Cristina Mondino (NYU) : Light thermal relic Dark Matter | 9/11/19
The leading candidate for dark matter that is thermally produced in the early Universe is the Weakly Interacting Massive Particle (WIMP). However, increasingly stringent bounds on WIMPs are now motivating the exploration of viable alternatives. One interesting possibility are DM candidates with sub-GeV masses. In this talk, I will present two such examples. First, I will focus on models where the dark matter abundance is set by mutual annihilations among multiple species. I will show how sizable mass splittings between the dark matter states naturally point to masses exponentially lighter than the weak scale. Light dark matter from coannihilation evades stringent bounds from the cosmic microwave background, but will be tested by future direct detection, fixed target, and long-lived particle experiments. Second, I will illustrate another viable thermal dark matter candidate with sub-GeV masses which has been overlooked in the literature: a cosmologically stable dark Higgs.
Sangmin Choi (Michigan) : Wilson line dressings as carriers of asymptotic symmetry charges | 9/18/19
It is known that for a gauge-invariant formulation of QED and gravity, one should dress particles with Wilson lines stretching out to infinity. When considering asymptotic particles of scattering processes, such dressed particle states reduce to the infrared-finite states of Faddeev and Kulish. In quantum field theories in flat spacetime, the dressings of asymptotic states are known to carry a definite leading soft charge of the asymptotic symmetry, which can be interpreted as soft hair at infinity. Some recent attempts to extend this to subleading order will be briefly mentioned. We explore how this analysis can be extended to curved spacetimes with boundary, in particular, the Rindler and Schwarzschild spacetimes. More specifically, we will show that infalling dressed matter on the future Rindler and Schwarzschild horizons implant soft horizon hair.
Claudius Krause (Fermilab) : Improving Numerical Integration and Event Generation with Normalizing Flows | 9/25/19
With the upcoming HL-LHC, the budget for computing will be insufficient to generate a sufficient amount of Monte-Carlo events for both signal and background predictions. The driving force behind these costs is the inefficiency of the Monte-Carlo phase space generators and the unweighting efficiencies.
After a short review of traditional algorithms, I will introduce a new Machine Learning algorithm that uses Normalizing Flows for efficient numerical integration and random sampling. This approach is especially efficient in high-dimensional integration spaces. I will show some preliminary results obtained with the matrix element generator of Sherpa and discuss different choices of hyperparameters and their influence on the result.
Laura Johnson (Case Western) : Massive Gravitons in Curved Spacetimes | 10/2/19
This talk will cover various interesting topics that occur in massive spin-2 on various spacetimes including de Sitter, anti-de Sitter, and flat space. In de Sitter, we examine what happens to massive gravity as its mass approaches the partially massless value. In this limit, if the interactions are chosen to be precisely those of the 'candidate' non-linear partially massless theory, the strong coupling scale is raised, giving the theory a wider range of applicability. In anti-de Sitter and flat spacetime, we show how shift symmetries acting on the vector modes emerge from massive spin-2 theories fixing the non-linear structure and discuss whether these theories have amplitudes that can be constructed via soft substracted recursion.
Simon Knapen (IAS) : Dark matter - phonon scattering | 10/9/19
Upcoming sensor technology allows for dark matter direct detection all the way down to the warm dark matter limit of ~ 10 keV. At such low masses, the usual nuclear recoil picture breaks down, as the dark matter recoils against individual athermal phonon modes instead. I will show how the rate for these processes can be calculated and why superfluid helium and polar materials are good targets for this type of dark matter. In the latter case the crystal axis can provide a daily modulation of the scattering rate.
Anthony Charles (KU Leuven) : Euclidean Black Saddles and AdS4 Black Holes | 10/16/19
The entropy of a class of asymptotically-AdS4 black holes can be reproduced by the partition function of the dual ABJM theory via localization.However, establishing this match requires a particular extremization over fieldheory parameters. This begs the question: what are the bulk dual geometries when we do not extremize in the field theory? In this talk, I will show that these bulk duals are smooth Euclidean geometries with finitely-capped throats. These geometries generically have no clear interpretation in Lorentzian signature, but when their throat becomes infinitely long they become black holes with an AdS2 near-horizon geometry. For any set of field theory parameters whose extremization is compatible with a black hole, we find a large family of Euclidean geometries whose on-shell action reproduces the ABJM partition function exactly, without the need to extremize,thus establishing a more complete understanding of AdS4/CFT3 holography.
Mark Mezei (Stonybrook) : Fine probes of quantum chaos | 10/23/19
Quantum chaotic dynamics manifests itself in transport, thermalization, and the butterfly effect. Hydrodynamics is the universal effective description of transport in the long distance, late time regime. We can gain insight into the process of thermalization from the time evolution of entanglement entropy, for which I introduce an effective theory valid in the hydrodynamic regime. I derive this theory in the special case of holographic gauge theories, and present strong evidence for its validity in any chaotic system. I discuss the interplay between this effective theory and chaotic operator growth that is responsible for the butterfly effect, and present new general results on the Lyapunov exponent characterizing this phenomenon. I conclude with some exciting implications for quantum gravity through gauge/gravity duality.
Andrea Caputo (University of Valencia) : Looking for Axion Dark Matter: from Dwarf Galaxies to Pulsars | 10/30/19
Axion and Axion-like particles are fascinating dark matter candidates and a great effort has been devoted to their study, both theoretically and experimentally. In this talk I will discuss two different astrophysical searches. One consists in looking with radio telescopes for the spontaneous decay of axion dark matter using different targets as Dwarf Galaxies, Clusters or the Galactic Center. The second one uses the parity violating axion interactions to exploit the extreme precision of pulsar timing measurements and look for oscillations in the polarization angle of the pulsar signal.
Grant Remmen (Berkeley) : Extremal Black Holes and EFTs | 11/6/19
Higher-dimension operators in the action modify the extremality condition for black holes. In this talk, I will explore implications for these extremality corrections as a consequence of bounds on Wilson coefficients coming from scattering amplitudes. I will discuss connections to the Weak Gravity Conjecture and generalizations to dyonic, spinning, and BTZ black holes, as well as bounds on Wilson coefficients coming from consistency of black hole entropy.
Ryan Janish (UC Berkeley) : Fundamental Physics with Supernovae and Superconductors | 11/13/19
In the first part of this talk I will describe how type 1a supernovae (SN) can be used to constrain the interactions of heavy dark matter (DM), which may heat a white dwarf (WD) sufficient to trigger runaway fusion and ignite a SN. Based on the existence of long-lived WDs and the observed supernovae rate, we constrain ultra-heavy DM candidates that produce high energy SM particles in a WD. This rules out supersymmetric Q-ball DM in parameter space complementary to terrestrial bounds. We also constrain DM which is captured by WDs and forms a self-gravitating DM core. Such a core may form a black hole that ignites a SN via Hawking radiation, or which causes ignition via a burst of annihilation during gravitational collapse. It is intriguing
that these DM-induced ignition scenarios provide an alternative mechanism of triggering SN from sub-Chandrasekhar mass progenitors. In the second part of the talk, I will present a new technique which utilizes superconducting RF cavities to significantly improve the sensitivity of "light shinning
through walls" searches for axion-like particles (ALPs). Our design uses a gapped toroid to confine the static magnetic field responsible for axion-photon conversion, and thereby prevent quenching of the superconducting cavities . Such a search has the potential to probe axion-photon couplings to g ~ 2 x 10^-11 GeV^-1, comparable to future optical and solar searches.
Charlotte Sleight (IAS) : A Mellin Space Approach to Scattering in de Sitter Space | 11/20/19
Boundary correlators in (anti)-de Sitter space-times are notoriously difficult beasts to tame. In AdS, where such observables are equivalent to CFT correlation functions, recent years have seen significant progress in our understanding of their structure owing to the development of numerous systematic techniques, many of which have drawn inspiration from the successes and the strengths of the scattering amplitudes programme in flat space. In dS however, the problem is more complicated owing to the time-dependence of the background and it is unclear how consistent time
evolution is encoded in spatial correlations on the boundary. This makes application of our hard-earned wisdom from flat and AdS spaces far from straightforward. In this talk we explain how boundary correlators in AdS and dS can be placed on an equal footing by adopting a Mellin-Barnes representation in momentum space, providing a framework in which techniques and results available in AdS can be generalised to de Sitter. This connection allows us to systematically derive expressions for exchange diagrams in de Sitter involving fields with and without spin. Throughout we shall keep in mind applications to the classification of possible non-Gaussianities in cosmological correlation functions, of both scalar and tensor fluctuations.
Oren Slone (Princeton) : The Inconsistency of Superfluid Dark Matter with Milky Way Dynamics | 12/11/19
There are many well-known correlations between dark matter and baryons that exist on galactic scales. These correlations can essentially be encompassed by a simple scaling relation between observed and baryonic accelerations, historically known as the Mass Discrepancy Acceleration
Relation (MDAR). The existence of such a relation has prompted many theories that attempt to explain the correlations by invoking additional fundamental forces on baryons. The standard lore has been that a theory that reduces to the MDAR on galaxy scales but behaves like cold dark matter (CDM) on larger scales provides an excellent fit to data, since CDM is desirable on scales of clusters and above. However, this statement should be revised in light of recent results showing that a fundamental force that reproduces the MDAR is challenged by Milky Way dynamics. In this study, we test this claim on the example of Superfluid Dark Matter. We find that a standard CDM model is strongly preferred over a static superfluid profile. This is due to the fact that the superfluid model over-predicts vertical accelerations, even while reproducing galactic rotation curves. Our results establish an important criterion that any dark matter model must satisfy within the Milky Way.
