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Winter 2016

Seminars take place Fridays 3-4pm in West Hall Room #335

Organizer: Leo Pando Zayas | Ratindranath Akhoury

Date Speaker Title Abstract
Jan 15 Martin Kruczenski (Purdue) Minimal area surfaces and Wilson loops in the AdS/CFT correspondence

Wilson loops are one of the most important observables in gauge theories. The AdS/CFT correspondence relates the computation of Wilson loops to the study of minimal area surfaces in hyperbolic and AdS space. In this talk I am going to discuss an approach to study such minimal area surfaces emphasizing their integrability properties and leading to new solutions and methods of computation.

Jan 22 Tom Hartman (Cornell) Causality constraints in conformal field theory

It is well known that some effective field theories cannot be UV completed -- perturbative amplitudes in the infrared may be at odds with ultraviolet consistency conditions, like the optical theorem.  A famous example is the causality constraint used in the proof of the a-theorem. In this talk I will revisit these constraints from a different point of view, and describe analogous constraints in strongly coupled conformal field theory. 

Jan 29 Alexey Petrov (Wayne State) Flavor-changing neutral currents with beauty and charm

I will discuss contemporary issues in searches for New Physics with flavor-changing neutral current transitions in beauty and charm systems. I will also discuss a novel method to study flavor-changing neutral currents in the e+ e− → D∗0 and e+ e− → B∗s transitions, tuning the energy of e+ e−- collisions to the mass of the narrow vector resonance D∗0 or B∗s . I will present a thorough study of both short-distance and long-distance contributions to those processes in the Standard Model and investigate possible contributions of New Physics.

Feb 5 Douglas Spolyar (Nordita and U Stockholm) Dark energy:Testing gravity in Voids

Modified gravity has garnered interest as a backstop against dark matter and dark energy (DE). As one possible modification, the graviton can become massive, which introduces a new scalar field - here with a Galileon-type symmetry. The field can lead to a nontrivial equation of state (EOS) of DE which is density-and-scale-dependent. In voids the scalar field dramatically alters the EOS of DE, induces a soon-observable gravitational slip between the two metric potentials, and develops a topological defect (domain wall) due to a nontrivial vacuum structure for the field. 

Feb 12 John Golden (UM)  Conformal Bootstrap in Fractional Dimensions

I will review the conformal bootstrap in fractional dimensions, with an emphasis on the Ising model in 1<d<2. I will discuss bounds on operator dimensions and compare the results with various theoretical and numerical models, in particular with resummed ε-expansion and Monte Carlo simulations of the Ising model on fractal lattices. I will also introduce some ongoing work on supersymmetric CFTs in 2<d<4. 

Feb 19 Alex Buchel (Perimeter) Gravitational instability in AdS and thermalization of dual gauge theories

We discuss gravitational collapse in asymptotically global anti de-Sitter space times. Holographic correspondence of Maldacena relates this dynamical gravitational phenomena to problem of equilibration of strongly coupled gauge theories. We review progress in this line of research and discuss ongoing projects.

Feb 26 Joachim Brod (TU Dortmand, Germany) Renormalization Group Effects in Dark-Matter Direct Detection

The existence of dark matter is one of the few solid hints for physics beyond the standard model. If dark matter indeed has particle nature, then direct detection via scattering on atomic nuclei is one of the most promising discovery channels. Effective field theories are the appropriate framework to describe the scattering process that involves physics at very different energy scales.

The state of the art is to include also subleading (for instance, velocity-suppressed or spin-dependent) interactions, either in an attempt to resolve tensions between different experimental results, or to accommodate concrete models of dark matter. Here, electroweak corrections can have a large impact on the interpretation of data, via the mixing of suppressed into unsuppressed operators.

In this talk I report on our effort to provide a complete framework of effective theories, connecting all relevant energy scales from the UV down to the nuclear scale. We also calculate the electroweak operator mixing for dark matter furnishing a general representation of the electroweak gauge group, and I will show preliminary results of our analysis.

Mar 4 Spring Break    
Mar 11 Daniel Areán Fraga (Max Planck Institute Munich, Germany) Noisy Branes Brane intersections are the prototypical example of string theory realizations of gauge theories with fundamental matter.  We employ the D3/D5 brane intersection to study the effects of disorder on strongly coupled compressible matter in 2+1 dimensions.  We consider the system at finite temperature in the presence of a disordered chemical potential, and first study the effects of disorder on the charge density and the quark condensate. Next, we focus on the DC conductivity and derive analytic expressions for the corrections induced by weak disorder. We present numerical simulations both for weak and moderate disorder, and show how strong enough disorder induces a sub-linear behavior for the conductivity as a function of the charge density. This behavior qualitatively agrees with that of the DC conductivity of semi-metal graphene in the proximityof the charge neutrality point. 
Mar 18 No Seminar    
Mar 22
Tues
**Special Seminar**
Kazuhiro Tobe (Nagoya University)
**3481 Randall**
 Lepton-flavor-violating Higgs decay h to mu tau and muon anomalous magnetic moment in a general two Higgs doublet model  
Mar 25 Graduate Student Gong Show    

Apr 1 Gordon Kane (UM) Compactifying M-theory on a G2 manifold to describe our world

Compactified M-theory generically describes many features of our world, including gravity; Yang-Mills forces like SU(3)xSU(2)xU(1); chiral fermions (so parity violation); softly broken supersymmetry; a solution to the  hierarchy problem; electroweak  symmetry breaking and Higgs physics (including  the ratio of the Higgs boson mass to  the Z mass, and Higgs decay branching ratios); grand unification; small EDMs; no flavor changing problems and more.  It predicts a non-thermal cosmological history and addresses the form(s) of dark matter and the ratio of matter to dark matter.  And it predicts the superpartner spectrum: heavy (tens of TeV) squarks and sleptons, light (~TeV) gluino and LSP. Superpartners should not have been found in Run I at LHC, and can be found in Run II (gluinos about 1..5 TeV, winos about 640 GeV). A few general assumptions are made, and there are no parameters to vary. There has been good progress in calculating and elucidating the predictions, but there is still much to do. I’ll present the theoretical foundations, and some predictions.

Apr 8 Masanori Hanada (Kyoto Univ, Stanford) Black hole evaporation from D0-brane quantum mechanics


I show that the D0-brane quantum mechanics describes various aspects of a black hole (black zero-brane) in type IIA superstring theory. Firstly, I explain the results of the Monte Carlo simulations, which show that the thermodynamic properties of the black hole is correctly reproduced. 

Then I explain recent results on real-time dynamics. It is explained that the "fast scrambling" in stringy regime can be confirmed numerically. I also show that the evaporation of the black hole can be explained from gauge theory side, by using only undergrad statistical mechanics and high school math (plus very basic knowledge about D0-brane quantum mechanics, which will be explained in the talk).

A large and cold black hole becomes hotter while it evaporates, the evaporation speeds up, and the black hole completely evaporates to freely propagating D0-branes, without leaving remnant. 

 

Apr 15 Keshav Dasgupta (McGill University) How hard is it to get a de Sitter solution in string theory?

In this talk I'll discuss some recent understanding of string theory embedding of de Sitter. I'll focus on aspects of the no-go theorem, ways to overcome it, and related recent study of nilpotent multiplets.