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 11:50am.
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, Yonatan Kahn at ykahn[at]mit[dot]edu, Daniel Kolodrubetz at dkolodru[at]mit[dot]edu, and Daniel Roberts at drob[at]mit[dot]edu.
DarkLight: Dark Photons at the MeV scale
High-luminosity experiments are able to search for new physics at low energies, which could have evaded detection thus far due to very weak couplings to the Standard Model. The DarkLight experiment at Jefferson Lab is designed to search for a new U(1) vector boson A', a so-called "dark photon," in the mass range 10-100 MeV through its decay A' -> e^{+} e^{-}. In this talk, I will review the theoretical motivations for dark photon models, and describe how DarkLight is capable of searching for an invisibly-decaying A'. Along the way I will introduce some novel analysis techniques which may be useful for other high-luminosity searches. This talk will be suitable for first-year graduate students: only knowledge of relativistic kinematics and extremely basic quantum field theory (QED amplitudes and cross sections) is required.
Faculty and post-docs are welcome.
Hot carriers in graphene
Recent experiments suggest that hot carriers can persist for long times in graphene. We will show that both the proliferation of hot carriers in graphene and their influence on mesoscopic phenomena can arise in unexpected and sometimes dramatic ways. First, we argue that cooling in graphene is anomalously sensitive to disorder wherein a disorder assisted cooling process dominates cooling in graphene over a wide range of technologically relevant temperature scales. Second, we contend that the proliferation of hot carriers can dominate transport phenomena in graphene. In particular, we find that slow electron-lattice cooling conspires to produce a dramatic twist in the story of graphene's photoresponse and drag resistivity.
Faculty and post-docs are welcome.
The F-theorem
The F-theorem is the statement that the three-sphere "free energy" of a 3d CFT decreases under renormalization group flow. In this talk, I will motivate the theorem and do some explicit computations for free fields.
Faculty and post-docs are welcome.
Exploring Quantum Process Characterization
When trying to build a quantum computer, it is critical to understand the operations that are being applied to the system. For example, you may want to implement a unitary U, but the system actually performs an operation E. In this talk, I will describe procedures for characterizing unknown operations, discussing what parameters can be extracted, and with what level of accuracy.
Faculty and post-docs are welcome.
Clarifications of Anomaly Mediation
Anomaly-Mediated Supersymmetry Breaking is the most ubiquitous form of supersymmetry-breaking in supergravity theories, but has long been the source of much theoretical confusion. I will discuss some recent progress in elucidating anomaly mediation---most notably how one type of it ("gravitino mediation") can be entirely determined from the infrared symmetry structure of unbroken supergravity in AdS space. Faculty and post-docs are welcome.
Faculty and post-docs are welcome.
A Holographic Examination of Entanglement Entropy during Thermalization
Entanglement entropy in field theories is a quantity we would like to characterize as quantitatively as possible, yet for which we have very limited tools for calculating. In this talk I will describe simple holographic systems in which the entanglement entropy evolves in time from the vacuum to a thermal state, and discuss analytical results for the scaling of entanglement entropy in various regimes of time-evolution. By studying the geometry of extremal surfaces corresponding to entanglement entropy, we derive power and logarithmic laws in the initial and final stages of thermalization, and a distinctive scaling behavior during the bulk of thermalization.
Faculty and post-docs are welcome.
FERMI 130 GeV Line: Dark Interpretations
Earlier this year strong evidence was claimed for a 130 GeV gamma ray line from the galactic center in the FERMI telescope data. In the first half of the talk I will review the status of the evidence, including recent suggestions which call it into question. In the second half of the talk, under the bold assumption that the line is a genuine signature of dark matter, I will review some of the properties required of dark matter to explain the line and the general features of models proposed to explain it. This second half will include material from recent work with Francesco and Jesse (arxiv:1210.7817), which suggests that the line is more readily explained by dark matter "semi-annihilation" rather than the standard annihilation interpretation.
Faculty and post-docs are welcome
Primordial Perturbations in Multifield Inflation with Nonminimal Couplings
Nonminimal couplings induce a nontrivial ﬁeld-space manifold in the Einstein frame, and they also yield an eﬀective potential in the Einstein frame with nontrivial curvature. The ridges or bumps in the Einstein-frame potential can lead to primordial non-Gaussianities of observable magnitude. I will describe a covariant formalism to study perturbations in such models and present calculations of the primordial bispectrum for a specific set of parameters, as well as examine the multifield behavior of Higgs inflation.
Faculty and post-docs are welcome
This seminar will be held in the Pappalardo Room, 4-349.J-E-T-S, Jets, Jets, Jets!
Jets are collimated streams of particles ubiquitous in QCD which are a consequence of asymptotic freedom and approximate scale invariance. I'll give a history of the understanding of jets, how to define jets and how jets can be used as a probe of short distance physics.
Faculty and post-docs are welcome
Dissipation from fluctuations: quantum friction in moving objects
Quantum fluctuations manifest themselves in a variety of macroscopic effects. In the context of moving objects (an accelerating mirror, for example), these fluctuations give rise to dissipation and radiation. I discuss a general framework based on scattering theory, and some quantum optics, to understand and compute the radiation. Specifically I show that a neutral spinning object – with or without rotational symmetry – spontaneously emits photons.
Faculty and post-docs are welcome.
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