Graduate Student Lunch Club

When & Where

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.

About the Seminar

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.

 

  • February 7
    Evangelos Sfakianakis

    Density perturbations in Hybrid Inflation

    Hybrid Inflation models lead to a spike in the density power spectrum at small scales, compared to the CMB. I will describe a new method for treating perturbations in these models, which avoids treating the fluctuations of the "waterfall" field as if they were quantum perturbations about a classical trajectory. In this method only the waterfall field is quantized, while being treated as a free quantum field with a time-dependent m2, which evolves from positive values to tachyonic values. An extension to the case of multiple waterfall fields will be presented, where the leading order results take a particularly simple form. Finally I will discuss the possibility of the perturbations to act as seeds of black holes, potentially supermassive ones.

  • February 14
    Jeongwan Haah

    Quantum memory and an exotic discrete gauge theory

    Can collective phenomena help maintain quantum coherence? Topologically ordered systems are thought to be natural media on which quantum information storage and processing would be implemented, since they have an energetically protected and locally inaccessible subspace of states. However, when thermal fluctuations are considered, the energetic protection is not sufficient to achieve reliability on a macroscopic time scale. Can we find a system that protects the quantum coherence better?

    In this talk, I will explain a three-dimensional lattice spin model, which can be viewed as a Z2 lattice gauge theory, motivated by the question above. The model has a degenerate ground-state subspace that is separated by an energy gap from excited states, and admits point-like excitations. The ground-state subspace is topologically ordered in the sense that there is no local observable that can distinguish two different ground states. Exotic is that the point-like excitations do not acquire any hopping term under small but arbitrary perturbations. The ground state degeneracy under periodic boundary conditions is an interesting number-theoretic function of system size. There is an infinite family of system sizes such that the degeneracy grows as exponential of linear system size, but for a different choice of system sizes the degeneracy is simply 4. Despite its new properties, the model is different from a conventional lattice gauge theory by a microscopic detail of gauge transformations.

  • February 21
    Stefan Meinel

    Beautiful particles

    One of the major experiments at the Large Hadron Collider is dedicated to the study of beauty quarks. These quarks have a mass equal to about five times the proton mass, and play a key role in searching for physics beyond the Standard Model. In this colloquium, I will give an elementary introduction to the different types of quarks and explain how the weak force can change one type into another. By studying rare decays of beauty quarks with high precision, we hope to reveal new fundamental physics. The challenge is that quarks are also subject to the strong interactions with gluons, and are bound inside hadrons. I will show how one can use supercomputers to reliably calculate these strong interactions and understand the data from LHCb and future experiments.

    Pizza will arrive at 12, and the talk will begin at 12:10.

  • February 28
    Jonathan Walsh

    How do we calculate properties of jet substructure?

    I'll describe a physical way to understand factorization, specializing to the case of nearby jets (or subjets). Factorization at the level of amplitudes gives a simple way to calculate many jet properties, and I will also show how this may be applied to do NLO calculations in full QCD. As an example, I will show how these techniques may be used to calculate a NNNLO contribution to the Higgs cross section.

    Pizza will arrive at 12, and the talk will begin at 12:10. Faculty and post-docs are welcome.

  • March 7
    Aditya Pathak

    Kinematic Extraction of Short Distance Top Mass

    Mass of top quark is currently measured up to an accuracy of about 1 GeV. The current top mass measurements at hadron colliders suffer from a lack of rigorous field theoretically well defined relationship between the experimentally measured value and the Lagrangian top mass parameter, m_t, which depends on the renormalization scheme used. I will describe an event shape observable for top mass determination which, through the use of a factorization framework, provides an organizational way of including perturbative corrections and yields a measurement in a well defined top mass scheme. I will try to keep the talk at a level which requires minimal knowledge of quantum field theory.

    Pizza will be served. Faculty and post-docs are welcome.

  • March 14
    Ethan Dyer

    Monopoles and Confinement in Three Dimensions

    will give an introduction to monopoles and the role they play in confinement of three dimensional gauge theories. I will discuss ongoing work studying properties of monopoles in theories with large amounts of matter.

    Pizza will be served. Faculty and post-docs are welcome.

  • March 21
    Andrey Sadofyev

    Chiral effects and physics of chiral media

    We will discuss chiral media with a non-vanishing chiral chemical potential. In such systems there are macroscopic manifestations of chiral anomaly which go beyond classical electrodynamics. These phenomena result in IR instability of such systems and on other hand add constraints to hydrodynamic description of them. I will try to make basic overview of the topic staying at the level of simple concepts.

    Pizza will be served. Faculty and post-docs are welcome.

  • April 4
    Matthew McCullough

    Searching for Beyond the Standard Model Higgs Signals Beyond Leading Order

    I will discuss ideas to look for the presence of new fields or interactions beyond the Standard Model in the Higgs sector using effects which show up at next-to-leading order, rather than at leading order.

    Pizza will be served. Faculty and post-docs are welcome.

  • April 11
    Jaehoon Lee

    Old but new method for studying CFTs

    Conformal symmetry is a powerful symmetry that has application to the real world phenomena. Although the basis and core idea of conformal field theories were established in early 80s, understanding of CFTs in higher dimension(D>2) was limited. Only recently, new ways to exploit constraints in CFTs was understood for higher dimensional CFTs. In particular, the constraints come from unitarity and crossing symmetry of 4-pt functions. In this talk, I'll describe, using the simplest example, how one can study properties of a CFT using unitarity and crossing symmetry.

    Pizza will be served. Faculty and post-docs are welcome.

  • April 18
    Sam Johnson

    Catching up with Lenny

    I will attempt to summarize in a pedagogical way the three most recent (already quite pedagogical) articles of Leonard Susskind. In 1311.3335, 1311.7579, and 1402.5674, Susskind fleshes out a proposal of his and Maldacena's, ER=EPR, which was motivated originally as an alternative solution to the AMPS ("firewall") paradox as presented in 1207.3123. The ER=EPR conjecture proposes that quantum entanglement and non-traversable wormholes are two sides of the same coin. This proposal is only schematic, and several unusual mechanisms are developed and invoked in order to put it on firmer ground, or at least make it more plausible: we will meet such strange objects as "timefolds" and the "complexity horizon." The playful novelty of these ideas--as well as the many yet-to-be-explored relations to holographic entanglement entropy--make them well worth getting to know. The talk will be at a conceptual, as opposed to detailed, level. There will be many pictures. There are no prerequisites save QM and GR, so I encourage all interested to attend. As I am not an expert in this field, I expect a lively contribution from the audience members who know more than I do.

    Pizza will be served. Faculty and post-docs are welcome.

  • April 25
    Elizabeth Crosson and Cedric Lin

    Different Strategies for Optimization with the Quantum Adiabatic Algorithm

    We randomly generated a large ensemble of instances of MAX 2-SAT at n = 20 bits, and numerically simulated the performance of the Quantum Adiabatic Algorithm. We found three strategies which consistently increase the success probability for the hardest instances in our ensemble: decreasing the overall evolution time, initializing the system in excited states, and adding random local Hamiltonian terms to the middle of the evolution path.

    Pizza will be served. Faculty and post-docs are welcome.

  • May 2
    Mark Hertzberg

    Inflation and Gravity Waves

    I will provide a pedagogical overview of cosmological inflation, including its motivations and successes. I will describe the basic field theory for inflation and describe in some detail the computation of inflationary fluctuations, both density and gravity waves. I will outline the predictions of inflation and how models are constrained. Then I will discuss the recent claims of detection of B-modes by BICEP; its implications for gravity waves, inflation, and fundamental physics

    Pizza will be served. Faculty and post-docs are welcome.

  • May 9
    Nicholas Rodd

    An Excess in the Inner Galaxy: Understanding a potential Dark Matter Signal

    Recent work has confirmed the presence of a gamma-ray excess in data from the Fermi Space Telescope extending at least 10 degrees from the Galactic Center. In this talk I will describe recent progress in characterizing this signal by using photons with the highest quality angular reconstruction. I will outline the case for a dark matter origin of the signal, but temper this with a retelling of the story of the Fermi Bubbles, which shows there can still be unexpected astrophysics in the Milky Way. Finally I will give a brief overview of the prospects for looking for this signal in dwarf spheroidal galaxies.

    Pizza will be served. Faculty and post-docs are welcome.

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