Mini-courses, Seminars, Communications & Posters
Mini-courses (3 hours)
Mini-course I: Tests of modified gravity
Abstract: Gravity has been tested at laboratory and solar system scales since centuries. Recently however the idea of a modification of gravity at astrophysical scales has been revived due to the discovery of cosmic acceleration and the possibility of employing the new tools offered by large-scale cosmological observations. In these lectures we review the most interesting models of modified gravity and their impact on cosmological observables (large scale structure, lensing, cosmic microwave background).
Mini-course II: Quantum Gravity
Abstract: After some justifications for quantising General Relativity as a theory of gravitation, we shall describe some of the attempts made until now. We next will introduce with more details one of them, namely Loop quantum Gravity, focusing on some simpler models for lower dimensional gravity, where the quantisation program can be performed up to the end. We finally will describe some applications to Cosmology.
Mini-course III: Topics in three-dimensional anti-de Sitter gravity
Abstract: Three-dimensional Einstein gravity has no local dynamical degree of freedom. Yet, it is far from being trivial when the cosmological constant is negative. (i) It admits black hole solutions. (ii) It easily allows for consistently interacting and tractable higher-spin extensions. (iii) It possesses remarkable asymptotic properties at infinity where an infinite-dimensional symmetry algebra emerges. These features make three-dimensional gravity a perfect ”theoretical laboratory” in which to explore the conceptual issues related to black holes and higher spins in a simpler context. The mini-course will discuss three-dimensional gravity assuming no previous knowledge of the subject and will also provide access to recent work where new results on points (i), (ii) and (iii) have been developed.
Mini-Course IV: Inflation and the origin of cosmic structures
Abstract: We will review the theory of Inflation and the generation of cosmic structures from quantum fluctuations that inflation predicts. In the first lecture we will discuss the dynamics of inflation and how it provides a natural explanation of several features of the gross appearance of our Universe. The second lecture will deal with the most remarkable feature of inflation: the generation of cosmic structures out of quantum vacuum fluctuations. In the third lecture we will
see how the properties of these fluctuations fare against observations and, conversely, what observations can tell us about inflation.
Special session - The 65th birthday of Philippe Spindel
Talk I: The quantum Coulomb solution as a coherent state of unphysical photons. A physical toy model for blackhole microstates (1 hour)
Abstract: By analyzing the Schwarzschild solution in linearized gravity, we argue that black hole entropy is related to non-proper gauge degrees of freedom rather than physical gravitons. This motivates the study of the analog problem in electromagnetism where the role of the black hole is played by the Coulomb solution. It is shown that, when all polarizations of the photon are quantised in an indefinite metric Hilbert space, the quantum state corresponding to the classical Coulomb solution is a coherent state of longitudinal and temporal photons.
Talk II: Dark Energy and Alternative Cosmologies: The Case for a Dynamical Λ-Term (1 hour)
José Ademir S. de Lima
Abstract: After decades of successful hot big-bang paradigm, Cosmology still lacks a framework in which the early inflationary phase of the universe smoothly matches the radiation epoch and evolves to the present quasi de Sitter space-time. No less intriguing is that the current value of the effective vacuum energy density is vastly smaller
than the value that triggered inflation. In my talk, after review the basic ideas behind alternative cosmologies, I will focus on a specific class of dynamical (H) models recently proposed. It will be argued that the models provide a complete cosmological picture and are also able to solve some theoretical problems plaguing the cosmic concordance cosmology (CDM).
Talk III: The Z3 - graded algebras and ternary generalization of Heisenberg’s algebra (1 hour)
Abstract: A concise study of ternary and cubic algebras with Z3 grading is presented. We discuss some underlying ideas leading to the conclusion that the discrete symmetry group of permutations of three objects, S3, and its abelian subgroup Z3 may play an important role in quantum physics. We show then how most of important algebras
with Z2 grading can be generalized with ternary composition laws combined with a Z3 grading.
We investigate in particular a ternary, Z3-graded generalization of the Heisenberg algebra. It turns out that introducing a non-trivia cubic root of unity, j = exp(2πi/3), one can define two types of creation operators instead of one, accompanying the usual annihilation operator.
The two creation operators are non-hermitian, but they are mutually conjugate. Together, the three operators form a ternary algebra, and some of their cubic combinations generate the usual Heisenberg algebra.
An analogue of Hamiltonian operator is constructed by analogy with the usual harmonic oscillator, and some properties of its eigenfunctions are briefly discussed.
Talk IV: Mini-Superspace Quantum Supergravity and its Hidden Hyperbolic Kac-Moody Structures (1 hour)
Abstract: We provide a detailed description of the space of solutions of N=1, D=4 Supergravity in the framework of a minisuperspace quantum cosmology obtained by dimensionally reducing (to one timelike dimension) the action of D = 4, N = 1, supergravity for an SO(3) homogeneous (Bianchi IX) cosmological model. The quantization of the homogeneous gravitino field leads to a 64-dimensional fermionic Hilbert space. The algebra of the supersymmetry constraints and of the Hamiltonian one is found to close. One finds that the quantum Hamiltonian is built from operators that generate a 64-dimensional representation of the (infinite-dimensional) maximally compact subalgebra of the rank-3 hyperbolic Kac-Moody algebra AE3. Some exponentials of these operators generate a spinorial extension of the
Weyl group of AE3 which describe (in the WKB limit) the chaotic quantum evolution of the universe near the cosmological singularity.
One of our main result are elements sustaining the conjecture that the quantum dynamic can made some branches of the universe to avoid its classical singular behavior.
Seminars (1 hour)
Seminar I: Quantum effects in anti-de Sitter spacetime
Abstract: We consider quantum vacuum effects for scalar and fermionic fields in background of ant-de Sitter spacetime in the presence of branes. The vacuum expectation values of the field squared and of the energy-momentum tensor are investigated. The nature of the vacuum forces acting on the branes and the problem of the radion stabilization in braneworld models are discussed. We also consider the generation of the cosmological constant on the visible brane by quantum fluctuations of bulk fields.
Seminar II: Constraining perturbations with lensing of supernovae
Abstract: Soon the number of type Ia supernova (SN) measurements should exceed 100,000. Understanding the effect of weak lensing by matter structures on the supernova brightness will then be more important than ever. Although SN lensing is usually seen as a source of systematic noise, we will show that it can be in fact turned into signal. More precisely, the non-Gaussianity introduced by lensing in the SN Hubble diagram dispersion depends rather sensitively on the amplitude and rate of growth of matter perturbations. By exploiting this relation, we are able to predict precent-level constraints on the normalization sigma8 and the growth rate index gamma. This method is independent of and complementary to the standard methods based on CMB, cosmic shear or cluster abundance observables.
Seminar III: Vortices in models with hidden sectors
Abstract: I will present vortex solutions of two Abelian Higgs models associated to visible and hidden sectors weakly coupled through a gauge mixing interaction. In particular I will discuss:
1- How the effects of the hidden sector depend on the strength of the mixing between the two U(1) gauge bosons, the gauge coupling constants and the scalar potentials.
2- The case in which one of the U(1) gauge symmetries remains un broken.
3- Vortex decay when both hidden and visible vortices are present. (in the case in which the hidden sector is absent, vortices with n - 1 units of magnetic flux could decay)
4- N = 2 Supersymmetry extensions and BPS equations.
Seminar IV: Motivations for Studying Superstring Theory
Abstract: In this seminar, I will review the main motivations for studying superstring theory. Although the non-perturbative definition of superstring theory is not yet understood, superstring theory is at the moment the only approach to quantum gravity which allows a perturbative computation of quantum corrections to graviton scattering amplitudes. Furthermore, the study of superstring theory has led to various new insights such as supersymmetry and dualities which have had an important impact on other areas of physics.
Seminar V: The effect of dark matter velocity dispersion on the evolution
of cosmological perturbations
Abstract: We investigate a modification of the standard CDM cosmological model in which the dark matter velocity dispersion is non-negligible. We calculate the effect of the latter on the evolution of cosmological perturbations and determine the modifications on the cosmic microwave background radiation spectrum and on the matter power spectrum by suitably modify the CAMB code.
Seminar VI: Similarities and differences between Scalar-Tensor theories and
Renormalization Group effects in gravity
Davi C. Rodrigues
Abstract: We show that the possible Renormalization Group (RG) modifications to the Einstein-Hilbert action for large scale physics need not (and perhaps should not) be particular cases of standard Scalar-Tensor (ST) gravity. We present a new class of ST actions, which has a new type of coupling to matter, and show that this newer extended ST model is formally equivalent to the RG case. Also, contrary to certain expectations, we stress that the use of external
fields do not constitute a dynamically relevant difference between standard ST gravity and the large scale RG induced modifications, since the latter can be reformulated with an action without external fields.
Seminar VII: Wheeler-DeWitt quantization and singularities
Abstract: We consider a Bohmian approach to the Wheeler-DeWitt quantization of the Friedmann-Lemaître-Robertson-Walker model and investigate the question whether or not there are singularities, in the sense that the universe reaches zero volume. We find that for generic wave functions (i.e., non-classical wave functions), there is a non-zero probability for a trajectory to be non-singular. This should be contrasted to the consistent histories approach for which it was recently shown by Craig and Singh that there is always a singularity. This result illustrates that the question of singularities depends much on which version of quantum theory one adopts.
Seminar VIII: Wheels in universal quantization formulas
Abstract: Kontsevich’s quantization formula defines a star-product associated to any Poisson bracket. This formula is expressed in terms of graphs and propagators. One feature of Kontsevich’s formula is that it involves graphs with oriented cycles (wheels) that makes it difficult to generalize to infinite-dimensional spaces. Some effort has been put in the quest for a universal quantisation formula without wheels and, hence, for a direct infinite-dimensional generalization. In this talk, we provide an elementary argument showing that any universal quantization formula necessarily involves graphs with wheels.
Seminar IX: Some remarks on a gravitational analog of the Casimir effect
Abstract: We consider the Casimir energy of the electromagnetic and massless spinor fields in some closed cosmological models containing a cosmic string. The vacuum energies of the fields under consideration are given in terms of the vacuum energies in the absence of the cosmic string multiplied by the parameter which codifies the presence of the topological defect. The thermal corrections to the Casimir free energies and some thermodynamic quantities are also obtained. These present the same structure.
Seminar X: Wormholes with cylindrical and axial symmetries
Abstract: We discuss the existence conditions of wormhole throats and wormholes as global configurations in general relativity under the assumptions of cylindrical and axial symmetries. It is pointed out, in particular, that wormhole throats can exist in static, cylindrically symmetric space-times under slightly different conditions as compared with spherical symmetry. In cylindrically symmetric spacetime with rotation, throats can exist in the presence of ordinary
matter or even in vacuum space-times. However, there are substantial difficulties in obtaining asymptotically flat wormhole configurations: such examples are yet to be found. Some features of interest are discussed in static, axially symmetric configurations including wormholes with singular rings and wrongly seeming regular wormhole throats in the Zipoy-Voorhees vacuum space-time.
Seminar XI: Dark Sector with internal couplings
Abstract: Interactions inside the cosmological dark sector influence the cosmological dynamics. As a consequence, the evolution of the Universe may be different from that predicted by the ΛCDM model. We review main features of several recently studied models with nongravitational couplings between dark matter and dark energy.
Short communications (1/2 hour)
Communication I: On the Lorentz symmetry breaking in supersymmetric theories
Abstract In this talk, we present a review of the approaches proposed to construct the supersymmetric extension of the Lorentz-breaking theories. Actually, there are three such approaches. The first of them is based on introducing a new superfield explicitly depending on the Lorentz-breaking parameters. The starting point of the second one is the Lorentz-breaking deformation of the supersymmetry algebra which allows to have aether-like extensions of the supersymmetric theories. Finally, the third one supposes introduing of the Lorentz-breaking terms on the superfield action level, which in some limit allows to have the Horava-Lifshitz-like terms in the classical action. We review the main results and advantages of each of these methods.
Communication II: Dark energy and galaxy formation
Abstract: The influence of Dark Energy parametrization on galaxy formation must be taken into account, especially in the era of precision cosmology. The different background evolutions can (depending on the behavior of the DE equation of state) either enhance or quench star formation with respect to a LCDM model, at a level similar to the variation of the stellar feedback parametrization, with strong effects on the final galaxy rotation curves.
Communication III: Finite Temperature Fermionic Current in Higher Dimensional
Cosmic String Spacetime
Abstract: We consider the vacuum expectation values of the fermionic charge and current densities induced by a constant magnetic flux for a massive fermion in higher dimensional cosmic string spacetime at finite temperature and in the presence of a nonvanishing chemical potential. The presence of the magnetic flux gives rise to Aharonov-
Bohm-like effects on the expectation values. They are periodic functions of magnetic fluxes with the period equal to the flux quantum. Besides obtaining general expression for these parameters, we discuss the results in limiting cases such as high and low temperatures, massless fermions, large and low distances from the string and compare them with the ones discussed in the literature.
Communication IV: Super-Renormalizable Gravity.
Abstract: I will review the so called super-renormalizable quantum gravity models, a new class of higherderivatives gravity models which is power-counting renormalizable on a flat background. In particular I will review the quantum properties and the cosmological behaviour of this models and I will discuss open problems.
The poster session will be open throughout the event. The discussions about the posters are expected to take place during the coffee breaks.