrial component could explain the neutron bottle-beam anomaly and can cause anomalous heating in cryogenic detectors.
Seth Koren (U Chicago): UV/IR Mixing and the Hierarchy Problem | 11/11/20
The persistence of the hierarchy problem points to a violation of effective field theory expectations. A compelling possibility is that this results from a physical violation of EFT, which may arise from correlations between UV and IR physics—as is broadly demanded by gravity. I will discuss Noncommutative Field Theory as a toy model of UV/IR mixing, where an emergent infrared scale is generated from ultraviolet dynamics. I’ll explore a variety of such theories to develop a picture of how this feature appears, and to glean lessons to guide the realization of UV/IR mixing in more realistic theories.
Yu-Dai Tsai (Fermilab): When High Energy Meets High Intensity | 11/25/20
Ofri Telem (UC Berkeley): Scattering Amplitudes for Monopoles: Pairwise Little Group and Pairwise Helicity | 12/8/20
On-shell methods are particularly suited for exploring the scattering of electrically and magnetically charged objects, for which there is no local and Lorentz invariant Lagrangian description. In this talk we show how to construct a Lorentz-invariant S-matrix for the scattering of electrically and magnetically charged particles, without ever having to refer to a Dirac string. A key ingredient is a revision of our fundamental understanding of multi-particle representations of the Poincar\'e group. Surprisingly, the asymptotic states for electric-magnetic scattering transform with an additional little group phase, associated with pairs of electrically and magnetically charged particles. The corresponding ``pairwise helicity'' is identified with the quantized ``cross product'' of charges, e_1 g_2 - e_2 g_1, for every charge-monopole pair, and represents the extra angular momentum stored in the asymptotic electromagnetic field. We define a new kind of pairwise spinor-helicity variable, which serves as an additional building block for electric-magnetic scattering amplitudes. We then construct the most general 3-point S-matrix elements, as well as the full partial wave decomposition for the 2\to 2 fermion-monopole S-matrix. In particular, we derive the famous helicity flip in the lowest partial wave as a simple consequence of a generalized spin-helicity selection rule, as well as the full angular dependence for the higher partial waves. Our construction provides a significant new achievement for the on-shell program, succeeding where the Lagrangian description has so far failed.
Felix Kling (SLAC): Looking forward to new Physics with FASER | 12/16/20
Physics searches and measurements at high-energy collider experiments traditionally focus on the high-pT region. However, if particles are light and weakly-coupled, this focus may be completely misguided: light particles are typically highly collimated around the beam line, allowing sensitive searches with small detectors, and even extremely weakly-coupled particles may be produced in large numbers there. The recently approved FASER experiment will use the opportunity and extend the LHC's physic potential by searching for long-lived particles and studying neutrino interactions at TeV energies. In this talk, I will present the physics potential of FASER for new physics searches, neutrino physics, QCD as well as cosmic ray and cosmic neutrino measurement, aiming to stimulate a fruitful discussion with my audience.
