The CTP Lunch Club meets every Friday at noon in the Cosman seminar room, 6C-442 (provided that there are sufficient speakers). Pizza will be provided.
The seminars are designed for graduate students and should be accessible to all students. First year students are particularly encouraged to attend so that they may learn about research being performed in the CTP. The goal is learning, and to encourage participation, the seminars will be for students only.
Email notification of the club will be sent to the ctp-all, ctp-postdocs and ctp-students email lists as appropriate. If you wish to speak, or have suggestions about speakers and/or possible workshop topics, please contact the organizers, Ian Moult at ianmoult[at]mit[dot]edu, Lina Necib at lnecib[at]mit[dot]edu, and Sam Johnson at samj[at]mit[dot]edu.
The Higgs and SUSY walk into a bar: ouch.
The discovery of the Higgs boson at 125 GeV, and the non-observation of any supersymmetric particles at the LHC, has forced us to reconsider our assumptions about supersymmetry. Very general arguments suggest we cannot have our cake and eat it too: either the weak scale is fine-tuned, or our simplest models of SUSY-breaking in the MSSM are wrong, or both. Even after abandoning naturalness, we should require a concrete model of the Higgs sector: in this sea of non-observations and limits, the Higgs mass is our one positive data point. Using auxiliary gauge mediation as a guiding example, I will discuss these issues pedagogically and illustrate some interesting features of gauge-mediated supersymmetry breaking. Knowledge of supersymmetry is very helpful, but not required; questions are STRONGLY encouraged.
Faculty and post-docs are welcome.
A Possible Dark Matter Signal in the Gamma-Ray Sky
Dark matter is one of the most solid pieces of evidence for physics beyond the Standard Model; however, at present we have only detected it via its gravitational interactions. I will first give a pedagogical review of what we know about dark matter and how we know it. I will then discuss a spectral feature found in gamma-ray data from the Fermi Gamma-Ray Space Telescope, and its interpretation as a possible signature of dark matter annihilation. I will explain how the potential signal was extracted from the data, and the current open questions regarding its interpretation. No background knowledge of dark matter or high-energy astrophysics is assumed; questions are strongly encouraged.
Anderson Localization explained simply by a simple person
I will try my best to explain what Anderson Localization is, how it arises, and what it explains. Since I am no expert, I may or may not fail on any one of those three fronts. Viewer beware.
Generalization of Goldstone's Theorem Without Lorentz Invariance
Quantum Adversary (Upper) Bound
I discuss a technique - the quantum adversary upper bound - that uses the structure of quantum algorithms to gain insight into the quantum query complexity of Boolean functions. Using this bound, I show that there must exist an algorithm for a certain Boolean formula that uses a constant number of queries. Since the method is non-constructive, it does not give information about the form of the algorithm. After describing the technique and applying it to a class of functions, I will outline quantum algorithms that match the non-constructive bound.
The Schwinger effect and the geometry of entanglement
Is there a connection between entanglement and space-time geometry? Recently Maldacena and Susskind proposed that entanglement is associated with Einstein-Rosen bridges, also called "non-traversable wormholes". I will approach this question by constructing a holographically dual description of a maximally entangled pair of quarks, using the Schwinger effect at large 't Hooft coupling \lambda in N=4 supersymmetric Yang Mills theory. We shall see that there is indeed a wormhole associated with the dual of the the pair of quarks, at least when they are causally disconnected.
Bulk Entanglement Spectrum Reveals Quantum Criticality within a Topological State
A quantum phase transition is usually achieved by tuning physical parameters in a Hamiltonian at zero temperature. We will demonstrate that the ground state of a topological phase itself encodes universal properties of its transition to a trivial phase. To extract this information, we introduce a partition of the system into two subsystems both of which extend throughout the bulk in all directions. The resulting bulk entanglement spectrum has a low-lying part that resembles the excitation spectrum of a bulk Hamiltonian, which allows us to access a topological phase transition from a single wavefunction by tuning either the geometry of the partition or the entanglement temperature. As an example, this remarkable correspondence between topological phase transition and entanglement criticality is rigorously established for integer quantum Hall states. (with Liang Fu, arXiv: 1305.1949)
Entanglement entropy and the number of degrees of freedom
Entanglement entropy is a useful probe of the ground state properties of a quantum system. We discuss its salient features including the famous area law. For quantum field theories entanglement entropy is divergent, however it has a universal piece that serves as a useful tool for calculating the number of degrees of freedom. If time permits we discuss some intriguing connections with gravity.
Faculty and post-docs are welcome.
Supersymmetric deformations of maximally supersymmetric Yang-Mills theories
This is going to be an introductory talk on the deformation theory of maximal super Yang-Mills (from zero to eleven dimensions). In supersymmetric field theories, supersymmetry generally constrains the possible terms that can appear in the effective theory Lagrangian. For maximal super Yang-Mills, one can classify “all” such terms as deformations of the bare Lagrangian while preserving all of the 16 supersymmetries. Such classification program can be done in the mathematical language of homological algebra and deformation theory. I will try to outline the program, the outcome, and hopefully explain some of the details.
Faculty and post-docs are welcome.
Jets (without Jets)
Jets play a key role in collider physics as they are the closest objects to partons that we can define. I will give a general overview of the current approaches used to define jets, and I will introduce a new paradigm to think about jets that I and Jesse proposed. In a standard approach a jet is typically defined as a cluster of particles. In our approach one can turn a broad class of jet-based observables into event shapes, that do not require any clustering. I will discuss features and potential applications of this approach.
Postdocs and faculty are welcome.
Fun with Goldstini
Since the hidden sector(s) in which SUSY-breaking takes place are very weakly coupled to the supersymmetric standard model (SSM), it is difficult to glean any information about them. One exception occurs when SUSY-breaking takes place in multiple hidden sectors, resulting in multiple light 'goldstini' to which SSM particles can decay. Such models can exhibit extremely unconventional phenomenology, of which I will discuss two examples. The first, relevant for the LHC, features a bino that can almost exclusively decay to a Higgs and a goldstino. The second, relevant for indirect detection of dark matter, features a two-body decay of a goldstino to photon and gravitino with substantial branching fraction.
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