Scientific Series

Displaying 3205 - 3216 of 5164

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 Maynooth University
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
New strong interactions and the t t-bar asymmetry

Joachim Brod University of Cincinnati
May 13, 2014

PIRSA:14050092
Particle Physics
Random models of inflation

Andrew Liddle University of Lisbon
May 13, 2014

PIRSA:14050007
Cosmology
The quest for self-correcting quantum memory

Olivier Landon-Cardinal California Institute of Technology
May 12, 2014

PIRSA:14050028
Quantum Information
Curvature in Noncommutative Geometry

masoud khalkhali Western University
May 09, 2014

PIRSA:14050064
Mathematical physics

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 Maynooth University
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).
New strong interactions and the t t-bar asymmetry

Joachim Brod University of Cincinnati
May 13, 2014

PIRSA:14050092
Particle Physics
The CDF and D0 experiments at Tevatron measure a top-quark forward-backward
asymmetry significantly larger than the standard-model prediction.
We construct a model that involves new strong interactions at the electroweak scale
and can explain the measured asymmetry. Our model possesses a flavor symmetry
which allows to evade flavor and collider constraints, while it still permits flavor-violating
couplings of order 1 which are needed to generate the asymmetry via light t-channel vectors.
Random models of inflation

Andrew Liddle University of Lisbon
May 13, 2014

PIRSA:14050007
Cosmology
Rather than writing down specific functional forms, one can generate inflation models via stochastic processes in order to explore generic properties of inflation models. I describe our explorations of the phenomenology of randomly-generated multi-field inflation models, both for canonical fields and for a braneworld-motivated scenario. Implications of some recent observational results, including BICEP2, will be discussed.
The quest for self-correcting quantum memory

Olivier Landon-Cardinal California Institute of Technology
May 12, 2014

PIRSA:14050028
Quantum Information
A self-correcting quantum memory is a physical system whose quantum state can be preserved over a long period of time without the need for any external intervention. The most promising candidates are topological quantum systems which would protect information encoded in their degenerate groundspace while interacting with a thermal environment. Many models have been suggested but several approaches have been shown to fail due to no-go results of increasingly general scope. In a nutshell, 2D topological models and many 3D topological models have point-like excitations which propagate freely and change the groundstate at any non-zero temperature. A recent suggestion is to introduce effective long-range interactions between those point-like excitations. In this presentation, I will first explain the desiderata for self-correction, review the recent advances and no-go results, and describe the current endeavours to define a self-correcting system in 2D and 3D. Time permitting, I will briefly present our recent work on the thermal instability of models which aim to introduce effective long-range interactions between point-like excitations (joint work with Beni Yoshida, John Preskill and David Poulin).
Curvature in Noncommutative Geometry

masoud khalkhali Western University
May 09, 2014

PIRSA:14050064
Mathematical physics
After the seminal work of Connes and Tretkoff on the Gauss-Bonnet theorem for the noncommutative 2-torus and its extension by Fathizadeh and myself, there have been significant developments in understanding the local differential geometry of these noncommutative spaces equipped with curved metrics. In this talk, I will review a series of joint works with Farzad Fathizadeh in which we compute the scalar curvature for curved noncommutative tori and prove the analogue of Weyl's law and Connes' trace theorem. Our final formula for the curvature matches precisely with the one computed independently by A. Connes and H. Moscovici. I will then report on our recent work on the computation of scalar curvature for noncommutative 4-tori (which involves intricacies due to violation of the Kähler condition). We show that metrics with constant curvature are extrema of the analogue of the Einstein–Hilbert action. A purely noncommutative feature in these works is the appearance of the modular automorphism from Tomita–Takesaki theory of KMS states in the final formulas for the curvature.

Title	Speaker(s)	Date	Talk Type	Info link
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
New strong interactions and the t t-bar asymmetry	Joachim Brod	2014-05-13	Scientific Series	View details
Random models of inflation	Andrew Liddle	2014-05-13	Scientific Series	View details
The quest for self-correcting quantum memory	Olivier Landon-Cardinal	2014-05-12	Scientific Series	View details
Curvature in Noncommutative Geometry	masoud khalkhali	2014-05-09	Scientific Series	View details

Scientific Series

Format results