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Renormalizing TGFTs: a 3d example on SU(2)
Sylvain Carrozza University of Burgundy
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Quantum one-time programs
Gus Gutowski Institute for Quantum Computing (IQC)
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Approaches to modeling pulsar magnetospheres
Anatoly Spitkovsky Princeton University
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Unitarity, black hole microstates and how Alices fuzzes but may not even know it
Andrea Puhm University of Amsterdam
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The Spectrum of Strings on Warped AdS3
Wei Song Harvard University
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New electroweak states in plain sight
Patrick Meade Stony Brook University - C. N. Yang Institute for Theoretical Physics
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CMB as a Probe of New Physics: The Story of Cosmic Birefringence
Cosmological birefringence is a postulated rotation of the linear polarization of photons that arises due to a Chern-Simons coupling of a new scalar field to electromagnetism. In particular, it appears as a generic feature of simple quintessence models for Dark Energy, and therefore, should it be detected, could provide insight into the microphysics of cosmic acceleration. Prior work has sought this rotation, assuming the rotation angle to be uniform across the sky, by looking for the parity-violating TB and EB correlations in the CMB temperature/polarization. However, if the scalar field that gives rise to cosmological birefringence has spatial fluctuations, then the rotation angle may vary across the sky. In this talk, I will present the results of the first CMB-based search for direction-dependent cosmological birefringence, using WMAP-7 data, and report the constraint on the rotation-angle power spectrum for all multipoles up to the resolution of the instrument. I will discuss the implications for a specific models for rotation, and show forecasts for Planck and future experiments. I will then conclude with a brief discussion of other exotic physical models, such as chiral gravity, and astrophysical scenarios, such as inhomogeneous reionization, that can be probed using the same analysis.
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Renormalizing TGFTs: a 3d example on SU(2)
Sylvain Carrozza University of Burgundy
I will recall the main motivations for considering spin foam models in their Group Field Theory (GFT) versions, which are quantum field theories defined on group manifolds. As for any other quantum field theory, a fully consistent definition of the latter must involve renormalization. I will briefly review a specific class of GFTs, called tensorial, for which progress in this direction has recently been possible. A new just-renormalizable model, in three dimensions and on the SU(2) group, will be presented. Interestingly, it includes the geometric constraint of the Boulatov model, and might as such be related to Euclidean quantum gravity in three dimensions. Furthermore, this opens the way to a similar analysis of current 4d gravity spin foam models.
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Quantum one-time programs
Gus Gutowski Institute for Quantum Computing (IQC)
A "one-time program" for a channel C is a hypothetical cryptographic primitive by which a user may evaluate C on only one input state of her choice. (Think Mission Impossible: "this tape will self-destruct in five seconds.") One-time programs cannot be achieved without extra assumptions such as secure hardware; it is known that one-time programs can be constructed for classical channels using a very basic hypothetical hardware device called a "one-time memory". Our main result is the construction of a one-time program for any quantum channel specified by a circuit, assuming the same basic one-time memory devices used for classical channels. The construction achieves universal composability -- the strongest possible security -- against any quantum adversary. It employs a technique for computation on authenticated quantum data and we present a new authentication scheme called the "trap" scheme for this purpose. Finally, we observe that there is a pathological class of channels that admit trivial one-time programs without any hardware assumptions whatsoever. We characterize these channels, assuming an interesting conjecture on the invertible (or decoherence-free) subspaces of an arbitrary channel. Joint work with Anne Broadbent and Douglas Stebila. http://arxiv.org/abs/1211.1080 -
Approaches to modeling pulsar magnetospheres
Anatoly Spitkovsky Princeton University
Pulsars are rotating magnetized neutron stars that emit broadband pulses of radiation. Our ability to model magnetospheres of pulsars has been hampered by the difficulty of solving the self-consistent behavior of strongly magnetized relativistic plasmas. I will describe
recent progress in numerical modeling of magnetically-dominated plasmas and show applications to pulsar magnetospheres in increasing levels of realism, including ideal and resistive force-free,
relativistic MHD and kinetic models. The knowledge of the magnetospheric shape together with the new observations of gamma-ray emission from pulsars with Fermi telescope allow to directly constrain the location and physics of the acceleration regions in the magnetosphere and the origin of high energy emission. The pulsar magnetosphere is a prototype for other strongly magnetized
astrophysical objects, and I will discuss how the lessons from pulsar modeling can be useful in predicting EM counterparts to gravitational wave sources. -
Unitarity, black hole microstates and how Alices fuzzes but may not even know it
Andrea Puhm University of Amsterdam
The information paradox and the infall problem have been long-standing puzzles in the understanding of black holes. The idea of free infall is in considerable tension with unitarity of the evaporation process and recent developements have made this tension sharp. In the first part of my talk I will address the information question and argue that unitarty requires every quantum of radiation leaving the black hole to carry information about the initial state. Unitary evaporation is thus inconsistent with an information-free horizon at every step of the evaporation process and this extends the recent firewall result. This immediately raises the question of What is the required horizon-scale structure? I will show an explicit construction of near-extremal black hole microstates which put flesh and branes on the fuzzball proposal and may realize firewalls in string theory. In the second part I will address the question of What happens to an observer falling into a fuzzball? I will argue that the answer is dependent on the energy scale of the infalling observer. -
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Local topological order inhibits thermal stability in 2D
We study the robustness of quantum information stored in the degenerate ground space of a local, frustration-free Hamiltonian with commuting terms on a 2D spin lattice. On one hand, a macroscopic energy barrier separating the distinct ground states under local transformations would protect the information from thermal fluctuations. On the other hand, local topological order would shield the ground space from static perturbations. Here we demonstrate that local topological order implies a constant energy barrier, thus inhibiting thermal stability. Joint work with David Poulin. arXiv:1209.5750 -
The Spectrum of Strings on Warped AdS3
Wei Song Harvard University
Warped AdS3 has isometry SL(2,R) x U(1). It is closed related to Kerr/CFT, non local dipole theories and AdS/CMT. In this talk I will derive the spectrum of string theory on Warped AdS3. This is possible because the worldsheet theory can be mapped to the worldsheet on AdS3 by a nonlocal field redefinition. -
If no information gain implies no disturbance, then any discrete physical theory is classical
(based on http://arxiv.org/abs/1210.0194) It has been suggested that nature could be discrete in the sense that the underlying state space of a physical system has only a finite number of pure states. For example, the Bloch ball of a single qubit could be discretized into small patches and only appear round to us due to experimental limitations. Here, we present a strong physical argument for the quantum theoretical property that every state space (even the smallest possible one, the qubit) has infinitely many pure states. We propose a simple physical postulate which dictates that in fact the only possible discrete theory is classical mechanics. More specifically, we postulate that no information gain implies no disturbance, or read in the contrapositive, that disturbance leads to some form of information gain. In a theory like quantum mechanics where we already know that the converse holds, i.e. information gain does imply disturbance, this can be understood as postulating an equivalence between disturbance and information gain. What is more, we show that non-classical discrete theories are still ruled out even if we relax the postulate to hold only approximately in the sense that no information gain only causes a small amount of disturbance. Finally, our postulate also rules out popular generalizations such as the PR-box that allows non-local correlations beyond the limits of quantum theory. -
Moduli Stabilization and Holographic RG
In this talk, I will relate moduli stabilization in AdS or de Sitter space to basic properties of the Wilsonian action in the holographic dual theory living on dS (of one lower dimension): the single-trace terms in the action have vanishing beta functions, and higher-trace couplings are determined purely from lower-trace ones (a property we refer to as the iterative structure of RG). In the dS case, this encodes the maximal symmetry of the bulk spacetime in a quantity which is accessible within a single observer's patch. -
New electroweak states in plain sight
Patrick Meade Stony Brook University - C. N. Yang Institute for Theoretical Physics
The LHC has made remarkable progress in exploring the SM at new energies and demonstrating remarkable agreement with theoretical predictions. In this talk I will discuss one area where the SM does not fit as well as expected, and what could be hints of new physics showing up in the electroweak sector.
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Amplitude mode of the d-density wave state and its relevance to high-Tc cuprates
Ipsita Mandal Shiv Nadar University
We study the spectrum of the amplitude mode, the analog of the Higgs mode in high energy physics, for the d-density wave (DDW) state proposed to describe the anomalous phenomenology of the pseudogap phase of the high Tc cuprates. Even though the state breaks translational symmetry by a lattice spacing and is described by a particle-hole singlet order parameter at the wave vector q = Q = (pi, pi), remarkably, we find that the amplitude mode spectrum can have peaks at both q = (0, 0) and q = Q = (pi , pi). In general, the spectra is non-universal, and, depending on the microscopic parameters, can have one or two peaks in the Brillouin zone, signifying confluence of two kinds of magnetic excitations. In light of the recent unexpected observations of multiple magnetic excitations in the pseudogap phase our theory sheds important light on how multiple inelastic neutron peaks at different wave vectors can arise even with an order parameter that condenses at Q = (pi, pi). [Reference: arXiv:1207.6834]