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 begining at 11:55am.

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, Michael Crossley at mikeyc[at]mit[dot]edu, Paolo Glorioso at paolo_g[at]mit[dot]edu, and Yifan Wang at yifan[at]mit[dot]edu.

 

  • September 23
    Teppo Jouttenus

    I will be talking about my work on jets at the LHC. I guarantee that the talk will be accessible to beginning graduate students. Otherwise you can throw tomatoes at me.

    The beginning will be an introduction to LHC physics at a level somewhere between what is given at research seminars (1 min) and departmental colloquia (>= 10 min). I will continue to explain why we need to understand QCD to answer most of the major questions at the LHC and what we have been working on to do our part."

    Graduate students and postdocs welcome.

  • October 7
    Rahul Nandkishore

    Chiral superconductivity from repulsive interactions in doped graphene

    We show that the d + id superconducting state, which has no known experimental realizations, can be realized in strongly doped graphene. We consider graphene that is doped to the M point of the Brilliouin zone, where the Fermi surface nesting and the divergent density of states can produce interaction driven instabilities to exotic phases with high energy scales. Analyzing the competition between various ordering tendencies within a renormalisation group framework, we find that the leading instability is to d-wave superconductivity, for any choice of weak repulsive interactions. The dx2 −y2 and dxy superconducting states have the same critical temperature Tc . Analysis of the competition of these orders below Tc reveals that both orders co-exist to produce d + id superconductivity

  • October 12
    Christopher Lee

    Skinny Jets and Large Logs: Resumming Perturbative Series Effectively

    Jets of hadrons are ubiquitous signatures for physics beyond the Standard Model and important probes of the strong interactions themselves. Calculating jet cross sections in perturbation theory is faced, however, with a challenge. At fixed orders in the strong coupling \alpha_s, perturbative predictions grow logarithmically to infinity as jets become narrower or softer. Effective field theory (EFT) and the renormalization group (RG) come to the rescue, however, and provide tools to resum these large logs to all orders in \alpha_s, resulting in finite, physical predictions.

    This talk is a crash course in using EFT and the RG to sum logs of jet invariant mass distributions to arbitrarily high orders in perturbation theory. It will also include an introduction to a class of logs, non-global logs (NGLs), that appear in more exclusive jet cross sections and that have so far eluded successful resummation in QCD. I will tell you about our recent progress uncovering tantalizing hints towards resumming NGLs.

    Students, postdocs, and faculty are welcome.

  • October 21
    Iain Stewart

    Jet Physics from Static Charges in AdS

    High energy collisions at the LHC probe the short distance structure of nature, and then hide the results amongst a pattern of highly energetic jets. The soft interactions of these jets are described by operators involving straight Wilson lines. In this talk I describe a simple setup that can be used to explore these interactions. With a special set of coordinates we map the Wilson lines into static charges on an AdS space. Many of the interesting properties of the anomalous dimensions of multi-Wilson line operators are easily understood from this point of view. For example, a classical energy computation in AdS yields the one-loop anomalous dimension. Motivated by this I introduce a new class of gauges, dubbed conformal gauges, which avoid mixing in R x AdS, and show how they simplify computations at two loops and beyond.

    Everyone is welcome. The talk will be aimed at young graduate students and questions from students are particularly encouraged.

  • October 28
    Ben Freivogel

    Making Predictions in the Multiverse

    I will briefly discuss reasons to think that we are living in an eternally inflating multiverse. Then I will describe some successes of the theory, along with some important open questions.

    Postdocs are welcome.

  • November 4 *Note: This seminar starts at 3:30 p.m.*
    Massimo Porrati

    On the Unitarity of Critical Gravity and Other Higher-Derivative Theories

    I show a simple and efficient way to compute the scalar product between one-particle states in theories with higher time derivatives. As an application, I show that "critical" gravity in dimension larger than 3 is non-unitary, but that the spectrum of certain other higher derivative theories contains a unitary subsector.

    Everyone is welcome. We will be serving coffee, tea, cookies and cakes.

  • November 22 *Note: This seminar is on a Tuesday and starts at 11:45 a.m.*
    Hyeyoun Chung

    Tunneling between black hole configurations

    In this talk I will consider the problem of mixing by quantum tunneling between different multi-centered black hole configurations, which correspond to degenerate ground states of the theory, analogous to the degenerate ground states of the symmetric double well in elementary quantum mechanics. In particular, I will cover a certain set of multi-centered black hole solutions to a theory of gravity coupled to massless scalars and vectors sourced by electric and magnetic charges. These solutions are analogous to extremal Reissner-Nordstrom black holes. I will discuss approaches to computing the tunneling rates between different configurations in both the extremal Reissner-Nordstrom case and the case of the more complicated black hole solutions, and present preliminary results in this direction.

    Students, postdocs, and faculty are welcome.

  • December 2
    Daekyoung Kang

    Universal Relations for Strongly Interacting Atoms

    Strongly interacting atoms are one example of systems interacting through a large scattering length. They display therefore similar features to nuclear systems but are more easily accessible and controllable in experiments. The theoretical study of these systems is challenging due to the nonperturbative nature of the interaction. Recently discovered universal relations that hold for any state of the system are therefore very valuable. These relations for fermions with two spin states involve a quantity called the 2-body contact that is proportional to energy change due to change of the inverse scattering length. For the fermions, the contact can be interpreted as the probability for 2 particles being close together. In this talk I would like to discuss the EFT with contact interactions and the Operator Product Expansion with the EFT that are excellent tools to derive these universal relations. New universal relations for identical bosons that involve both 2- and 3-body contacts will also be discussed.

    Students, postdocs, and faculty are welcome.

  • December 9
    Yoni Kahn

    Locality and Unitarity in Theory Space

    Lower-dimensional systems can have higher-dimensional descriptions, with the most striking example being AdS/CFT: a d-dimensional CFT can be described by a (d+1)-dimensional gravitational theory. The fact that physics is local in the bulk coordinate is also striking, and we investigate in what sense a lower-dimensional theory "prefers" its higher-dimensional description to be local. Using the formalism of dimensional deconstruction, and using the scale of unitarity violation as a diagnostic of the health of a theory, we demonstrate a preference for locality in a toy example: 5-dimensional Yang-Mills compactified on a circle violates unitarity sooner when nonlocal interactions are included.

    Students, postdocs, and faculty are welcome.

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