Graduate Student Lunch Club

When & Where

The CTP Lunch Club meets at 12pm in the CTP Cosman seminar room every Friday (provided that there are sufficient speakers). A light lunch will be provided (usually pizza, however some other options may be explored).

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.

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, Nikhil Raghuram at srivat91-at-mit[dot]edu or Chih-Liang Wu at cliang-at-mit[dot]edu.

  • February 10, 12pm
    Aditya Pathak

    Precision Top Mass Determination at the LHC with Jet Grooming

    Top mass is one of the most important Standard Model parameters that is being measured at the LHC. The measurement is currently limited by O(1 GeV) theory uncertainty due to our inability to precisely specify mass scheme for the top mass parameter built in the Monte Carlo simulations used at the LHC. We show how the top mass can be extracted kinematically using cross sections for event shapes observables calculated using effective field theory methods. With the help of Soft Drop grooming to the level that does not disturb the radiation that can modify the top mass definition, while still isolating the top jet, we obtain a distribution that is only mildly sensitive to the underlying event and initial state radiation. The data from LHC for top jets can thus be made to look very similar to e+e- collisions. We derive, for the first time, an effective theory analysis for Soft Drop groomed top jets.

  • March 10, 12pm
    Nikhil Raghuram

    Matter in Transition

    In certain supergravity theories coming from string compactifications, there are interesting transitions that change the representation content of the theory without changing the gauge group or other parts of the spectrum. For example, in a theory with SU(3) gauge symmetry, matter in the adjoint and singlet representations can be exchanged for matter in the symmetric and fundamental representation. Such transitions involve passing through superconformal field theories at the transition point. In this talk, I will discuss how these transitions work in 6D supergravity theories constructed with F-theory. I will first review some aspects in 6D supergravity and F-theory. I will then describe the superconformal transition points and give an example of a matter transition. Based on 1512.05791 with Lara Anderson, James Gray, and Wati Taylor.

  • March 17, 12pm
    Andrey Sadofyev

    Chiral vortical effect for bosons

    Macroscopic manifestations of the axial anomaly attracted significant attention in the literature. In a chiral medium, the anomaly results in currents along local angular velocity and magnetic field: chiral effects. These anomalous phenomena considerably modify the dynamics of the system and provide a new example of a macroscopic transport with a microscopic (quantum) origin. I'll give an overview of this field completed with our recent results. While anomalous transport is usually discussed in media with massless fermionic constituents, we predict a novel class of chiral effects for higher spin particles. In particular, I'll derive an anomalous contribution to the spin current of vector bosons caused by the medium rotation.

  • March 24, 12pm
    Usman Naseer

    One loop tests of supersymmetric gauge theories on spheres

    In recent years there has been extensive progress on exact computation of partition functions for supersymmetric quantum field theories on spheres via supersymmetric localization. However such progress for certain 𝒩=1​ supersymmetric theories remains elusive. After briefly reviewing the procedure of supersymmetric localization I will discuss difficulties in extending these results to 𝒩=1​ theories. I will present a conjecture for the form of partition function for these theories and perform various consistency checks. Based on: arXiv:1703.07435

  • April 14, 12pm
    Hongwan Liu

    Enabling Forbidden Dark Matter

    The thermal relic density of dark matter is conventionally set by two-body annihilations. We point out that in many simple models, 3 to 2 annihilations can play an important role in determining the relic density over a broad range of model parameters. This occurs when the two-body annihilation is kinematically forbidden, but the 3 to 2 process is allowed; we call this scenario "Not-Forbidden Dark Matter". We illustrate this mechanism for a vector portal dark matter model, showing that for a dark matter mass in the MeV - 10 GeV range, 3 to 2 processes not only lead to the observed relic density, but also imply a self-interaction cross section that can solve the cusp/core problem. This can be accomplished while remaining consistent with stringent CMB constraints on light dark matter, and can potentially be discovered at future direct detection experiments.

  • April 21, 12pm
    Gherardo Vita

    Subleading Hard Scattering Operators in SCET

    I'll give an introduction about SCET, its application for computing cross sections at the LHC and factorization at leading and subleading powers in SCET. I'll present a complete basis of power suppressed operators for Higgs production in gluon fusion classifying all operators which contribute to the amplitude at Next to Leading Power and identifying the subset of operators which contribute in the cross section at this order. I'll show how helicity selection rules significantly simplify the construction of the operator basis and I'll give some examples of the matching calculations needed to determine the tree level Wilson coefficients of these subleading operators.

  • May 12, 12pm
    Sarah Geller

    Total Mass of a Patch of a Matter-Dominated Friedmann—Robertson—Walker Universe

    In 1975, Cosmologist Ya. B. Zeldovich calculated the total mass of a patch of a semiclosed universe described by the Friedmann—Robertson—Walker (FRW) metric to argue that the total mass of a matter-dominated closed universe vanishes. By considering a spherically symmetric patch of an open FRW universe as a manifold with boundary glued smoothly to a Schwarzschild spacetime, we have carried out a calculation to determine the total mass of matter dominated open universes and compared our results to those expected from calculations in newtonian cosmology. After briefly reviewing the mathematics of embedded hypersurfaces and the junction conditions which govern the gluing procedure, I will present the results of our calculations and their interpretations and will comment on further calculations in which we are engaged.

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