Organizers: Cindy Keeler and Nausheen Shah
Arthur Lipstein (Oxford): "From dlogs to dilogs" | Sep 12
In this talk, I will describe a new form of hidden simplicity in the planar scattering amplitudes of N=4 super-Yang-Mills theory, notably that the loop integrands can be expressed in dlog form. I will explain how this form arises geometrically from computing the scattering amplitudes using a holomorphic Wilson loop in twistor space. I will also describe a systematic method for evaluating such integrals and use it to obtain a new formula for the 1-loop MHV amplitude. These techniques can be extended to higher loop amplitudes and may lead to a simple and efficient method for computing scattering amplitudes more generally.
Yue Zhao (SLAC): "Search for signatures of dark matter induced nucleon decay" | Sep 18
If dark matter carries baryon and/or lepton number, a DM particle may annihilate with a nucleon by flipping to anti-DM. We introduce a model where DM is asymmetric and carries B and L as -1/2. It can annihilate with a nucleon to meson, lepton and anti-DM. Such signal may be observed in proton decay experiments, similar signal has been studied in detail in arXiv:1008.2399, though in a different channel. If DM is captured in the Sun, the DM induced nucleon decay could generate a large flux of neutrinos, which could be observed in neutrino experiments. Furthermore, the anti-DM particle in the final state obtains a relatively large momentum (few hundred MeV), and escape the Sun. These fast anti-DM particles could also induce interesting signals in various ground experiments.
Miguel Paulos (Brown): "Exploring Exotic Production of the 126 GeV Higgs" | Oct 2
Brian Batell: "Searching for Light Dark Matter at Neutrino Factories" | Oct 23
I will describe a new way to search for dark matter using an intense proton beam - target - detector setup, such as those used to study neutrino oscillations. This gives new motivation to experiments like MiniBooNE, MINOS, MicroBooNE, NOvA, LBNE and a future Project X facility. A specific proposal to perform the first search of this kind at the MiniBooNE experiment at Fermilab will be presented.
David Pinner (Berkeley): "BBN and the Unnatural Weak Scale" | Oct 30
The discovery of a perturbatively-coupled, 125 GeV Higgs, together with the absence of LHC signals for supersymmetry, places the principle of naturalness under tension. In this talk I will discuss the possibility that the weak scale is unnatural, with its value determined environmentally in the landscape. In particular, this environmental selection may be driven by BBN: as the weak scale is increased, the abundance of Hydrogen in the early universe is rapidly depleted. That our own universe contains an O(1) fraction of primordial Helium arises as a conspiracy among the weak scale, the neutron-proton mass difference, and the planck scale.
Jacob Bourjaily (Harvard): "Scattering Amplitudes, Unitarity and the Positve Grassmannian" | Nov 6
In recent years, a complete reformulation of perturbative quantum field theory has been found for certain theories. Although a similar reformulation is likely to exist for any quantum field theory, it is exceptionally simple in the case of planar, maximally supersymmetric Yang-Mills. I will (briefly) review this new formulation, describing the connections between certain field-theoretic quantities called `on shell diagrams' and a space known as the `positive Grassmannian', how both can be characterized combinatorially, and how the entire S-matrix can be defined in terms of these combinatorial objects. I will then describe how these ideas can be applied to teach us about multi-loop amplitudes, and some surprising new features that appear at 2-loops and beyond, even for planar N=4 super Yang-Mills.
Debajyoti Sarkar: "Black hole formation process at the correspondence point" | Nov 13
We study the process of bound state formation in clusters of Dp- brane collision and Dp shell/ Membrane collapse processes. We consider two mechanisms for bound state formation. The first, operative at weak coupling in the worldvolume gauge theory, is creation of W-bosons. The second, operative at strong coupling, corresponds to formation of a black hole in the dual supergravity. These two processes agree qualitatively at intermediate coupling, in accord with the correspondence principle of Horowitz and Polchinski. We show that the size of the bound state and timescale for formation of a bound state agree at the correspondence point, along with other relevant thermodynamic quantities. The timescale involves matching a parametric resonance in the gauge theory to a quasinormal mode in supergravity. Work based on 1303.7278 and 1306.3256.
Liam Fitzpatrick (Stanford): "Wilsonian and Large N Approaches to Non-Fermi Liquids" | Nov 20
We study the problem of metals near a quantum critical point using a local Wilsonian effective field theory of Fermi surface fermions coupled to massless boson (i.e. order parameter) fields, and integrating out only high energy boson and fermion modes. Below the upper critical dimension of the theory (d=3 spatial dimensions), we find new fixed points in which the bosons are described by the Wilson-Fisher fixed point and are coupled to a non-Fermi liquid metal. We describe different behaviors of the theory in various large N limits.
Stefania Gori (Perimeter): "Almost invisible electroweakinos" | Dec 4
LHC started to test directly produced electroweak particles in the multi-hundred GeV range, if they decay to a long lived massless particle. Scenarios with a smaller mass splitting are instead much more challenging to be probed. In this talk, after a brief review of models with a compressed spectrum, I discuss the several techniques one could use to test scenarios with a mass splitting in the range (0 - 40) GeV. In particular, I will focus on the role of a relatively hard initial state radiation jet. Some emphasis will also be dedicated to the intriguing possibility of having production of electroweak particles through the decay of the 125 GeV Higgs boson.
