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An informal discussion about topological gauge theory
Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics
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Self-localization of a single hole in Mott antiferromagnets
Zheng-Yu Weng Tsinghua University
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Towards an Asymptotically AdS Description of Heavy Ion Collisions
Hans Bantilan Princeton University
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Constraining RG flow in three-dimensional field theory
Benjamin Safdi Massachusetts Institute of Technology (MIT)
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Now what?: Higgs physics after discovery
Nathaniel Craig University of California, Santa Barbara
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The effect of initial correlations on the evolution of quantum states
Mark Byrd Southern Illinois University Carbondale
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Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.
David Jennings Imperial College London
I will discuss the central role of correlations in thermodynamic directionality, how strong correlations can distort the thermodynamic arrow and contrast these distortions in both the classical and quantum regimes. These distortions constitute non-linear entanglement witnesses, and give rise to a rich information-theoretic structure. I shall explain how these results are then cast into the language of fluctuation theorems to derive a generalized exchange fluctuation theorem, and discuss the limitations of such a framework. -
From Effective Strings to the Simplest theory of Quantum Gravity
String-like objects arise in many quantum field theories. Well known examples include flux tubes in QCD and cosmic strings. To a first approximation, their dynamics is governed by the Nambu-Goto action, but for QCD flux tubes numerical calculations of the energy levels of these objects have become so accurate that a systematic understanding of corrections to this simple description is desirable. In the first part of my talk, I discuss an effective field theory describing long relativistic strings. The construction parallels that of the chiral Lagrangian in that it is based on the pattern of symmetry breaking. To compare with previous works, I will present the results of the calculation of the S-matrix describing the scattering of excitations on the string worldsheet. In the second part of my talk, I will discuss critical strings from the same point of view and show that the worldsheet S-matrix in this case is non-trivial but can be calculated exactly. I will show that it encodes the familiar square-root formula for the energy levels of the string, the Hagedorn behavior of strings, and argue that the theory on the string worldsheet behaves like a 1+1 dimensional theory of quantum gravity rather than a field theory. If time permits, I will return to the task of computing the energy levels of flux-tubes using lessons learned from the second part of my talk. -
An informal discussion about topological gauge theory
Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics
Reference:
Topological gauge theories and group cohomology
Robbert Dijkgraaf and Edward Witten
http://projecteuclid.org/DPubS?service=UI&version=1.0&verb=Display&handle=euclid.cmp/1104180750
Braiding statistics approach to symmetry-protected topological phases
Michael Levin, Zheng-Cheng Gu
http://arxiv.org/abs/1202.3120
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New Results in Jet Substructure
We present new results on the performance of jet substructure techniques and their use in distinguishing the signatures of new boosted massive particles from the QCD background. Advanced approaches to jet reconstruction using jet grooming algorithms such as filtering, trimming, and pruning are compared. Measurements of the jet invariant mass for each jet algorithm are compared both at the particle level to multiple Monte Carlo event generators and at the detector level for several configurations of the jet grooming algorithms. The performance of these strategies and improvements in search sensitivity for new boosted hadronic particles are compared. Recent results using these techniques for both boosted RPV gluinos and top quark pairs from new particles are presented. The result is a comprehensive foundation for the use of substructure algorithms in the search for new physics at the LHC -
Self-localization of a single hole in Mott antiferromagnets
Zheng-Yu Weng Tsinghua University
Anderson localization - quantum suppression of carrier diffusion due to disorders - is a basic notion of modern condensed matter physics. Here I will talk about a novel localization phenomenon totally contrary to this common wisdom. Strikingly, it is purely of strong interaction origin and occurs without the assistance of disorders. Specifically, by combined numerical (density matrix renormalization group) method and analytic analysis, we show that a single hole injected in a quantum antiferromagnetic ladder is generally self-localized even though the system respects the translational symmetry. The localization length is found to monotonically decrease with the increase of leg number, indicating stronger self-localization in the two-dimensional limit. We find that a peculiar coupling between the doped charge and the quantum spin background causes quantum interference among different hole paths. The latter brings the hole's itinerant motion to a halt, a phenomenological analogy to Anderson localization. Our findings are opposite to the common belief of the quasiparticle picture for the doped hole and unveil a completely new paradigm for lightly doped Mott insulators. -
Understanding black hole entropy through the renormalization group
PIRSA:12100053It is known that the entanglement entropy of quantum fields on the black hole background contributes to the Bekenstein-Hawking entropy,and that its divergences can be absorbed into the renormalization of gravitational couplings. By introducing a Wilsonian cutoff scale and the concepts of the renormalization group, we can expand this observation into a broader framework for understanding black hole entropy. At a given RG scale, two contributions to the black hole entropy can be identified: the "gravitational" contribution coming from the running effective gravitational action, and the entanglement entropy of the quantum degrees of freedom below the cutoff scale. At different RG scales the balance is different, though the total black hole entropy is invariant. I will describe this picture for free fields, considering both minimal and non-mininal coupling, and discuss the extension to interacting fields and the difficulties it raises. -
Towards an Asymptotically AdS Description of Heavy Ion Collisions
Hans Bantilan Princeton University
I will discuss recent work in simulating asymptotically anti-de Sitter spacetimes, and its relation to heavy ion collider physics. For this purpose, I intend to focus on a class of oblately deformed black hole spacetime solutions. For each of these solutions, I will map the gravitational metric in the spacetime bulk to a stress tensor one-point function of the conformal field theory defined on the spacetime boundary. During the ring-down process, wherein the deformed black hole settles down to the AdS analog of the Schwarzschild solution, I will exhibit evidence that the dual CFT stress tensor on the boundary is that of an N=4 SYM fluid, even for black holes of significant deformation well outside the perturbative regime. We will conformally map the boundary fluid onto a real-world fluid in Minkowski space, and discover a temperature profile which can be thought of as approximating that of a head-on heavy ion collision at its moment of impact. I will close with a description of recent parallel explorations. -
Astrophysical shear-driven turbulence
Jeremy Goodman Princeton University
PIRSA:12100043Astronomical hydrodynamics is usually almost ideal in the sense that the Reynolds number (Re) is enormous and any effective viscosity must be due to shocks or turbulence. Astronomical magnetohydrodynamics (MHD) is often also nearly ideal, so that magnetic fields and plasma are well coupled. In particular, dissipation of orbital energy in accretion disks around black holes is readily explained by MHD turbulence. On the other hand, the planet-bearing disks around protostars are magnetically far from ideal because of very low fractional ionization. MHD turbulence is at best marginal in these disks, yet accretion is observed. The Reynolds numbers based on orbital-velocity gradients are enormous, so by analogy with high-Re terrestrial flows, one might expect hydrodynamic (i.e., unmagnetized) turbulence. Direct numerical simulations indicate that such turbulence is somehow suppressed by keplerian rotation, though the mechanism is
unclear and the simulations are limited in Re. Recently, a few groups have studied the question via Taylor-Couette experiments at somewhat higher Re, obtaining conflicting results. Complicating and enriching this debate is the recent discovery that turbulence tends to have a finite lifetime in shear flows that admit a formally linearly stable laminar solution: this includes flow in smooth pipes and probably also unmagnetized keplerian disks. Some suggestions will be offered as to how these open questions might be resolved. -
Constraining RG flow in three-dimensional field theory
Benjamin Safdi Massachusetts Institute of Technology (MIT)
The entanglement entropy S(R) across a circle of radius R has been invoked recently in deriving general constraints on renormalization group flow in three-dimensional field theory. At conformal fixed points, the negative of the finite part of the entanglement entropy, which is called F, is equal to the free energy on the round three-sphere. The F-theorem states that F decreases under RG flow. Along the RG flow it has recently been shown that the renormalized entanglement entropy {\cal F}(R) = -S(R) + R S'(R), which is equal to F at the fixed points, is a monotonically decreasing function. I will review various three-dimensional field theories where we can calculate F on the three-sphere and compute its change under RG flow, including free field theories, perturbative fixed points, large N field theories with double trace deformations, gauge theories with large numbers of flavors, and supersymmetric theories with at least {\cal N} = 2 supersymmetry. I will also present calculations of the renormalized entanglement entropy along the RG flow in free massive field theory and in holographic examples. -
Now what?: Higgs physics after discovery
Nathaniel Craig University of California, Santa Barbara
With the discovery of a new Higgs-like particle at the LHC, there is an unprecedented opportunity to use the Higgs as a probe for physics beyond the Standard Model. I will discuss a variety of recent ideas to look for new physics via the Higgs, including measurements of Higgs couplings and associated indirect observables; searches for Higgs production in association with new physics; and strategies for probing extended electroweak symmetry breaking sectors. -
Maximum entropy, the universal dark matter density profile... and its destruction
Andrew Pontzen University of Oxford
I review some recent developments in attempting to reconcile the observed galaxy population with numerical models of structure formation in the 'LCDM' concordance cosmology. Focussing on behaviour of dwarf galaxies, I describe the infamous 'cusp-core' dichotomy -- a long-standing challenge to the LCDM picture on small scales -- and use toy models to show how it is resolved in recent numerical simulations (Pontzen & Governato 2012). I then discuss the current observational status of this picture (Teyssier, Pontzen & Read 2012; Penarrubia et al 2012).
In the second half of the talk, I apply the analytic techniques developed for probing the effect of gas on dark matter dynamics to the question of how, in the absence of baryons, a universal "NFW" dark matter halo profile emerges (independent of scale or details of the initial conditions).
Thus the generation of NFW halos on the one hand and the destruction of their central cusps on the other can be ascribed to surprisingly similar physical arguments. -
The effect of initial correlations on the evolution of quantum states
Mark Byrd Southern Illinois University Carbondale
Until fairly recently, it was generally assumed that the initial state of a quantum system prepared for information processing was in a product state with its environment. If this is the case,
the evolution is described by a completely positive map. However, if the system and environment are initially correlated, or entangled, such that the so-called quantum discord is non-zero, then the
evolution is described by a map which is not completely positive. Maps that are not completely positive are not as well understood and the implications of having such a map are not completely known. I will discuss a few examples and a theorem (or two) which may help us understand the implications of having maps which are not completely positive.