Scientific Series

Displaying 3049 - 3060 of 5012

Are the recent IceCube events hinting at O(100) TeV decaying dark matter?

Atri Bhattacharya
University of Liège
May 22, 2014

PIRSA:14050118
Particle Physics
Equality

Tobias Fritz
Universität Innsbruck

May 21, 2014

PIRSA:14050063
Designing exotic circuitry with non-Abelian anyons
May 20, 2014

PIRSA:14050029
Condensed Matter
Local quanta, unitary inequivalence, and vacuum entanglement

Hans Westman
May 20, 2014

PIRSA:14050117
Quantum Foundations
M-strings and their orbifolds

Babak Haghighat
Harvard University
May 20, 2014

PIRSA:14050005
Quantum Fields and Strings
Black holes and Boyle's Law --- the thermodynamics of Einstein's greatest mistake

Brian Dolan
National University of Ireland
May 20, 2014

PIRSA:14050093
Cosmology
From locally covariant QFT to quantum gravity

Katarzyna Rejzner
University of York
May 15, 2014

PIRSA:14050004
Quantum Gravity
Gravity waves from Kerr/CFT

Achilleas Porfyriadis
Harvard University
May 15, 2014

PIRSA:14050009
Strong Gravity
A polynomial-time algorithm for the ground state of 1D gapped local Hamiltonians

Thomas Vidick
Weizmann Institute of Science

May 14, 2014

PIRSA:14050039
What can we learn from modifing gravity ?

Claudia de Rham
Imperial College London
May 14, 2014

PIRSA:14050003
Cosmology
Unitarity and crossing symmetry in the S-matirx of large N Chern-Simons theory with fundamental matter

Shiraz Minwalla
Tata Institute of Fundamental Research (TIFR)
May 13, 2014

PIRSA:14050006
Quantum Fields and Strings
Gapless spin liquids in frustrated Heisenberg models

Federico Becca
SISSA International School for Advanced Studies
May 13, 2014

PIRSA:14050074
Condensed Matter

Are the recent IceCube events hinting at O(100) TeV decaying dark matter?

Atri Bhattacharya
University of Liège
May 22, 2014

PIRSA:14050118
Particle Physics
The IceCube detector has recently reported the observation of 28 events at previously unexplored energies. While the statistics of the observed events are still low, these events hint at the existence of a neutrino flux over and above the atmospheric neutrino background. We investigate the possibility that a significant component of the additional neutrino flux originates due to the decay of a very heavy dark matter (VHDM) particle via several possible channels into standard model particles. We show that a combination of a power law astrophysical neutrino spectrum and the neutrino flux from the decay of a DM species of mass in the range 150-400 TeV improves the fit to the observed neutrino events than that obtained from a best-fit astrophysical flux alone. Assuming the existence of an astrophysical background described by the IC best-fit, we also show that, for the decay of even heavier DM particles ($m_{\text{DM}} \sim 1$ PeV), the same observations impose significant constraints on the decay lifetimes. Allowing the astrophysical flux normalization to vary leads to modifications of these limits; however, there is still a range of dark matter mass and lifetime that is excluded by the IC results.
Equality

Tobias Fritz
Universität Innsbruck

May 21, 2014

PIRSA:14050063

Equality of two mathematical objects is a seemingly simple and well-understood concept. In this talk, I will do three things to explain why this is a misconception: I will survey different notions of equality, explain how revising the notion of equality has led to an emerging alternative foundation of mathematics called "homotopy type theory", and try to convince you that thinking about equality is relevant to your research in quantum field theory, quantum gravity or quantum foundations.
Designing exotic circuitry with non-Abelian anyons
May 20, 2014

PIRSA:14050029
Condensed Matter
Non-Abelian anyons are widely sought for the exotic fundamental physics they harbor as well as for their possible applications for quantum information processing. Currently, there are numerous blueprints for stabilizing the simplest type of non-Abelian anyon, a Majorana zero energy mode bound to a vortex or a domain wall. One such candidate system, a so-called "Majorana wire" can be made by judiciously interfacing readily available materials; the experimental evidence for the viability of this approach is presently emerging.
Following this idea, we introduce a device fabricated from conventional fractional quantum Hall states, s-wave superconductors and insulators with strong spin-orbit coupling. Similarly to a Majorana wire, the ends of our “quantum wire” would bind "parafermions", exotic non-Abelian anyons which can be viewed as fractionalised Majorana zero modes.
I will discuss their properties and describe how such parafermions can be used to construct new and potentially useful circuit elements which include current and voltage mirrors, transistors for fractional charge currents and "flux capacitors".
Local quanta, unitary inequivalence, and vacuum entanglement

Hans Westman
May 20, 2014

PIRSA:14050117
Quantum Foundations
In this work we develop a formalism for describing localised quanta for a real-valued Klein-Gordon field in a one-dimensional box [0, R]. We quantise the field using non-stationary local modes which, at some arbitrarily chosen initial time, are completely localised within the left or the right side of the box. In this concrete set-up we directly face the problems inherent to a notion of local field excitations, usually thought of as elementary particles. Specifically, by computing the Bogoliubov coefficients relating local and standard (global) quantizations, we show that the local quantisation yields a Fock space F^L which is unitarily inequivalent to the standard one F^G. In spite of this, we find that the local creators and annihilators remain well defined in the global Fock space F^G, and so do the local number operators associated to the left and right partitions of the box. We end up with a useful mathematical toolbox to analyse and characterise local features of quantum states in F^G . Specifically, an analysis of the global vacuum state |0_G> ∈ F^G in terms of local number operators shows, as expected, the existence of entanglement between the left and right regions of the box. The local vacuum |0_L> ∈ F^L , on the contrary, has a very different character. It is neither cyclic nor separating and displays no entanglement. Further analysis shows that the global vacuum also exhibits a distribution of local excitations reminiscent, in some respects, of a thermal bath. We discuss how the mathematical tools developed herein may open new ways for the analysis of fundamental problems in local quantum field theory.
M-strings and their orbifolds

Babak Haghighat
Harvard University
May 20, 2014

PIRSA:14050005
Quantum Fields and Strings
We consider M-theory in the presence of M parallel M5-branes probing a transverse A_{N-1} singularity. This leads to a superconformal theory with (1,0) supersymmetry in six dimensions. We compute the supersymmetric partition function of this theory on a two-torus, with arbitrary supersymmetry preserving twists, using the topological vertex formalism. Alternatively, we show that this can also be obtained by computing the elliptic genus of an orbifold of recently studied M-strings. The resulting 2d theory is a (4,0) supersymmetric quiver gauge theory whose Higgs branch corresponds to strings propagating on the moduli space of SU(N)^(M-1) instantons on R^4 where the right-moving fermions are coupled to a particular bundle.
Black holes and Boyle's Law --- the thermodynamics of Einstein's greatest mistake

Brian Dolan
National University of Ireland
May 20, 2014

PIRSA:14050093
Cosmology
The thermodynamics of black holes will be reviewed and recent developments incorporating pressure into the first law described. The asymptotically AdS Kerr metric has a van der Waals type critical point with a line of first order phase transitions terminating at a critical point with mean field exponents. The phase structure and stability of black holes in higher dimensions will also be described.
From locally covariant QFT to quantum gravity

Katarzyna Rejzner
University of York
May 15, 2014

PIRSA:14050004
Quantum Gravity
Locally covariant quantum field theory (LCQFT) has proven to be a very successful framework for QFT on curved spacetimes. It is natural to ask, how far these ideas can be generalized and if one can learn something about quantum gravity, using LCQFT methods. In particular, one can use the relative Cauchy evolution to formulate the notion of background independence. Recently we have proven that background independence in this sense holds for effective quantum gravity, formulated as a perturbative QFT. Remarkably, the formalism of LCQFT can be extended to structures more general than spacetimes. The essential feature is the presence of the causal structure. An example application would be QFT on causal sets (work in progress).
Gravity waves from Kerr/CFT

Achilleas Porfyriadis
Harvard University
May 15, 2014

PIRSA:14050009
Strong Gravity
Astronomical observation suggests the existence of near-extreme Kerr black holes whose horizons spin at nearly the speed of light. Properties of diffeomorphisms imply that the dynamics of the high-redshift near-horizon region of near-extreme Kerr, which includes the innermost-stable-circular-orbit (ISCO), is governed by an infinite-dimensional emergent conformal symmetry. This symmetry may be exploited to analytically, rather than numerically, compute a variety of potentially observable processes. In this talk I will show how we compute and study the conformal transformation properties of the gravitational radiation emitted by an orbiting massive object in the large-redshift near-horizon region. I will also use conformal symmetry of the near-horizon region to compute the gravitational radiation produced during the plunge phase following the object's crossing of the ISCO.
A polynomial-time algorithm for the ground state of 1D gapped local Hamiltonians

Thomas Vidick
Weizmann Institute of Science

May 14, 2014

PIRSA:14050039

Computing ground states of local Hamiltonians is a fundamental problem in condensed matter physics. We give the first randomized polynomial-time algorithm for finding ground states of gapped one-dimensional Hamiltonians: it outputs an (inverse-polynomial) approximation, expressed as a matrix product state (MPS) of polynomial bond dimension. The algorithm combines many ingredients, including recently discovered structural features of gapped 1D systems, convex programming, insights from classical algorithms for 1D satisfiability, and new techniques for manipulating and bounding the complexity of MPS. Our result provides one of the first major classes of Hamiltonians for which computing ground states is provably tractable despite the exponential nature of the objects involved. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-style-parent:""; font-size:11.0pt; font-family:"Calibri","sans-serif";}
What can we learn from modifing gravity ?

Claudia de Rham
Imperial College London
May 14, 2014

PIRSA:14050003
Cosmology
I will review models of modified gravity in the infrared and show how extra degrees of freedom present in these theories get screened via the Vainshtein mechanism. That mechanism comes hand in hand with its own share of peculiarities: classical superluminalities, strong coupling and perturbative non-analyticity of the S-matrix to name a few. From a traditional effective field viewpoint such effects are disastrous but I will present the first hints in understanding these theories beyond the traditional perspective and their implications not only for gravity but also for our understanding of a certain class of field theories.
Unitarity and crossing symmetry in the S-matirx of large N Chern-Simons theory with fundamental matter

Shiraz Minwalla
Tata Institute of Fundamental Research (TIFR)
May 13, 2014

PIRSA:14050006
Quantum Fields and Strings
We present explicit computations and conjectures for 2 → 2 scattering matrices in large N U(N) Chern-Simons theories coupled to fundamental bosonic or fermionic matter to all orders in the ’t Hooft coupling expansion. The bosonic and fermionic S-matrices map to each other under the recently conjectured Bose-Fermi duality after a level-rank transposition. The S-matrices presented in this paper may be regarded as relativistic generalization of Aharonov-Bohm scattering. They have unusual structural features: they include a non analytic piece localized on forward scattering, and obey modified crossing symmetry rules. We conjecture that these unusual features are properties of S-matrices in all Chern-Simons matter theories. The S-matrix in one of the exchange channels in our paper has an anyonic character; the parameter map of the conjectured Bose-Fermi duality may be derived by equating the anyonic phase in the bosonic and fermionic theories.
Gapless spin liquids in frustrated Heisenberg models

Federico Becca
SISSA International School for Advanced Studies
May 13, 2014

PIRSA:14050074
Condensed Matter
We present our recent numerical calculations for the Heisenberg model on the square and
Kagome lattices, showing that gapless spin liquids may be stabilized in highly-frustrated
regimes. In particular, we start from Gutzwiller-projected fermionic states that may
describe magnetically disordered phases,[1] and apply few Lanczos steps in order to improve
their accuracy. Thanks to the variance extrapolation technique,[2] accurate estimations of
the energies are possible, for both the ground state and few low-energy excitations.
Our approach suggests that magnetically disordered phases can be described by Abrikosov
fermions coupled to gauge fields.

For the Kagome lattice, we find that a gapless U(1) spin liquid with Dirac cones
is competitive with previously proposed gapped spin liquids when only the nearest-neighbor
antiferromagnetic interaction is present.[3,4] The inclusion of a next-nearest-neighbor term
lead to a Z_2 gapped spin liquid,[5] in agreement with density-matrix renormalization group
calculations.[6] In the Heisenberg model on the square lattice with both nearest- and
next-nearest-neighbor interactions, a Z_2 spin liquid with gapless spinon excitations is
stabilized in the frustrated regime.[7] This results are (partially) in agreement with recent
density-matrix renormalization group on large cylinders.[8]

[1] X.-G. Wen, Phys. Rev. B {\bf 44}, 2664 (1991); Phys. Rev. B {\bf 65}, 165113 (2002).
[2] S. Sorella, Phys. Rev. B {\bf 64}, 024512 (2001).
[3] Y. Iqbal, F. Becca, S. Sorella, and D. Poilblanc, Phys. Rev. B 87, 060405(R) (2013).
[4] Y. Iqbal, D. Poilblanc, and F. Becca, Phys. Rev. B 89, 020407(R) (2014).
[5] W.-J. Hu, Y. Iqbal, F. Becca, D. Poilblanc, and D. Sheng, unpublished.
[6] H.-C. Jiang, Z. Wang, and L. Balents, Nat. Phys. 8, 902 (2012);
S. Yan, D. Huse, and S. White, Science 332, 1173 (2011).
[7] W.-J. Hu, F. Becca, A. Parola, and S. Sorella, Phys. Rev. B 88, 060402(R) (2013).
[8] S.-S. Gong, W.Z., D.N. Sheng, O.I. Motrunich, and M.P.A. Fisher, arXiv:1311.5962 (2013).

Title	Speaker(s)	Date	Talk Type	Info link
Are the recent IceCube events hinting at O(100) TeV decaying dark matter?	Atri Bhattacharya	2014-05-22	Scientific Series	View details
Equality	Tobias Fritz	2014-05-21	Scientific Series	View details
Designing exotic circuitry with non-Abelian anyons		2014-05-20	Scientific Series	View details
Local quanta, unitary inequivalence, and vacuum entanglement	Hans Westman	2014-05-20	Scientific Series	View details
M-strings and their orbifolds	Babak Haghighat	2014-05-20	Scientific Series	View details
Black holes and Boyle's Law --- the thermodynamics of Einstein's greatest mistake	Brian Dolan	2014-05-20	Scientific Series	View details
From locally covariant QFT to quantum gravity	Katarzyna Rejzner	2014-05-15	Scientific Series	View details
Gravity waves from Kerr/CFT	Achilleas Porfyriadis	2014-05-15	Scientific Series	View details
A polynomial-time algorithm for the ground state of 1D gapped local Hamiltonians	Thomas Vidick	2014-05-14	Scientific Series	View details
What can we learn from modifing gravity ?	Claudia de Rham	2014-05-14	Scientific Series	View details
Unitarity and crossing symmetry in the S-matirx of large N Chern-Simons theory with fundamental matter	Shiraz Minwalla	2014-05-13	Scientific Series	View details
Gapless spin liquids in frustrated Heisenberg models	Federico Becca	2014-05-13	Scientific Series	View details

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