##### When & Where

The CTP Lunch Club meets every Friday at noon in the Cosman seminar room, 6C-442 (provided that there are sufficient speakers). A light lunch will be provided begining at 11:50am (usually pizza, however some other options may be explored).

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, Jae Hoon Lee at jaehlee_at_mit[dot]edu, Josephine Suh at sjsuh_at_mit[dot]edu and Mindaugas Lekaveckas at lekaveck_at_mit[dot]edu.

• February 12
Andrew Lutomirski

Quantum Money

Quantum mechanics allows bizarre kinds of cryptography. I'll tell you what quantum cryptography is and how we might be able to make quantum money someday.

• February 19
Nabil Iqbal

Holography and Condensed Matter Physics

A great deal of recent research has focused on applications of string theory-inspired ideas to problems that appear to have nothing to do with quantum gravity. I will give a string-theory-free introduction to these holographic ideas and explain why using black holes to study ("strange") metals is a fun and potentially even useful thing to do.

Post-docs are welcome.

• February 26
Alexander Turbiner

Quartic oscillator $ℋ$ = d2dx2 + m2 x2 + g x4 (m2> 0 - an harmonic oscillator, m2<0 - double well) is one of the most important problems of quantum mechanics, which appears in different physical sciences. A simple method which combines the perturbation theory, WKB approximation and a feature of tunneling in their appropriate domains of applicability is proposed. The lowest eigenvalues found in this method provides 9-11 significant digits for any -20 ≤ m2 ≤ 20. Presented method is more accurate conceptually than the instanton calculus for the exponentially small energy gaps.

• March 5
Olaf Hohm

Massive Gauge and Gravity Theories in 3D

I give a pedagogical introduction into gauge theories in 3D that have massive excitations despite the fact that the gauge symmetries are unbroken. Following 0911.3061, I present a systematic way to construct theories of this type, which include topologically massive gravity' and new massive gravity'. The latter two have attracted attention in particular due to their possible relevance for AdS/CFT dualities, and the recent developments are reviewed.

• March 12
Si-Hui Tan

Quantum Hypothesis Testing

I shall discuss quantum hypothesis testing as a means of interpreting outcomes of quantum measurements. Some interesting questions in quantum hypothesis testing are: How does the geometry of quantum states affect the outcome of these tests? What are the differences between classical and quantum theory? Can we construct the optimal measurement? After motivating the topic, I shall give some examples of optimal and near-optimal measurements in simple quantum optical setups.

• April 9
Christiana Athanasiou

Searching for the QCD Critical Point

Mapping the QCD phase diagram is one of the main goals of heavy-ion collision experiments. The QCD critical point is one of the distinct features of the phase diagram but locating it from first principles is very challenging. A characteristic experimental signature of the critical point is the divergence of fluctuations, for example, of particle multiplicities. I will be describing how one can use fluctuation observables in heavy-ion collisions in order to search for the critical point.

• April 16
Koushik Balasubramanian

Holography for Non-relativistic Physics

The AdS/CFT correspondence is an equivalence between a relativistic conformal field theory (CFT) and gravity in higher dimensions. Recently, this correspondence has been used to model strong coupling phenomena in condensed matter systems. Some of these systems exhibit relativistic dispersion relations and the dynamics of such systems can be described by relativistic CFTs. There are many systems that are described by non-relativistic scale-invariant theories. A lot of these systems can be experimentally realized in laboratories. There is a prospect of getting insight into strong coupling phenomena observed in these experiments using this holographic equivalence.

I will present a brief review of some recent work on holographic description of such non-relativistic scale-invariant theories.

Postdocs and faculty are welcome.

• May 7
Mustafa Amin

Inflaton fragmentation into oscillons

Inflaton fragmentation at the end of inflation can lead to a very inhomogeneous universe on sub-horizon scales. I will discuss the emergence of long lived, localized lumps (oscillons) of the inflaton field during this period. These non-topological, pseudo-solitons tend to take up a large fraction of the energy density of the inflaton. For a class of models, I will derive their individual characteristics and provide estimates for their cosmological number densities. I will briefly discuss implications for the early universe and possible observational consequences.

Note: This is the same talk I gave two weeks ago for the MIT/CfA/Tufts Cosmology seminar. Faculty and postdocs are welcome.

• May 21
Carola F. Berger

Feynman versus Witten: Why parts of your QFT textbook may soon be outdated

Since the 1940s, Feynman diagrams have been used to calculate scattering amplitudes perturbatively. However, despite a lot of progress and the invention of a host of ingenious tricks to tackle the computations at one and higher loops, these traditional methods have only slowly yielded results that are especially relevant at the LHC. Many processes at the LHC have high-multiplicity final states, and these processes need to be known as precisely as possible in order to distinguish new physics signals from Standard Model backgrounds. In this talk I will present new methods for the calculation of scattering amplitudes at tree level and one loop, which are based on reusing previously-computed on-shell amplitudes instead of off-shell, gauge-dependent Feynman diagrams. If time permits I will show some brand-new results for vector boson + n jet production ( n >= 3 ) at next-to-leading order that were obtained with the computer library BlackHat, which is based on these on-shell techniques.

Further reading: C. F. Berger, D. Forde, arXiv:0912.3534, Ann Rev Nucl Part Sci, vol 60 (2010), in press. Faculty and postdocs are welcome.

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