John L. Loeb Associate Professor of the Natural Sciences
569 Jefferson Lab
617 496 9123
mreece at g dot harvard dot edu
Research interests: physics beyond the Standard Model; cosmology; quantum field theory; quantum gravity
I am a co-organizer of an upcoming Summer 2019 Aspen Center for Physics program on "String Theory and the Hidden Universe" (with Jim Halverson, Arthur Hebecker, and Liam McAllister). Applications are due by January 31.
Videos of some of my recent talks are online: the Simons Summer Workshop; Cosmo-18 in Korea; and the Vistas over the Swampland meeting in Madrid.
The nature of dark matter and its interactions is one of the biggest mysteries in fundamental physics. Some of my work on the subject includes:
In the last few years I have been interested in what my colleague Cumrun Vafa named the "Swampland Program": how quantum gravity might provide constraints on low-energy physics. In a series of papers with Ben Heidenreich and Tom Rudelius (on the topics: sharpening the WGC [JHEP], the sublattice WGC [JHEP], emergence and the WGC [Eur Phys J C], emergence and long distances in field space [PRL]), I have developed arguments for a "Sublattice Weak Gravity Conjecture" implying that towers of charged particles become light in quantum gravity theories containing weak gauge couplings. This can be proven in a wide range of string theory constructions, and we have argued that it is related to the fact that many different amplitudes in a quantum gravity theory become strongly coupled at the same characteristic energy scale.
As one example of the potential utility of these ideas for conventional particle physics, I have recently argued that it is only in the quantum gravity context that we can argue that the photon mass must be exactly zero. Furthermore, various theories of dark photon dark matter are put under strain by these "Swampland" ideas.
Since the beginning of my career I have maintained a strong interested in the physics of the TeV scale and the question of the mechanism underlying electroweak symmetry breaking. This continues to be a target for the LHC and other particle physics experiments. Some of my work in this direction includes:
I have worked on a range of other topics, and maintain an interest in all of the many possible experimental directions that might shed the first light on what lies beyond the Standard Model.
A short expository note on inflation, the Lyth bound, and the consequences of observable tensor modes.
A short expository note on the electron EDM in new physics models.
BRIDGE software for computing branching ratios and decays (written with Patrick Meade)
Some simulation tools for a GeV dark sector (written with Lian-Tao Wang)
Code for stop decay to goldstino (gravitino) in MadGraph
Stealth SUSY Simplified Models (see the associated paper with J. Fan, R. Krall, D. Pinner, and J. Ruderman)