Triangle Seminars
July 2007
Fri
20 Jul 2007
Graded D-branes and skew-categories
📍 London
Calin Lazaroiu
(Trinity College Dublin)
Wed
11 Jul 2007
Black Hole Production in Gravity Duals and Experimental Implications for QCD and RHIC
Horatiu Nastase
(Tokyo Institute of Technology)
Abstract:
Please see the Graduate Program web page at
http://www.strings.ph.qmw.ac.uk/
for more details.
Please see the Graduate Program web page at
http://www.strings.ph.qmw.ac.uk/
for more details.
Posted by: QMW
Tue
10 Jul 2007
QCD from String Theory? Describing Nuclear Forces by Gravitational Physics
Horatiu Nastase
(Tokyo Institute of Technology)
June 2007
Thu
7 Jun 2007
Nonperturbative QFT from Lattice Simulations: Current Status and Future Perspectives
Luigi Del Debbio
(Edinburgh)
Tue
5 Jun 2007
Worldline Approach to Higher Spin Fields
Olindo Corradini
(Bologna)
Mon
4 Jun 2007
Knot homologies via singular instantons
Tom Mrowka
(MIT)
Abstract:
I will discuss some work in progress with Peter Kronheimer on a variant of Floer's instanton homology dealing with connections that are singular along codimension two submanifolds. As observed by Kronheimer earlier there are some interesting relations with Khovanov homology.
I will discuss some work in progress with Peter Kronheimer on a variant of Floer's instanton homology dealing with connections that are singular along codimension two submanifolds. As observed by Kronheimer earlier there are some interesting relations with Khovanov homology.
Posted by: IC
May 2007
Thu
31 May 2007
Singularities of the Magnon S-matrix
Nick Dorey
(DAMTP, Cambridge)
Wed
30 May 2007
Geometry and String Theory Lecture
Peter Topping
(Warwick)
Abstract:
In this lecture, I will give an overview of Ricci flow, focusing on
Perelman's work, accessible to non-experts.
In this lecture, I will give an overview of Ricci flow, focusing on
Perelman's work, accessible to non-experts.
Posted by: KCL
Thu
24 May 2007
Holographic methods and applications to black holes
Kostas Skenderis
(University of Amsterdam)
Abstract:
We discuss how to extract quantum field theory data from solutions that are asympotically (AdS_p x S_q). We apply this method to general 2-charge fuzzball solutions that is, horizon-free non-singular solutions of IIB supergravity characterized by a number of curves. We propose a precise map that relates any given curve to a specific superposition of R ground states of the D1-D5 system. To test this proposal we compute the holographic 1-point functions associated with these solutions, namely the conserved charges and the vacuum expectation values of chiral primary operators of the boundary theory, and find perfect agreement within the approximations used. All kinematical constraints are satisfied and the proposal is compatible with dynamical constraints.
We discuss how to extract quantum field theory data from solutions that are asympotically (AdS_p x S_q). We apply this method to general 2-charge fuzzball solutions that is, horizon-free non-singular solutions of IIB supergravity characterized by a number of curves. We propose a precise map that relates any given curve to a specific superposition of R ground states of the D1-D5 system. To test this proposal we compute the holographic 1-point functions associated with these solutions, namely the conserved charges and the vacuum expectation values of chiral primary operators of the boundary theory, and find perfect agreement within the approximations used. All kinematical constraints are satisfied and the proposal is compatible with dynamical constraints.
Posted by: IC
Thu
17 May 2007
On the phase diagram of fuzzy scalar field theory
Christian Saemann
(Dublin Institute of Advanced Study)
Abstract:
We consider the hermitian matrix model corresponding to scalar field theory on the fuzzy sphere. Using an expansion of the model which is similar to a high-temperature expansion, we are able to reformulate the model in terms of
its eigenvalues. Applying subsequently the saddle point method allows us to extract analytically information on the phase diagram of the theory. Eventually, we can also predict qualitatively the effect of proposed modifications of this theory which are necessary for the theory to be a regularized version of scalar field theory on the plane.
We consider the hermitian matrix model corresponding to scalar field theory on the fuzzy sphere. Using an expansion of the model which is similar to a high-temperature expansion, we are able to reformulate the model in terms of
its eigenvalues. Applying subsequently the saddle point method allows us to extract analytically information on the phase diagram of the theory. Eventually, we can also predict qualitatively the effect of proposed modifications of this theory which are necessary for the theory to be a regularized version of scalar field theory on the plane.
Posted by: IC
Thu
17 May 2007
Giants in Beta-deformed Backgrounds
Emiliano Imeroni
(Swansea)
Thu
10 May 2007
The twistor programme and twistor strings (From twistor-strings to quantum gravity)
Lionel Mason
(Oxford University)
Abstract:
The twistor programme was introduced by Roger Penrose as an approach to quantum gravity in which twistor space should provide the primary geometric background for physics from which space-time should emerge. This talk will review the programme, i.e., the early successes in formulating the self-dual parts of Yang-Mills and gravity on twistor space. It will go on to review the impact of twistor-string theory, in giving at least a perturbative approach to full Yang Mills and conformal gravity, and outline arguments that prove the equivalence between the twistor-string models and the space-time theories. Finally, twistor-string models for Einstein gravity will be reviewed.
The twistor programme was introduced by Roger Penrose as an approach to quantum gravity in which twistor space should provide the primary geometric background for physics from which space-time should emerge. This talk will review the programme, i.e., the early successes in formulating the self-dual parts of Yang-Mills and gravity on twistor space. It will go on to review the impact of twistor-string theory, in giving at least a perturbative approach to full Yang Mills and conformal gravity, and outline arguments that prove the equivalence between the twistor-string models and the space-time theories. Finally, twistor-string models for Einstein gravity will be reviewed.
Posted by: IC
Thu
10 May 2007
Completing MHV Rules via Equivalence Theorem Evasion
Tim Morris
(Southampton)
Tue
8 May 2007
Critical edge behavior in unitary random matrix ensembles and the thirty fourth Painleve transcendent
Jorgen Ostensson
(Leuven)
Abstract:
I will discuss a recent work which concerns the critical behavior of eigenvalues in ensembles
1/Z(n,N) det M(2 alpha) exp(-N Tr V(M)) dM with
alpha greater than -1/2, where the factor det M(2alpha) induces critical eigenvalue behavior near the origin. Supposing that the limiting mean eigenvalue density associated with V is
regular, and that the origin is a right endpoint of its support, one can compute (using the Deift-Zhou steepest-descent method) the limiting eigenvalue correlation kernel in the double scaling limit as n, N to infinity such that n(2/3) (n/N-1) = O(1). It turns out that the limiting kernel can be described through a distinguished solution of the thirty fourth Painleve equation. This solution is related to a particular solution of the Painleve II equation,
which however is different from the usual Hastings-McLeod solution.
The talk is based on joint work with Alexander Its and Arno Kuijlaars.
I will discuss a recent work which concerns the critical behavior of eigenvalues in ensembles
1/Z(n,N) det M(2 alpha) exp(-N Tr V(M)) dM with
alpha greater than -1/2, where the factor det M(2alpha) induces critical eigenvalue behavior near the origin. Supposing that the limiting mean eigenvalue density associated with V is
regular, and that the origin is a right endpoint of its support, one can compute (using the Deift-Zhou steepest-descent method) the limiting eigenvalue correlation kernel in the double scaling limit as n, N to infinity such that n(2/3) (n/N-1) = O(1). It turns out that the limiting kernel can be described through a distinguished solution of the thirty fourth Painleve equation. This solution is related to a particular solution of the Painleve II equation,
which however is different from the usual Hastings-McLeod solution.
The talk is based on joint work with Alexander Its and Arno Kuijlaars.
Posted by: brunel
Thu
3 May 2007
A proposal on time dependent AdS/CFT correspondence and null-singularity
Chong-Sun Chu
(Durham University)
Abstract:
The understanding of the nature of spacetime singularity and whether and how it is resolved is one of the most important problem in quantum gravity. Important examples are black hole singularity and cosmological singularity in the big bang. In this talk we will be interested in the later type and an approach to the problem using AdS/CFT correspondence for time-dependent background will be discussed. Our gauge theory results suggest that spacetime singularity is indeed resolved and the mechanism will be discussed.
The understanding of the nature of spacetime singularity and whether and how it is resolved is one of the most important problem in quantum gravity. Important examples are black hole singularity and cosmological singularity in the big bang. In this talk we will be interested in the later type and an approach to the problem using AdS/CFT correspondence for time-dependent background will be discussed. Our gauge theory results suggest that spacetime singularity is indeed resolved and the mechanism will be discussed.
Posted by: IC
April 2007
Wed
25 Apr 2007
Some lessons from higher spins
📍 London
Augusto Sagnotti
(Pisa)
Wed
25 Apr 2007
Topology changing transitions in N=4
📍 London
Timothy J. Hollowood
(Swansea)
Abstract:
N=4 SYM is known to have a confinement-deconfinement type phase
transition in finite volume as the temperature is raised. This phase transition has been conjectured to smoothly become the Hawking-Page transition between hot AdS space and an AdS black hole as the 't Hooft coupling becomes larger. I show that this phase transition at weak coupling is actually a topology changing transition for the VEVs of the scalar fields and Polyakov loop. This means that the high temperature phase cannot be, as previously thought, the black hole in the dual. I then argue for the existence of a new second order phase transition at a higher temperature to a new phase which has the right symmetries to be identified with the black hole. This is work based on the recent paper hep-th/0703100 with Umut Gursoy, Sean Hartnoll and Prem Kumar.
N=4 SYM is known to have a confinement-deconfinement type phase
transition in finite volume as the temperature is raised. This phase transition has been conjectured to smoothly become the Hawking-Page transition between hot AdS space and an AdS black hole as the 't Hooft coupling becomes larger. I show that this phase transition at weak coupling is actually a topology changing transition for the VEVs of the scalar fields and Polyakov loop. This means that the high temperature phase cannot be, as previously thought, the black hole in the dual. I then argue for the existence of a new second order phase transition at a higher temperature to a new phase which has the right symmetries to be identified with the black hole. This is work based on the recent paper hep-th/0703100 with Umut Gursoy, Sean Hartnoll and Prem Kumar.
Posted by: KCL
Tue
24 Apr 2007
Universality in critical unitary random matrix ensembles and Painleve equations
Tom Claeys
(Leuven)
Abstract:
The eigenvalues of large unitary random matrices show universal local behavior, only depending on the so-called scaling regime. It is known that in the bulk of the spectrum, local correlations of the eigenvalues are given in terms of the sine kernel, while at the edge one obtains the Airy
kernel. In certain critical random matrix ensembles, other limiting correlation kernels can occur. Near singular interior points, the limiting kernel is related to the Hastings-McLeod solution of the Painleve II equation. Near singular edge points on the other hand, one obtains a kernel related to the second member of the Painleve I hierarchy. We
describe how one can obtain these kernels rigorously in double scaling limits using the Riemann-Hilbert approach.
The eigenvalues of large unitary random matrices show universal local behavior, only depending on the so-called scaling regime. It is known that in the bulk of the spectrum, local correlations of the eigenvalues are given in terms of the sine kernel, while at the edge one obtains the Airy
kernel. In certain critical random matrix ensembles, other limiting correlation kernels can occur. Near singular interior points, the limiting kernel is related to the Hastings-McLeod solution of the Painleve II equation. Near singular edge points on the other hand, one obtains a kernel related to the second member of the Painleve I hierarchy. We
describe how one can obtain these kernels rigorously in double scaling limits using the Riemann-Hilbert approach.
Posted by: brunel
Tue
3 Apr 2007
On the universality of random matrix distributions
Thomas Kriecherbauer
(Bochum)
Abstract:
The distributions of eigenvalues of random matrices display universal behavior in two ways. On the one hand these distributions appear in many areas of mathematics and physics including such fields as number theory and combinatorics which have no obvious connection to random matrices. On the other hand these distributions are universal in the sense that there are large classes of ensembles displaying the same distributions in the limit of large matrix dimensions. In this talk both aspects of universality will be briefly
surveyed. We will also present recent universality results (of the second type) for orthogonal and symplectic ensembles.
The distributions of eigenvalues of random matrices display universal behavior in two ways. On the one hand these distributions appear in many areas of mathematics and physics including such fields as number theory and combinatorics which have no obvious connection to random matrices. On the other hand these distributions are universal in the sense that there are large classes of ensembles displaying the same distributions in the limit of large matrix dimensions. In this talk both aspects of universality will be briefly
surveyed. We will also present recent universality results (of the second type) for orthogonal and symplectic ensembles.
Posted by: brunel
March 2007
Wed
28 Mar 2007
High-energy String Thermodynamics
Larus Thorlacius
(University of Iceland)
Wed
28 Mar 2007
Defect lines in conformal field theory
Ingo Runkel
(King's College London)
Abstract:
TBA
TBA
Posted by: CityU
Tue
27 Mar 2007
Replica symmetry breaking condition exposed by a random matrix calculation
Ian Williams
(Nottingham)
Abstract:
We consider the statistical mechanics of a single classical
particle placed in an N dimensional gaussian random potential. This is a model system showing several features of glassy systems. The connection between replica symmetry breaking and the complexity of stationary points and minima is revealed in this model by random matrix methods.
We consider the statistical mechanics of a single classical
particle placed in an N dimensional gaussian random potential. This is a model system showing several features of glassy systems. The connection between replica symmetry breaking and the complexity of stationary points and minima is revealed in this model by random matrix methods.
Posted by: brunel
Wed
21 Mar 2007
Integrability, Transcendentality and Crossing
Burkhard Eden
(Utrecht University)
Abstract:
We analyze the all-loop Bethe ansatz for the sl(2) twist
operator sector of the N=4 gauge theory in the limit
of large spacetime spin at large but finite twist, and find a
novel all-loop scaling function. This function obeys the
Kotikov-Lipatov transcendentality principle and does not depend
on the twist.
We discuss possible phase factors for the
S-matrix, leading to modifications at four-loop order and beyond.
While these result in a four-loop breakdown of perturbative BMN-scaling,
transcendentality may be preserved in the universal scaling function.
One particularly natural dressing phase, unique up to one
constant, modifies the overall contribution of all terms
in the scaling function that contain odd zeta functions.
Excitingly, we present evidence that this choice is non-perturbatively
related to a recently conjectured crossing-symmetric phase factor
for perturbative string theory on AdS(5)xS(5) once the constant is
fixed to a particular value.
Our proposal, if true, might therefore resolve the long-standing
AdS/CFT discrepancies between gauge and string theory.
We analyze the all-loop Bethe ansatz for the sl(2) twist
operator sector of the N=4 gauge theory in the limit
of large spacetime spin at large but finite twist, and find a
novel all-loop scaling function. This function obeys the
Kotikov-Lipatov transcendentality principle and does not depend
on the twist.
We discuss possible phase factors for the
S-matrix, leading to modifications at four-loop order and beyond.
While these result in a four-loop breakdown of perturbative BMN-scaling,
transcendentality may be preserved in the universal scaling function.
One particularly natural dressing phase, unique up to one
constant, modifies the overall contribution of all terms
in the scaling function that contain odd zeta functions.
Excitingly, we present evidence that this choice is non-perturbatively
related to a recently conjectured crossing-symmetric phase factor
for perturbative string theory on AdS(5)xS(5) once the constant is
fixed to a particular value.
Our proposal, if true, might therefore resolve the long-standing
AdS/CFT discrepancies between gauge and string theory.
Posted by: KCL
Wed
21 Mar 2007
A warm-up for solving noncompact sigma models: The Sinh-Gordon model
Joerg Teschner
(DESY Hamburg)
Abstract:
Standard methods like the Bethe ansatz will typically fail when the target space of an integrable model is non-compact like, for example, in the case of the nonlinear sigma models associated to AdS-spaces. New methods are needed. We will discuss some of them in the simplest possible example, the Sinh-Gordon model.
Standard methods like the Bethe ansatz will typically fail when the target space of an integrable model is non-compact like, for example, in the case of the nonlinear sigma models associated to AdS-spaces. New methods are needed. We will discuss some of them in the simplest possible example, the Sinh-Gordon model.
Posted by: KCL
Wed
21 Mar 2007
A new paradigm for symmetry in viral architecture
Reidun Twarock
(University of York)
Abstract:
We show that the full three-dimensional architecture of simple viruses is encoded by affine symmetries. In particular, the locations and structures of all material boundaries can be predicted with our method, including the organisation of the capsid proteins and the genomic material. This approach departs radically from the 2-dimensional schematic representations of viral capsids in Caspar-Klug Theory and its recent generalisations, and opens up new possibilities to study the immuno-dominant epitopes and viral evolution. Applications to the modelling of virus assembly are also discussed, and we show that the counting of assembly pathways can be cast into a Hamiltonian paths problem
We show that the full three-dimensional architecture of simple viruses is encoded by affine symmetries. In particular, the locations and structures of all material boundaries can be predicted with our method, including the organisation of the capsid proteins and the genomic material. This approach departs radically from the 2-dimensional schematic representations of viral capsids in Caspar-Klug Theory and its recent generalisations, and opens up new possibilities to study the immuno-dominant epitopes and viral evolution. Applications to the modelling of virus assembly are also discussed, and we show that the counting of assembly pathways can be cast into a Hamiltonian paths problem
Posted by: CityU
Tue
20 Mar 2007
Informal Lecture on the Geometric Langlands Correspondence (1 of 2)
📍 London
Joerg Teschner
(DESY Hamburg)
Abstract:
(the second lecture will be on Wednesday morning)
(the second lecture will be on Wednesday morning)
Posted by: KCL
Thu
15 Mar 2007
The Zamolodchikov-Faddeev Algebra for AdS5 x S5 Superstring
Sergey Frolov
(Trinity College, Dublin)
Abstract:
We discuss the Zamolodchikov-Faddeev algebra for the superstring sigma-model on AdS5 x S5. We find the canonical su(2,2)2 invariant S-matrix satisfying the standard Yang-Baxter and crossing symmetry equations. Its near-plane-wave expansion matches exactly the leading order term recently obtained by the direct perturbative computation. We also show that the S-matrix obtained by Beisert in the gauge theory framework does not satisfy the standard Yang-Baxter equation, and, as a consequence, the corresponding ZF algebra is twisted. The S-matrices in gauge and string theories however are physically equivalent and related by a non-local transformation of the basis states which is explicitly constructed.
We discuss the Zamolodchikov-Faddeev algebra for the superstring sigma-model on AdS5 x S5. We find the canonical su(2,2)2 invariant S-matrix satisfying the standard Yang-Baxter and crossing symmetry equations. Its near-plane-wave expansion matches exactly the leading order term recently obtained by the direct perturbative computation. We also show that the S-matrix obtained by Beisert in the gauge theory framework does not satisfy the standard Yang-Baxter equation, and, as a consequence, the corresponding ZF algebra is twisted. The S-matrices in gauge and string theories however are physically equivalent and related by a non-local transformation of the basis states which is explicitly constructed.
Posted by: IC
Thu
15 Mar 2007
Black Holes, Instantons on Toric Singularities and q-Deformed Yang-Mills
Richard Szabo
(Heriot-Watt)
Wed
14 Mar 2007
Bubbling geometries from gauge theories
📍 London
Diego Correa
(DAMTP)
Wed
14 Mar 2007
From the parafermionic CFT basis to RSOS lattice paths
Patrick Jacob
(University of Durham)
Abstract:
We discuss a bijection between the Z_k parafermions CFT quasi-particle
basis and the RSOS lattice paths. This bijection also implies a
bijection between Bressoud lattice paths and RSOS lattice paths. We generalize this result for the graded parafermionic models and use it to construct a new fermionic character formula for the M(k+1,2k+3) minimal models, which are dual to the graded parafermions.
We discuss a bijection between the Z_k parafermions CFT quasi-particle
basis and the RSOS lattice paths. This bijection also implies a
bijection between Bressoud lattice paths and RSOS lattice paths. We generalize this result for the graded parafermionic models and use it to construct a new fermionic character formula for the M(k+1,2k+3) minimal models, which are dual to the graded parafermions.
Posted by: CityU
Tue
13 Mar 2007
Matrix models topological expansion and invariants of algebraic curves
Nicolas Orantin
(CEA Saclay)
Abstract:
Considering an arbitrary algebraic curve E(x,y)=0, I will build a infinite families of invariants, Fg(E) and Wkg(E), wrt deformations of the complexe and modular structure of the curve. I will show that, when the curve is the spectral curve of a matrix model, i.e. the limit of the loop equations of the model when the size N of the matrix
tends to infinity, these objects give the terms of the topological ('t Hooft) expansion of the free energy and the correlations functions of the corresponding matrix model. As an exemple, if E is the spectral curve of the hermitian 2-Matrix Model, one computes the generating functions of 2-colored discretized surfaces closed or open, with boundary operators or not.
Considering an arbitrary algebraic curve E(x,y)=0, I will build a infinite families of invariants, Fg(E) and Wkg(E), wrt deformations of the complexe and modular structure of the curve. I will show that, when the curve is the spectral curve of a matrix model, i.e. the limit of the loop equations of the model when the size N of the matrix
tends to infinity, these objects give the terms of the topological ('t Hooft) expansion of the free energy and the correlations functions of the corresponding matrix model. As an exemple, if E is the spectral curve of the hermitian 2-Matrix Model, one computes the generating functions of 2-colored discretized surfaces closed or open, with boundary operators or not.
Posted by: brunel
Tue
13 Mar 2007
Arbitrary Correlation functions for the Harish-Chandra measure, Duistermaat-Heckman theorem and Triangular Matrices
Aleix Prats
(LPTHE Jussieu)
Abstract:
The integral over a group of the Harish-Chandra measure has been known for a long time. On the other side, the moments of this measure (or correlation functions) are not known in general and a general formalism to compute them is lacking. I will present a formalism that allows us to compute correlation functions of the Harish-Chandra measure for any of the classical simple groups in terms of integrals over nihilpotent algebras (triangular matrices). This formulas are, in a sense, a generalization of the Duistermaat-Heckman theorem, in other words, a localization formula.
The integral over a group of the Harish-Chandra measure has been known for a long time. On the other side, the moments of this measure (or correlation functions) are not known in general and a general formalism to compute them is lacking. I will present a formalism that allows us to compute correlation functions of the Harish-Chandra measure for any of the classical simple groups in terms of integrals over nihilpotent algebras (triangular matrices). This formulas are, in a sense, a generalization of the Duistermaat-Heckman theorem, in other words, a localization formula.
Posted by: brunel
Mon
12 Mar 2007
Orbifold Gromov-Witten invariants and topological strings
Vincent Bouchard
(Berkeley)
Fri
9 Mar 2007
Quantum Mechanics of the Doubled Torus
Emily Hackett-Jones
(Edinburgh)
Thu
8 Mar 2007
The wave function behavior of the open topological string
Amir-Kian Kashani-Poor
(University of Amsterdam)
Abstract:
Suppose we could calculate the string partition function to all genera using worldsheet methods. What could we learn from this expression about a potentially underlying (non-perturbative) target space description of the theory? We address this question in the context of the open topological A-model.
Suppose we could calculate the string partition function to all genera using worldsheet methods. What could we learn from this expression about a potentially underlying (non-perturbative) target space description of the theory? We address this question in the context of the open topological A-model.
Posted by: IC
Thu
8 Mar 2007
Ordinary Differential Equations and Quantum Integrability
Patrick Dorey
(Durham)
Wed
7 Mar 2007
Twisted tori and (new) string vacua
📍 London
Ruben Minasian
(Saclay)
Wed
7 Mar 2007
Introduction to Topological Strings
Alessandro Tanzini
(SISSA - Trieste)
Abstract:
This is the first of a three lecture series aiming to provide a basic introduction to topological strings. For more details, please visit our Graduate Program webpage at:
http://www.strings.ph.qmw.ac.uk/
This is the first of a three lecture series aiming to provide a basic introduction to topological strings. For more details, please visit our Graduate Program webpage at:
http://www.strings.ph.qmw.ac.uk/
Posted by: QMW
Wed
7 Mar 2007
Cycles from resonant amplification of demographic stochasticity
Alan McKane
(University of Manchester)
Abstract:
In this talk I will discuss how the formalism of master equations
may be applied to study the stochastic dynamics of a number of
problems in population biology and biochemistry. When they contain a
large number of constituents, the behaviour of these systems may be
analysed using an expansion in the system size. To leading order the
deterministic analogues of the models can be compared to the
equations which are normally written down on phenomenological
grounds. At next to leading order a simplified stochastic
description is obtained. Attention will focus on systems for which
the deterministic description fails to predict cycles, but where
large cycles are found at next-to-leading order through a resonant
amplification of demographic fluctuations. The generality and
applicability of these results will be discussed.
In this talk I will discuss how the formalism of master equations
may be applied to study the stochastic dynamics of a number of
problems in population biology and biochemistry. When they contain a
large number of constituents, the behaviour of these systems may be
analysed using an expansion in the system size. To leading order the
deterministic analogues of the models can be compared to the
equations which are normally written down on phenomenological
grounds. At next to leading order a simplified stochastic
description is obtained. Attention will focus on systems for which
the deterministic description fails to predict cycles, but where
large cycles are found at next-to-leading order through a resonant
amplification of demographic fluctuations. The generality and
applicability of these results will be discussed.
Posted by: CityU
Mon
5 Mar 2007
Ricci flow and black holes
Toby Wiseman
(Imperial College)
February 2007
Wed
28 Feb 2007
Type II actions from 11D Chern-Simons theories
📍 London
Dmitriy Belov
(Imperial)
Abstract:
This talk continues the discussion of hep-th/0605038, applying the holographic formulation of self-dual theory to the Ramond-Ramond fields of type II supergravity. We formulate the RR partition function, in the presence of nontrivial H-fields, in terms of the wavefunction of an 11-dimensional Chern-Simons theory. Using the methods of hep-th/0605038 we show how to formulate an action principle for the RR fields of both type IIA and type IIB supergravity, in the presence of RR current. We find a new
topological restriction on consistent backgrounds of type IIA supergravity, namely the fourth Wu class must have a lift to the H-twisted cohomology.
This talk continues the discussion of hep-th/0605038, applying the holographic formulation of self-dual theory to the Ramond-Ramond fields of type II supergravity. We formulate the RR partition function, in the presence of nontrivial H-fields, in terms of the wavefunction of an 11-dimensional Chern-Simons theory. Using the methods of hep-th/0605038 we show how to formulate an action principle for the RR fields of both type IIA and type IIB supergravity, in the presence of RR current. We find a new
topological restriction on consistent backgrounds of type IIA supergravity, namely the fourth Wu class must have a lift to the H-twisted cohomology.
Posted by: KCL
Tue
27 Feb 2007
Statistics of electric current through chaotic systems: random matrix theory and semiclassics
Marcel Novaes
(Bristol)
Abstract:
The electric current that flows through a chaotic system like a quantum dot may, as a function of time, be characterized by its moments. The first and second moments are called the conductance and the shot noise. We consider the problem of calculating all higher moments, both within a random matrix theory formulation and by resorting to classical action correlations.
The electric current that flows through a chaotic system like a quantum dot may, as a function of time, be characterized by its moments. The first and second moments are called the conductance and the shot noise. We consider the problem of calculating all higher moments, both within a random matrix theory formulation and by resorting to classical action correlations.
Posted by: brunel
Mon
26 Feb 2007
Sigma model RG flow and Perelman's entropy
Arkady Tseytlin
(Imperial College)
Wed
21 Feb 2007
Geometric Transitions and Typical Black Hole Microstates
Iosif Bena
(SPhT Saclay)
Wed
21 Feb 2007
Advances in String Field Theory
Martin Schnabl
(IAS)
Wed
21 Feb 2007
On a systematic approach to defects in classical integrable field theories
Vincent Caudrelier
(University of York)
Abstract:
After introducing very generally the idea of defect and why they are
important, I will review an approach to incorporate them in
classical integrable field theories. It is essentially a lagrangian
approach in which a defect is implemented as internal boundary
conditions on the fields. The various models treated in this way so
far (sine-Gordon, nonlinear Schrodinger, Korteweg-de Vries and its
modified version) share common features which suggested an
underlying general structure. I will propose another approach,
directly based on the inverse scattering method, which exhibits
these common features in a unified way. The main advantage of this
approach is that it allows to discuss integrability in the presence
of a defect systematically. It may also simplify the quantization of
the models.
After introducing very generally the idea of defect and why they are
important, I will review an approach to incorporate them in
classical integrable field theories. It is essentially a lagrangian
approach in which a defect is implemented as internal boundary
conditions on the fields. The various models treated in this way so
far (sine-Gordon, nonlinear Schrodinger, Korteweg-de Vries and its
modified version) share common features which suggested an
underlying general structure. I will propose another approach,
directly based on the inverse scattering method, which exhibits
these common features in a unified way. The main advantage of this
approach is that it allows to discuss integrability in the presence
of a defect systematically. It may also simplify the quantization of
the models.
Posted by: CityU
Mon
19 Feb 2007
Ricci Flow, the Poincare Conjecture and Physics, Parts I and II
Marc Haskins
(Imperial College)
Abstract:
The first two of a series of seminars and lectures on Ricci Flow and its applications, lecture I at at 1330 and lecture II at 1450 on Mon February 19th.
Abstract:
This is an introductory two part lecture on the Poincare conjecture, Geometrization and Ricci flow intended for both mathematicians and physicists (assuming some familiarity with the basic notions of differential geometry).
Part I: The Poincare conjecture and Thurston's Geometrization Conjecture.
We will begin by describing the 3-dimensional Poincare conjecture, a pure topology problem about 3-manifolds. Motivated by analogies with the 2-dimensional case we will see how Thurston brought geometry into 3-dimensional topology, the goal being to describe Thurston's Geometrization Conjecture. To do this we will describe both a little more topology (the sphere and torus decompositions) and a little geometry (a discussion of the 8 different types of homogeneous 3-manifolds). We will then see how the Poincare conjecture follows straightforwardly from the Geometrization Conjecture.
Part II: Ricci flow and applications to Geometrization.
After a very brief reminder of basic notions of curvature in differential geometry, we introduce the Ricci flow and try to explain why it should be seen as a natural nonlinear heat-type equation which diffuses curvature around a manifold. We will discuss (without proof) some of the very basic analytic results for Ricci flow and discuss the simplest solutions to Ricci flow (e.g. Einstein metrics, Ricci solitons, product metrics). We will describe some of Hamilton's fundamental early work which showed that Ricci flow can be used to geometrize certain 3-manifolds, and discuss why for topological reasons we know that the Ricci flow must usually develop singularities in finite-time. We discuss the general framework in which to analyse singularities of the Ricci flow, the pre-Perelman progress in this theory and what obstructions Perelman needed to overcome to use Ricci-flow (with surgery) to prove the Geometrization Conjecture. (A discussion of Perelman's contributions will be left for another occasion).
The first two of a series of seminars and lectures on Ricci Flow and its applications, lecture I at at 1330 and lecture II at 1450 on Mon February 19th.
Abstract:
This is an introductory two part lecture on the Poincare conjecture, Geometrization and Ricci flow intended for both mathematicians and physicists (assuming some familiarity with the basic notions of differential geometry).
Part I: The Poincare conjecture and Thurston's Geometrization Conjecture.
We will begin by describing the 3-dimensional Poincare conjecture, a pure topology problem about 3-manifolds. Motivated by analogies with the 2-dimensional case we will see how Thurston brought geometry into 3-dimensional topology, the goal being to describe Thurston's Geometrization Conjecture. To do this we will describe both a little more topology (the sphere and torus decompositions) and a little geometry (a discussion of the 8 different types of homogeneous 3-manifolds). We will then see how the Poincare conjecture follows straightforwardly from the Geometrization Conjecture.
Part II: Ricci flow and applications to Geometrization.
After a very brief reminder of basic notions of curvature in differential geometry, we introduce the Ricci flow and try to explain why it should be seen as a natural nonlinear heat-type equation which diffuses curvature around a manifold. We will discuss (without proof) some of the very basic analytic results for Ricci flow and discuss the simplest solutions to Ricci flow (e.g. Einstein metrics, Ricci solitons, product metrics). We will describe some of Hamilton's fundamental early work which showed that Ricci flow can be used to geometrize certain 3-manifolds, and discuss why for topological reasons we know that the Ricci flow must usually develop singularities in finite-time. We discuss the general framework in which to analyse singularities of the Ricci flow, the pre-Perelman progress in this theory and what obstructions Perelman needed to overcome to use Ricci-flow (with surgery) to prove the Geometrization Conjecture. (A discussion of Perelman's contributions will be left for another occasion).
Posted by: IC
Fri
16 Feb 2007
Reduction by Spinor
Ruth Britto
(University of Amsterdam)
Wed
14 Feb 2007
Sigma Models on Superspaces
📍 London
Volker Schomerus
(DESY Theory Group)
Abstract:
The solution of 2D Sigma models on superspaces (-groups,-cosets, etc.) is a problem with various potential applications in condensed matter theory and string theory, in particular in the context of the AdS/CFT
correspondence. At the example of the PSU(1,1/ 2) sigma model, I shall illustrate some of the intriguing novel features of such theories, review a few recent results and assess the prospects for a complete or partial solution.
The solution of 2D Sigma models on superspaces (-groups,-cosets, etc.) is a problem with various potential applications in condensed matter theory and string theory, in particular in the context of the AdS/CFT
correspondence. At the example of the PSU(1,1/ 2) sigma model, I shall illustrate some of the intriguing novel features of such theories, review a few recent results and assess the prospects for a complete or partial solution.
Posted by: KCL
Mon
12 Feb 2007
Global geometry of the supersymmetric AdS/CFT correspondence
Oisin Mac Conamhna
(Imperial College)
Thu
8 Feb 2007
Gauged Supergravity and U-duality
Henning Samtleben
(ENS-Lyon)
Wed
7 Feb 2007
Stability and Susy, fake and pseudo
📍 London
Paul Townsend
(University of Cambridge)
Fri
2 Feb 2007
Balanced metrics in string theory
Mike Douglas
(Rutgers)
Thu
1 Feb 2007
N=2 Braine Surgery
Christian Romelsberger
(Trinity Dublin)
Abstract:
I present the generating functions which count the BPS operators in the chiral ring of a N=2 quiver gauge theory that lives on N D3 branes probing an ALE singularity. The difficulty in this computation arises from the fact that this quiver gauge theory has a moduli space of vacua that splits into many branches – the Higgs, the Coulomb and mixed branches. As a result there can be operators which explore those different branches and the counting gets complicated by having to deal with such operators while avoiding over or under counting. The solution to this problem turns out to be very elegant and is presented in this note. Some surprises with surgery of generating functions arises.
I present the generating functions which count the BPS operators in the chiral ring of a N=2 quiver gauge theory that lives on N D3 branes probing an ALE singularity. The difficulty in this computation arises from the fact that this quiver gauge theory has a moduli space of vacua that splits into many branches – the Higgs, the Coulomb and mixed branches. As a result there can be operators which explore those different branches and the counting gets complicated by having to deal with such operators while avoiding over or under counting. The solution to this problem turns out to be very elegant and is presented in this note. Some surprises with surgery of generating functions arises.
Posted by: IC
January 2007
Wed
31 Jan 2007
Anti-de Sitter black holes
📍 London
Harvey Reall
(University of Nottingham)
Wed
31 Jan 2007
Topology Change in Thermal N=4 SYM and the AdS Black Hole at Weak Coupling
Prem Kumar
(Swansea)
Tue
30 Jan 2007
Teleparallelism: difficult word but simple way of reinterpreting the Dirac Equation
Dmitri Vassiliev
(UCL)
Abstract:
The main result of the talk is a new representation for the Weyl Lagrangian (massless Dirac Lagrangian). As the dynamical variable we use the coframe, i.e. field of orthonormal bases. We write down a simple Lagrangian and show that variation of the resulting action with respect to the coframe produces the Weyl equation. The advantage of our approach is that it does not require the use of spinors, Pauli matrices or covariant differentiation. The only geometric concepts we use are those of a metric, differential form, wedge product and exterior derivative.
The construction presented in the talk is similar to that used in the so-called Cosserat theory of elasticity (multipolar elasticity).
Reference: D.Vassiliev, Phys. Rev. D75, 025006 (2007).
The main result of the talk is a new representation for the Weyl Lagrangian (massless Dirac Lagrangian). As the dynamical variable we use the coframe, i.e. field of orthonormal bases. We write down a simple Lagrangian and show that variation of the resulting action with respect to the coframe produces the Weyl equation. The advantage of our approach is that it does not require the use of spinors, Pauli matrices or covariant differentiation. The only geometric concepts we use are those of a metric, differential form, wedge product and exterior derivative.
The construction presented in the talk is similar to that used in the so-called Cosserat theory of elasticity (multipolar elasticity).
Reference: D.Vassiliev, Phys. Rev. D75, 025006 (2007).
Posted by: brunel
Mon
29 Jan 2007
Type II actions from 11-dimensional Chern-Simons theories
Dmitriy Belov
(Imperial College)
Abstract:
This paper continues the discussion of hep-th/0605038, applying the
holographic formulation of self-dual theory to the Ramond-Ramond
fields of type II supergravity. We formulate the RR partition
function, in the presence of nontrivial H-fields, in terms of the
wavefunction of an 11-dimensional Chern-Simons theory. Using the
methods of hep-th/0605038 we show how to formulate an action principle
for the RR fields of both type IIA and type IIB supergravity, in the
presence of RR current. We find a new topological restriction on
consistent backgrounds of type IIA supergravity, namely the fourth Wu
class must have a lift to the H-twisted cohomology.
This paper continues the discussion of hep-th/0605038, applying the
holographic formulation of self-dual theory to the Ramond-Ramond
fields of type II supergravity. We formulate the RR partition
function, in the presence of nontrivial H-fields, in terms of the
wavefunction of an 11-dimensional Chern-Simons theory. Using the
methods of hep-th/0605038 we show how to formulate an action principle
for the RR fields of both type IIA and type IIB supergravity, in the
presence of RR current. We find a new topological restriction on
consistent backgrounds of type IIA supergravity, namely the fourth Wu
class must have a lift to the H-twisted cohomology.
Posted by: IC
Fri
26 Jan 2007
Wetting and Minimal Surfaces
📍 London
Costas Bachas
(ENS Paris)
Abstract:
The phenomena of capillarity and (partial) wetting have been studied for two centuries, yet they continue to be of great current interest. After a brief historical review, I will discuss some recent results on the associated minimal-surface problem. In conclusion, I will draw some analogies with problems facing present-day string theory.
The phenomena of capillarity and (partial) wetting have been studied for two centuries, yet they continue to be of great current interest. After a brief historical review, I will discuss some recent results on the associated minimal-surface problem. In conclusion, I will draw some analogies with problems facing present-day string theory.
Posted by: KCL
Wed
24 Jan 2007
E11 extended spacetime and gauged supergravities
Fabio Riccioni
(KCL)
Wed
24 Jan 2007
Seven-branes, Instantons and Supersymmetry
Eric Bergshoeff
(University of Groningen)
Wed
24 Jan 2007
Conformal Field Theories, BPS states and Geometry
Alberto Zaffaroni
(Univerisy di Milano-Bicocca and INFN, Italy)
Abstract:
I discuss some aspects of the conformal field theories obtained by placing D3 branes at conical singularities focusing on the rich interplay between the properties of the gauge theories and the geometry of the internal manifold. I discuss in particular the role of baryons, a character for counting all BPS baryonic operators and its geometrical interpretation.
I discuss some aspects of the conformal field theories obtained by placing D3 branes at conical singularities focusing on the rich interplay between the properties of the gauge theories and the geometry of the internal manifold. I discuss in particular the role of baryons, a character for counting all BPS baryonic operators and its geometrical interpretation.
Posted by: KCL
Mon
22 Jan 2007
Non-geometric vacua in string theory
Brian Wecht
(MIT)
Thu
18 Jan 2007
Duality Groups, Automorphic Forms and Higher Derivative Corrections
Neil Lambert
(King's College)
Abstract:
We discuss how the duality group G controls the higher derivative corrections that arise in the effective action of M-theory compactified on a torus.
In particular we show that the perturbative contributions always involve the weights of G and that this is a consequence of the appearance of automorphic forms of G in the complete quantum effective action.
We discuss how the duality group G controls the higher derivative corrections that arise in the effective action of M-theory compactified on a torus.
In particular we show that the perturbative contributions always involve the weights of G and that this is a consequence of the appearance of automorphic forms of G in the complete quantum effective action.
Posted by: IC
Thu
18 Jan 2007
Twisted Tori and (New) String Vacua
Ruben Minasian
(CEA/Saclay)
Wed
17 Jan 2007
The dynamics of cosmic superstrings
📍 London
Edmund Copeland
(University of Nottingham)
Tue
16 Jan 2007
Wavepacket dynamics of the nonlinear Harper model
Tsampikos Kottos
(MPI Goettingen)
Abstract:
The destruction of anomalous diffusion of the Harper model at
criticality, due to weak non-linearity chi is analyzed. It
is shown that the second moment grows sub-diffusively as its expectation value is proportional to t to the power alpha, up to times t star proportional to chi to the power gamma. The exponents alpha and gamma reflect the multifractal properties of the spectra and eigenfunctions of the linear model. For t larger than t star the anomalous diffusion law is recovered, however the evolving profile has different shape with respect to the linear case. Applications to waveguide structures, and arrays of magnetic micro-traps for atomic Bose-Einstein condensates are discussed.
The destruction of anomalous diffusion of the Harper model at
criticality, due to weak non-linearity chi is analyzed. It
is shown that the second moment grows sub-diffusively as its expectation value is proportional to t to the power alpha, up to times t star proportional to chi to the power gamma. The exponents alpha and gamma reflect the multifractal properties of the spectra and eigenfunctions of the linear model. For t larger than t star the anomalous diffusion law is recovered, however the evolving profile has different shape with respect to the linear case. Applications to waveguide structures, and arrays of magnetic micro-traps for atomic Bose-Einstein condensates are discussed.
Posted by: brunel
Mon
15 Jan 2007
Black holes, qubits and the Fano plane
Mike Duff
(Imperial College)
Thu
11 Jan 2007
Recoil of low-dimensional D-branes
Ben Craps
(University of Brussel)
Abstract:
String perturbation theory in the presence of D-branes is usually described
in terms of conformal field theory (CFT) on worldsheets with boundaries. In
this formalism, closed string scattering amplitudes in the presence of
static Dp-branes exhibit infrared divergences for p=0 and p=1, so the
worldsheet CFT description breaks down.
For p=0, it is known that these divergences are due to D0-brane recoil. A
systematic framework to take recoil into account is the worldline formalism,
where fixed boundary conditions are replaced by dynamical D0-brane
worldlines. In this formalism, the divergences that plague the worldsheet
CFT are automatically cancelled in a non-trivial way. The amplitudes derived
in the worldline formalism can be reproduced by deforming the CFT with a
specific bilocal recoil operator.
For p=1, the divergences are due to local recoil of D1-branes, which
(classically) end up displaced a finite distance from their original
position. The quantum version of this phenomenon can be viewed as a simple
geometric manifestation of the absence of spontaneous symmetry breaking in
1+1 dimensions. Through a Dirac-Born-Infeld analysis, it is possible to
resum these divergences in a way that yields finite, momentum-conserving
amplitudes.
String perturbation theory in the presence of D-branes is usually described
in terms of conformal field theory (CFT) on worldsheets with boundaries. In
this formalism, closed string scattering amplitudes in the presence of
static Dp-branes exhibit infrared divergences for p=0 and p=1, so the
worldsheet CFT description breaks down.
For p=0, it is known that these divergences are due to D0-brane recoil. A
systematic framework to take recoil into account is the worldline formalism,
where fixed boundary conditions are replaced by dynamical D0-brane
worldlines. In this formalism, the divergences that plague the worldsheet
CFT are automatically cancelled in a non-trivial way. The amplitudes derived
in the worldline formalism can be reproduced by deforming the CFT with a
specific bilocal recoil operator.
For p=1, the divergences are due to local recoil of D1-branes, which
(classically) end up displaced a finite distance from their original
position. The quantum version of this phenomenon can be viewed as a simple
geometric manifestation of the absence of spontaneous symmetry breaking in
1+1 dimensions. Through a Dirac-Born-Infeld analysis, it is possible to
resum these divergences in a way that yields finite, momentum-conserving
amplitudes.
Posted by: IC
Thu
11 Jan 2007
SUSY Breaking by a Metastable Ground State: Why the Early Universe Preferred the Non-Supersymmetric Vacuum
Valya Khoze
(Durham)