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, Ben Elder at belder13-at-mit[dot]edu and Yinan Wang at wangyn-at-mit[dot]edu.

- September 18, 12pm

Yifan Wang

Supersymmetry constraints from superamplitudes

Supersymmetry puts strong constraints on the dynamics of supersymmetric field theories and supergravities. In particular, certain higher derivative couplings in the quantum effective action of these supersymmetric theories turn out to have intriguing moduli independence. In this talk, we will discuss a simple method to derive such constraints using basic tools such as unitarity (factorization) and supersymmetry in the language of superamplitudes. The talk should be accessible even if you don’t have backgrounds in supersymmetry.

- September 25, 12pm

Alejandro Jenkins

Self-oscillation

A self-oscillator generates and maintains a periodic motion at the expense of an energy source without a corresponding periodicity. Small perturbations about equilibrium are negatively damped, leading to instability of the linear equations of motion. Non-linearity accounts for the steady-state oscillation and for the ability of coupled self-oscillators to exhibit spontaneous synchronization ("entrainment") and chaos. The theory of self-oscillators has achieved its greatest sophistication in control theory and in the theory of ordinary differential equations. I shall explain how an understanding better suited to the needs of engineers and physicists can be founded on considerations of energy, efficiency, and irreversibility.

After reviewing how forced and parametric resonances are described by energy flow into a driven oscillator, I shall explain how a simple example of self-oscillation (the swaying of the London Millennium Footbridge in 2000) results from positive feedback between the oscillation and an external energy source (the motion of pedestrians on the bridge). I shall explain how the nonlinearity of self-oscillators connects to entrainment and to the thermodynamic irreversibility of motors, before commenting on how this approach throws new light on concrete problems, like electromagnetic super-radiance and the maintenance of the Chandler wobble in geophysics.

This talk will be based on the review article A. Jenkins, Phys. Rep. 525, 167 (2013).

- October 16, 12pm

Yinan Wang

The total space of string geometries

I’ll be talking about a classification program of geometries used in F-theory compactification. I’ll mention some impacts on string phenomenology. Minimal mathematical details are involved. References: 0803.1194 (Denef’s lecture notes), 1412.6112, 1504.07689

- October 23, 12pm

Huaxing Zhu

Soft gluon approximation with loops

Soft gluon approximation, also known as eikonal approximation, has been an extremely useful tool for calculating hard scattering cross section in QCD, for both fixed order and resummed calculation. In this talk I will explain the usefulness of tree-level soft gluon approximation by an explicit example. Then I will briefly review the generalization of soft gluon approximation to loop level, using both diagramatic method and effective field theory method. I will then talk about an recent calculation of a universal two-loop soft factor, which is required for the application of soft gluon approximation at two-loop level. Finally, I will discuss the implication for factorization violation at amplitude level from the two-loop soft gluon approximation.

- October 30, 12pm

Lina Necib

Indirect detection signals from asymmetric Dark Matter

In this talk, I will present an asymmetric Dark matter model with potential indirect detection signals, including the GC excess. This model portrays a feature of "shared asymmetry" in which the mechanism of producing the original asymmetry of the baryons is related in a novel way to that of the dark matter.

- November 6, 12pm

Jasmine Brewer

Evidence for non-hydrodynamic transport in unitary Fermi gases

Transient, non-equilibrium dynamics cannot be described within the framework of (Navier-Stokes) hydrodynamics and is therefore characterized by non-hydrodynamic transport properties. In this talk, I will discuss the unitary regime of Fermi gases and motivate the search for non-hydrodynamic modes in this system. I will then discuss the presence of non-hydrodynamic modes in strongly coupled fluids described by black holes, and non-hydrodynamic transport as it emerges in kinetic theory and beyond-Navier-Stokes hydrodynamics. Finally I will present the results of a re-analysis of previously published experimental data on collective oscillations that is suggestive of the presence of non-hydrodynamic modes in unitary Fermi gases. Reference: 1508.01199

- November 13, 12pm

Andrey Sadofyev

Anomalous Transport and Dissipation

I'm going to make an educational overview of the novel transports in chiral media caused by the axial anomaly. They are a macroscopic manifestation of the quantum phenomenon (the anomaly of QFT) and in this sense similar to the superfluidity and superconductivity. The set of anomalous kinetic coefficients is quite universal and keeps the same form for a large class of systems. They also appear to be of non-dissipative nature in wide range of regimes. We will try to investigate how universal they are and to get to their dissipative properties.

- November 20, 12pm

Phiala Shanahan

Strangeness and charge symmetry violation in the nucleon from lattice QCD

Strange-quark properties of the nucleon, arising entirely from non-valence quark effects, are a key testing-ground for our understanding of nonperturbative QCD. I will describe how numerical (lattice) simulations of QCD can be combined with effective field theory and experimental results to precisely determine these effects for the case of the electromagnetic form factors. I’ll start with some brief background about lattice QCD and chiral perturbation theory.

- December 4, 12pm

Markus Schulze

Fully differential NNLO QCD computation for Higgs+jet at the LHC

I will present results for the fully differential Higgs plus jet cross section at NNLO in perturbative QCD which include decays of the Higgs boson to electroweak gauge bosons. I will review some technical details of the novel computation framework, present kinematic distributions for a realistic final state and compare our findings with the experimental measurements.

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