Triangle Seminars
December 2009
Thu
17 Dec 2009
Cosmological quantum billiards
Hermann Nicolai
(MPI, Potsdam)
Abstract:
The mini-superspace quantization of D=11 Supergravity is
equivalent to the quantization of a E10-K(E10) coset
space sigma model when the latter is restricted to the E10 Cartan
subalgebra. As a consequence, the wavefunctions solving the relevant
mini-superspace Wheeler-DeWitt equation involve automorphic (Maass wave)
forms under the modular group W+(E10) cong PSL2(O). Using Dirichlet
boundary conditions on the billiard domain a general inequality for the
Laplace eigenvalues of these automorphic forms can be derived, which
implies that the wave function of the universe is generically complex
and always tends to zero when approaching the initial singularity. The
potential significance of these properties for the question of
singularity resolution in quantum cosmology is discussed, also in
comparison with other approaches. The present approach offers
interesting new perspectives on some long-standing issues in canonical
quantum gravity.
The mini-superspace quantization of D=11 Supergravity is
equivalent to the quantization of a E10-K(E10) coset
space sigma model when the latter is restricted to the E10 Cartan
subalgebra. As a consequence, the wavefunctions solving the relevant
mini-superspace Wheeler-DeWitt equation involve automorphic (Maass wave)
forms under the modular group W+(E10) cong PSL2(O). Using Dirichlet
boundary conditions on the billiard domain a general inequality for the
Laplace eigenvalues of these automorphic forms can be derived, which
implies that the wave function of the universe is generically complex
and always tends to zero when approaching the initial singularity. The
potential significance of these properties for the question of
singularity resolution in quantum cosmology is discussed, also in
comparison with other approaches. The present approach offers
interesting new perspectives on some long-standing issues in canonical
quantum gravity.
Posted by: IC
Tue
15 Dec 2009
The archaeology of unipotent radicals of the exceptional algebraic groups
David Stewart
(Imperial College London)
Abstract:
We want to know all reductive subgroups of the five exceptional algebraic groups. In low characteristic some unusual subgroups appear which are contained inside parabolic subgroups. I will show how to find these by an archaeological dig.
We want to know all reductive subgroups of the five exceptional algebraic groups. In low characteristic some unusual subgroups appear which are contained inside parabolic subgroups. I will show how to find these by an archaeological dig.
Posted by: KCL
Wed
9 Dec 2009
Multi-center non-BPS black holes (and what can they teach us about the information paradox)
Iosif Bena
(Paris)
Abstract:
I will review the construction of BPS and non-BPS multicenter black hole solutions, and describe a class of smooth solutions that have the same charges and asymptotics as black holes, but do not have a horizon. I will then discuss some of the properties of these solutions and argue that they should correspond to typical microstates of extremal black holes. If so, string theory would imply that a classical extremal black hole solution is a thermodynamic approximation of an ensemble of horizonless configurations, and that this solution stops giving a valid description of the physics at the scale of the horizon. I will finish by discussing the extension of this to non-extremal black holes and its implications for the information paradox.
I will review the construction of BPS and non-BPS multicenter black hole solutions, and describe a class of smooth solutions that have the same charges and asymptotics as black holes, but do not have a horizon. I will then discuss some of the properties of these solutions and argue that they should correspond to typical microstates of extremal black holes. If so, string theory would imply that a classical extremal black hole solution is a thermodynamic approximation of an ensemble of horizonless configurations, and that this solution stops giving a valid description of the physics at the scale of the horizon. I will finish by discussing the extension of this to non-extremal black holes and its implications for the information paradox.
Posted by: KCL
Wed
9 Dec 2009
The gauge dual of Romans mass
Alessandro Tomasiello
(Universita' di Milano Bicocca)
Abstract:
The Romans mass is a discrete parameter in type IIA string
theory. It is perhaps the most mysterious piece of the theory: for example, its non-perturbative, M-theoretic interpretation is still not known. In this talk, we will review recent efforts to understand it through another non-perturbative tool: holography. We will see how this
parameter modifies the recent holographic interpretation of certain string vacua via Chern-Simons theories. This leads to certain field theory results that, in turn, help find new families of supersymmetric vacua of string theory with negative cosmological constant.
The Romans mass is a discrete parameter in type IIA string
theory. It is perhaps the most mysterious piece of the theory: for example, its non-perturbative, M-theoretic interpretation is still not known. In this talk, we will review recent efforts to understand it through another non-perturbative tool: holography. We will see how this
parameter modifies the recent holographic interpretation of certain string vacua via Chern-Simons theories. This leads to certain field theory results that, in turn, help find new families of supersymmetric vacua of string theory with negative cosmological constant.
Posted by: KCL
Tue
8 Dec 2009
Aspects of Gauge-Strings duality
Carlos Nunez
(Swansea University)
Abstract:
After an overview of some of the achievements of the AdS/CFT correspondence when applied to realistic field theories, I will describe recent progress in the area.
After an overview of some of the achievements of the AdS/CFT correspondence when applied to realistic field theories, I will describe recent progress in the area.
Posted by: KCL
Thu
3 Dec 2009
Yangian symmetry and a new regularization of scattering amplitudes in N=4 SYM
Jan Plefka
(Humboldt University)
Abstract:
In this talk we will review the appearance of an infinite dimensional symmetry algebra
of tree level scattering amplitudes of N=4 super Yang-Mills theory, known as the Yangian
of psu(2,2 4). It arises through the commutation of standard superconformal and the recently
discovered dual superconformal symmetries of scattering amplitudes. At the loop level the
conformal and dual conformal symmetry is destroyed by infrared divergencies. The present challenge
is whether it may be repaired. We point out a novel IR regularization based on a suitable Higgsing of
the theory, which is natural from the dual string perspective. It turns out that in this regularization
an extended conformal symmetry of the loop amplitudes arises, which remains free of anomalies.
In this talk we will review the appearance of an infinite dimensional symmetry algebra
of tree level scattering amplitudes of N=4 super Yang-Mills theory, known as the Yangian
of psu(2,2 4). It arises through the commutation of standard superconformal and the recently
discovered dual superconformal symmetries of scattering amplitudes. At the loop level the
conformal and dual conformal symmetry is destroyed by infrared divergencies. The present challenge
is whether it may be repaired. We point out a novel IR regularization based on a suitable Higgsing of
the theory, which is natural from the dual string perspective. It turns out that in this regularization
an extended conformal symmetry of the loop amplitudes arises, which remains free of anomalies.
Posted by: QMW
Wed
2 Dec 2009
Ultraviolet Structure of Maximal Supersymmetric Theories
📍 London
Kelly Stelle
(Imperial)
Wed
2 Dec 2009
Local E11 and gauged maximal supergravities
Fabio Riccioni
(KCL)
Abstract:
We give a method of deriving the field-strengths of all massless and massive, i.e. gauged, maximal supergravity theories in any dimension starting from the Kac-Moody algebra E11. Considering the subalgebra of E11 that acts on the fields in the non-linear realisation as a global symmetry, we show how this is promoted to a gauge symmetry enlarging the algebra by the inclusion of additional generators. Given the enlarged algebra corresponding to the massless theory, we show that this can be deformed to obtain the algebra corresponding to the gauged theory. We show how this works in detail for the case of Scherk-Schwarz reduction of IIB to nine dimensions. We then classify all the possible deformations in any dimensions and show that these are in one to one correspondence with all the possible gauged supergravities. This provides a very efficient, simple and unified derivation of the field strengths and gauge transformations of all the bosonic fields of any maximal supergravity theory.
We give a method of deriving the field-strengths of all massless and massive, i.e. gauged, maximal supergravity theories in any dimension starting from the Kac-Moody algebra E11. Considering the subalgebra of E11 that acts on the fields in the non-linear realisation as a global symmetry, we show how this is promoted to a gauge symmetry enlarging the algebra by the inclusion of additional generators. Given the enlarged algebra corresponding to the massless theory, we show that this can be deformed to obtain the algebra corresponding to the gauged theory. We show how this works in detail for the case of Scherk-Schwarz reduction of IIB to nine dimensions. We then classify all the possible deformations in any dimensions and show that these are in one to one correspondence with all the possible gauged supergravities. This provides a very efficient, simple and unified derivation of the field strengths and gauge transformations of all the bosonic fields of any maximal supergravity theory.
Posted by: IC
Tue
1 Dec 2009
Quantum Gravity and Signatures of noncommutative spacetime
Richard Szabo
(Heriot-Watt University, Edinburgh )
Abstract:
A pedagogical introduction into the ideas, propects and successes of spacetime quantization will be presented, with emphasis on what it tells us about hte problems of quantizing gravity and renormalizing quantum field theory.
A pedagogical introduction into the ideas, propects and successes of spacetime quantization will be presented, with emphasis on what it tells us about hte problems of quantizing gravity and renormalizing quantum field theory.
Posted by: KCL
Tue
1 Dec 2009
Avoiding the characteristic function in the supersymmetry method
Mario Kieburg
(Univ. Duisburg-Essen)
November 2009
Thu
26 Nov 2009
Conformal chiral boson models and non-geometric string vacua
Nikolaos Prezas
(Bern University)
Abstract:
I will discuss recent progress in understanding non-geometric string
backgrounds.
These are inherently stringy constructions that are globally well-
defined only up to T-dualities.
One approach in analyzing such backgrounds is through the
corresponding effective gauged
supergravities. The classification of the latter in terms of
embedding tensors provides us
with a picture of the landscape of such backgrounds, realized in
terms of non-geometric fluxes.
Also, it is by now evident that a doubling of the coordinates of the
underlying geometry
is necessary for describing these backgrounds, since their stringy
nature implies that
winding modes should be treated on equal footing with the momentum
modes. This leads
us to doubled geometries and in particular twisted doubled tori, that
are expected to
underlie general supergravity gaugings. Of particular interest is the
worldsheet description
of such doubled geometries which involves chiral boson models.
Although these models
are not Lorentz invariant in general, for the twisted doubled tori
Lorentz invariance is restored.
Furthermore, the conditions for conformal invariance of those models
agree with the conditions
from minimizing the corresponding supergravity potential. This result
firmly establishes that
chiral boson models with twisted doubled tori target spaces are the
worldsheet theories underlying
a very broad class of supergravity gaugings.
I will discuss recent progress in understanding non-geometric string
backgrounds.
These are inherently stringy constructions that are globally well-
defined only up to T-dualities.
One approach in analyzing such backgrounds is through the
corresponding effective gauged
supergravities. The classification of the latter in terms of
embedding tensors provides us
with a picture of the landscape of such backgrounds, realized in
terms of non-geometric fluxes.
Also, it is by now evident that a doubling of the coordinates of the
underlying geometry
is necessary for describing these backgrounds, since their stringy
nature implies that
winding modes should be treated on equal footing with the momentum
modes. This leads
us to doubled geometries and in particular twisted doubled tori, that
are expected to
underlie general supergravity gaugings. Of particular interest is the
worldsheet description
of such doubled geometries which involves chiral boson models.
Although these models
are not Lorentz invariant in general, for the twisted doubled tori
Lorentz invariance is restored.
Furthermore, the conditions for conformal invariance of those models
agree with the conditions
from minimizing the corresponding supergravity potential. This result
firmly establishes that
chiral boson models with twisted doubled tori target spaces are the
worldsheet theories underlying
a very broad class of supergravity gaugings.
Posted by: IC
Thu
26 Nov 2009
Stability walls in heterotic theories
James Gray
(Oxford)
Abstract:
We study the sub-structure of the heterotic Kahler moduli space due to the presence of non-Abelian internal gauge fields from the perspective of the four-dimensional effective theory. Internal gauge fields can be supersymmetric in some regions of the Kahler moduli space but break supersymmetry in others. In the context of the four-dimensional theory, we investigate what happens when the Kahler moduli are changed from the supersymmetric to the non-supersymmetric region. Our results provide a low-energy description of supersymmetry breaking by internal gauge fields as well as a physical picture for the mathematical notion of bundle stability. Specifically, we find that at the transition between the two regions an additional anomalous U(1) symmetry appears under which some of the states in the low-energy theory acquire charges. We compute the associated D-term contribution to the four-dimensional potential which contains a Kahler-moduli dependent Fayet-Iliopoulos term and contributions from the charged states. We show that this D-term correctly reproduces the expected physics. Several mathematical conclusions concerning vector bundle stability are drawn from our arguments. We also discuss possible physical applications of our results to heterotic model building and moduli stabilization.
We study the sub-structure of the heterotic Kahler moduli space due to the presence of non-Abelian internal gauge fields from the perspective of the four-dimensional effective theory. Internal gauge fields can be supersymmetric in some regions of the Kahler moduli space but break supersymmetry in others. In the context of the four-dimensional theory, we investigate what happens when the Kahler moduli are changed from the supersymmetric to the non-supersymmetric region. Our results provide a low-energy description of supersymmetry breaking by internal gauge fields as well as a physical picture for the mathematical notion of bundle stability. Specifically, we find that at the transition between the two regions an additional anomalous U(1) symmetry appears under which some of the states in the low-energy theory acquire charges. We compute the associated D-term contribution to the four-dimensional potential which contains a Kahler-moduli dependent Fayet-Iliopoulos term and contributions from the charged states. We show that this D-term correctly reproduces the expected physics. Several mathematical conclusions concerning vector bundle stability are drawn from our arguments. We also discuss possible physical applications of our results to heterotic model building and moduli stabilization.
Posted by: QMW
Wed
25 Nov 2009
Attractors in Supergravity
📍 London
Alessio Marrani
(Stanford)
Abstract:
An introductory review of the foundations of the Attractor Mechanism in extremal black holes in d=4 supergravity theories will be given. The issues of the classification of black hole attractors, of their stability and of the definition of an effective potential in the scalar manifold will be addressed. Finally, some recent developments will be shortly considered, such as the charge orbits and the moduli spaces of attractor solutions in N=2 and extended supergravities, and the generalization of the Attractor Mechanism to intersecting configurations of black branes in higher dimensions.
An introductory review of the foundations of the Attractor Mechanism in extremal black holes in d=4 supergravity theories will be given. The issues of the classification of black hole attractors, of their stability and of the definition of an effective potential in the scalar manifold will be addressed. Finally, some recent developments will be shortly considered, such as the charge orbits and the moduli spaces of attractor solutions in N=2 and extended supergravities, and the generalization of the Attractor Mechanism to intersecting configurations of black branes in higher dimensions.
Posted by: KCL
Tue
24 Nov 2009
Truncations of random unitary matrices and their eigenvalues
Boris Khoruzhenko
(Queen Mary)
Abstract:
Choose at random a matrix from the unitary group and cut a square block from it. The obtained matrix is a random contraction. Such matrices appear in a variety of mathematical contexts and are also used for modelling physical processes. After surveying some of these applications, I will talk about universal statistical patterns in the distribution of eigenvalues of random contractions in the limit of infinite matrix dimension.
Choose at random a matrix from the unitary group and cut a square block from it. The obtained matrix is a random contraction. Such matrices appear in a variety of mathematical contexts and are also used for modelling physical processes. After surveying some of these applications, I will talk about universal statistical patterns in the distribution of eigenvalues of random contractions in the limit of infinite matrix dimension.
Posted by: brunel
Tue
24 Nov 2009
Integrable field theory with a new class of defects
Cristina Zambon
(Durham University)
Abstract:
A new framework within which an integrable defect may be described is introduced in the classical context (type II defect). It relays on the introduction of a new degree of freedom located on the defect and coupled to the discontinuity of the fields across the defect. Its features will be analyzed and few concrete examples will be provided. In particular, this new scheme allows to provide a description of the Tzitzeica model with a defect, which was not possible in the previous approach (type I defect).
A new framework within which an integrable defect may be described is introduced in the classical context (type II defect). It relays on the introduction of a new degree of freedom located on the defect and coupled to the discontinuity of the fields across the defect. Its features will be analyzed and few concrete examples will be provided. In particular, this new scheme allows to provide a description of the Tzitzeica model with a defect, which was not possible in the previous approach (type I defect).
Posted by: KCL
Wed
18 Nov 2009
N=2 generalized quiver theories, Liouville theory and loop operators
📍 London
Nadav Drukker
(Humboldt)
Abstract:
A large family of interacting conformal field theories in four
dimensions with N=2 supersymmetry was recently constructed by Gaiotto.
Each gauge theory is associated to a Riemann surface with certain
allowed singularities. In fact, it was proposed by Alday, Gaiotto and
Tachikawa that the partition function of these theories (based on
SU(2) gauge groups) is equal to correlation function in Liouville
theory with central charge c=25.
After reviewing these constructions I will turn to a detailed
exploration of S-duality using loop operators: Wilson, 't Hooft and
dyonic. I will explain the classification and evaluation of arbitrary
loops in arbitrary theories and show how they transform into
each-other under S-duality.
A large family of interacting conformal field theories in four
dimensions with N=2 supersymmetry was recently constructed by Gaiotto.
Each gauge theory is associated to a Riemann surface with certain
allowed singularities. In fact, it was proposed by Alday, Gaiotto and
Tachikawa that the partition function of these theories (based on
SU(2) gauge groups) is equal to correlation function in Liouville
theory with central charge c=25.
After reviewing these constructions I will turn to a detailed
exploration of S-duality using loop operators: Wilson, 't Hooft and
dyonic. I will explain the classification and evaluation of arbitrary
loops in arbitrary theories and show how they transform into
each-other under S-duality.
Posted by: IC
Wed
18 Nov 2009
Holographic Vortices and Quasiparticles in Strongly Coupled Systems
📍 London
Clifford Johnson
(USC)
Abstract:
The dynamics of vortices and quasiparticles in holographic realizations of 2+1 dimensional strongly interacting systems are studied in the presence of magnetic field. The first part of the seminar will discuss holographic superconductors and the second part will discuss holographic realizations of Fermi surfaces.
The dynamics of vortices and quasiparticles in holographic realizations of 2+1 dimensional strongly interacting systems are studied in the presence of magnetic field. The first part of the seminar will discuss holographic superconductors and the second part will discuss holographic realizations of Fermi surfaces.
Posted by: QMW
Tue
17 Nov 2009
Quantum 1D Hamiltonians from statistical models
Yacine Ikhlef
(Universite de Geneve)
Abstract:
Motivated by recent work on frustrated spin chains and anyonic fusion chains, we define a 1D quantum Hamiltonian (based on the Temperley-Lieb algebra) which contains these models as special cases. This Hamiltonian contains a new integrable point with Z_2-symmetry, which we have solved exactly. In this talk, I will first explain the physical motivations and recall basic facts on the Temperley-Lieb algebra, a central object in 2D Statistical Mechanics. Then I will present analytical and numerical results for the phase diagram, and comment on perspectives in the fields of Condensed Matter Theory and Integrable Models.
Motivated by recent work on frustrated spin chains and anyonic fusion chains, we define a 1D quantum Hamiltonian (based on the Temperley-Lieb algebra) which contains these models as special cases. This Hamiltonian contains a new integrable point with Z_2-symmetry, which we have solved exactly. In this talk, I will first explain the physical motivations and recall basic facts on the Temperley-Lieb algebra, a central object in 2D Statistical Mechanics. Then I will present analytical and numerical results for the phase diagram, and comment on perspectives in the fields of Condensed Matter Theory and Integrable Models.
Posted by: KCL
Mon
16 Nov 2009
SEMINAR CANCELLED
Steve Giddings
(CERN)
Thu
12 Nov 2009
Gauge threshold corrections for local string models
Joseph Conlon
(Oxford)
Abstract:
Local string models are those where Standard Model degrees of freedom arise on a small region inside a large bulk volume. I study threshold effects on gauge coupling running for such models. The Kaplunovsky-Louis formula for locally supersymmetric gauge theories predicts the unification scale should be the bulk winding mode scale, parametrically large than the string scale where divergences are naively cut off. Analysis of explicit string models on orbifold/orientifold geometries confirms this. The winding mode scale arises from the presence of tadpoles uncancelled in the local model. I briefly discuss phenomenological applications to supersymmetry breaking and gauge coupling unification.
Local string models are those where Standard Model degrees of freedom arise on a small region inside a large bulk volume. I study threshold effects on gauge coupling running for such models. The Kaplunovsky-Louis formula for locally supersymmetric gauge theories predicts the unification scale should be the bulk winding mode scale, parametrically large than the string scale where divergences are naively cut off. Analysis of explicit string models on orbifold/orientifold geometries confirms this. The winding mode scale arises from the presence of tadpoles uncancelled in the local model. I briefly discuss phenomenological applications to supersymmetry breaking and gauge coupling unification.
Posted by: QMW
Wed
11 Nov 2009
Superconductors and quantum criticality in M-theory
📍 London
Julian Sonner
(Imperial)
Abstract:
Quantum phase transitions imply certain scaling relations among space and time. A subclass of quantum critical systems is in fact invariant under relativstic conformal symmetries. Such theories have recently been studied as a new class of duals in AdS/CFT. I will describe how one can exactly embed so-called holographic superconductors in M-theory and how this embedding has already lead to new insights about the low-temperature behaviour of holgraphic superconductors with an underlying quantum critical point.
Quantum phase transitions imply certain scaling relations among space and time. A subclass of quantum critical systems is in fact invariant under relativstic conformal symmetries. Such theories have recently been studied as a new class of duals in AdS/CFT. I will describe how one can exactly embed so-called holographic superconductors in M-theory and how this embedding has already lead to new insights about the low-temperature behaviour of holgraphic superconductors with an underlying quantum critical point.
Posted by: KCL
Wed
11 Nov 2009
Toy Models of CFT/AdS: Matrix Models Approach
Norihiro Iizuka
(Santa Barbara)
Abstract:
We study various matrix models as toy models of the gauge dual of the AdS spacetime
and black hole. I will summarize what these matrix models teach us about
the information paradox and emergence of the light speed limit.
We study various matrix models as toy models of the gauge dual of the AdS spacetime
and black hole. I will summarize what these matrix models teach us about
the information paradox and emergence of the light speed limit.
Posted by: IC
Tue
10 Nov 2009
Parametrically forced patterns and quasipatterns
Alastair Rucklidge
(University of Leeds)
Abstract:
The classic Faraday wave experiment consists of a horizontal layer of fluid that spontaneously develops a pattern of standing waves on its surface as it is driven by vertical oscillation with amplitude exceeding a critical value. Faraday wave experiments have consistently produced patterns with remarkably high degrees of symmetry. Quasipatterns, which are quasiperiodic in any spatial direction, are particularly interesting since there is, as yet, no satisfactory theoretical understanding of their formation. We use multi-frequency parametric forcing to investigate the formation of patterns and approximate quasipatterns in a model partial differential equation, which plays the same role for the Faraday wave experiment that the Swift–Hohenberg equation plays for convection. We exploit three-wave resonant interactions to design forcing functions that ought to produce complex patterns, and make quantitative comparisons between weakly nonlinear predictions and the solutions of the PDE. This comparison reveals the limitations of the theory, and we explore ways in which these limitations can be addressed.
Based on:
Design of parametrically forced patterns and quasipatterns, by A.M. Rucklidge and M. Silber. SIAM J. Applied Dynamical Systems 8 (2009) 298-347.
The classic Faraday wave experiment consists of a horizontal layer of fluid that spontaneously develops a pattern of standing waves on its surface as it is driven by vertical oscillation with amplitude exceeding a critical value. Faraday wave experiments have consistently produced patterns with remarkably high degrees of symmetry. Quasipatterns, which are quasiperiodic in any spatial direction, are particularly interesting since there is, as yet, no satisfactory theoretical understanding of their formation. We use multi-frequency parametric forcing to investigate the formation of patterns and approximate quasipatterns in a model partial differential equation, which plays the same role for the Faraday wave experiment that the Swift–Hohenberg equation plays for convection. We exploit three-wave resonant interactions to design forcing functions that ought to produce complex patterns, and make quantitative comparisons between weakly nonlinear predictions and the solutions of the PDE. This comparison reveals the limitations of the theory, and we explore ways in which these limitations can be addressed.
Based on:
Design of parametrically forced patterns and quasipatterns, by A.M. Rucklidge and M. Silber. SIAM J. Applied Dynamical Systems 8 (2009) 298-347.
Posted by: KCL
Tue
10 Nov 2009
Directed polymers and the quantum Toda lattice
Neil O'Connell
(Warwick)
Thu
5 Nov 2009
Gauge theories and string theory
Carlos Nunez
(Swansea)
Abstract:
I will present two recent results in the are of Gauge-Strings dualities, applied to field theories with a possible interest in phenomenology.
I will present two recent results in the are of Gauge-Strings dualities, applied to field theories with a possible interest in phenomenology.
Posted by: QMW
Wed
4 Nov 2009
Twistor Theory and Differential Equations
📍 London
Maciej Dunajski
(DAMTP)
Wed
4 Nov 2009
Transport in QGP and Non-critical Holography
Umut Gursoy
(Utrecht)
Abstract:
I will present a phenomenological model of the quark-gluon plasma that stem from 5 dimensional holography.
The model is superior to the previous 5D models as it incorporates the running of the gauge coupling. It is
constructed by requirements from QCD and a few lattice data. I will describe the transport properties of the quark-gluon plasma
such as the bulk viscosity, energy loss of heavy quarks etc and their effects on the observables.
I will present a phenomenological model of the quark-gluon plasma that stem from 5 dimensional holography.
The model is superior to the previous 5D models as it incorporates the running of the gauge coupling. It is
constructed by requirements from QCD and a few lattice data. I will describe the transport properties of the quark-gluon plasma
such as the bulk viscosity, energy loss of heavy quarks etc and their effects on the observables.
Posted by: IC
Tue
3 Nov 2009
Quantum Field theory, String Theory and Twistor Theory, towards a perturbative duality
Ronald Reid-Edwards
(City University London)
Abstract:
In this seminar, I will give an introduction to a series of ideas which suggest that many aspects of quantum fied theories, including the celebrated N=4 super Yang-Mills, may be most simply understood in terms of a dual theory in twistor space. No previous knowledge of string theory or twistor theory will be assumed.
In this seminar, I will give an introduction to a series of ideas which suggest that many aspects of quantum fied theories, including the celebrated N=4 super Yang-Mills, may be most simply understood in terms of a dual theory in twistor space. No previous knowledge of string theory or twistor theory will be assumed.
Posted by: KCL
Tue
3 Nov 2009
Quantum transport in chaotic cavities, Schur functions and Selberg integral
Dmitry Savin
(Brunel)
Abstract:
Statistical properties of quantum transport are considered for a chaotic cavity with an arbitrary number of open channels. In the framework of the random matrix approach, we establish the relevance of the Selberg integral theory to the problematic and apply it to calculate exact explicit expressions of low-order cumulants of the conductance and shot-noise. By further exploiting the marriage of the Selberg integral with the theory of symmetric functions (Schur functions), we develop a powerful method for computing the moments of the conductance and shot-noise (including their joint moments) of arbitrary order and at any number of open channels. The approach is applicable equally well for systems with and without time-reversal symmetry. We also give a detailed discussion of the corresponding cumulants, the distribution functions, etc.
Statistical properties of quantum transport are considered for a chaotic cavity with an arbitrary number of open channels. In the framework of the random matrix approach, we establish the relevance of the Selberg integral theory to the problematic and apply it to calculate exact explicit expressions of low-order cumulants of the conductance and shot-noise. By further exploiting the marriage of the Selberg integral with the theory of symmetric functions (Schur functions), we develop a powerful method for computing the moments of the conductance and shot-noise (including their joint moments) of arbitrary order and at any number of open channels. The approach is applicable equally well for systems with and without time-reversal symmetry. We also give a detailed discussion of the corresponding cumulants, the distribution functions, etc.
Posted by: brunel
October 2009
Thu
29 Oct 2009
Wilson loops: from pseudo-holomorphic surfaces to 2d Yang-Mills
Riccardo Ricci
(Imperial)
Abstract:
In this talk, I will discuss a new family of supersymmetric Wilson loop operators in N=4 SYM. These operators can be defined for any loop on a three-sphere in space-time and generically preserve two super-conformal charges. On the string side, via AdS/CFT duality, these loops map to surfaces which are 'pseudo-holomorphic' with respect to a novel almost-complex structure defined on a suitable subspace of AdS5xS5. Of particular interest is the subclass of loops lying on a two-sphere in space-time whose expectation value is conjectured to be computed exactly in terms of the analogous observables in bosonic 2d Yang-Mills on S2. Several evidences for this conjecture, both on the gauge theory and on the string theory side will be discussed.
In this talk, I will discuss a new family of supersymmetric Wilson loop operators in N=4 SYM. These operators can be defined for any loop on a three-sphere in space-time and generically preserve two super-conformal charges. On the string side, via AdS/CFT duality, these loops map to surfaces which are 'pseudo-holomorphic' with respect to a novel almost-complex structure defined on a suitable subspace of AdS5xS5. Of particular interest is the subclass of loops lying on a two-sphere in space-time whose expectation value is conjectured to be computed exactly in terms of the analogous observables in bosonic 2d Yang-Mills on S2. Several evidences for this conjecture, both on the gauge theory and on the string theory side will be discussed.
Posted by: QMW
Wed
28 Oct 2009
Cohomological reduction of sigma models
📍 London
Vladimir Mitev
(Desy)
Abstract:
Sigma models endowed with target space supersymmetry have an array of peculiar properties and important applications. A new method is presented, whereby the computation of certain correlation functions in these theories is drastically simplified. In particular, this allows for the identification of new families of conformally invariant 2d sigma models.
Sigma models endowed with target space supersymmetry have an array of peculiar properties and important applications. A new method is presented, whereby the computation of certain correlation functions in these theories is drastically simplified. In particular, this allows for the identification of new families of conformally invariant 2d sigma models.
Posted by: KCL
Wed
28 Oct 2009
Operator mixing, 3-point correlators and the AdS/CFT correspondence.
George Georgiou
(QM)
Abstract:
We will discuss a direct prescription for computing the
mixing among gauge invariant operators in N=4 SYM. This approach is
based on the action of the superalgebra on the states of the theory
and circumvents the problem of diagonalising the dilatation matrix.
As an example, we will derive the leading and subleading planar
quantum corrections to the BMN-like operators belonging to the
supermultiplet with 2 impurities. Furthermore, we will discuss the
relation to Beisert's SU(2,2) dynamic S-matrix approach.
The same method can be applied in the BMN limit of the dual string
description. The string theory expressions for the states match nicely
the field theory ones up to order lambda'.
We will also focus on the implications of the mixing terms for 3-point
functions of 2 BPS and one non-BPS operator. Namely, should the
mixing terms were not there, constraints following from the
superconformal and the bonus U(1)Y symmetries would be violated.
Subsequently, we will utilise the BMN limit of the AdS5xS5 string
theory to analyse the string amplitudes corresponding to the 3-point
functions studied above.
The mixing is again crucial to ensure the cancellation of various
amplitudes that would otherwise violate symmetry constaints.
However,on the string side, we find examples of interactions which
violate expectations coming from superconformal Ward identities and
the U(1)Y symmetry.
Finally, we will comment on the possible resolution of this mismatch.
We will discuss a direct prescription for computing the
mixing among gauge invariant operators in N=4 SYM. This approach is
based on the action of the superalgebra on the states of the theory
and circumvents the problem of diagonalising the dilatation matrix.
As an example, we will derive the leading and subleading planar
quantum corrections to the BMN-like operators belonging to the
supermultiplet with 2 impurities. Furthermore, we will discuss the
relation to Beisert's SU(2,2) dynamic S-matrix approach.
The same method can be applied in the BMN limit of the dual string
description. The string theory expressions for the states match nicely
the field theory ones up to order lambda'.
We will also focus on the implications of the mixing terms for 3-point
functions of 2 BPS and one non-BPS operator. Namely, should the
mixing terms were not there, constraints following from the
superconformal and the bonus U(1)Y symmetries would be violated.
Subsequently, we will utilise the BMN limit of the AdS5xS5 string
theory to analyse the string amplitudes corresponding to the 3-point
functions studied above.
The mixing is again crucial to ensure the cancellation of various
amplitudes that would otherwise violate symmetry constaints.
However,on the string side, we find examples of interactions which
violate expectations coming from superconformal Ward identities and
the U(1)Y symmetry.
Finally, we will comment on the possible resolution of this mismatch.
Posted by: IC
Tue
27 Oct 2009
An open problem in integrability and the AdS/CFT correspondence
Fabian Spill
(Imperial College London)
Abstract:
Using methods of integrability, enormous progress has been done in calculating the spectrum of operators in N=4 Super Yang-Mills theory as well as of energies of strings. I will discuss advances in finding the spectrum of the Konishi operator, the simplest nontrivial operator of finite size, which is already a hard problem. A further mathematical problem is to prove integrability. I will discuss the algebraic objects appearing in the AdS/CFT correspondence, namely Yangians, and also show how they are related to the spectral equations.
Using methods of integrability, enormous progress has been done in calculating the spectrum of operators in N=4 Super Yang-Mills theory as well as of energies of strings. I will discuss advances in finding the spectrum of the Konishi operator, the simplest nontrivial operator of finite size, which is already a hard problem. A further mathematical problem is to prove integrability. I will discuss the algebraic objects appearing in the AdS/CFT correspondence, namely Yangians, and also show how they are related to the spectral equations.
Posted by: KCL
Thu
22 Oct 2009
Modifications of Holomorphic Bundles, Integrable Systems and Monopoles. 2
Andrew Zotov
(ITEP, Moscow)
Abstract:
We review some results concerning integrable systems on the moduli spaces of
holomorphic bundles. The interrelations between bundles of different
topological types are given by modifications (singular gauge
transformations). The modification provides canonical maps between
corresponding integrable systems. It also allows to describe the Backlund
transformations. We apply the general scheme to the elliptic Calogero-Moser
model and construct a map to an integrable Euler-Arnold top (the elliptic
SL(N)-rotator). The models correspond to the bundles of degree zero and one.
Explicit formulae represent a bosonization of the coadjoint orbit. The later
describes the phase space of the rotator while the Poisson structure of the
Calogero model is canonical. The construction can be generalized to more
complicated models. For example, field generalization (loop group or 1+1
theories) leads to relation between the field Calogero model and the
Landau-Lifshitz equation for XYZ model while the generalization to the
isomonodromic deformations leads to relation between Painleve VI equation
and Zhukovsky-Volterra gyrostat. In the end we note that the classification
of models is described by the center of the structure group which are shown
to be characteristic classes of the bundles. This remark allows to
generalize the construction to the case of an arbitrary simple Lie group.
Three-dimensional generalization of the construction naturally leads to the
Bogomolny equations. The modification in this case provides non-trivial
charge of the monopole solution. We find the Dirac monopole solution in the
case (R)x(Elliptic curve). This solution is a three-dimensional
generalization of the Kronecker series. We give two representations for this
solution and derive a functional equation for it.
We review some results concerning integrable systems on the moduli spaces of
holomorphic bundles. The interrelations between bundles of different
topological types are given by modifications (singular gauge
transformations). The modification provides canonical maps between
corresponding integrable systems. It also allows to describe the Backlund
transformations. We apply the general scheme to the elliptic Calogero-Moser
model and construct a map to an integrable Euler-Arnold top (the elliptic
SL(N)-rotator). The models correspond to the bundles of degree zero and one.
Explicit formulae represent a bosonization of the coadjoint orbit. The later
describes the phase space of the rotator while the Poisson structure of the
Calogero model is canonical. The construction can be generalized to more
complicated models. For example, field generalization (loop group or 1+1
theories) leads to relation between the field Calogero model and the
Landau-Lifshitz equation for XYZ model while the generalization to the
isomonodromic deformations leads to relation between Painleve VI equation
and Zhukovsky-Volterra gyrostat. In the end we note that the classification
of models is described by the center of the structure group which are shown
to be characteristic classes of the bundles. This remark allows to
generalize the construction to the case of an arbitrary simple Lie group.
Three-dimensional generalization of the construction naturally leads to the
Bogomolny equations. The modification in this case provides non-trivial
charge of the monopole solution. We find the Dirac monopole solution in the
case (R)x(Elliptic curve). This solution is a three-dimensional
generalization of the Kronecker series. We give two representations for this
solution and derive a functional equation for it.
Posted by: IC
Wed
21 Oct 2009
The torsional conifold: Wrapped fivebranes and the Klebanov-Strassler theory
Dario Martelli
(Swansea)
Abstract:
I will discuss a supergravity solution corresponding to
fivebranes wrapped on the S2 of the resolved conifold. By changing a
parameter the solution continuously interpolates between the deformed
conifold with flux and the resolved conifold with branes. Therefore, it
displays a geometric transition, purely in the supergravity context. The
solution is a simple example of torsional geometry and may be thought of
as a non-Kahler analog of the conifold. I will discuss how one can obtain
supersymmetric solutions of type IIB supergravity starting from simpler
non-Kahler geometries, by U-dualities or other methods. Applying these
transformations to the torsional conifold solution we obtain a solution
dual to the baryonic branch of the Klebanov-Strassler theory. Far along
the baryonic branch the solution resembles D5 branes wrapping a fuzzy
two-sphere in the resolved conifold and this can be matched to a weakly
coupled field theory analysis.
I will discuss a supergravity solution corresponding to
fivebranes wrapped on the S2 of the resolved conifold. By changing a
parameter the solution continuously interpolates between the deformed
conifold with flux and the resolved conifold with branes. Therefore, it
displays a geometric transition, purely in the supergravity context. The
solution is a simple example of torsional geometry and may be thought of
as a non-Kahler analog of the conifold. I will discuss how one can obtain
supersymmetric solutions of type IIB supergravity starting from simpler
non-Kahler geometries, by U-dualities or other methods. Applying these
transformations to the torsional conifold solution we obtain a solution
dual to the baryonic branch of the Klebanov-Strassler theory. Far along
the baryonic branch the solution resembles D5 branes wrapping a fuzzy
two-sphere in the resolved conifold and this can be matched to a weakly
coupled field theory analysis.
Posted by: KCL
Wed
21 Oct 2009
Essentials of blackfold dynamics
Niels Obers
(Niels Bohr Institute)
Tue
20 Oct 2009
Integrable models in gauge/string duality
Konstantin Zarembo
(Ecole Normale Superieure, Paris, France)
Abstract:
The AdS/CFT correspondence establishes an equivalence of a four-dimensional supersymmetric gauge theory and string theory in Anti-de-Sitter space. Remarkably, the AdS/CFT system can be solved exactly with the help of integrability methods typical for two-dimensional models. I will review the general framework of the AdS/CFT duality, describe how integrability arises in AdS/CFT and how it can be used to compute the exact non-perturbative spectrum of supersymmetric Yang-Mills theory.
The AdS/CFT correspondence establishes an equivalence of a four-dimensional supersymmetric gauge theory and string theory in Anti-de-Sitter space. Remarkably, the AdS/CFT system can be solved exactly with the help of integrability methods typical for two-dimensional models. I will review the general framework of the AdS/CFT duality, describe how integrability arises in AdS/CFT and how it can be used to compute the exact non-perturbative spectrum of supersymmetric Yang-Mills theory.
Posted by: KCL
Mon
19 Oct 2009
Modifications of Holomorphic Bundles, Integrable Systems and Monopoles. 1
Andrew Zotov
(Moscow)
Abstract:
We review some results concerning integrable systems on the moduli spaces of
holomorphic bundles. The interrelations between bundles of different
topological types are given by modifications (singular gauge
transformations). The modification provides canonical maps between
corresponding integrable systems. It also allows to describe the Backlund
transformations. We apply the general scheme to the elliptic Calogero-Moser
model and construct a map to an integrable Euler-Arnold top (the elliptic
SL(N)-rotator). The models correspond to the bundles of degree zero and one.
Explicit formulae represent a bosonization of the coadjoint orbit. The later
describes the phase space of the rotator while the Poisson structure of the
Calogero model is canonical. The construction can be generalized to more
complicated models. For example, field generalization (loop group or 1+1
theories) leads to relation between the field Calogero model and the
Landau-Lifshitz equation for XYZ model while the generalization to the
isomonodromic deformations leads to relation between Painleve VI equation
and Zhukovsky-Volterra gyrostat. In the end we note that the classification
of models is described by the center of the structure group which are shown
to be characteristic classes of the bundles. This remark allows to
generalize the construction to the case of an arbitrary simple Lie group.
Three-dimensional generalization of the construction naturally leads to the
Bogomolny equations. The modification in this case provides non-trivial
charge of the monopole solution. We find the Dirac monopole solution in the
case (R)x(Elliptic curve). This solution is a three-dimensional
generalization of the Kronecker series. We give two representations for this
solution and derive a functional equation for it.
We review some results concerning integrable systems on the moduli spaces of
holomorphic bundles. The interrelations between bundles of different
topological types are given by modifications (singular gauge
transformations). The modification provides canonical maps between
corresponding integrable systems. It also allows to describe the Backlund
transformations. We apply the general scheme to the elliptic Calogero-Moser
model and construct a map to an integrable Euler-Arnold top (the elliptic
SL(N)-rotator). The models correspond to the bundles of degree zero and one.
Explicit formulae represent a bosonization of the coadjoint orbit. The later
describes the phase space of the rotator while the Poisson structure of the
Calogero model is canonical. The construction can be generalized to more
complicated models. For example, field generalization (loop group or 1+1
theories) leads to relation between the field Calogero model and the
Landau-Lifshitz equation for XYZ model while the generalization to the
isomonodromic deformations leads to relation between Painleve VI equation
and Zhukovsky-Volterra gyrostat. In the end we note that the classification
of models is described by the center of the structure group which are shown
to be characteristic classes of the bundles. This remark allows to
generalize the construction to the case of an arbitrary simple Lie group.
Three-dimensional generalization of the construction naturally leads to the
Bogomolny equations. The modification in this case provides non-trivial
charge of the monopole solution. We find the Dirac monopole solution in the
case (R)x(Elliptic curve). This solution is a three-dimensional
generalization of the Kronecker series. We give two representations for this
solution and derive a functional equation for it.
Posted by: IC
Thu
15 Oct 2009
Non-perturbative topological strings
Sara Pasquetti
(CERN)
Abstract:
A characteristic feature of string theory is the asymptotic nature of the free energy genus expansion indicating the presence of non-perturbative effects due to branes. In certain toy models, such as minimal models or topological strings, the theory admits a matrix model description. In these cases the non-perturbative effects can be interpreted in terms of eigenvalues tunneling in the dual matrix model and the finite N matrix model can be naturally regarded as the non-perturbative completion of the theory. We address the case of the topological string on the Resolved Conifold. We compute the exact non-perturbative contribution to the free energy via Borel analysis and show how it controls the large order behavior of the theory. We interpreted the non-perturbative effects in the dual Chern-Simons matrix models and in the space-time in terms of toric branes.
A characteristic feature of string theory is the asymptotic nature of the free energy genus expansion indicating the presence of non-perturbative effects due to branes. In certain toy models, such as minimal models or topological strings, the theory admits a matrix model description. In these cases the non-perturbative effects can be interpreted in terms of eigenvalues tunneling in the dual matrix model and the finite N matrix model can be naturally regarded as the non-perturbative completion of the theory. We address the case of the topological string on the Resolved Conifold. We compute the exact non-perturbative contribution to the free energy via Borel analysis and show how it controls the large order behavior of the theory. We interpreted the non-perturbative effects in the dual Chern-Simons matrix models and in the space-time in terms of toric branes.
Posted by: QMW
Wed
14 Oct 2009
Adding Flavor to AdS4/CFT3
📍 London
Andy O'Bannon
(MPI Munich)
Abstract:
Gauge-gravity duality is an extremely useful tool for studying strongly-coupled gauge theories, and has many applications to real-world systems, such as the quark-gluon plasma and quantum critical points. Most gauge-gravity dualities involve a gauge theory with fields only in the adjoint representation of the gauge group. In many strongly-coupled systems, however, such as the quark-gluon plamsa, fields in the fundamental representation of the gauge group, 'flavor fields', are crucially important. For (3+1)-dimensional gauge theories with gravity duals (AdS5/CFT4), the supergravity description of flavor fields is well-understood: flavor fields appear in supergravity as probe D-branes in AdS5. The story for (2+1)-dimensional gauge theories (AdS4/CFT3) is much less developed. Indeed, for supergravity on AdS4 x S7, the dual (2+1)-dimensional field theory (without flavor) was only recently discovered. In this talk I will describe how to add flavor to this theory. In particular, I will present a general recipe to determine the field theory, and in particular the couplings of the flavor fields, given a probe D-brane in AdS4.
Gauge-gravity duality is an extremely useful tool for studying strongly-coupled gauge theories, and has many applications to real-world systems, such as the quark-gluon plasma and quantum critical points. Most gauge-gravity dualities involve a gauge theory with fields only in the adjoint representation of the gauge group. In many strongly-coupled systems, however, such as the quark-gluon plamsa, fields in the fundamental representation of the gauge group, 'flavor fields', are crucially important. For (3+1)-dimensional gauge theories with gravity duals (AdS5/CFT4), the supergravity description of flavor fields is well-understood: flavor fields appear in supergravity as probe D-branes in AdS5. The story for (2+1)-dimensional gauge theories (AdS4/CFT3) is much less developed. Indeed, for supergravity on AdS4 x S7, the dual (2+1)-dimensional field theory (without flavor) was only recently discovered. In this talk I will describe how to add flavor to this theory. In particular, I will present a general recipe to determine the field theory, and in particular the couplings of the flavor fields, given a probe D-brane in AdS4.
Posted by: KCL
Wed
14 Oct 2009
Universal Phenomena at Strong Coupling and Gravity
Ayan Mukhopadhyay
(HRI, India)
Abstract:
There is good evidence that a class of conformal gauge theories at strong
gauge coupling and for large rank of the gauge group can be described by
classical gravity in five dimensions. In this gauge/gravity duality, the
theory of classical gravity always admits a consistent truncation to pure
gravity so that there is a sector in the dual gauge theories where the
dynamics is universal. This universal sector constitutes phenomena like
hydrodynamics, but also other phenomena far away from equilibrium such as
decoherence and relaxation.
We will use field theoretic tools to understand how the time evolution of
all states and the expectation values of all observables in the universal
sector get determined by the energy-momentum tensor alone. We will find a
way to extrapolate our field-theoretic results to strong coupling to
propose a condition on the energy-momentum tensor such that the dual
solution in gravity has a smooth future horizon, as a test of our
approach. We will also do a first study of how irreversibility emerges at
long time scales of observation through gravity.
There is good evidence that a class of conformal gauge theories at strong
gauge coupling and for large rank of the gauge group can be described by
classical gravity in five dimensions. In this gauge/gravity duality, the
theory of classical gravity always admits a consistent truncation to pure
gravity so that there is a sector in the dual gauge theories where the
dynamics is universal. This universal sector constitutes phenomena like
hydrodynamics, but also other phenomena far away from equilibrium such as
decoherence and relaxation.
We will use field theoretic tools to understand how the time evolution of
all states and the expectation values of all observables in the universal
sector get determined by the energy-momentum tensor alone. We will find a
way to extrapolate our field-theoretic results to strong coupling to
propose a condition on the energy-momentum tensor such that the dual
solution in gravity has a smooth future horizon, as a test of our
approach. We will also do a first study of how irreversibility emerges at
long time scales of observation through gravity.
Posted by: IC
Wed
14 Oct 2009
Quantum Entropy Function and Localization
Rajesh Gupta
(HRI, India)
Abstract:
AdS2-CFT1 correspondence leads to a prescription for computing the degeneracy of a single centered extremal black hole in terms of path integral over string fields living on the near horizon geometry of the extremal black hole. This prescription is called quantum entropy function. In four dimension the near horizon isometry group SL(2,R) x SU(2) for BPS black hole gets enhanced to full SU(1,1,2). Using these enhanced supersymmetries and localization techniques, we will argue that the path integral receives contribution only from special class of field configurations which are invariant under a particular subgroup of SU(1,1,2). We will identify saddle points which are invariant under this subgroup.
AdS2-CFT1 correspondence leads to a prescription for computing the degeneracy of a single centered extremal black hole in terms of path integral over string fields living on the near horizon geometry of the extremal black hole. This prescription is called quantum entropy function. In four dimension the near horizon isometry group SL(2,R) x SU(2) for BPS black hole gets enhanced to full SU(1,1,2). Using these enhanced supersymmetries and localization techniques, we will argue that the path integral receives contribution only from special class of field configurations which are invariant under a particular subgroup of SU(1,1,2). We will identify saddle points which are invariant under this subgroup.
Posted by: IC
Tue
13 Oct 2009
Topological effects in classical and quantum gravity
Maulik Parikh
(IUCAA, Pune)
Abstract:
We consider some novel topological effects, with potentially observable consequences, in classical and quantum gravity. In one scenario, we find that the topology of extra dimensions generically breaks global Lorentz symmetry, leading to distinct experimental signatures in the context of brane worlds. In a different scenario, we show that topological terms in the gravitational action, such as those expected in heterotic string theory, can greatly enhance the instability of four-dimensional de Sitter space by favouring the nucleation of primordial black holes.
We consider some novel topological effects, with potentially observable consequences, in classical and quantum gravity. In one scenario, we find that the topology of extra dimensions generically breaks global Lorentz symmetry, leading to distinct experimental signatures in the context of brane worlds. In a different scenario, we show that topological terms in the gravitational action, such as those expected in heterotic string theory, can greatly enhance the instability of four-dimensional de Sitter space by favouring the nucleation of primordial black holes.
Posted by: QMW
Tue
13 Oct 2009
The Solar Dynamo and Magnetic Buoyancy
Lara Silvers
(City University London)
Abstract:
The 11 year solar magnetic cycle is driven by a hydromagnetic dynamo. However, the exact nature of this dynamo mechanism is still not fully understood, and there are several scenarios proposed to explain the observed behaviour.
Here I will briefly overview observations of the solar magnetic field before moving on to discuss why magnetic buoyancy is a key ingredient in the models proposed to explain the observations of the large-scale magnetic field. I will go on to discuss the recent progress in our understanding of magnetic buoyancy with emphasis on double-diffusive magnetic buoyancy.
The 11 year solar magnetic cycle is driven by a hydromagnetic dynamo. However, the exact nature of this dynamo mechanism is still not fully understood, and there are several scenarios proposed to explain the observed behaviour.
Here I will briefly overview observations of the solar magnetic field before moving on to discuss why magnetic buoyancy is a key ingredient in the models proposed to explain the observations of the large-scale magnetic field. I will go on to discuss the recent progress in our understanding of magnetic buoyancy with emphasis on double-diffusive magnetic buoyancy.
Posted by: KCL
Tue
13 Oct 2009
Phase transitions in the quantum conductance problem
Pierpaolo Vivo
(ICTP Trieste)
Abstract:
Linear statistics on ensembles of random matrices occur frequently in many applications. We present a general method to compute probability distributions of linear statistics for large matrix size N. This is applied to the calculation of conductance and shot noise for ballistic scattering in chaotic cavities, in the limit of large number of open channels. The method is based on a mapping to a Coulomb gas problem in Laplace space, displaying phase transitions as the Laplace parameter is varied. As a consequence, the sought distributions generally display a central Gaussian region flanked on both sides by non-Gaussian tails, and weak non-analytical points at the junction of the two regimes.
Linear statistics on ensembles of random matrices occur frequently in many applications. We present a general method to compute probability distributions of linear statistics for large matrix size N. This is applied to the calculation of conductance and shot noise for ballistic scattering in chaotic cavities, in the limit of large number of open channels. The method is based on a mapping to a Coulomb gas problem in Laplace space, displaying phase transitions as the Laplace parameter is varied. As a consequence, the sought distributions generally display a central Gaussian region flanked on both sides by non-Gaussian tails, and weak non-analytical points at the junction of the two regimes.
Posted by: brunel
Thu
8 Oct 2009
Kerr-CFT and gravitational perturbations
Harvey Reall
(Cambridge)
Thu
8 Oct 2009
Flavor-branes in gauge/string duality and M-theory
Johannes Schmude
(Swansea)
Abstract:
Over the last years, gauge/string duality has been extended to include
gauge theories with an arbitrary number of flavors. We study the
flavoring procedure in the light of calibrated geometry and discuss the
special case of a type IIA dual of N=1 super Yang-Mills with flavors.
Relating our results to the standard type IIA/M-theory duality, we find
that the usual oxidation formulas cannot accommodate for the additional
flavor branes. We address and solve this issue by considering M-theory
with torsion, which allows us to construct source-modified equations of
motion for eleven-dimensional supergravity.
Over the last years, gauge/string duality has been extended to include
gauge theories with an arbitrary number of flavors. We study the
flavoring procedure in the light of calibrated geometry and discuss the
special case of a type IIA dual of N=1 super Yang-Mills with flavors.
Relating our results to the standard type IIA/M-theory duality, we find
that the usual oxidation formulas cannot accommodate for the additional
flavor branes. We address and solve this issue by considering M-theory
with torsion, which allows us to construct source-modified equations of
motion for eleven-dimensional supergravity.
Posted by: IC
Thu
8 Oct 2009
Twisted tori and flux backgrounds of type II and heterotic string theory
David Andriot
(LPTHE, Paris)
Abstract:
Solvmanifolds, in particular nilmanifolds, commonly known as twisted tori,
provide several examples of internal manifolds in flux compactifications
towards de Sitter, Minkowski or Anti de Sitter. The relation between
these manifolds and the six-dimensional torus, and the string vacua
obtained on them, are the main interests of this talk.
We will first present some properties of these manifolds. We will give a
generic construction of their Maurer-Cartan forms out of the
six-dimensional torus, via a transformation called the twist.
We will then describe several Minkowski flux backgrounds of type II
supergravity obtained on these manifolds. Thanks to the generalized
complex geometry approach, we will show that one can obtain those
solutions from solutions on the torus, via the twist transformation. The
latter then acts as a solution generating technique, being able to relate
backgrounds which are not T-duals.
Finally, we will apply this twist transformation technique to relate
Kahler/non-Kahler solutions of the heterotic string.
This talk is based on a work with Enrico Goi, Ruben Minasian and Michela
Petrini.
Solvmanifolds, in particular nilmanifolds, commonly known as twisted tori,
provide several examples of internal manifolds in flux compactifications
towards de Sitter, Minkowski or Anti de Sitter. The relation between
these manifolds and the six-dimensional torus, and the string vacua
obtained on them, are the main interests of this talk.
We will first present some properties of these manifolds. We will give a
generic construction of their Maurer-Cartan forms out of the
six-dimensional torus, via a transformation called the twist.
We will then describe several Minkowski flux backgrounds of type II
supergravity obtained on these manifolds. Thanks to the generalized
complex geometry approach, we will show that one can obtain those
solutions from solutions on the torus, via the twist transformation. The
latter then acts as a solution generating technique, being able to relate
backgrounds which are not T-duals.
Finally, we will apply this twist transformation technique to relate
Kahler/non-Kahler solutions of the heterotic string.
This talk is based on a work with Enrico Goi, Ruben Minasian and Michela
Petrini.
Posted by: IC
Wed
7 Oct 2009
Wilson loops: from pseudo-holomorphic surfaces to 2d YM
📍 London
Riccardo Ricci
(Imperial)
Abstract:
In this talk, I will discuss a new family of supersymmetric Wilson loop operators in N=4 SYM. These operators can be defined for any loop on a three-sphere in space-time and generically preserve two super-conformal charges. On the string side, via AdS/CFT duality, these loops map to surfaces which are 'pseudo-holomorphic' with respect to a novel almost-complex structure defined on a suitable subspace of AdS5xS5. Of particular interest is the subclass of loops lying on a two-sphere in space-time whose expectation value is conjectured to be computed
exactly in terms of the analogous observables in bosonic 2d Yang-Mills on S2.
Several evidences for this conjecture, both on the gauge theory and on the string theory side will be discussed.
In this talk, I will discuss a new family of supersymmetric Wilson loop operators in N=4 SYM. These operators can be defined for any loop on a three-sphere in space-time and generically preserve two super-conformal charges. On the string side, via AdS/CFT duality, these loops map to surfaces which are 'pseudo-holomorphic' with respect to a novel almost-complex structure defined on a suitable subspace of AdS5xS5. Of particular interest is the subclass of loops lying on a two-sphere in space-time whose expectation value is conjectured to be computed
exactly in terms of the analogous observables in bosonic 2d Yang-Mills on S2.
Several evidences for this conjecture, both on the gauge theory and on the string theory side will be discussed.
Posted by: KCL
Wed
7 Oct 2009
A virtual scaling function of AdS/CFT
Stefan Zieme
(MPI, Potsdam)
Abstract:
I talk about finite corrections to the large spin asymptotics
of N=4 SYM twist operators. These
corrections are an all-loop result, not affected by wrapping effects,
and agree, after
determining the strong coupling expansion, with string theory predictions.
The finite order corrections enter the sub-leading poles of the
logarithm of multi loop gluon
scattering amplitudes and describes the difference between the former
and the expectation
value of certain Wilson lines. For the complete sub-leading pole
structure however a second
function is needed. A few comments on the quest for a search of a
possible description of the
latter in terms of local operators will be given.
I talk about finite corrections to the large spin asymptotics
of N=4 SYM twist operators. These
corrections are an all-loop result, not affected by wrapping effects,
and agree, after
determining the strong coupling expansion, with string theory predictions.
The finite order corrections enter the sub-leading poles of the
logarithm of multi loop gluon
scattering amplitudes and describes the difference between the former
and the expectation
value of certain Wilson lines. For the complete sub-leading pole
structure however a second
function is needed. A few comments on the quest for a search of a
possible description of the
latter in terms of local operators will be given.
Posted by: IC
Tue
6 Oct 2009
The gauge/string correspondence
Bogdan Stefanski
(City University London)
Abstract:
I will review the gauge/string correspondence, with particular emphasis on recent exact results based on integrable techniques.
I will review the gauge/string correspondence, with particular emphasis on recent exact results based on integrable techniques.
Posted by: KCL
September 2009
Wed
23 Sep 2009
On deriving the self-dual antisymmetric tensor field model
Igor Samsonov
(Tomsk, Russia)
Abstract:
We review the derivation of a 6d gauge theory related to
the M5 brane from the Bagger-Lambert-Gustavsson (BLG) model
with the volume preserving diffeomorphisms gauge
group. In particular, the Lagrangian for the 6d self-dual
antisymmetric tensor field appears upon converting three of eight
scalars in the BLG theory into the components of antisymmetric
tensor field in D=6. We develop also a Lorentz-covariant
Lagrangian formulation for such an antisymmetric tensor field in
the free case. This formulation admits a natural
supersymmetrization as well as coupling to 6d gravity.
We review the derivation of a 6d gauge theory related to
the M5 brane from the Bagger-Lambert-Gustavsson (BLG) model
with the volume preserving diffeomorphisms gauge
group. In particular, the Lagrangian for the 6d self-dual
antisymmetric tensor field appears upon converting three of eight
scalars in the BLG theory into the components of antisymmetric
tensor field in D=6. We develop also a Lorentz-covariant
Lagrangian formulation for such an antisymmetric tensor field in
the free case. This formulation admits a natural
supersymmetrization as well as coupling to 6d gravity.
Posted by: IC
Thu
17 Sep 2009
SUSY Restoration on Non-Abelian Vortices
Victor Mikhaylov
(Moscow)
Thu
17 Sep 2009
Holographic renormalization for correlators of operators with large R-charge
Robert de Mello-Koch
(University of Witwatersrand)
Wed
16 Sep 2009
Brane-Antibrane Dynamics From the Tachyon DBI Action
Oleg Lunin
(Chicago)
Abstract:
The Tachyon-Dirac-Born-Infeld (TDBI) action captures some aspects of the dynamics of non-BPS D-branes in type II string theory. We show that it can also be used to study the classical interactions of BPS branes and antibranes. Our analysis sheds light on real time D-Dbar tachyon condensation, on the proposal that the tachyon field can be thought of as an extra spatial dimension whose role is similar to the radial direction in holography, and on Sen's open string completeness conjecture.
The Tachyon-Dirac-Born-Infeld (TDBI) action captures some aspects of the dynamics of non-BPS D-branes in type II string theory. We show that it can also be used to study the classical interactions of BPS branes and antibranes. Our analysis sheds light on real time D-Dbar tachyon condensation, on the proposal that the tachyon field can be thought of as an extra spatial dimension whose role is similar to the radial direction in holography, and on Sen's open string completeness conjecture.
Posted by: IC
Wed
9 Sep 2009
Static black hole in 4d higher-spin gauge theory
Vyatcheslav Didenko
(Moscow)
Abstract:
Exact solution of 4d nonlinear bosonic higher-spin gauge theory, that provides a higher-spin deformation of the AdS4 Schwarzschild black hole, is found.
Exact solution of 4d nonlinear bosonic higher-spin gauge theory, that provides a higher-spin deformation of the AdS4 Schwarzschild black hole, is found.
Posted by: IC