Day 4

Jorge Zanelli

U-SUSY: A Pedagogical Review

Abstract:

In supersymmetric extensions of the Standard Model (SM), all particles come in fermion–boson pairs necessary for the realization of supersymmetry (SUSY). In spite of the expected abundance of super-partners for all the known particles, not a single supersymmetric pair has been reported to date. Although a hypothetical SUSY breaking mechanism, operating at high energy inaccessible to current experiments cannot be ruled out, this reduces SUSY’s predictive power and it is unclear whether SUSY, in its standard form, can help reducing the remaining puzzles of the SM. Here we argue that SUSY can be realized in a different way, connecting spacetime and internal bosonic symmetries, combining bosonic gauge fields and fermionic matter particles in a single gauge field, a Lie superalgebra-valued connection. In this unconventional representation, states do not come in SUSY pairs, avoiding the doubling of particles and fields and SUSY is not a fully off-shell invariance of the action. The resulting systems are remarkably simple, closely resembling a standard quantum field theory and SUSY still emerges as a contingent symmetry that depends on the features of the vacuum/ground state.

Rodrigo Olea

Conformal Renormalization and Energy Functionals in AdS gravity

Abstract:

Within a holographic framework, we explore the physical consequences of embedding Einstein-AdS gravity in Conformal Gravity in four and six dimensions. In the bulk, the procedure is equivalent to Holographic Renormalization, as the Einstein-AdS action appears augmented by the correct boundary counterterms. In codimension-2 surfaces, 4D Conformal Gravity induces a conformal invariant which, for given conditions on the ambient space and the surface itself, reproduces different functionals: Renormalized Area, Willmore Energy and Reduced Hawking Mass.

Julio Oliva

New aspects of black strings with higher curvature corrections

Abstract:

In this talk, I will start reviewing the original results on the stability of black strings, and then I will consider a perturbative Gauss-Bonnet term supplementing the Einstein-Hilbert action, and evaluate its effect on the spectrum of the scalar mode that triggers the Gregory-Laflamme instability of black strings in five dimensional General Relativity. After studying some properties of the static black string, I provide the correction to the Lichnerowicz operator up to O(α^2). For the scalar mode of the gravitational perturbation, we find a master variable and study its spectrum, providing an analysis of the regime of validity of our scheme. I will show that the instability persists under the inclusion of the R^2-correction, and that the critical wavelength increases with the value of α/r^2_+<<1, providing new evidence of the phenomenon which was already observed in other approaches. We also construct the boosted black strings and compute the correction to the mass, the momentum and the tension due to the higher curvature term. The presence of the dimensionful coupling α spoils the validity of the Smarr relation, which is the gravitational version of the Euler relation which must hold for every homogeneous, thermodynamic system. We show that this identity can be restored by working in an extended thermodynamic setup that includes variations of the Gauss-Bonnet coupling.

Stefan Prohazka

Gravitation beyond Lorentz symmetry

Abstract:

I will discuss symmetries and gravitational models that go beyond the well-known lorentzian setup. In particular, I will highlight galilean and carrollian gravitational theories and their Chern-Simons and BF formulations.

Branislav Cvetkovic

Black hole entropy in Poincaré gauge theory

Abstract:

The canonical generator G of local symmetries in Poincaré gauge theory is constructed as an integral over a spatial section Σ of spacetime. Its regularity (differentiability) on the phase space is ensured by adding a suitable surface term, an integral over the boundary of Σ at infinity, which represents the asymptotic canonical charge. For black hole solutions, Σ has two boundaries, one at infinity and the other at horizon. It is shown that the canonical charge at horizon defines entropy, whereas the regularity of G implies the first law of black hole thermodynamics. The approach is tested for several black hole types in vaccuum. The canonical approach to black hole entropy in Poincaré gauge theory without matter can be extended to include Maxwell field and scalar fields as matter sources. The new formalism is used to calculate asymptotic charges and entropy of Kerr--Newmann--AdS with torsion and MTZ black hole.

Olivera Miskovic

Topologically nontrivial supersymmetric black holes in Chern-Simons AdS supergravity

Abstract:

We construct BPS states in Chern-Simons AdS supergravity in five dimensions. Obtained solutions describe an extremal black hole and a soliton – antisoliton system with non-trivial topological charges. We find many similarities of this solution with standard supergravity black holes, and also with three-dimensional BTZ geometries.

Turmoli Neogi

Asymptotic dynamics of (higher spin) AdS$_3$ (super)gravity with two asymptotic regions

Abstract:

We consider the Hamiltonian reduction of the action for $3$ dimensional AdS supergravity and $W_3$ higher spin AdS gravity in the Chern-Simons formulation under asymptotically anti de-Sitter boundary conditions. We take into account the holonomy of the Chern-Simons connection and show that this manifests itself as the zero mode of momentum of chiral bosons on the boundary. An equivalent formulation of the boundary chiral action is found to be the geometric action on the symplectic leaves of a (super) Virasoro Poisson manifold, where the representative can be identified as the bulk holonomy. We then also discuss the case of non-linear algebras where the notion of coadjoint representation is not well defined.