High Energy Physics

Massive neutral fermions can be realized in Nature as Majorana particles. Are neutrinos Majorana particles? Our most accepted theoretical prejudice can be verified by searching for neutrinoless double-beta decay. I will overview the current knowledge of the neutrino mass spectrum and discuss theoretical scenarios where cosmological data can contribute to resolve this challenging question. Some cosmological observables sensitive to neutrino masses are outlined.

Based on results in quantum gravity we conjecture a sharp bound on the rate of growth of chaos in thermal quantum systems with a large number of degrees of freedom. Chaos can be diagnosed using an out-of-time-order correlation function closely related to the commutator of operators separated in time. We conjecture that the influence of chaos on this correlator can develop no faster than exponentially, with Lyapunov exponent λL ≤ 2πkBT/\hbar. We give a precise mathematical argument, based on plausible physical assumptions, establishing this conjecture. 

There have been recent claims that the weak gravity conjecture (WGC) rules out multi-field natural inflation. I review these claims and then show how 2-field natural inflation can be consistent with even the most stringent form of WGC. I also discuss my recent attempt at numerically proving the WGC via the conformal bootstrap.

The concept of quantum entanglement entropy is playing a key role in understanding the mechanism underlying holography. In this talk we will discuss how entanglement can capture non-trivial geometric properties of the bulk spacetime. The goal is to exploit the interplay between anomalies and entanglement entropy, and for concreteness we will focus on AdS3/CFT2.  Anomalies play as well a key role in RG flows, and in this context we will see how entanglement, anomalies and geometry conspire to capture dynamically the correct physics.

 Super-massive black holes that grow at the center of dark matter halos distort the dark matter within their zone of influence into a steep density spike.  This spike can give rise to strong enhancements of standard indirect detection signals, and can lead to qualitatively new windows onto the physics of the early universe.   I will talk about potential dark matter signals from the Milky Way's central black hole, some astrophysical caveats, and the possible use of black holes as dark matter accelerators.

Recent landmark measurement of the muonic hydrogen Lamb shift generated more questions than answers, as it stands in a sharp disagreement with what was predicted based on known properties of muons and protons. It adds on top of the existing anomalies in the muon sector (discrepancy in g-2 and in radiative muon capture). I will critically review some suggestions for the new physics explanations of these anomalies, and describe their implications. One of the outstanding effects, not tested for muons, is the parity violation in the neutral current channel, which has proven to be an extremely difficult problem, and where the enhancement relative to the standard model prediction is still possible. Following my suggestion for a new way to approach this measurement, this summer the Paul Scherrer Institute in Switzerland will conduct a preliminary muonic atom experiment, tentatively called mu-ARC.

Freeze-in is a general and calculable mechanism for dark matter production in the early universe. Assuming a standard cosmological history, such a framework predicts metastable particles with a lifetime generically too long to observe their decays in a collider environment. In this talk I will report work in progress where we consider alternative cosmologies, where entropy dumped in the primordial Standard Model plasma leads to shorter lifetime for the metastable particles in order to reproduce the observed dark matter density. Famous examples are moduli decays in SUSY theories and inflationary reheating. Remarkably, for a large region of the parameter space the decay lengths are in the displaced vertex range and they can be observable at present and future colliders.

A classical Einstein-Rosen bridge changes the topology of spacetime,allowing (for example) electric field lines to penetrate it. It has recently been suggested that in the bulk of a theory of quantum gravity, the quantum entanglement of ordinary perturbative quanta should be viewed as creating a quantum version of an Einstein-Rosen bridge between the quanta, or a “quantum wormhole”. For this “ER=EPR” correspondence to make sense it then seems necessary for a quantum wormhole to allow (for example) electric field lines to penetrate it. I will discuss (within low-energy effective field theory) whether or not this happens.

String Theory LEGOs for Black Holes

Four decades ago, Stephen Hawking posed a paradox about black holes and quantum theory that still challenges the imaginations of theoretical physicists today. One of the most promising approaches to resolving the "information paradox" (the notion that nothing, not even information itself, survives beyond a black hole's point-of-no-return event horizon) is string theory, a part of modern physics that has wiggled its way into the popular consciousness.

Dr. Amanda Peet, a physicist at the University of Toronto, will describe how the string toolbox allows study of the extreme physics of black holes in new and fruitful ways. Dr. Peet will unpack that toolbox to reveal the versatility of strings and (mem)branes, and will explore the intriguing notion that the world may be a hologram.

We review recent versions of the information paradox, framed in the context of the AdS/CFT correspondence. We describe how they can be resolved using "state dependent" bulk to boundary maps for the black hole interior in AdS/CFT. We argue that this feature is necessary not only for single sided black holes but also for the eternal black hole.

We resolve some potential ambiguities in this map. We extend this construction of the black hole interior to entangled systems and show how a version of the ER=EPR conjecture emerges naturally in this process. Finally, we comment on the possible semi-classical origins of state-dependence.

Astrophysical observations suggest that the majority of matter in the Universe is made up of novel Weakly Interacting Massive Particles (WIMPs).  Such WIMPs are often predicted by extensions to the Standard Model.  Efforts have been underway for more than two decades to detect WIMPs directly in detectors on earth.  The challenge is great because of the small energies involved and the low interaction rates. The field has been driven by progress in detectors able to identify radioactive backgrounds. I will review how recent enthusiasm for low-mass WIMPs, which was generated by tantalizing hints seen in several experiments, has waned.  Lastly, I will discuss various ideas to check the longstanding DAMA WIMP-detection claim, including the feasibility of alkali-halide cryogenic detectors.

Can we learn about New Physics with astronomical and astro-particle data? Understanding how this is possible is key to unraveling one of the most pressing mysteries at the interface of cosmology and particle physics: the fundamental, particle nature of the dark matter.
I will discuss some of the recent puzzling findings in astro-particle and astronomical observations that might be related to signals from dark matter. I will first review the status of explanations to the cosmic-ray positron excess, emphasizing how we might be able to discriminate between astrophysical sources and dark matter. 
I will then discuss the evidence for an X-ray line at 3.5 keV, and present new results on systematic effects and on the role of previously underestimated astrophysical lines.
Finally, I will discuss a reported excess of gamma rays from the central regions of the Galaxy.  I will address the question of whether we are possibly observing a signal from dark matter annihilation, how to test this hypothesis, and which astrophysical mechanisms constitute the relevant background.