Triangle Seminars
August 2009
Wed
26 Aug 2009
Holographic Baryons
Jacob Sonnenschein
(Tel Aviv)
July 2009
Wed
15 Jul 2009
Correlation functions of quantum spin chains
Frank Goehmann
(Bergische Universitaet Wuppertal)
Abstract:
Recently the mathematical structure of the static correlation functions of the spin-1/2 Heisenberg chain has been completely understood. It has been proved by Boos, Jimbo, Miwa and Smirnov that, after appropriate regularizations, all static correlation functions become polynomials in a one-point and a special neighbour-two-point correlation function. We review this important result and show that those two functions allow for an efficient
description in terms of the solutions of linear and non-linear integral equations. This opens the way for applications in quantum field theory and condensed matter physics.
Recently the mathematical structure of the static correlation functions of the spin-1/2 Heisenberg chain has been completely understood. It has been proved by Boos, Jimbo, Miwa and Smirnov that, after appropriate regularizations, all static correlation functions become polynomials in a one-point and a special neighbour-two-point correlation function. We review this important result and show that those two functions allow for an efficient
description in terms of the solutions of linear and non-linear integral equations. This opens the way for applications in quantum field theory and condensed matter physics.
Posted by: KCL
June 2009
Wed
17 Jun 2009
TBA
Simon Ross
(Durham)
Abstract:
TBA
TBA
Posted by: IC
Mon
15 Jun 2009
Supersymmetric D-branes from a worldsheet point of view
Alexander Sevrin
(Vrije Universiteit Brussel )
Abstract:
The N=2 boundary superspace formulation of RNS models in the
presence of arbitrary NSNS fluxes is developed. This allows for a systematic classification of supersymmetric D-brane configuration which leads e.g. to generalized lagrangian and coisotropic branes.
The N=2 boundary superspace formulation of RNS models in the
presence of arbitrary NSNS fluxes is developed. This allows for a systematic classification of supersymmetric D-brane configuration which leads e.g. to generalized lagrangian and coisotropic branes.
Posted by: IC
Wed
10 Jun 2009
Fuzzy geometry of membranes in M-theory
Sanjaye Ramgoolam
(QMUL)
Abstract:
Recent work on membranes of M-theory has lead to a new type of physical realization of fuzzy 2-spheres in Matrix Brane actions. In standard realizations, the fuzzy two-sphere coordinates transforming in the vector of the spherical rotation symmetry are identified with matrix variables in the adjoint representation of the unitary symmetry of the Matrix brane actions.In these new realizations, spinors of the rotational symmetry are identified with variables in bi-fundamental representations of the unitary symmetry. The vector coordinates of the fuzzy 2-sphere are recovered from bilinears in the spinors by a fuzzy version of the projection map of the Hopf fibration over the two-sphere. The outcome is the emergence of a five dimensional theory from a three dimensional one as expected from the intersection of the fundamental branes of M-Theory in ABJM quotients of eleven dimensional spacetime. The demonstration of the emergent six dimensional theory expected for the brane intersection in M-Theory without a quotient remains an open problem.
Recent work on membranes of M-theory has lead to a new type of physical realization of fuzzy 2-spheres in Matrix Brane actions. In standard realizations, the fuzzy two-sphere coordinates transforming in the vector of the spherical rotation symmetry are identified with matrix variables in the adjoint representation of the unitary symmetry of the Matrix brane actions.In these new realizations, spinors of the rotational symmetry are identified with variables in bi-fundamental representations of the unitary symmetry. The vector coordinates of the fuzzy 2-sphere are recovered from bilinears in the spinors by a fuzzy version of the projection map of the Hopf fibration over the two-sphere. The outcome is the emergence of a five dimensional theory from a three dimensional one as expected from the intersection of the fundamental branes of M-Theory in ABJM quotients of eleven dimensional spacetime. The demonstration of the emergent six dimensional theory expected for the brane intersection in M-Theory without a quotient remains an open problem.
Posted by: IC
Mon
8 Jun 2009
Gauge theory on G2 manifolds and bundles over Calabi-Yau moduli spaces
Simon Donaldson
(Imperial College)
Abstract:
In the first part of the talk I will review differential geometric background involving associative submanifolds of 7 manifolds with G2 holonomy and an analogue of the Yang Mills instanton equation for connections on bundles over such a manifold. Then I will describe joint work with Ed Segal in which, assuming these objects have suitable formal properties, we define holomorphic bundles over moduli spaces of Calabi-Yau 3-folds which can be viewed as the complexification of Floer theory. In the last part of the talk I will consider in more detail the problem of establishing the foundations required for the theory. This involves pertubations of the equations and the question of how to count solutions at infinity, which are pairs consisting of a connection and an associative submanifold. The counting problem leads to a nonlinear generalisation of the spectral flow for eigenvalues of Dirac operators.
In the first part of the talk I will review differential geometric background involving associative submanifolds of 7 manifolds with G2 holonomy and an analogue of the Yang Mills instanton equation for connections on bundles over such a manifold. Then I will describe joint work with Ed Segal in which, assuming these objects have suitable formal properties, we define holomorphic bundles over moduli spaces of Calabi-Yau 3-folds which can be viewed as the complexification of Floer theory. In the last part of the talk I will consider in more detail the problem of establishing the foundations required for the theory. This involves pertubations of the equations and the question of how to count solutions at infinity, which are pairs consisting of a connection and an associative submanifold. The counting problem leads to a nonlinear generalisation of the spectral flow for eigenvalues of Dirac operators.
Posted by: IC
Mon
8 Jun 2009
Characteristic polynomials of random matrices: Why they are important
Christopher Hughes
(University of York)
Abstract:
In this talk I will show how the characteristic polynomial of a random unitary matrix has been successfully used in number theory to model the Riemann zeta function, and then I will present some new work re-interpreting and generalizing the previous random matrix results in a probabilistic setting. This is joint work with Paul Bourgade, Ashkan Nikeghbali and Marc Yor.
In this talk I will show how the characteristic polynomial of a random unitary matrix has been successfully used in number theory to model the Riemann zeta function, and then I will present some new work re-interpreting and generalizing the previous random matrix results in a probabilistic setting. This is joint work with Paul Bourgade, Ashkan Nikeghbali and Marc Yor.
Posted by: brunel
Thu
4 Jun 2009
Black hole microstate geometries and the information paradox
Iosif Bena
(Saclay)
Thu
4 Jun 2009
Stringy modifications to spacetime structure and the CMB
Subodh Patil
(Humboldt University)
Abstract:
In this talk, we will review recent work which asks the question, what, if any effects stringy modifications to geometry might have on the predictions of inflation? We couch our discussion within two well motivated frameworks– non-commutative geometry (likely to be present during brane inflation), and modifications to mode propagation coming from a field theory representation of the stringy uncertainty principle. In the former case, we find that UV/IR mode mixing can imprint potentially observable signatures onto the CMB independent of the scale of inflation. In the latter case, we analytically compute corrections, and comment on the possibility of observing these in the fortunate circumstance that we happen to find ourselves in a weakly coupled corner of moduli space.
In this talk, we will review recent work which asks the question, what, if any effects stringy modifications to geometry might have on the predictions of inflation? We couch our discussion within two well motivated frameworks– non-commutative geometry (likely to be present during brane inflation), and modifications to mode propagation coming from a field theory representation of the stringy uncertainty principle. In the former case, we find that UV/IR mode mixing can imprint potentially observable signatures onto the CMB independent of the scale of inflation. In the latter case, we analytically compute corrections, and comment on the possibility of observing these in the fortunate circumstance that we happen to find ourselves in a weakly coupled corner of moduli space.
Posted by: IC
Tue
2 Jun 2009
Quasi-classical quantisation of AdS4 x CP3 superstring and giant magnons
Igor Shenderovich
(St Petersburg)
Abstract:
We discuss quasi-classical quantization of AdS4 x CP3
superstring using the algebraic curve techinque. We exemplify this procedure
on some configurations so called giant magnons. It turns out that there are
two types of configurations and they are quantizied in slightly different
ways. Also we discuss testing AdS/CFT correspondence in this case.
We discuss quasi-classical quantization of AdS4 x CP3
superstring using the algebraic curve techinque. We exemplify this procedure
on some configurations so called giant magnons. It turns out that there are
two types of configurations and they are quantizied in slightly different
ways. Also we discuss testing AdS/CFT correspondence in this case.
Posted by: IC
Tue
2 Jun 2009
World-sheet dualities for superspace sigma models
📍 London
Thomas Quella
(University of Amsterdam)
Mon
1 Jun 2009
Numerical metrics on moduli spaces of Calabi-Yau manifolds
Sergio Lukic
(Imperial College)
Abstract:
I will explain two algorithms that compute numerically the Weil-Petersson metric on the moduli space of polarized Calabi-Yau manifolds. I will show some explicit examples. Finally, I will outline some applications of these techniques in the physics of Calabi-Yau compactifications of string theory.
I will explain two algorithms that compute numerically the Weil-Petersson metric on the moduli space of polarized Calabi-Yau manifolds. I will show some explicit examples. Finally, I will outline some applications of these techniques in the physics of Calabi-Yau compactifications of string theory.
Posted by: IC
May 2009
Thu
28 May 2009
N=4 magnons and BFKL
Rafael Hernandez
(Madrid)
Abstract:
TBA
TBA
Posted by: QMW
Thu
21 May 2009
D-dimensional unitarity and applications to W+3jets at the LHC
Giulia Zanderighi
(Oxford)
Abstract:
TBA
TBA
Posted by: QMW
Thu
14 May 2009
TBA
Vittorio Del Duca
(Frascati - Rome)
Abstract:
TBA
TBA
Posted by: QMW
Tue
12 May 2009
A Simple Approach To the Circular Law
Tim Rogers
(King's College)
Thu
7 May 2009
1/N corrections to gluon scattering in N=4 SYM and relation to N=8 supergravity
Horatiu Nastase
(RLNR - Tokyo)
Abstract:
Motivated by the BDS conjecture, we look at 1/N corrections to gluon amplitudes in N=4 SYM.Infrared divergences are analyzed in two formalisms, of Catani and of Sterman/Tejeda-Yeomans. I willanalyze the 1/N expansion of the IR divergences, and find some systematics, at 3-loops, and iterated to any number of loops. Then we observe that up to 2-loop we have an exact relation to graviton scattering in N=8 supergravity, with a simple interpretation in a 't Hooft-like picture, but the higher loop extrapolation is problematic. Finally, I discuss the transcendentality of amplitudes and Catani IR divergent operators
Motivated by the BDS conjecture, we look at 1/N corrections to gluon amplitudes in N=4 SYM.Infrared divergences are analyzed in two formalisms, of Catani and of Sterman/Tejeda-Yeomans. I willanalyze the 1/N expansion of the IR divergences, and find some systematics, at 3-loops, and iterated to any number of loops. Then we observe that up to 2-loop we have an exact relation to graviton scattering in N=8 supergravity, with a simple interpretation in a 't Hooft-like picture, but the higher loop extrapolation is problematic. Finally, I discuss the transcendentality of amplitudes and Catani IR divergent operators
Posted by: QMW
Thu
7 May 2009
Generalized E(7(7)) coset dynamics and D=11 supergravity
📍 London
Christian Hillmann
(IHES)
Abstract:
The hidden on-shell E(7(7)) symmetry of maximal supergravity is usually discussed in a truncation from D=11 to four dimensions. In my talk, I will reverse this logic and start from a theory with manifest off-shell E(7(7)) symmetry inspired by West's coset construction. I will start with a short motivation of the generalized coset dynamics by explaining the procedure of symmetry enhancement for the familiar example of general relativity. Maximal supergravity will then be related to an extension of this procedure, whose dynamics takes place in a 4+56 dimensional exceptional geometry, following de Wit and Nicolai. Requiring a bosonic symmetry enhancement will be shown to uniquely fix the couplings in the Lagrangian as well as potential supersymmetry variations for the 56 dimensional subsector. Truncating this theory to seven dimensions exactly coincides with the truncation of both the dynamics and the supersymmetry variations of D=11supergravity in a truncation to d=7 and in the restriction to the bosonic fields contained in the Cremmer-Julia coset E(7(7))/SU(8).
The hidden on-shell E(7(7)) symmetry of maximal supergravity is usually discussed in a truncation from D=11 to four dimensions. In my talk, I will reverse this logic and start from a theory with manifest off-shell E(7(7)) symmetry inspired by West's coset construction. I will start with a short motivation of the generalized coset dynamics by explaining the procedure of symmetry enhancement for the familiar example of general relativity. Maximal supergravity will then be related to an extension of this procedure, whose dynamics takes place in a 4+56 dimensional exceptional geometry, following de Wit and Nicolai. Requiring a bosonic symmetry enhancement will be shown to uniquely fix the couplings in the Lagrangian as well as potential supersymmetry variations for the 56 dimensional subsector. Truncating this theory to seven dimensions exactly coincides with the truncation of both the dynamics and the supersymmetry variations of D=11supergravity in a truncation to d=7 and in the restriction to the bosonic fields contained in the Cremmer-Julia coset E(7(7))/SU(8).
Posted by: KCL
Tue
5 May 2009
Random matrices with external source
Arno Kuijlaars
(Leuven)
April 2009
Tue
7 Apr 2009
Spectral statistics of a pseudo-integrable map: the general case
Remy Dubertrand
(Bristol)
Abstract:
It is well established numerically that the spectral statistics of
pseudo-integrable models differ considerably from the reference statistics of
integrable and chaotic systems.
In a previous paper by Bogomolny and Schmit the statistical properties of a
certain quantized pseudo-integrable map had been calculated analytically but
only for a special sequence of matrix dimensions. This talk aims at describing
the method in order to obtain the spectral
statistics of the same quantum map for all matrix dimensions.
It is well established numerically that the spectral statistics of
pseudo-integrable models differ considerably from the reference statistics of
integrable and chaotic systems.
In a previous paper by Bogomolny and Schmit the statistical properties of a
certain quantized pseudo-integrable map had been calculated analytically but
only for a special sequence of matrix dimensions. This talk aims at describing
the method in order to obtain the spectral
statistics of the same quantum map for all matrix dimensions.
Posted by: brunel
Tue
7 Apr 2009
Cluster Mutation-Periodic Quivers and Associated Laurent Sequences
Allan Fordy
(University of Leeds)
Abstract:
We consider quivers/skew-symmetric matrices under the action of mutation (in the cluster algebra sense). We classify those which are isomorphic to their own mutation via a cycle
permuting all the vertices, and give families of quivers which have higher periodicity. The periodicity means that sequences given by recurrence relations arise in a natural way from the associated cluster algebras. We present a number of interesting, new nonlinear recurrences, necessarily with the Laurent property, of both the real line and the plane. In particular, we show that some of these recurrences can be
linearised and, with certain initial conditions, give integer sequences which contain all solutions of some particular Pell equations.
We consider quivers/skew-symmetric matrices under the action of mutation (in the cluster algebra sense). We classify those which are isomorphic to their own mutation via a cycle
permuting all the vertices, and give families of quivers which have higher periodicity. The periodicity means that sequences given by recurrence relations arise in a natural way from the associated cluster algebras. We present a number of interesting, new nonlinear recurrences, necessarily with the Laurent property, of both the real line and the plane. In particular, we show that some of these recurrences can be
linearised and, with certain initial conditions, give integer sequences which contain all solutions of some particular Pell equations.
Posted by: KCL
Thu
2 Apr 2009
Extremal Black Holes
James Lucietti
(Durham)
March 2009
Tue
31 Mar 2009
Solitons and topological sectors in nonintegrable quantum field theories
Gabor Takaks
(Eotvos Lorand University, Budapest)
Abstract:
Many integrable field theories are known to have topological excitations, so-called solitons in their spectra. Although their
existence is not directly tied to integrability, the existence of infinitely many local conserved quantities plays an important role in their dynamics. Recently we investigated whether such excitations can survive a nonintegrable perturbation. We found a very simple and comprehensive picture for models that are formulated as perturbations of conformal field theories. It turns out that in many cases solitons are confined by the nonintegrable perturbations, but there are large classes of models for which nontrivial topological excitations do survive.
Many integrable field theories are known to have topological excitations, so-called solitons in their spectra. Although their
existence is not directly tied to integrability, the existence of infinitely many local conserved quantities plays an important role in their dynamics. Recently we investigated whether such excitations can survive a nonintegrable perturbation. We found a very simple and comprehensive picture for models that are formulated as perturbations of conformal field theories. It turns out that in many cases solitons are confined by the nonintegrable perturbations, but there are large classes of models for which nontrivial topological excitations do survive.
Posted by: KCL
Tue
31 Mar 2009
Bayesian probability and quantum foundations
Ruediger Schack
(Royal holloway)
Thu
26 Mar 2009
TBA
Sergey Cherkis
(Trinity College, Dublin)
Wed
25 Mar 2009
Amplitudes, Wilson loops and dual superconformal symmetry
Paul Heslop
(Queen Mary)
Abstract:
We introduce the Wilson loop/amplitude duality, which states that
certain gluon amplitudes in N=4 SYM are equivalent to light-like
polygonal Wilson loops. We will illustrate the duality's power by
computing the one loop Wilson loop analytically (matching with the
known amplitudes) and then the two loop Wilson loop numerically for
any number of edges. If the duality continues to hold we can thus
compute two loop MHV amplitudes for any number of incoming particles.
In the second part of the talk we discuss the recently conjectured new
symmetry dual superconformal symmetry of the complete S-matrix of
N=4 SYM. We prove its presence at tree-level and find new constraints
it puts on the one loop amplitude.
We introduce the Wilson loop/amplitude duality, which states that
certain gluon amplitudes in N=4 SYM are equivalent to light-like
polygonal Wilson loops. We will illustrate the duality's power by
computing the one loop Wilson loop analytically (matching with the
known amplitudes) and then the two loop Wilson loop numerically for
any number of edges. If the duality continues to hold we can thus
compute two loop MHV amplitudes for any number of incoming particles.
In the second part of the talk we discuss the recently conjectured new
symmetry dual superconformal symmetry of the complete S-matrix of
N=4 SYM. We prove its presence at tree-level and find new constraints
it puts on the one loop amplitude.
Posted by: IC
Tue
24 Mar 2009
Double- Diffusive Intrusions
Liora Malki-Epshtein
(University College London)
Abstract:
When a salt-stratified fluid is cooled from the side, a two-dimensional convection pattern of cells is formed along the vertical side-wall and develops into horizontal intrusions which grow away from the wall. Such conditions exist in the oceans along melting icebergs, and the growth of these intrusions prevents melt-water from rising to the surface. As the intrusions grow, a series of layers is created in the salt water, with stepped temperature and salinity profiles. In this talk, I will describe an experimental and theoretical study carried out while at the ITG in Cambridge on the formation and growth of these double-diffusive intrusions.
Observations were made of growth rates of the intrusions, of internal velocities, and of temperature and salinity distributions. The rate of growth of the intrusions was found, surprisingly, to depend on the length of the experimental tank, with the end-wall playing a role in their evolution right from the beginning of the experiment (Malki-Epshtein, Phillips and Huppert, JFM 2004).
Internal waves are visualised using particle tracing methods and are shown to propagate throughout the experimental tank, maintaining hydrostatic equilibrium and having a strong role in setting up the layers.
Future application of the results of this study to the large scale could have significant implications for the modelling of oceanic double-diffusive processes, which are believed to drive large vertical and lateral fluxes of heat and salt.
When a salt-stratified fluid is cooled from the side, a two-dimensional convection pattern of cells is formed along the vertical side-wall and develops into horizontal intrusions which grow away from the wall. Such conditions exist in the oceans along melting icebergs, and the growth of these intrusions prevents melt-water from rising to the surface. As the intrusions grow, a series of layers is created in the salt water, with stepped temperature and salinity profiles. In this talk, I will describe an experimental and theoretical study carried out while at the ITG in Cambridge on the formation and growth of these double-diffusive intrusions.
Observations were made of growth rates of the intrusions, of internal velocities, and of temperature and salinity distributions. The rate of growth of the intrusions was found, surprisingly, to depend on the length of the experimental tank, with the end-wall playing a role in their evolution right from the beginning of the experiment (Malki-Epshtein, Phillips and Huppert, JFM 2004).
Internal waves are visualised using particle tracing methods and are shown to propagate throughout the experimental tank, maintaining hydrostatic equilibrium and having a strong role in setting up the layers.
Future application of the results of this study to the large scale could have significant implications for the modelling of oceanic double-diffusive processes, which are believed to drive large vertical and lateral fluxes of heat and salt.
Posted by: KCL
Tue
24 Mar 2009
Leaking quantized chaotic systems
Stefan Nonnenmacher
(CEA Saclay)
Mon
23 Mar 2009
Wilson loops: from pseudo-holomorphic surfaces to 2d Yang-Mills and Matrix Models
Simone Giombi
(Harvard)
Abstract:
In this talk, I will present several results concerning a class of supersymmetric Wilson loop operators in N=4 SYM. These operators can be defined for any loop on a three-sphere and are in general 1/16-BPS. On the string theory side of the AdS/CFT duality, these supersymmetric Wilson
loops are described by string worldsheets which are pseudo-holomorphic with respect to a novel almost complex structure defined on a AdS4xS2 subspace of AdS5xS5. A notable subclass of the general 1/16-BPS
operators, which will be the main focus of this talk, is obtained by restricting the loop to lie on a S2 in space-time. In this case supersymmetry is doubled, and we propose a conjecture that the expectation value of these operators can be computed exactly in terms of the analogous
observables in bosonic 2d Yang-Mills on S2, or equivalently by a gaussian matrix model. Several evidences for this conjecture, both on the gauge theory and on the string theory side, will be presented.
In this talk, I will present several results concerning a class of supersymmetric Wilson loop operators in N=4 SYM. These operators can be defined for any loop on a three-sphere and are in general 1/16-BPS. On the string theory side of the AdS/CFT duality, these supersymmetric Wilson
loops are described by string worldsheets which are pseudo-holomorphic with respect to a novel almost complex structure defined on a AdS4xS2 subspace of AdS5xS5. A notable subclass of the general 1/16-BPS
operators, which will be the main focus of this talk, is obtained by restricting the loop to lie on a S2 in space-time. In this case supersymmetry is doubled, and we propose a conjecture that the expectation value of these operators can be computed exactly in terms of the analogous
observables in bosonic 2d Yang-Mills on S2, or equivalently by a gaussian matrix model. Several evidences for this conjecture, both on the gauge theory and on the string theory side, will be presented.
Posted by: IC
Fri
20 Mar 2009
Moduli Space Dynamics of ADS Strings
Antal Jevicki
(Brown University)
Wed
18 Mar 2009
Integrability for the Full Spectrum of Planar AdS/CFT
📍 London
Pedro Vieira
(MPI, Potsdam)
Abstract:
We present a set of functional equations defining the anomalous
dimensions of arbitrary local single trace operators in planar N=4 SYM
theory. It takes the form of a Y-system based on the integrability of
the dual superstring sigma-model on the AdS5 x S5 background. This
Y-system passes some very important tests: it reproduces the full
asymptotic Bethe ansatz at large L, including the dressing factor, and
it confirms all recently found wrapping corrections. We shall also
describe the derivation of these equations in some detail.
We present a set of functional equations defining the anomalous
dimensions of arbitrary local single trace operators in planar N=4 SYM
theory. It takes the form of a Y-system based on the integrability of
the dual superstring sigma-model on the AdS5 x S5 background. This
Y-system passes some very important tests: it reproduces the full
asymptotic Bethe ansatz at large L, including the dressing factor, and
it confirms all recently found wrapping corrections. We shall also
describe the derivation of these equations in some detail.
Posted by: IC
Wed
18 Mar 2009
Bounding operator dimensions in CFT4
📍 London
Riccardo Rattazzi
(Ecole Polytechnique Federale de Lausanne)
Abstract:
The hierarchy problem can be represented as a tension between the
need for a large cut-off scale suggested, for instance, by
flavor physics and the need for a low cut-off scale suggested by
naturalness in electroweak symmetry breaking. I will illustrate
how this tension could be largely alleviated if the Standard
Model flowed to an approximate CFT above the weak scale with a
specific relation among the scaling dimensions of the Higgs
sector fields. To investigate the viability of that scenario one
is led to ask the following simple question: in an arbitrary CFT,
given a scalar operator phi, and the operator S=phi phi defined
as the lowest dimension scalar S which appears in the OPE
phi phi, what is the bound (that is d(S) is smaller than f(d(phi)))
on the scaling dimensions of the two operators? I will present a
derivation of the bound based on general considerations of OPE,
conformal block decomposition, and crossing symmetry. The
function f(d(phi)) is computed numerically. When d(phi) goes to
1, one has f(d(phi))=2+O(sqrt(d(phi)-1)), which shows that the
free theory limit is approached continuously. An analogous bound
can be derived in 2D where some non-trivial consistency check can
be made. I will discuss the relevance of the result for the
hierarchy problem and illustrate the directions of future
investigation.
The hierarchy problem can be represented as a tension between the
need for a large cut-off scale suggested, for instance, by
flavor physics and the need for a low cut-off scale suggested by
naturalness in electroweak symmetry breaking. I will illustrate
how this tension could be largely alleviated if the Standard
Model flowed to an approximate CFT above the weak scale with a
specific relation among the scaling dimensions of the Higgs
sector fields. To investigate the viability of that scenario one
is led to ask the following simple question: in an arbitrary CFT,
given a scalar operator phi, and the operator S=phi phi defined
as the lowest dimension scalar S which appears in the OPE
phi phi, what is the bound (that is d(S) is smaller than f(d(phi)))
on the scaling dimensions of the two operators? I will present a
derivation of the bound based on general considerations of OPE,
conformal block decomposition, and crossing symmetry. The
function f(d(phi)) is computed numerically. When d(phi) goes to
1, one has f(d(phi))=2+O(sqrt(d(phi)-1)), which shows that the
free theory limit is approached continuously. An analogous bound
can be derived in 2D where some non-trivial consistency check can
be made. I will discuss the relevance of the result for the
hierarchy problem and illustrate the directions of future
investigation.
Posted by: KCL
Tue
17 Mar 2009
Dynamical Stability of topological Order
Dimitris Tsomokos
(University of Hertfordshire)
Abstract:
Topological orders are non-symmetry breaking phases of matter, which provide a new paradigm in condensed-matter physics. Their characterization is a major open problem, although considerable progress has been made since the proposal of the topological entanglement entropy. In this talk I will review how topological orders have been proposed to serve as robust quantum memories. Then the dynamical stability of topologically ordered quantum states will be examined. Conditions will be derived on the type of dynamical evolution that allows quantum recurrence and preservation of the initial topological order.
Topological orders are non-symmetry breaking phases of matter, which provide a new paradigm in condensed-matter physics. Their characterization is a major open problem, although considerable progress has been made since the proposal of the topological entanglement entropy. In this talk I will review how topological orders have been proposed to serve as robust quantum memories. Then the dynamical stability of topologically ordered quantum states will be examined. Conditions will be derived on the type of dynamical evolution that allows quantum recurrence and preservation of the initial topological order.
Posted by: KCL
Mon
16 Mar 2009
Integrable aspects of Ulam's problem
Percy Deift
(Courant Institute, NYU)
Abstract:
The speaker will show how Ulam's increasing subsequence problem
is connected to a variety of classical integrable systems.
The speaker will show how Ulam's increasing subsequence problem
is connected to a variety of classical integrable systems.
Posted by: brunel
Mon
16 Mar 2009
AdS/CFT and generalized geometry
James Sparks
(Oxford)
Fri
13 Mar 2009
Some aspects of flux compactifications.
Michela Petrini
(Jussieu Paris)
Abstract:
This is the first lecture of a short course on flux compactifications. For more information on the course and the schedule, please visit
http://www.strings.ph.qmw.ac.uk/index.htm
and follow the link to the Graduate Program in String/Field Theory.
This is the first lecture of a short course on flux compactifications. For more information on the course and the schedule, please visit
http://www.strings.ph.qmw.ac.uk/index.htm
and follow the link to the Graduate Program in String/Field Theory.
Posted by: QMW
Thu
12 Mar 2009
Open string wavefunctions in warped compactifications
Fernando Marchesano
(CERN)
Abstract:
I will discuss the wavefunctions for open strings in warped compactifications, and in particular for D7-branes in warped Calabi-Yau orientifolds, which provide a string theory realizations of the Randall-Sundrum scenario. I will show how certain background fluxes, necessary in the presence of warping, couple to the fermionic wavefunctions and qualitatively change their behavior. Finally, the warped Kahler potential for the D7-brane light modes will be discussed, as well as a proposal to embed it in the full open+closed Kahler potential.
I will discuss the wavefunctions for open strings in warped compactifications, and in particular for D7-branes in warped Calabi-Yau orientifolds, which provide a string theory realizations of the Randall-Sundrum scenario. I will show how certain background fluxes, necessary in the presence of warping, couple to the fermionic wavefunctions and qualitatively change their behavior. Finally, the warped Kahler potential for the D7-brane light modes will be discussed, as well as a proposal to embed it in the full open+closed Kahler potential.
Posted by: QMW
Thu
12 Mar 2009
Lattice Sine-Gordon Model: Explicit Construction of Separation of Variable Basis
Giuliano Niccoli
(DESY Hamburg)
Abstract:
tba
tba
Posted by: KCL
Wed
11 Mar 2009
On reduced model for strings in AdS5 x S5
📍 London
Arkady Tseytlin
(Imperial College)
Wed
11 Mar 2009
Integrability for the Full Spectrum of Planar AdS/CFT
Nikolai Gromov
(DESY)
Abstract:
We review a duality between N=4 super Yang-Mills and
a string theory in AdS5xS5 background and integrability
arising in both theories. New results conserning
finite length operators/short strings will be presented.
We review a duality between N=4 super Yang-Mills and
a string theory in AdS5xS5 background and integrability
arising in both theories. New results conserning
finite length operators/short strings will be presented.
Posted by: IC
Tue
10 Mar 2009
Three recent results on asymptotics of oscillations
Sir Michael Berry
(Physics Department, University of Bristol)
Abstract:
The results are separate, and apparently paradoxical, and have implications for physics. First, when two exponentials compete, their interference can be dominated by the contribution with smaller exponent. Second, repeated differentiation of almost all functions in a wide class generates trigonometric oscillations ('almost all functions tend to cosx'). Third, it is possible to find band-limited functions that oscillate arbitrarily faster than their fastest Fourier component ('superoscillations').
The results are separate, and apparently paradoxical, and have implications for physics. First, when two exponentials compete, their interference can be dominated by the contribution with smaller exponent. Second, repeated differentiation of almost all functions in a wide class generates trigonometric oscillations ('almost all functions tend to cosx'). Third, it is possible to find band-limited functions that oscillate arbitrarily faster than their fastest Fourier component ('superoscillations').
Posted by: KCL
Tue
10 Mar 2009
Statistics of eigenfunctions in open chaotic systems: a perturbative approach
Charles Poli
(LPMC Nice)
Mon
9 Mar 2009
QUANTUM THEORY IN SIX DIMENSIONS
Mans Henningson
(Chalmers, Goteborg)
Abstract:
We first quickly review some basic facts about quantum theories in 1+5 dimensions with 2,0 superconformal symmetry. They arise as decoupled subsectors of string or M theories on space times containing certain defects like branes or singularities. By compactification,
they are also related to Yang-Mills theories in lower dimensions. We then describe, in somewhat more detail, recent work on these theories considered on a spatial five torus. In particular, one may determine the
spectrum of vacuum states, and also learn much about the spectrum of
BPS states. Hopefully, this will eventually be helpful for giving a definition of
these mysterious theories.
We first quickly review some basic facts about quantum theories in 1+5 dimensions with 2,0 superconformal symmetry. They arise as decoupled subsectors of string or M theories on space times containing certain defects like branes or singularities. By compactification,
they are also related to Yang-Mills theories in lower dimensions. We then describe, in somewhat more detail, recent work on these theories considered on a spatial five torus. In particular, one may determine the
spectrum of vacuum states, and also learn much about the spectrum of
BPS states. Hopefully, this will eventually be helpful for giving a definition of
these mysterious theories.
Posted by: IC
Wed
4 Mar 2009
Brane Tilings, M2 Branes and Chern Simons theories
📍 London
Amihay Hanany
(Imperial College)
Abstract:
Brane Tilings are known to describe the largest known class of SCFT's in 3+1 dimensions. There is a well established formalism to find AdS_5 x SE_5 duals to these SCFT's and to compare results on both sides. This talk extends this formalism to 2+1 dimensional SCFT's, living on the world volume of M2 branes, which are dual to AdS_4 x SE_7 backgrounds of M theory. The SCFT's are quiver gauge theories with 4 supercharges (N=2 in 2+1 dimensions) and Chern Simons (CS) couplings. They admit a moduli space of vacuum configurations which is a CY4 cone over SE_7. The talk will go over the formalism and look at several examples in detail. The computation of scaling dimensions will be mentioned and relations to regular toric Fano 3-folds if time permits.
Brane Tilings are known to describe the largest known class of SCFT's in 3+1 dimensions. There is a well established formalism to find AdS_5 x SE_5 duals to these SCFT's and to compare results on both sides. This talk extends this formalism to 2+1 dimensional SCFT's, living on the world volume of M2 branes, which are dual to AdS_4 x SE_7 backgrounds of M theory. The SCFT's are quiver gauge theories with 4 supercharges (N=2 in 2+1 dimensions) and Chern Simons (CS) couplings. They admit a moduli space of vacuum configurations which is a CY4 cone over SE_7. The talk will go over the formalism and look at several examples in detail. The computation of scaling dimensions will be mentioned and relations to regular toric Fano 3-folds if time permits.
Posted by: KCL
Wed
4 Mar 2009
M5-brane Quantum Geometry
Douglas Smith
(Durham)
Abstract:
We attempt to indirectly deduce the form of quantum geometry on
the M5-brane in the presence of a constant C-field 3-form potential. We
first show how the noncommutative geometry on the D3-brane in a constant
2-form B-field can be deduced by analysing open strings ending on the
D3-brane. We show that the string boundary condition is a modified Nahm
equation, and that these modifications can be understood in terms of the
noncommutative geometry. Similarly, the boundary condition for M2-branes
ending on the M5-brane is given by the Basu-Harvey equation, modified by
the C-field. By an analogy, we interpret this modification in terms of a
proposed quantum geometry on the M5-brane. This geometry is specified by a
3-bracket, unlike the usual 2-bracket for noncommutative geometry.
We attempt to indirectly deduce the form of quantum geometry on
the M5-brane in the presence of a constant C-field 3-form potential. We
first show how the noncommutative geometry on the D3-brane in a constant
2-form B-field can be deduced by analysing open strings ending on the
D3-brane. We show that the string boundary condition is a modified Nahm
equation, and that these modifications can be understood in terms of the
noncommutative geometry. Similarly, the boundary condition for M2-branes
ending on the M5-brane is given by the Basu-Harvey equation, modified by
the C-field. By an analogy, we interpret this modification in terms of a
proposed quantum geometry on the M5-brane. This geometry is specified by a
3-bracket, unlike the usual 2-bracket for noncommutative geometry.
Posted by: IC
Tue
3 Mar 2009
Quantum simulation in ion traps and Bose Einstein condensates
Alexander Retzker
(Imperial College London)
Abstract:
In this talk I will describe proposals for quantum simulations in Ion traps and BECs.
It will be shown that the radial degree of freedom of strings of trapped ions in the quantum regime may be prepared and controlled accurately through the variation of the external trapping potential while at the same time its properties are measurable with high spatial and temporal resolution. This provides a new test-bed giving access to static and dynamical properties of the physics of quantum-many-body systems and quantum phase transitions that are hard to simulate on classical computers. Furthermore, it allows for the creation of double well potentials with experimentally accessible tunnelling rates and with applications in testing the foundations of quantum physics and precision sensing.
A scheme for the study of methods for detecting Unruh-like acceleration radiation effects in a Bose-Einstein condensate in a 1+1 dimensional setup will be descried. In particular, the dispersive effects of the Bogoliubov spectrum on the ideal case of exact thermalization will be explained.
In this talk I will describe proposals for quantum simulations in Ion traps and BECs.
It will be shown that the radial degree of freedom of strings of trapped ions in the quantum regime may be prepared and controlled accurately through the variation of the external trapping potential while at the same time its properties are measurable with high spatial and temporal resolution. This provides a new test-bed giving access to static and dynamical properties of the physics of quantum-many-body systems and quantum phase transitions that are hard to simulate on classical computers. Furthermore, it allows for the creation of double well potentials with experimentally accessible tunnelling rates and with applications in testing the foundations of quantum physics and precision sensing.
A scheme for the study of methods for detecting Unruh-like acceleration radiation effects in a Bose-Einstein condensate in a 1+1 dimensional setup will be descried. In particular, the dispersive effects of the Bogoliubov spectrum on the ideal case of exact thermalization will be explained.
Posted by: KCL
Mon
2 Mar 2009
Instanton Floer Homology for Sutured Manifolds
Tom Mrowka
(MIT)
Abstract:
In some recent work with Kronheimer we have carried over a version of Juhasz' Heegaard Floer Homology for sutured three manifolds to Instanton Floer Homology. This leads to amongst over things a streamlined proofs of property P for all knots and that symplectic manifolds have non-vanishing Donaldson invariants.
In some recent work with Kronheimer we have carried over a version of Juhasz' Heegaard Floer Homology for sutured three manifolds to Instanton Floer Homology. This leads to amongst over things a streamlined proofs of property P for all knots and that symplectic manifolds have non-vanishing Donaldson invariants.
Posted by: IC
February 2009
Thu
26 Feb 2009
D-branes and giant gravitons in AdS4xCP3
Andrea Prinsloo
(University of Cape Town)
Abstract:
The AdS4/Chern-Simons theory duality, recently conjectured by Aharony, Bergman, Jafferis and Maldacena, provides not only a new testing ground for the gauge theory/gravity correspondence, but also a possible way to access M-theoretic degrees of freedom. In this talk, I shall discuss some of our recent results on the open string sector of the type IIA string theory in AdS4xCP3, with emphasis on D-branes and giant gravitons in particular. Specifically, I shall focus on the so-called dual giant, a D2-brane extended on an S2 in AdS4, its spectrum of small fluctuations and open strings attached to it.
The AdS4/Chern-Simons theory duality, recently conjectured by Aharony, Bergman, Jafferis and Maldacena, provides not only a new testing ground for the gauge theory/gravity correspondence, but also a possible way to access M-theoretic degrees of freedom. In this talk, I shall discuss some of our recent results on the open string sector of the type IIA string theory in AdS4xCP3, with emphasis on D-branes and giant gravitons in particular. Specifically, I shall focus on the so-called dual giant, a D2-brane extended on an S2 in AdS4, its spectrum of small fluctuations and open strings attached to it.
Posted by: QMW
Wed
25 Feb 2009
TBA
Pau Figueras
(Durham)
Wed
25 Feb 2009
Non-planar ABJM Theory, Integrability and Parity
Charlotte Kristjansen
(NBI)
Abstract:
First we review existing results concerning the non-planar spectrum of
N=4 SYM. Next, using an effective vertex method we explicitly
derive the two-loop dilatation generator of ABJM theory in its
SU(2) x SU(2) sector, including all non-planar corrections. This
generator is then applied to a series of finite length operators as well
as to two different types of BMN operators. As in N=4 SYM, at the
planar level the finite length operators are found to exhibit a degeneracy
between certain pairs of operators with opposite parity – a degeneracy
which can be attributed to the existence of an extra conserved charge and
thus to the integrability of the planar theory.When non-planar corrections
are taken into account the degeneracies between parity pairs disappear
hinting the absence of higher conserved charges. The analysis of the BMN
operators resembles that of N=4 SYM. Additional non-planar terms
appear for BMN operators of finite length but once the strict BMN limit is
taken these terms disappear.
First we review existing results concerning the non-planar spectrum of
N=4 SYM. Next, using an effective vertex method we explicitly
derive the two-loop dilatation generator of ABJM theory in its
SU(2) x SU(2) sector, including all non-planar corrections. This
generator is then applied to a series of finite length operators as well
as to two different types of BMN operators. As in N=4 SYM, at the
planar level the finite length operators are found to exhibit a degeneracy
between certain pairs of operators with opposite parity – a degeneracy
which can be attributed to the existence of an extra conserved charge and
thus to the integrability of the planar theory.When non-planar corrections
are taken into account the degeneracies between parity pairs disappear
hinting the absence of higher conserved charges. The analysis of the BMN
operators resembles that of N=4 SYM. Additional non-planar terms
appear for BMN operators of finite length but once the strict BMN limit is
taken these terms disappear.
Posted by: KCL
Wed
25 Feb 2009
D-branes and matrix factorisations in supersymmetric coset models
Stefan Fredenhagen
(AEI Potsdam)
Abstract:
In Landau-Ginzburg models, B-type boundary conditions are described by matrix factorisations of the superpotential. In cases where such a model corresponds to a rational conformal field theory (e.g. a coset model), we can compare the matrix factorisations to known boundary states. The connection between these complementary descriptions can on the one hand be used to improve the understanding of closed and open string moduli space, on the other hand it could give hints towards the construction of new boundary states.
In Landau-Ginzburg models, B-type boundary conditions are described by matrix factorisations of the superpotential. In cases where such a model corresponds to a rational conformal field theory (e.g. a coset model), we can compare the matrix factorisations to known boundary states. The connection between these complementary descriptions can on the one hand be used to improve the understanding of closed and open string moduli space, on the other hand it could give hints towards the construction of new boundary states.
Posted by: KCL
Tue
24 Feb 2009
Towards the solution of the spectral problem of the planar AdF/CFT correspondence
Adam Rej
(Imperial College London)
Abstract:
In this talk we will review the recent developments in the field of integrability of the AdS/CFT correspondence. In particular, we will discuss the novel dynamical tests of the duality and summarize the breakdown of the asymptotic spin-chain picture at the wrapping order. We will also discuss the latest attempts to incorporate the non-local wrapping interactions.
In this talk we will review the recent developments in the field of integrability of the AdS/CFT correspondence. In particular, we will discuss the novel dynamical tests of the duality and summarize the breakdown of the asymptotic spin-chain picture at the wrapping order. We will also discuss the latest attempts to incorporate the non-local wrapping interactions.
Posted by: KCL
Mon
23 Feb 2009
Dimer Models and Calabi-Yau Algebras
Nathan Broomhead
(Bath University)
Abstract:
From dimer models, as introduced in string theory, we can
produce a class of Calabi Yau algebras which are candidates for non-commutative crepant resolutions of Gorenstein 3 fold affine toric singularities. In this talk I will introduce, via examples, dimers and their corresponding toric varieties. I will then talk about the consistency condition that underlies the Calabi Yau property.
From dimer models, as introduced in string theory, we can
produce a class of Calabi Yau algebras which are candidates for non-commutative crepant resolutions of Gorenstein 3 fold affine toric singularities. In this talk I will introduce, via examples, dimers and their corresponding toric varieties. I will then talk about the consistency condition that underlies the Calabi Yau property.
Posted by: IC
Thu
19 Feb 2009
Quantum Symmetries and Marginal Deformations
Konstantinos Zoubos
(NBI)
Abstract:
I will discuss the Hopf algebraic (quantum symmetry) structures underlying certain four-dimensional finite quantum field theories which are related to the N=4 SYM theory by marginal deformations. The motivation is to understand why these theories, despite being
finite (like N=4 SYM), are generically not integrable in the planar limit (unlike N=4 SYM). Apart from a better understanding of integrability, these hidden symmetries might eventually provide insight into the construction of the (still unknown) dual AdS/CFT geometries for these field theories.
I will discuss the Hopf algebraic (quantum symmetry) structures underlying certain four-dimensional finite quantum field theories which are related to the N=4 SYM theory by marginal deformations. The motivation is to understand why these theories, despite being
finite (like N=4 SYM), are generically not integrable in the planar limit (unlike N=4 SYM). Apart from a better understanding of integrability, these hidden symmetries might eventually provide insight into the construction of the (still unknown) dual AdS/CFT geometries for these field theories.
Posted by: QMW
Thu
19 Feb 2009
D-branes and giant gravitons in AdS4xCP3
Andrea Prinsloo
(Cape Town University)
Abstract:
The AdS4/Chern-Simons theory duality, recently conjectured by Aharony, Bergman, Jafferis and Maldacena, provides not only a new testing ground for the gauge theory/gravity correspondence, but also a possible way to access M-theoretic degrees of freedom. In this talk, I shall discuss some of our recent results on the open string sector of the type IIA string theory in AdS4xCP3, with emphasis on D-branes and giant gravitons in particular. Specifically, I shall focus on the so-called dual giant, a D2-brane extended on an S2 in AdS4, its spectrum of small fluctuations and open strings attached to it.
The AdS4/Chern-Simons theory duality, recently conjectured by Aharony, Bergman, Jafferis and Maldacena, provides not only a new testing ground for the gauge theory/gravity correspondence, but also a possible way to access M-theoretic degrees of freedom. In this talk, I shall discuss some of our recent results on the open string sector of the type IIA string theory in AdS4xCP3, with emphasis on D-branes and giant gravitons in particular. Specifically, I shall focus on the so-called dual giant, a D2-brane extended on an S2 in AdS4, its spectrum of small fluctuations and open strings attached to it.
Posted by: IC
Wed
18 Feb 2009
Supersymmetric Five-Dimensional Black Holes
📍 London
Jan Gutowski
(KCL)
Wed
18 Feb 2009
Superprotected n-point functions in N=4 super Yang-Mills theory
Jan Plefka
(Humboldt)
Wed
18 Feb 2009
TBA
Sean Nowling
(Helsinki)
Tue
17 Feb 2009
Inverse Problems: From Medical Imaging to Boundary Value Problems
Thanasis Fokas
(Cambridge University)
Abstract:
Two different types of inverse problems will be discussed: (a) The inversion of certain integral transforms arising in medical imaging. (b) The generalized Dirichlet to Neumann map for certain physically significant boundary value problems, including the biharmonic equation in a semi strip and the Helmholtz equation in the interior of a canonical polygon.
Two different types of inverse problems will be discussed: (a) The inversion of certain integral transforms arising in medical imaging. (b) The generalized Dirichlet to Neumann map for certain physically significant boundary value problems, including the biharmonic equation in a semi strip and the Helmholtz equation in the interior of a canonical polygon.
Posted by: KCL
Mon
16 Feb 2009
TBA
Amihay Hanany
(IC)
Wed
11 Feb 2009
Vacua of Gauged Extended Supergravities
📍 London
Thomas Fischbacher
(Southampton)
Abstract:
This talk briefly explains why finding the vacuum solutions of gauged maximal supergravity models is a mathematically challenging problem, and which techniques exist that are powerful enough to actually solve it. As these techniques require joint effort between physicists and computer scientists, the problem is explained in a way that should be
accessible to both groups.
In models of extended supergravity with more than one
gravitino, the symmetry group transforming the gravitini into one another can be promoted to a local symmetry. In order to maintain supersymmetry, such a deformation mandates the introduction of a potential for the scalar fields whose stationary points correspond to vacua with spontaneously broken symmetry. The most famous such model
is the SO(8)-gauged N=8 supergravity in four dimensions by de Wit and Nicolai, which also can be obtained by dimensional reduction of M-theory on the 7-sphere. The mathematical problem in the determination of the vacua lies in the complexity of the potential, which is a function on a high-dimensional Riemannian symmetric space based on an E-series exceptional Lie group. While previous group
theoretic arguments allowed a partial investigation of the problem only, there are powerful semi-numeric computational techniques that indeed seem to be strong enough to solve the problem in full. These methods are explained using as an example the most challenging supergravity potential, that of N=16 in D=3 with SO(8)xSO(8) gauge group, and some first data on new vacua of N=8 supergravity in D=4 are
presented.
This talk briefly explains why finding the vacuum solutions of gauged maximal supergravity models is a mathematically challenging problem, and which techniques exist that are powerful enough to actually solve it. As these techniques require joint effort between physicists and computer scientists, the problem is explained in a way that should be
accessible to both groups.
In models of extended supergravity with more than one
gravitino, the symmetry group transforming the gravitini into one another can be promoted to a local symmetry. In order to maintain supersymmetry, such a deformation mandates the introduction of a potential for the scalar fields whose stationary points correspond to vacua with spontaneously broken symmetry. The most famous such model
is the SO(8)-gauged N=8 supergravity in four dimensions by de Wit and Nicolai, which also can be obtained by dimensional reduction of M-theory on the 7-sphere. The mathematical problem in the determination of the vacua lies in the complexity of the potential, which is a function on a high-dimensional Riemannian symmetric space based on an E-series exceptional Lie group. While previous group
theoretic arguments allowed a partial investigation of the problem only, there are powerful semi-numeric computational techniques that indeed seem to be strong enough to solve the problem in full. These methods are explained using as an example the most challenging supergravity potential, that of N=16 in D=3 with SO(8)xSO(8) gauge group, and some first data on new vacua of N=8 supergravity in D=4 are
presented.
Posted by: KCL
Wed
11 Feb 2009
A deformed detour in AdS/CFT space
Teresia Mansson
(KTH, Stockholm)
Abstract:
N=4 super Yang-Mills theory has a remarkable feature of being integrable.
This discovery has made it possible to achieve strong evidence for the AdS/CFT
duality.
But what about its siblings: marginal deformations of N=4 SYM
that preserve conformal symmetry. In this case much less is known about the
conjectured supergravity dual. In particular, the Leigh-Strassler deformations
are of this kind, which are only integrable for some special values of the
deformation parameters, or in some restricted subsectors.
In order to gain more insight into the theory, one would like to understand
the symmetries of the theory better. We know that the symmetries of
integrable systems can be described by Hopf algebras. Here we would like
to show that a Hopf algebra structure actually emerges for the generic
Leigh-Strassler deformation.
N=4 super Yang-Mills theory has a remarkable feature of being integrable.
This discovery has made it possible to achieve strong evidence for the AdS/CFT
duality.
But what about its siblings: marginal deformations of N=4 SYM
that preserve conformal symmetry. In this case much less is known about the
conjectured supergravity dual. In particular, the Leigh-Strassler deformations
are of this kind, which are only integrable for some special values of the
deformation parameters, or in some restricted subsectors.
In order to gain more insight into the theory, one would like to understand
the symmetries of the theory better. We know that the symmetries of
integrable systems can be described by Hopf algebras. Here we would like
to show that a Hopf algebra structure actually emerges for the generic
Leigh-Strassler deformation.
Posted by: IC
Tue
10 Feb 2009
Chaotic Dynamics and Modelling
Celso Grebogi
(University of Aberdeen)
Abstract:
The talk is based on a 1990 Phys. Rev. milestone paper
Scientists attempt to understand physical phenomena by constructing models. A model serves as a link between scientists and nature, and one basic goal is to develop models whose solutions accurately reflect the nature of the physical process. But a dynamical model uses simplifying assumptions and approximations. The question of whether a model accurately reflects nature is one constantly faced by scientists. I will argue that there exist levels of mathematical difficulty, brought from the theory of dynamical systems, which can limit our ability to represent chaotic processes in nature using deterministic models. Specifically, in such cases, no model of such a system produces solutions of reasonable length that are realized by nature. Furthermore, for these processes, the numerical solutions of the models do not approximate any actual model solutions.
The talk is based on a 1990 Phys. Rev. milestone paper
Scientists attempt to understand physical phenomena by constructing models. A model serves as a link between scientists and nature, and one basic goal is to develop models whose solutions accurately reflect the nature of the physical process. But a dynamical model uses simplifying assumptions and approximations. The question of whether a model accurately reflects nature is one constantly faced by scientists. I will argue that there exist levels of mathematical difficulty, brought from the theory of dynamical systems, which can limit our ability to represent chaotic processes in nature using deterministic models. Specifically, in such cases, no model of such a system produces solutions of reasonable length that are realized by nature. Furthermore, for these processes, the numerical solutions of the models do not approximate any actual model solutions.
Posted by: KCL
Tue
10 Feb 2009
Electrostatic equilibrium problems and zeros of orthogonal polynomials
Mourad Ismail
(University of Central Florida)
Wed
4 Feb 2009
Interacting membranes
📍 London
David Berman
(Queen Mary)
Wed
4 Feb 2009
Buzzword bingo: MHV, CSW and BCFW in string amplitudes
Rutger Boels
(NBI)
Abstract:
In recent years there have been quantum leaps in the development of
calculational technology for field theory amplitudes, partly captured by
the buzzwords in the title of this talk. Interestingly, most of these
developments are rooted within field theory ideas of the sixties which
centered around the 'analytic S-matrix'. This line of thought led to the
birth of string theory with Veneziano's amplitude. It therefore seems a
natural question if these recent field theory ideas can be found within
the frame-work of string theory amplitudes. On the basis of three
examples, I will argue that this is not only natural but profitable.
In recent years there have been quantum leaps in the development of
calculational technology for field theory amplitudes, partly captured by
the buzzwords in the title of this talk. Interestingly, most of these
developments are rooted within field theory ideas of the sixties which
centered around the 'analytic S-matrix'. This line of thought led to the
birth of string theory with Veneziano's amplitude. It therefore seems a
natural question if these recent field theory ideas can be found within
the frame-work of string theory amplitudes. On the basis of three
examples, I will argue that this is not only natural but profitable.
Posted by: IC
Tue
3 Feb 2009
An Introduction to ADS/CFT correspondence
Bogdan Stefanski
(City University London)
Abstract:
We give a brief introduction to recent advances in the AdS/CFT correspondence with particular emphasis on the role integrable structures enter this duality.
We give a brief introduction to recent advances in the AdS/CFT correspondence with particular emphasis on the role integrable structures enter this duality.
Posted by: KCL
January 2009
Wed
28 Jan 2009
Black rings in Taub-NUT and the D0-D6 system
Stefano Giusto
(CEA Saclay)
Abstract:
We construct new exact solutions of pure gravity in five
dimensions representing black rings in Taub-NUT spaces, both at zero and at non-zero temperature. We use these solutions to study properties of the D0-D6 system in the supergravity approximation. In particular we compute the interaction energy between D0 and D6 branes, analyze equilibrium configurations and their stability.
We construct new exact solutions of pure gravity in five
dimensions representing black rings in Taub-NUT spaces, both at zero and at non-zero temperature. We use these solutions to study properties of the D0-D6 system in the supergravity approximation. In particular we compute the interaction energy between D0 and D6 branes, analyze equilibrium configurations and their stability.
Posted by: KCL
Wed
28 Jan 2009
D-instantons and Twistors
Stefan Vandoren
(Utrecht University)
Abstract:
Finding the exact, quantum corrected metric on the hypermultiplet moduli space in Type II string compactifications on Calabi-Yau threefolds is an outstanding open problem. We address this issue by writing the quaternionic geometry on the hypermultiplet moduli space in terms of twistor geometry.
Using this twistor space approach, we are able to express the effects of all D-instantons in Type II compactifications concisely as a sum of dilogarithm functions.
Finding the exact, quantum corrected metric on the hypermultiplet moduli space in Type II string compactifications on Calabi-Yau threefolds is an outstanding open problem. We address this issue by writing the quaternionic geometry on the hypermultiplet moduli space in terms of twistor geometry.
Using this twistor space approach, we are able to express the effects of all D-instantons in Type II compactifications concisely as a sum of dilogarithm functions.
Posted by: KCL
Tue
27 Jan 2009
The Silver Blaze Problem and how Random Matrix Theory solves it
Kim Splittorff
(Niels Bohr Institute)
Abstract:
Phase transitions can often be linked to the spectral properties of certain physical operators. In the theory of the strong interactions the fundamental breaking of chiral symmetry is intimately linked to the spectrum of the Dirac operator. When, however, quarks are favored over anti quarks by means of a chemical potential the Dirac operator becomes non hermitian. In this case the link between the Dirac spectrum and breaking of chiral symmetry has remained a puzzle (The Silver Blaze Problem) for more than two decades. In this talk we discuss how Random Matrix Theory solves this problem.
Phase transitions can often be linked to the spectral properties of certain physical operators. In the theory of the strong interactions the fundamental breaking of chiral symmetry is intimately linked to the spectrum of the Dirac operator. When, however, quarks are favored over anti quarks by means of a chemical potential the Dirac operator becomes non hermitian. In this case the link between the Dirac spectrum and breaking of chiral symmetry has remained a puzzle (The Silver Blaze Problem) for more than two decades. In this talk we discuss how Random Matrix Theory solves this problem.
Posted by: brunel
Fri
23 Jan 2009
An Introduction to non-geometric backgrounds in string theory
Ron Reid-Edwards
(Queen Mary)
Abstract:
This is the first lecture of a short course on non-geometric backgrounds. For more information on the course and the schedule, please visit
http://www.strings.ph.qmw.ac.uk/index.htm
and follow the link to the Graduate Program in String/Field Theory.
This is the first lecture of a short course on non-geometric backgrounds. For more information on the course and the schedule, please visit
http://www.strings.ph.qmw.ac.uk/index.htm
and follow the link to the Graduate Program in String/Field Theory.
Posted by: QMW
Thu
22 Jan 2009
Berry Phase and Supersymmetry
David Tong
(DAMTP, Cambridge)
Wed
21 Jan 2009
Nonlocal Dynamics in String Field Theory and Cosmological Applications
Liudmila Joukovskaya
(DAMTP)
Abstract:
In this talk we will consider dynamics with infinitely many time
derivatives, such equations follow directly from string field theory and
have many interesting properties. First we will review results for the case
of Minkowski background and then consider coupling to nontrivial
background, in particular, to Friedmann-Robertson-Walker metric. New
methods for solving corresponding nonlocal Friedmann equations will be
presented and resulting solutions in the view of cosmological applications
will be discussed.
In this talk we will consider dynamics with infinitely many time
derivatives, such equations follow directly from string field theory and
have many interesting properties. First we will review results for the case
of Minkowski background and then consider coupling to nontrivial
background, in particular, to Friedmann-Robertson-Walker metric. New
methods for solving corresponding nonlocal Friedmann equations will be
presented and resulting solutions in the view of cosmological applications
will be discussed.
Posted by: IC
Tue
20 Jan 2009
Edge scaling limits for non-Hermitian random matrices
Martin Bender
(KU Leuven)
Abstract:
The eigenvalue statistics at the edge of the spectrum of large random matrices from the Gaussian unitary ensemble (GUE) are described by the Airy point process and the maximal eigenvalue is asymptotically Tracy-Widom distributed.
In contrast, for the complex Ginibre ensemble (consisting of matrices with iid complex Gaussian entries), extreme eigenvalues behave like a Poisson process and the maximal modulus (or maximal real part) of the eigenvalues converges to a Gumbel-distributed random variable.
In this talk, a family of ensembles interpolating between these models is considered, and we show how a non-trivial transition between Airy and Poisson statistics occurs for the eigenvalues near the edge of the spectrum.
The eigenvalue statistics at the edge of the spectrum of large random matrices from the Gaussian unitary ensemble (GUE) are described by the Airy point process and the maximal eigenvalue is asymptotically Tracy-Widom distributed.
In contrast, for the complex Ginibre ensemble (consisting of matrices with iid complex Gaussian entries), extreme eigenvalues behave like a Poisson process and the maximal modulus (or maximal real part) of the eigenvalues converges to a Gumbel-distributed random variable.
In this talk, a family of ensembles interpolating between these models is considered, and we show how a non-trivial transition between Airy and Poisson statistics occurs for the eigenvalues near the edge of the spectrum.
Posted by: brunel
Mon
19 Jan 2009
Coamoeba and equivariant homological mirror symmetry for the projective space
Kazushi Ueda
(Oxford)
Abstract:
A brane tiling is a bicolored graph on an oriented real 2torus, which conjecturally describes both the derived category of coherent sheaves on a 2dimensional toric Fano stack and the derived category of the directed Fukaya category of the mirror. When the toric Fano stack is the projective plane, the corresponding brane tiling divides the torus into three hexagons. In the talk, based on a joint work in progress with Masahiro Futaki, I will describe the analogue of brane tiling for the projective space, which divides the real 3torus into four truncated octahedra, and explain how it helps to study a torus-equivariant version of homological mirror symmetry.
A brane tiling is a bicolored graph on an oriented real 2torus, which conjecturally describes both the derived category of coherent sheaves on a 2dimensional toric Fano stack and the derived category of the directed Fukaya category of the mirror. When the toric Fano stack is the projective plane, the corresponding brane tiling divides the torus into three hexagons. In the talk, based on a joint work in progress with Masahiro Futaki, I will describe the analogue of brane tiling for the projective space, which divides the real 3torus into four truncated octahedra, and explain how it helps to study a torus-equivariant version of homological mirror symmetry.
Posted by: IC
Wed
14 Jan 2009
Non-relativistic CFTs and gravity
📍 London
Mukund Rangamani
(Durham)
Abstract:
I will discuss how field theories with non-relativistic conformal symmetry, arise naturally in string theory and furthermore describe how one can construct gravitational duals for such theories. Using the gravitational description we will discuss aspects of thermal physics of these theories.
I will discuss how field theories with non-relativistic conformal symmetry, arise naturally in string theory and furthermore describe how one can construct gravitational duals for such theories. Using the gravitational description we will discuss aspects of thermal physics of these theories.
Posted by: KCL
Wed
14 Jan 2009
String creation and effective field theory.
Janet Hung
(DAMTP, Cambridge)
Abstract:
We will discuss the missing pieces in the understanding of the
effective field theory description of string creation, the S-dual of the
Hanany-Witten effect, both in the open and closed string picture. We
explain the origin of a crucial bare Chern-Simons term, that used to be
added in by hand for consistency. Finally we summarize the remaining
unsettled issues, concerning the need to modify the DBI action and the
interpretation of the bare term in M-theory.
We will discuss the missing pieces in the understanding of the
effective field theory description of string creation, the S-dual of the
Hanany-Witten effect, both in the open and closed string picture. We
explain the origin of a crucial bare Chern-Simons term, that used to be
added in by hand for consistency. Finally we summarize the remaining
unsettled issues, concerning the need to modify the DBI action and the
interpretation of the bare term in M-theory.
Posted by: IC