Skip to Content

Search: {{$root.lsaSearchQuery.q}}, Page {{$root.page}}

Winter 2011

Organizer: James Liu

 

Date Speaker Title Abstract
Jan 7 Hai-Bo Yu
(Michigan)
Turning off the Lights: How Dark is Dark Matter?  
Jan 14 Matthew Headrick
(Brandeis)
Entanglement, information, and holography

Ryu and Takayanagi have conjectured a simple formula for the entanglement entropy of an arbitrary spatial region in an arbitrary holographic field theory. This conjecture, which remains unproven, makes a number of interesting predictions. A rather dramatic one is that the mutual information between separated regions drops to zero at a finite separation. We will present independent evidence for this prediction in two-dimensional conformal field theories, based on calculations of entanglement Renyi entropies using both holographic and CFT techniques. The necessary background material from quantum information theory will be explained along the way.

Jan 21
Niayesh Afshordi
(Perimeter Institute)
Largest and smallest dark matter clusters, and what we can learn from them

A ubiquitous feature of cold dark matter paradigm is emergence of dark matter clusters (or haloes) on a large range of scales. Observational studies of these clusters can teach us a wealth of information, ranging from cosmology to particle physics. I first talk about largest of these clusters, and how they can teach us about cosmology. In particular, I will discuss how well linear growth of density perturbations can be tied to cluster number counts. I will then turn to dark matter clustering on small scales, and introduce a novel analytic framework to predict its properties. This leads to interesting signatures in dark matter direct and indirect detection experiments, and even pulsar timing observations.

Feb 4 Jure Zupan
(Cincinnati)
Minimal Flavor violation and experimental heavy quark anomalies

Recently two experimental results show deviations from standard model (SM) above 3 sigma. The CDF measured forward-backward asymmetry 3.4 sigma away from SM expectation. The D0 Collaboration reported a 3.2sigma deviation from the SMl prediction in the like-sign dimuon asymmetry. I will discuss the two anomalies assuming a particular solution to new physics flavor problem - Minimal flavor violation.

Feb 11 Michael Douglas
(Stony Brook)
Holographic dual of free field theory

The simplest possible example of AdS/CFT duaiity was proposed around 1999 by Sundborg, between free quantum field theory and a theory of gravity and higher spin fields developed by Vasiliev and others. Evidence has accumulated for it, most recently in work of Giombi and Yin, but as yet there is no proof. In the recent work arXiv:1011.4926 with Luca Mazzucato and Shlomo Razamat, we prove the duality between free quantum fields and a modified version of higher spin gravity, by re-interpreting the exact renormalization group.

Feb 18 Henriette Elvang
(Michigan)
Symmetry Restrictions of Candidate Counterterms in N=8 Supergravity

There has recently been renewed interest in the UV structure of loop amplitudes in perturbative N=8 supergravity in four dimensions. We explore the symmetries of prospective local counterterm operators in this theory by examining if their matrix elements satisfy the constraints of SUSY and R-symmetry Ward identities. This allow us to eliminate certain classes of operators as candidate counterterms. We impose further restrictions by studying compatibility with the spontaneously broken global E7(7)-symmetry of the theory; this is done with the help of soft-scalar theorems. The current status of N=8 UV finiteness/divergences will be summarized at the end of the talk.

Feb 25 Katrin Becker
(TAMU)
Higher derivative D-brane couplings from T-duality and scattering amplitudes

The Wess-Zumino coupling on D-branes in string theory is known to receive higher derivative corrections which couple the Ramond-Ramond potential to terms involving the square of the space-time curvature tensor. Consistency with T-duality implies that the brane action should also contain four-derivative couplings that involve the NS-NS B-field. T-duality is used to predict some of these couplings. Then I will describe string world-sheet computations which confirm the predicted couplings.

Mar 11 Jay Wacker
(SLAC)
Dipolarity: Using Color Information in Top Tagging

A new jet observable, dipolarity, is introduced that can distinguish whether a pair of subjets arises from a color singlet source. This observable is incorporated into the HEPTopTagger and is shown to improve discrimination between top jets and QCD jets for moderate to high pT.

Mar 18 Erich Poppitz
(Toronto)
Deformations, bions, and (de)confinement

Recent observations, first made in string theory, led to the realization that introducing various "deformations" (finite volume, appropriate double-trace operators...) allows for an analytic study of many nonperturbative aspects of arbitrary four-dimensional gauge theories. Notably, the confinement mechanism, the generation of mass gap, and, in some cases, chiral symmetry breaking can be studied in a theoretically controlled manner. In this talk, I will review: i) the ideas and tools involved, ii) the main results obtained so far in this approach and its limitations, iii) our understanding of its relation to other approaches to (non-)supersymmetric gauge dynamics, iv) ongoing and possible future work.

Mar 25 Jay Hubisz
(Syracuse)
SUSY digs up a buried Higgs

The Higgs boson may dominantly decay to 4 light jets through a light pseudo-scalar intermediary: h → 2η → 4j, making reconstruction at the LHC particularly challenging. We explore the phenomenology of such "Buried Higgs" scenarios in which the primary discovery channel of the Higgs is in cascade decays of superpartners. QCD backgrounds that would otherwise overwhelm the Higgs decay are suppressed by the requirement of high pT jets, and large missing transverse momentum that are the typical signatures of TeV scale supersymmetry. We also discuss utilizing jet substructure techniques to isolate the Higgs signal from hadronically decaying SM electroweak gauge bosons.

Apr 1 David Shih
(Rutgers)
Anomalous Dimensions of Double-Trace Operators from AdS/CFT

In this talk I will describe a new method for computing the leading-order anomalous dimensions of double-trace operators in 4d SCFTs with weakly-coupled gravity duals. This new method considerably simplifies previous approaches based on the four-point function. Studying a minimal toy model, I will show that for a range of parameters, the anomalous dimension of φ†φ can be positive. Finally, I will discuss the potential applications of this to SUSY model building.

Apr 5 Michael Schulz
(Bryn Mawr)
T-folds, Doubled Geometry, and the SU(2) WZW Model

Generalized compactifications of string theory relax the condition that there be a globally well defined space in the extra dimensions. We give up the usual distinction between a Riemannian manifold and other fields living on that manifold, so that the two become intrinsically intertwined. Such compactifications are the natural result of lifting generic gauging of lower dimensional supergravity theories to the full 10D string theory. But, what is the topological choice that *defines* such a string theory compactification? In my talk, I will advocate one possible answer: the "doubled geometry" seen simultaneously by left plus right moving string excitations. This geometry neatly packages the fields into purely metric degrees of freedom. Its topology unifies the traditional choice of spatial topology and magnetic flux into a single generalized choice. I'll begin with a simple motivating example, then describe the framework of Hull and Reid-Edwards for locally reconstructing physical from doubled geometry. Finally, I'll describe insights from applying this framework to the SU(2) WZW model, a simple soluble model which nevertheless exhibits interesting and surprising features.

Apr 8 Ted Jacobson
(Maryland)
Aspects of Aethereal Gravity

I will discuss deformations of general relativity incorporating a dynamical preferred rest frame (Einstein-aether theory) or absolute time function (Horava gravity). The talk will touch on a variety of topics, such as the relation between these theories, their stability, viability, cosmological features, black holes, and Hamiltonian structure.

Apr 15 George Sterman
(Stony Brook)
The t-tbar asymmetry and soft gluons

Measurements of top/anti-top asymmetries at the Tevatron has generated considerable interest recently. I'll review how the asymmetry arises in QCD and describe what we learn from soft gluon resummation.