Triangle Seminars
Tuesday, 1 Feb 2022
Stabilising relativistic fluids on slowly expanding cosmological spacetimes
Zoe Wyatt
(King's College London)
Abstract:
On a background Minkowski spacetime, the relativistic Euler equations are known, for a relatively general equation of state, to admit unstable homogeneous solutions with finite-time shock formation. By contrast, such shock formation can be suppressed on background cosmological spacetimes whose spatial slices expand at an accelerated rate. The critical case of linear, ie zero-accelerated, spatial expansion, is not as well understood. In this talk, I will present two recent works concerning the relativistic Euler and the Einstein-Dust equations for geometries expanding at a linear rate. This is based on joint works with David Fajman, Todd Oliynyk and Max Ofner.
Email m.godazgar@qmul.ac.uk for zoom link
On a background Minkowski spacetime, the relativistic Euler equations are known, for a relatively general equation of state, to admit unstable homogeneous solutions with finite-time shock formation. By contrast, such shock formation can be suppressed on background cosmological spacetimes whose spatial slices expand at an accelerated rate. The critical case of linear, ie zero-accelerated, spatial expansion, is not as well understood. In this talk, I will present two recent works concerning the relativistic Euler and the Einstein-Dust equations for geometries expanding at a linear rate. This is based on joint works with David Fajman, Todd Oliynyk and Max Ofner.
Email m.godazgar@qmul.ac.uk for zoom link
Posted by: QMW
Small Cosmological Constants in String Theory
Liam McAllister
(Cornell University)
Abstract:
We construct vacua of string theory in which all moduli are stabilized and the magnitude of the cosmological constant is exponentially small. The vacua are supersymmetric AdS4 solutions in flux compactifications of type IIB string theory on orientifolds of Calabi-Yau hypersurfaces. I will explain the advances in computing topological data in Calabi-Yau compactifications that led to these solutions, then speculate about implications for the cosmological constant problem. The vacuum energy is small because we ensure the exact cancellation of all perturbative contributions, through an explicit choice of integer parameters determined by the topology and quantized fluxes. The nonperturbative contributions that remain are exponential in these integers. Finding cosmological constants of small magnitude in this landscape is exponentially easier than in Bousso-Polchinski landscapes. Extending this approach to positive cosmological constants in realistic universes is a difficult open problem.
We construct vacua of string theory in which all moduli are stabilized and the magnitude of the cosmological constant is exponentially small. The vacua are supersymmetric AdS4 solutions in flux compactifications of type IIB string theory on orientifolds of Calabi-Yau hypersurfaces. I will explain the advances in computing topological data in Calabi-Yau compactifications that led to these solutions, then speculate about implications for the cosmological constant problem. The vacuum energy is small because we ensure the exact cancellation of all perturbative contributions, through an explicit choice of integer parameters determined by the topology and quantized fluxes. The nonperturbative contributions that remain are exponential in these integers. Finding cosmological constants of small magnitude in this landscape is exponentially easier than in Bousso-Polchinski landscapes. Extending this approach to positive cosmological constants in realistic universes is a difficult open problem.
Posted by: IC
Wednesday, 2 Feb 2022
1/4 BPS operators in N=4 Super Yang Mills
Agnese Bissi
(Uppsala)
Abstract:
I will discuss how to constrain four-point correlators involving at least one quarter BPS operator in N=4 Super Yang-Mills. I will present what can be learned by using crossing symmetry, chiral algebra, superspace techniques, and the structure of the operator product expansion. Finally, I will show how to make contact with the superconformal bootstrap program.
Contact your local Triangle organiser or Bogdan Stefanski for Zoom link.
I will discuss how to constrain four-point correlators involving at least one quarter BPS operator in N=4 Super Yang-Mills. I will present what can be learned by using crossing symmetry, chiral algebra, superspace techniques, and the structure of the operator product expansion. Finally, I will show how to make contact with the superconformal bootstrap program.
Contact your local Triangle organiser or Bogdan Stefanski for Zoom link.
Posted by: CityU2
Gravitational Regge bounds
Alexander Zhiboedov
(CERN)
Abstract:
I will review the basic assumptions and spell out the detailed arguments that lead to the bound on the Regge growth of gravitational scattering amplitudes. The minimal extra ingredient compared to the gapped case - in addition to unitarity, analyticity, and crossing - that goes into the derivation is the assumption that scattering at large impact parameters is controlled by known semi-classical physics. I will also discuss bounds on the local growth of scattering amplitudes.
Contact your local Triangle organiser or Bogdan Stefanski for Zoom link.
I will review the basic assumptions and spell out the detailed arguments that lead to the bound on the Regge growth of gravitational scattering amplitudes. The minimal extra ingredient compared to the gapped case - in addition to unitarity, analyticity, and crossing - that goes into the derivation is the assumption that scattering at large impact parameters is controlled by known semi-classical physics. I will also discuss bounds on the local growth of scattering amplitudes.
Contact your local Triangle organiser or Bogdan Stefanski for Zoom link.
Posted by: CityU2
Thursday, 3 Feb 2022
Large N Factorization for Matrix Model Observables With Continuous and Discrete Symmetry
George Barnes
(QMUL)
Abstract:
Part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
Part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)
Posted by: QMW
Jordan blocks and the Bethe ansatz: The eclectic spin chain as a limit
Juan Miguel Nieto Garcia
(University of Surrey)
Abstract:
In this talk, I will present a procedure to extract the generalised eigenvectors of a non-diagonalisable matrix by considering a diagonalisable perturbation of it and computing the non-diagonalisable limit of its eigenvectors. As an example, I will show how to compute a subset of the spectrum of the eclectic spin chain by computing the appropriate limit of the Bethe states of a twisted su(3) spin chain.
–––– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. Link emailed on Tuesday.
In this talk, I will present a procedure to extract the generalised eigenvectors of a non-diagonalisable matrix by considering a diagonalisable perturbation of it and computing the non-diagonalisable limit of its eigenvectors. As an example, I will show how to compute a subset of the spectrum of the eclectic spin chain by computing the appropriate limit of the Bethe states of a twisted su(3) spin chain.
–––– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. Link emailed on Tuesday.
Posted by: andrea