Forthcoming events in this series
String Axiverse
Abstract
String theory suggests the simultaneous presence of many ultralight axions possibly populating each decade of mass down to the Hubble scale 10^-33eV. Conversely the presence of such a plenitude of axions (an "axiverse") would be evidence for string theory, since it arises due to the topological complexity of the extra-dimensional manifold and is ad hoc in a theory with just the four familiar dimensions. We investigate how upcoming astrophysical experiments will explore the existence of such axions over a vast mass range from 10^-33eV to 10^-10eV. Axions with masses between 10^-33eV to 10^-28eV cause a rotation of the CMB polarization that is constant throughout the sky. The predicted rotation angle is of order \alpha~1/137. Axions in the mass range 10^-28eV to 10^-18eV give rise to multiple steps in the matter power spectrum, that will be probed by upcoming galaxy surveys and 21 cm line tomography. Axions in the mass range 10^-22eV to 10^-10eV affect the dynamics and gravitational wave emission of rapidly rotating astrophysical black holes through the Penrose superradiance process. When the axion Compton wavelength is of order of the black hole size, the axions develop "superradiant" atomic bound states around the black hole "nucleus". Their occupation number grows exponentially by extracting rotational energy from the ergosphere, culminating in a rotating Bose-Einstein axion condensate emitting gravitational waves. This mechanism creates mass gaps in the spectrum of rapidly rotating black holes that diagnose the presence of axions. The rapidly rotating black hole in the X-ray binary LMC X-1 implies an upper limit on the decay constant of the QCD axion f_a
Berry Phase and Supersymmetry
Abstract
Cybersusy--a new mechanism for supersymmetry breaking in the standard supersymmetric mode
Abstract
Dynamical Logic
Abstract
Twistor Methods for Scattering Amplitudes
Abstract
Tree-level scattering amplitudes in N=4 SYM are now known to possess a Yangian symmetry, formed by combining the original PSU(2,2|4) superconformal invariance with a second "dual" copy. I will also discuss very recent work constructing scattering amplitudes in a twistor space in which this dual superconformal symmetry acts geometrically.
(0,2) Landau-Ginzburg Models and Residues
Abstract
Twistor diagrams for gauge-theoretic amplitudes
Abstract
The UV question in maximally supersymmetric field theories
Abstract
Calabi-Yau Groups
Abstract
Non-relativistic holography and massive Kaluza-Klein reductions
Abstract
Yukawa Couplings from Monad Bundles
Abstract
Topology changing T-dualities
Abstract
AdS/CFT and Generalized Complex Geometry
Abstract
Black branes beyond thermal equilibrium
Abstract
Born-Infeld gravity, bigravity, and their cosmological applications
Abstract
Free fermions on quantum curves
Abstract
Abstract: In this talk we show that various holomorphic quantities in supersymmetric gauge theories can be conveniently computed by configurations of D4-branes and D6-branes. These D-branes intersect along a Riemann surface that is described by a holomorphic curve in a complex surface. The resulting I-brane carries two-dimensional chiral fermions on its world-volume. This system can be mapped directly to the topological string on a large class of non-compact Calabi-Yau manifolds. Inclusion of the string coupling constant corresponds to turning on a constant B-field on the complex surface, which makes this space non-commutative. Including all string loop corrections the free fermion theory is formulated in terms of holonomic D-modules that replace the classical holomorphic curve in the quantum case. We show how to associate a quantum state to the I-brane system, and subsequently how to compute quantum invariants. As a first example, this yields an insightful formulation of (double scaled as well as general Hermitian) matrix models. Secondly, our formalism elegantly reconstructs the dual Nekrasov-Okounkov partition function from a quantum Seiberg-Witten curve.
Summing the Instantons in the Heterotic String
Abstract
Abstract: I will discuss some recent developments in understanding compactifications of the Heterotic string on Calabi-Yau manifolds. These compactifications are well-described by linear sigma models with (0,2) supersymmetry. I will show how to use these models to compute physical observables, such as genus zero Yukawa couplings, their singularity structure, and dependence on bundle moduli.
Chern-Simons quivers and Sasaki-Einstein manifolds
Abstract
Abstract: There has been considerable interest recently in the relation between certain 3d supersymmetric Chern-Simons theories, M2-branes, and the AdS_4/CFT_3 correspondence. In this talk I will show that the moduli space of a 3d N=2 Chern-Simons quiver gauge theory always contains a certain branch of the moduli space of a parent 4d N=1 quiver gauge theory. In particular, starting with a 4d quiver theory dual to a Calabi-Yau 3-fold singularity, for certain general choices of Chern-Simons levels this branch of the corresponding 3d theory is a Calabi-Yau 4-fold singularity. This leads to a simple general method for constructing candidate 3d N=2 superconformal Chern-Simons quivers with AdS_4 gravity duals. As simple, but non-trivial, examples, I will identify a family of Chern-Simons quiver gauge theories which are candidate AdS_4/CFT_3 duals to an infinite class of toric Sasaki-Einstein seven-manifolds with explicit metrics.
Non-Kahler Ricci solitons
Abstract
Gravity, Twistors and the MHV Formalism
Abstract
Abstract: Recent developments in quantum field theory and twistor-string theory have thrown up surprising structures in the perturbative approach to gravity that cry out for a non-perturbative explanation. Firstly the MHV scattering amplitudes, those involving just two left handed and n-2 right handed outgoing gravitons are particularly simple, and a formalism has been proposed that constructs general graviton scattering amplitudes from these MHV amplitudes as building blocks. This formalism is chiral and suggestive of deep links with Ashtekar variables and twistor theory. In this talk, the MHV amplitudes are calculated ab initio by considering scattering of linear gravitons on a fully nonlinear anti-self-dual background using twistor theory, and a twistor action formulation is provided that produces the MHV formalism as its Feynman rules.
M2 Branes and Chern-Simons-Matter Theories
Abstract
Abstract: In this talk, I will give an overview of the new developments in the AdS_4/CFT_3 correspondence. I will present in detail an N=6 Chern-Simons-matter theory with gauge group U(N) x U(N) that is dual to N M2 branes in the orbifold C^4/Z_k. This theory can be derived from a construction involving D3 branes intersecting (p,q) fivebranes. I will also discuss various quantum mechanical aspects of this theory, including an enhancement of its supersymmetry algebra at Chern-Simons levels 1 and 2, and some novel phenomenon that arise in the U(N) x U(M) theory dual to configurations with N-M fractional branes. A generalization to N=3 CSM theories dual to AdS_4 x M_7, where M_7 is a 3-Sasakian 7-manifold, will be explained. The seminar will be based primarily on Aharony, Bergman, DJ, Maldacena; Aharony, Bergman, DJ; DJ, Tomasiello.
Noncommutative Geometry and the Spectrum of the Dirac operator
Abstract
Calabi-Yau Manifolds with Small Hodge Numbers
Abstract
Abstract: It is known that many Calabi-Yau manifolds form a connected web. The question of whether all CY manifolds form a single web depends on the degree of singularity that is permitted for the varieties that connect the distinct families of smooth manifolds. If only conifolds are allowed then, since shrinking two-spheres and three-spheres to points cannot affect the fundamental group, manifolds with different fundamental groups will form disconnected webs. We examine these webs for the tip of the distribution of CY manifolds where the Hodge numbers $(h^{11},h^{21})$ are both small. In the tip of the distribution the quotient manifolds play an important role. We generate via conifold transitions from these quotients a number of new manifolds. These include a manifold with $\chi =-6$, that is an analogue of the $\chi=-6$ manifold found by Yau, and manifolds with an attractive structure that may prove of interest for string phenomenology.