Particle Physics

Astrophysical observations spanning dwarf galaxies to galaxy clusters indicate that dark matter halos are less dense in their central regions compared to expectations from collisionless dark matter N-body simulations. Using detailed fits to dark matter halos of galaxies and clusters, we show that self-interacting dark matter may provide a consistent solution to the dark matter deficit problem across all scales, even though individual systems exhibit a wide diversity in halo properties. 

The High-Energy community is only now in the process of fully appreciating the opportunities the LHC provides by producing electroweak-scale resonances beyond threshold. On the one hand this is reflected by changing from the so-called 'kappa framework’ to effective operators and on the other hand by studying Higgs and gauge boson production in processes with large momentum transfer. Accessing more exclusive phase space regions will allow to either discover New Physics or improve Higgs-boson couplings measurements. I will discuss implications of and tools necessary for these measurements, focusing on Higgs boson and Dark Matter phenomenology.

I explain the hierarchy problem of the standard model of particle physics, and discuss some of the ideas which have been put forward to resolve it. I then show that a specific class of theories, built around a framework known as neutral naturalness, can help address this problem while remaining consistent with all current experimental tests. I explain that while certain theories in this class give rise to striking signals, others are extremely difficult to test, and require a detailed study of the properties of the Higgs boson. I consider the implications of these results for the Large Hadron Collider, and for future experimental programs.

Light sterile neutrinos are predicted in many theories beyond the Standard Model and may be hinted at in short-baseline data. However cosmological data seems to rule out these neutrinos. Intriguingly, this tension is ameliorated when these new neutrinos are self-interacting. I will explore the impact of this self-interaction on their evolution in the early universe and on the spectrum and flavor of IceCube's ultrahigh energy neutrinos.

The venerable proton continues to play a central role in fundamental particle physics.   Neutrinos scatter from protons in neutrino oscillation experiments, Weakly Interacting Massive Particles (WIMPs) are expected to scatter from protons in dark matter searches, and electrons or muons are bound by protons in precision atomic spectroscopy.   Our understanding of the proton is an obstacle to the success of next generation experiments hoping to discover CP violation in the lepton sector and determine the neutrino mass hierarchy, discover the particle nature of dark matter, or reveal new interactions such as those that violate lepton universality.  In this talk I present (i) an overview of the current state of knowledge in the neutrino sector, and theoretical advances that will determine a crucial missing ingredient in the predicted signal process of neutrino-nucleus scattering at long baseline neutrino oscillation experiments (ii) the first complete calculation of the scattering cross section of a proton on a static electroweak source, which determines WIMP-nucleus scattering rates at underground direct detection experiments and (iii) the status of the proton radius puzzle, whose most "mundane" resolution requires a 5 standard deviation shift in the value of the Rydberg constant.   I describe how each of these problems has spurred the development of powerful new methods in effective quantum field theory.

I will discuss the recent LHC excess in the di-photon distribution at an invariant mass of 750 GeV.  Various explanations in terms of weakly coupled and strongly coupled physics will be presented. Possible connection with Dark Matter will also be discussed.

In this talk, I will investigate the structure of certain protected operator algebras that arise in threedimensional N = 4 superconformal field theories. I will show that these algebras can be understood as a quantization of (either of) the half-BPS chiral ring(s). An important feature of this quantization is that it has a preferred basis in which the structure constants of the quantum algebra are equal to the OPE coefficients of the underlying superconformal theory. I will present evidence in examples that for a given choice of quantum algebra (defined up to a certain gauge equivalence), there is at most one choice of canonical basis, and conjecture that this is true in general.

Understanding the microscopic nature of dark matter (DM) is one of the most outstanding problems facing modern physics.  There is to-date no evidence for non-gravitational interactions of DM with the rest of the Standard Model and also no hint for any particular DM mass.  My talk with focus on new techniques to search for GeV-TeV scale weakly-interacting DM by looking for DM annihilating in the cosmos into cosmic rays such as gamma-rays and neutrinos. These potential signs of new physics are easily confused with standard but poorly understood astrophysical backgrounds, such as populations of dim point sources (PSs) like millisecond pulsars.  I will present new methods to characterize Galactic and extra-Galactic PS populations, which have complicated DM searches in these regions.  I will show that accounting for unresolved PSs in Fermi gamma ray data leads both to new constraints on the dark sector along with some unexpected surprises.  I will conclude by briefly describing a new idea for a laboratory experiment able to probe ultra-light axion DM, with masses some 20 orders of magnitude smaller than the weak scale.

I will demonstrate that SL(2,Z) duality is a property of all low-energy effective Abelian theories with electric or magnetic charges  The duality will be verified at one loop by comparing the amplitudes in the case of an electron and the dyon that is its SL(2,Z) image, and I will show that it can be extended order by order in perturbation theory.  I will discuss how the duality generically breaks down at high energies, and show how the results apply to the Seiberg-Witten theory.

In this talk, I discuss several application of semileptonic B-meson form factors.  Topics include the determination of $|V_{ub}|$ and $|V_{cb}|$, hints for new physics in semitauonic decays, and Standard-Model predictions for flavor-changing-neutral-current processes: $B\to P\nu\bar{\nu}$ and $B\to P\ell^+\ell^-$, where $P$ denotes a pion or kaon.
I will also cover some details of the underlying lattice-QCD calculations at a nontechnical level.

The Weak Gravity Conjecture (WGC), in its original form, says that given an abelian gauge theory there should be at least one charged particle whose charge is bigger than its mass in Planck units. This has surprisingly powerful implications for the possibility of large-field inflation. In this talk I will explore some of the arguments linking the WGC to inflation before taking a closer look at a different question: which version of the WGC should we be trying to prove? I suggest that the right version to focus on is much stronger than the original WGC, and requires a sufficiently light particle to exist in every representation of the gauge group. I will present some evidence for this statement from both weakly-coupled string theory and semiclassical GR. This talk is based on work with Ben Heidenreich and Tom Rudelius (arXiv:1506.03447, 1509.06374, and further work in progress).