Triangle Seminars
Monday, 9 Mar 2015
Graduate Lectures: M-theory
David Berman
(QMUL)
Abstract:
Graduate Lectures: This short course will cover the origin of M-theory and brane physics with its applications.
Graduate Lectures: This short course will cover the origin of M-theory and brane physics with its applications.
Posted by: QMW
Wednesday, 11 Mar 2015
On conformal windows and the phase structure of 2+1d and 3+1d QCD
Ofer Aharony
(Weizmann Institute)
Abstract:
Many gauge theories, such as 3+1d and 2+1d SU(N) gauge theories with N_f massless Dirac fermions in the fundamental representation, exhibit "conformal windows" - a range of values of N_f for which the theory flows to a non-trivial conformal field theory at low energy. It is interesting to ask how these windows end and transition into phases with confinement and with spontaneous breaking of the flavor symmetry. I will begin by reviewing what is known about 3+1 dimensional QCD, focusing on the large N and N_f limit and on the conformal window there, and I will review the standard "merger scenario" for the end of its conformal window.
I will then move on to QCD in 2+1 dimensions, and discuss its phase diagram as a function of the mass and of the discrete parameters N, N_f and the Chern-Simons level k, focusing again on the limit of large N, N_f, k. I will argue that this theory also has a conformal window (corresponding to a second order phase transition when changing the mass) but that it does not always end at a merger, and I will suggest two other possibilities for the end of general conformal windows. The different scenarios can be distinguished by the behavior of the theory as the boundary of the conformal window is approached from either side. Based on work in progress with Thomas Dumitrescu, Zohar Komargodski and Jiangyuan Qian.
Many gauge theories, such as 3+1d and 2+1d SU(N) gauge theories with N_f massless Dirac fermions in the fundamental representation, exhibit "conformal windows" - a range of values of N_f for which the theory flows to a non-trivial conformal field theory at low energy. It is interesting to ask how these windows end and transition into phases with confinement and with spontaneous breaking of the flavor symmetry. I will begin by reviewing what is known about 3+1 dimensional QCD, focusing on the large N and N_f limit and on the conformal window there, and I will review the standard "merger scenario" for the end of its conformal window.
I will then move on to QCD in 2+1 dimensions, and discuss its phase diagram as a function of the mass and of the discrete parameters N, N_f and the Chern-Simons level k, focusing again on the limit of large N, N_f, k. I will argue that this theory also has a conformal window (corresponding to a second order phase transition when changing the mass) but that it does not always end at a merger, and I will suggest two other possibilities for the end of general conformal windows. The different scenarios can be distinguished by the behavior of the theory as the boundary of the conformal window is approached from either side. Based on work in progress with Thomas Dumitrescu, Zohar Komargodski and Jiangyuan Qian.
Posted by: IC2
Multiboundary wormholes and holographic entanglement
Simon Ross
(Durham)
Holography for N=2(star) on S4
Nikolay Bobev
(Leuven)
Abstract:
I will discuss the gravitational dual of a mass deformation of N=4 SYM, called N=2* SYM, on S^4. Using holographic techniques one can calculate the universal contribution to the corresponding free energy in the planar limit and at large 't Hooft coupling. The result matches the expression recently computed using supersymmetric localization in the field theory. This agreement constitutes a non-trivial precision test of holography in a non-conformal setting. I will also briefly discuss the extension of these results to mass deformations of N=4 SYM with N=1 supersymmetry.
I will discuss the gravitational dual of a mass deformation of N=4 SYM, called N=2* SYM, on S^4. Using holographic techniques one can calculate the universal contribution to the corresponding free energy in the planar limit and at large 't Hooft coupling. The result matches the expression recently computed using supersymmetric localization in the field theory. This agreement constitutes a non-trivial precision test of holography in a non-conformal setting. I will also briefly discuss the extension of these results to mass deformations of N=4 SYM with N=1 supersymmetry.
Posted by: QMW
Thursday, 12 Mar 2015
On type II string theory on AdS3 times S3 times T4 and its CFT dual
Ofer Aharony
(Weizmann Institute)
Abstract:
I will review and discuss in detail type II string theory on \(AdS_3\times S^3\times T^4\) and its \(1+1\) dimensional superconformal field theory dual, emphasizing the string theoretic aspects of this duality. For one unit of NS-NS 5-brane flux (\(Q_5=1\)), this string theory has been suggested to be dual to a grand-canonical ensemble of \(T^{4N}/S_N\) free symmetric orbifold CFTs, and one goal will be to understand how this is consistent and how it fits with the description of other values of \(Q_5\). I will discuss how the strong coupling limit of the NS-NS string theory arises (even at large \(N\)) in the free orbifold description, and why this limit does not have a weakly coupled R-R description. The dual CFT includes (for all values of \(Q_5\)) an extra \(T^4\) factor that is decoupled from perturbative string theory, and I will discuss how this appears and how it is coupled to the CFT. Based on 2406.14605 with Erez Urbach.
I will review and discuss in detail type II string theory on \(AdS_3\times S^3\times T^4\) and its \(1+1\) dimensional superconformal field theory dual, emphasizing the string theoretic aspects of this duality. For one unit of NS-NS 5-brane flux (\(Q_5=1\)), this string theory has been suggested to be dual to a grand-canonical ensemble of \(T^{4N}/S_N\) free symmetric orbifold CFTs, and one goal will be to understand how this is consistent and how it fits with the description of other values of \(Q_5\). I will discuss how the strong coupling limit of the NS-NS string theory arises (even at large \(N\)) in the free orbifold description, and why this limit does not have a weakly coupled R-R description. The dual CFT includes (for all values of \(Q_5\)) an extra \(T^4\) factor that is decoupled from perturbative string theory, and I will discuss how this appears and how it is coupled to the CFT. Based on 2406.14605 with Erez Urbach.
Posted by: IC2
Gluon scattering amplitudes as flux-tube partition functions
Benjamin Basso
(ENS Paris)
Abstract:
In this talk I will explain how to compute gluon scattering
amplitudes at finite coupling in planar N=4 SYM theory, using the duality
with null polygonal Wilson loops, conformal symmetry, and the
integrability of the colour flux tube dynamics. After introducing the main
ideas and results, I will present some applications of this formalism at
strong coupling and discuss the validity of the semiclassical (dual)
string description.
In this talk I will explain how to compute gluon scattering
amplitudes at finite coupling in planar N=4 SYM theory, using the duality
with null polygonal Wilson loops, conformal symmetry, and the
integrability of the colour flux tube dynamics. After introducing the main
ideas and results, I will present some applications of this formalism at
strong coupling and discuss the validity of the semiclassical (dual)
string description.
Posted by: QMW