High Energy Physics

Lack of fine tuning in effective field theory does not ensure that a particular scenario is natural or even realizable in a UV complete theory of quantum gravity. Large field axion inflation appears natural from the effective field theory perspective, but I argue that it is tuned from a quantum gravity perspective. The argument is based on the Weak Gravity Conjecture (WGC), a conjectural universal feature of quantum gravity that is present in all known string theory examples. In the process, I highlight recent progress in understanding the WGC and related conjectures about the charged spectrum of quantum gravity and discuss other potential applications, both formal and phenomenological.

In my talk I will consider resurgence properties of Chern-Simons
theory on compact 3-manifolds. I will also describe what role
resurgence plays in the problem of categorification of Chern-Simons
theory, that is the problem of generalizing Khovanov homology of knots
to compact 3-manifolds.

Supposing there exists no new physics stabilizing the weak scale, the Standard Model Higgs potential exhibits a true vacuum at large field values, rendering the electroweak vacuum metastable (i.e., long lived relative to the age of the Universe). While this scenario need not preclude our current existence, it may not reconcile with a period of large(ish)-field inflation---large fluctuations in the Higgs field, induced by the inflationary energy density, can lead to the field locally sampling the unstable/true vacuum part of the potential, with potentially disastrous consequences. Evaluating the extent to which large-field inflation and the Higgs vacuum instability are incompatible requires understanding (i) how Higgs fluctuations evolve during inflation and (ii) the fate of large local fluctuations that sample the part of the potential beyond the barrier that separates the electroweak and true vacua. In this talk, I will discuss both of these aspects, and explain the implications for large-field inflation.

We discuss information loss from black hole physics in AdS3, focusing on two sharp signatures infecting CFT2 correlators at large central charge c: `forbidden singularities' arising from Euclidean-time periodicity due to the effective Hawking temperature, and late-time exponential decay in the Lorentzian region. We show that these signatures can be derived from the behavior of the Virasoro conformal blocks at large central charge.  At finite c, we compute non-perturbative effects that resolve the unitarity-violation from forbidden singularities.  Finally, we elaborate on the non-perturbative behavior of Virasoro blocks by classifying all `saddles’ that can contribute for arbitrary values of external and internal operator dimensions in the semiclassical large central charge limit, and discuss their potential to resolve the problem of late-time decay in the Lorentzian regime.  

In this talk, I will present a framework in which Weinberg's anthropic explanation of the cosmological constant problem also solves the hierarchy problem. The weak scale is selected by chiral dynamics that controls the stabilization of an extra dimension. When the Higgs vacuum expectation value is close to a fermion mass scale, the radius of an extra dimension becomes large, and develops an enhanced number of vacua available to scan the cosmological constant down to its observed value. The fermion sector that controls the size of the extra dimension consists of a pair of electroweak doublets and several singlets. These leptons satisfy approximate mass relations related to the weak scale and are accessible to the LHC and future colliders. At low energies, the radion necessarily appears as an unnaturally light scalar, in a range of masses and couplings accessible to fifth-force searches as well as scalar dark matter searches with atomic clocks and gravitational-wave detectors.

The fundamental constants of our universe may have been set to maximize the production of similar universes, through repeated parametric variation. In this context, I will advocate that by the time the maximum entropy producer in our universe has reached maximum complexity, the majority of its energy should be re-purposed towards the production of additional universes. This builds on elements of prior proposals, including cosmological natural selection, the nonsingular universe, and the causal entropic principle. The phenomena and properties of dark matter, which realizes this proposal by copious conversion of halo baryons to black holes in ten trillion years, will be discussed.