Perspectives of Fundamental Cosmology

5 Nov 2012, 08:00 → 30 Nov 2012, 18:00 Europe/Stockholm

132:028 (Nordita)

Kristina Giesel (University Erlangen), Mairi Sakellariadou (King's College, London), Martin Bojowald (Penn State University), Sabine Hossenfelder (Nordita)

Venue

Nordita, Stockholm, Sweden

Scope

Current cosmology provides a fascinating mix of a wealth of new observational data with deep conceptual problems still to be addressed. Several approaches in the general context of quantum gravity aim at a fundamental description of the relevant stages in the history of the universe, but none of them appears to be fully convincing and comparisons between different directions are difficult to draw. This workshop brings together a large set of experts, from both fundamental and phenomenological theory, in order to provide a snapshot of the current status and to focus future activities.

Timetable

Format

This four-week long program will be composed of introductory lectures by experts in the fields and more specialized seminars on recent developments and open questions.

The tentative plan is to cover the following topics:

• Week 1: Fundamental theories of space-time. Here, the main approaches will be introduced by some of the experts in the fields, with a focus on the resulting models for early-universe cosmology.
• Week 2: Cosmological and high-energy phenomenology. The various implications of fundamental theories for cosmology and high-energy physics will be discussed.
• Week 3: Cosmology and high-energy physics. In this week, a general discussion of the potential of cosmological and high-energy observations will be carried out.
• Week 4: Several combinations of topics covered in the previous weeks are possible to arrive at concluding statements. (Details of this week will be scheduled short notice, capturing those topics that have emerged as the most important ones.)

Application

If you want to apply for participation in the program, please fill in the application form. You will be informed by the organizers shortly after the application deadline whether your application has been approved. Due to space restrictions, the total number of participants is strictly limited.

Application deadline: 31 August 2012

A minimum stay of one working week is required and we encourage participants to stay for a period of at least two weeks.

There is no registration fee.

Sponsored by:

Monday 5 November

10:00 → 11:00 Isotropy-breaking in Quantum Cosmology

We present a new perspective on QFT on quantum cosmological space-times. Naively, the semiclassical limit of a quantum space-time can be taken by averaging the gravitational operators on a semiclassical state of geometry. The result is an effective classical metric (which in general does not obey Einstein equation). We show that, once quantum matter is taken into account, a new possibility arises: the dynamics of matter on quantum space-time can be equivalently described by standard QFT on a classical space-time, whose geometry is encoded in a so-called "dressed metric", a classical metric which is different than the naive semiclassical one. Such matter-dependent dressed metric can be thought of as the metric "seen" by the matter field. We explore this interpretation and its consequences in various instances, such as scalar field on quantum cosmological space-times, addressing the question of observable effects on the propagation of matter. Indeed, since the dressed metric depends on the matter, Lorentz-violating phenomena are expected (such as deformation of dispersion relations). We prove that for massless field on FRW [1] or Bianchi I [2] quantum geometries, no violation takes place at test-field level. We present a way to take into account the matter back- reaction (in which case a deformation in the dispersion relation is present). Finally, we address the case of a massive field on FRW quantum geometry [3], and show that an isotropy-breaking is present already at the test- field level, since the dressed metric depends on the direction of propagation of the mode of the field. References: [1] A. Ashtekar, W. Kaminski, J. Lewandowski - "Quantum field theory on a cosmological, quantum space-time", Phys. Rev. D 79, 064030 (2009) [2] A. Dapor, J. Lewandowski, Y. Tavakoli - "Lorentz Symmetry in QFT on Quantum Bianchi I Space-Time", Phys. Rev. D 86, 064013 (2012) [3] A. Dapor, J. Lewandowski - "Isotropy-Breaking in Quantum Cosmology", in preparation

Speaker: Andrea Dapor

11:00 → 12:00 Models of Quantum Spacetime, and Quantum Geometry.

We will review the DFR approach to Quantum Space- Time and discuss the state of the art and the open issues. The DFR model is a fully covariant model of flat quantum spacetime generated by selfadjoint coordinates, where covariance is unitarily implemented, and the commutation relations among the coordinates are derived from a stability condition of spacetime under localisation alone. It must be regarded as a sort of analogue of semiclassical quantisation, providing the noncommutative geometric background for the quantum theory of fields at an intermediate regime, where few processes take place at very high energy; attempts to construct dynamical models also will be shortly reviewed and discussed. The stability condition is enforced through uncertainty relations which should prevent the purely kynematical black-hole formation. The quantum geometry arising from the interplay of the universal differential calculus with the specific algebra of the model provides a precise framework for discussing bounds to measurements of position,length, and n-volumes operators. We will conclude with an outlook. References: [arXiv:hep-th/0303037], [arXiv:1005.2130], [arXiv:hep-th/0301100],[arXiv:1201.2519], [arXiv:1206.3067]. See also the review [arXiv:1004.5261v3].

Speaker: Gherardo Piacitelli

Slides 2012-11-05-piacitelli.pdf

12:00 → 14:00 Lunch break

14:00 → 15:00 Gravity's Rainbow and f(R) theories at work

We compute the Zero Point Energy in a spherically symmetric background distorted at high energy as predicted by Gravity's Rainbow. In this context we setup a Sturm-Liouville problem with the cosmological constant considered as the associated eigenvalue. The eigenvalue equation is a reformulation of the Wheeler- DeWitt equation. With the help of a canonical decomposition, we find that the relevant contribution to one loop is given by the graviton quantum fluctuations around the given background. By means of a variational approach based on gaussian trial functionals, we find that the ordinary divergences can here be handled by an appropriate choice of the rainbow's functions, in contrast to what happens in other conventional approaches. A generalization including f(R) theories of gravity is presented, where f(R) is a generic analytic function of the Ricci curvature scalar R in 4D and in 3D. The explicit calculation is performed for a Schwarzschild metric. A final discussion on the connection of our result with the observed cosmological constant is also reported.

Speaker: Garattini Remo

Slides 2012-11-05-garattini.pdf

Tuesday 6 November

10:00 → 12:00 Compact Course on LQG

We introduce the basic physical ideas and mathematical methods underlying Loop Quantum Gravity (LQG).

Speaker: Thomas Thiemann

12:00 → 14:00 Lunch break

14:00 → 16:00 Compact Course on LQG

We introduce the basic physical ideas and mathematical methods underlying Loop Quantum Gravity (LQG).

Speaker: Thomas Thiemann

Wednesday 7 November

10:00 → 11:00 Theory of Cosmological Perturbations

The theory of cosmological perturbations makes the link between quantum gravity theories of the very early universe and current cosmological observations. In this lecture, I will present the basics of this theory and its application to inflationary cosmology.

Speaker: Robert Brandenberger

11:00 → 12:00 Cosmological Perturbations in Non-Inflationary Early Universe Scenarios

I will study the generation and evolution of cosmological perturbations in early universe models without a period of inflation. Specifically, I will study "emergent models" such as "string gas cosmology" and non-singular bouncing models.

Speaker: Robert Brandenberger

12:00 → 14:00 Lunch break

14:00 → 15:00 Noncommutative geometry for Quantum Spacetime

I will present the motivation for a generalization of geometry due to gravity. I will then describe the standard examples of noncommutative geometries and in particular Connes framework.

Speaker: Fedele Lizzi

Slides 2012-11-07-lizzi-01.pdf

15:00 → 16:00 The spectral point of view of interactions, renormalization and the early universe

I will describe the spectral action, its relations with anomalies and the consequences it may have for the early universe. The renormalization flow of the action and the running of physical quantities plays a central role in the discussion, which connects geometry, Higgs physics and some aspects of cosmology.

Speaker: Fedele Lizzi

Slides 2012-11-07-lizzi-02.pdf

Thursday 8 November

10:00 → 11:00 Branes in Yang-Mills matrix models and their physical significance

We discuss brane solutions in matrix models, focusing on the IKKT model. The effective geometry of the branes is described, and the significance of fluctuations is clarified. This leads to nonabelian gauge fields, scalar fields and fermions propagating on the brane, governed by an effective metric. The emphasis is to demonstrate how all degrees of freedom required for physics may arise from the matrix model. The quantization of the IKKT model is briefly discussed

Speaker: Harold Steinacker

Slides 2012-11-08-steinacker-01.pdf

11:00 → 12:00 The geometry and the dynamics of branes: towards emergent gravity

The geometry of the brane solutions in matrix models is discussed in more detail. In particular, the relation between the metric and the symplectic structure is elaborated. The equations of motion for the geometry is discussed, aiming at an understanding of the effective brane gravity. Possible mechanisms for the brane gravity are discussed.

Speaker: Harold Steinacker

Slides 2012-11-08-steinacker-02.pdf

12:00 → 14:00 Lunch break

14:00 → 15:00 Discussion: Which geometry for universe at the big bang?

A free wheel discussion on our prejudices on how we would like the creator to shape geometry at the beginning of the universe, confronting how the geometry at Planck length appears in various theories and models (strings, Loop Quantum gravity, noncommutative geometry...)

Speaker: Fedele Lizzi

Slides 2012-11-08-lizzi-03.pdf

15:00 → 16:00 Discussion

Speakers: Kristina Giesel, Mairi Sakellariadou, Martin Bojowald, Sabine Hossenfelder

17:00 → 19:00 Reception

Friday 9 November

10:00 → 12:00 Quantum Gravity from Causal Dynamical Triangulations - Whence and Whither

My morning lecture will consist of a (reasonably self- contained) introduction to Causal Dynamical Triangulations, a non-perturbative path integral method to constructing a fundamental theory of quantum gravity, including its motivation, ingredients, computational implementation and an overview of results in the dimensions the theory has been studied (1+1, 2+1 and the physically relevant case of 3+1 dimensions).

Speaker: Renate Loll

Slides 2012-11-09-loll.pdf

12:00 → 14:00 Lunch break

14:00 → 16:00 Quantum Gravity from Causal Dynamical Triangulations - Whence and Whither

In the afternoon lecture I will focus on recent results, including the phase structure in 3+1 dimensions, ongoing projects, open questions and the general lessons that have been learned for the nonperturbative quantization of gravity.

Speaker: Renate Loll

Monday 12 November

10:00 → 11:00 Noncommutative geometry and the standard model of particle physics

The aim of this lecture is to give a intuitive introduction to noncommutative geometry and explain how it allows to unify general relativity with the SU(2)xU(1)xSU(3) model of electro-weak and strong forces. We will review the phenomenological constraints resulting from this unification, in particular on the Higgs mass.

Speaker: Thomas Schucker

Slides 2012-11-12-schucker-01.pdf

11:00 → 12:00 Noncommutative geometry and the standard model of cosmology

In this lecture we will focus on the modifications to the Hilbert-Einstein action coming from noncommutative geometry: At lowest order approximation, we have curvature squared corrections, boundary terms and torsion terms. Applications of these first order corrections to cosmology are reviewed. Higher order terms will be briefly mentioned and how little we know about the exact spectral action even in the commutative case i.e. Riemannian geometry and even after the dramatic reduction of gravitational degrees of freedom by use of the cosmological principle.

Speaker: Thomas Schucker

Slides 2012-11-12-schucker-02.pdf

12:00 → 14:00 Lunch break

14:00 → 15:00 Maximal symmetry at the speed of light

A relativistic version of the cosmological principle is presented where maximal symmetry is not postulated on surfaces of `simultaneity', but rather on past light-cones. This principle is then confronted with observational data: the Hubble diagram of supernovae, weak lensing, CMB and BAO. (joint work with Andre Tilquin)

Speaker: Thomas Schucker

Slides 2012-11-12-schucker-03.pdf

Tuesday 13 November

10:00 → 11:00 Some aspects of quantum gravity phenomenology

In the first part of the talk I will review the status of searches of Quantum Gravity (QG) models that entail non trivial ``optical'' properties of the vacuum, such as a refractive index and/or birefringence, which may be consequences of quantum fluctuating space times during the propagation of high energy cosmic photons from distant astrophysical sources. I will be careful in explaining why recent arrival-time-of-photons measurements from FERMI LAT do not necessarily exclude QG models with induced modifications in the photon's dispersion relation suppressed by a single power of Planck mass. In the second part of the lecture, I will discuss other potential aspects of quantum gravity models, such as Lorentz and CPT Violations, and/or decoherence effects on matter, which do not necessarily lead to the aforementioned energy dependent effective speed of light in the QG medium. In the framework of CPT Violation (CPTV), I will discuss prospects for constraining QG-induced CPTV in entangled states of neutral mesons in future facilities such as DA$Phi$NE 2, as well as prospects for precision measurements in atomic transitions, and comparison of properties of atoms vs those of anti-atoms, especially in view of the recently available antimatter ``factories''. I will finish the talk with some discussion on using neutrinos from intense astrophysical sources, such as supernovae, as probes of such Lorentz and/or CPT Violating and Decoherening models of QG.

Speaker: Nikolaos Mavromatos

Slides 2012-11-13-mavromatos.pdf

11:00 → 12:00 CPT Violation in the early Universe and matter over antimatter dominance

Several Models of gravitational Leptogenesis, that is a lepton over antilepton asymmetry at early epochs of the Universe, do exist in the literature and involve coupling of fermions with non trivial curvatures of the early Universe space-time, leading to different dispersion relations between particles and antiparticles. Such differences in the Lepton sector can then be communicated in the baryon sector via baryon plus (or minus) Lepton conserving processes, such as sphalerons (or grand unified models). One can thus obtain phenomenologically correct values for the so-induced baryon asymmetry in the Universe, without the need for extra sources of CP violation, such as Supersymmetry and/or Sterile Neutrinos, for which at present we have no (concrete) experimental evidence. Nevertheless, such models suffer from fine tuning problems, which I will outline during the lecture. To avoid such problems, I will discuss an alternative way of obtaining such differences in the dispersion relation between matter and antimatter, and in particular neutrinos, by coupling the latter to space-time defects in early epochs of our Universe. The defects can be provided by certain compactified brane structures in brane/string-inspired Cosmologies. I will explain carefully why there is a preferential role of neutrinos, compared to other charged leptons and quarks in the Standard Model, in interacting with the ``medium'' of the brane defects, and how such a coupling leads to different dispersion relations between neutrinos and antineutrinos, when the latter propagate in dense media of these brane defects. I will also discuss how in such models overclosure of the early universe can be avoided, despite the presence of a dense medium of massive defects, with masses of order up to Planck mass. This stems from specific properties of the stringy/brane model, and requires an extra bulk space, onto which the brane Universe is embedded and moves. Phenomenologically correct values of the baryon asymmetry and matter over antimatter dominance can be obtained in this model without the aforementioned fine tuning problems that characterise other models of gravitational leptogenesis. As a spin off of this model, which is also a topic appropriate for further discussion in this workshop, I will discuss such CPT Violating issues in Finsler Cosmologies, that is cosmological space-times, in which the metric tensor depends on phase-space variables, instead of only coordinates.

Speaker: Nikolaos Mavromatos

12:00 → 14:00 Lunch break

14:00 → 14:30 Uniqueness of kinematics in loop quantum cosmology

One of the celebrated results in loop quantum gravity is the uniqueness of its kinematical structure. We will show that a similar result also holds at the level of loop quantum cosmology.

Speaker: Miguel Campiglia

14:30 → 16:00 Discussion

Discussion on the phenomenology of quantum gravity.

Speaker: Nikolaos Mavromatos

Wednesday 14 November

10:00 → 11:00 Cosmological implications of noncommutative spectral action

Speaker: Mairi Sakellariadou

Slides 2012-11-14-sakellariadou.pdf

11:00 → 12:00 The quantum measurement problem in inflation.

Cosmological perturbations are said to be seeded by quantum vacuum fluctuations of the inflaton and metric field. Yet, they are used successfully in numerical simulations as classical sources since squeezing and decoherence render their quantum distribution undistinguishable from a classical stochastic distribution. However, an actual realization did take place at some stage, from which large scale structure subsequently developed. I will discuss two extensions of quantum mechanics, hidden variables and dynamical collapse, in the framework of which the measurement problem is naturally solved (and the Born rule recovered) and apply those to cosmological perturbation theory.

Speaker: Patrick Peter

Slides 2012-11-14-peter.pdf

12:00 → 14:00 Lunch break

14:00 → 15:00 Spinfoam and Cosmology

In the recent years the major developments in Loop Quantum Gravity have arisen in the covariant framework (spinfoam) where the dynamics is coded by transition amplitudes. These provide an evolution for "quanta of spacetime" in terms of a local product of interaction vertices, reconstructing a Lorentzian spacetime. The first part of the talk will be devoted to a general presentation of these results. The second part of the talk will show how these results find a good testing framework in cosmology and how, viceversa, spinfoam could provide a fertile framework for the description of the early- universe physics.

Speaker: Francesca Vidotto

Slides 2012-11-14-vidotto.pdf

15:00 → 15:30 A fully-covariant natural ultraviolet cutoff in inflationary cosmology

The effects that quantum gravity-motivated natural UV cutoffs at the Planck scale have on inflationary predictions for the CMB have garnered much interest in the literature. These studies have so far been mostly confined to UV cutoffs that are locally Lorentz symmetry- breaking. Here, we propose a locally Lorentz covariant approach which takes the form of a cutoff on the local density of dynamical degrees of freedom of the field theory. This cutoff thus has an intuitive information theoretic interpretation. We are studying the type and magnitude of possible signatures that this covariant cutoff would have in the CMB. The techniques we employ tie in naturally with recent results in spectral geometry that showed that spacetime could be simultaneously continuous and discrete in the same way that information can be.

Speaker: Aidan Chatwin-Davies

Thursday 15 November

10:00 → 12:00 CDT: a theory of the quantum universe

I discuss how a lattice approach (CDT) to quantum gravity leads to an "emergent" semiclassical universe around which one can study the quantum fluctuations. Further, this approach allows us to construct the renormalization group flow of the effective coupling constants.

Speaker: Jan Ambjorn

12:00 → 14:00 Lunch break

14:00 → 16:00 2d gravity and the moduli space of Riemann surfaces using dynamical triangulations.

TBA

Speaker: Jan Ambjorn

17:45 → 19:45 Dinner

We'll go to http://kvarnen.com/

Meeting: Either at 5:45 pm at the institute, and go there together. Or at the restaurant at 6:30pm, address on the webpage.

Friday 16 November

10:00 → 11:00 Quantum field theory on curved backgrounds and Hadamard states

Goal of this lecture is to introduce the audience to the algebraic quantization of field theories as first formulated by Haag and Kastler. Particular emphasis will be given to the principle of general local covariance and to the existence of an explicit characterization for physically relevant quantum states: the Hadamard condition. These states will be discussed both from a mathematical and from a physical point of view. Furthermore, it will be shown that, in the case of free field theories, a novel application of an holographic procedure allows to construct them explicitly on a wide variety of backgrounds, including the cosmological ones.

Speaker: Claudio Dappiaggi

Slides 2012-11-16-dappiaggi-1.pdf

11:00 → 12:00 Stable cosmological models and the semiclassical Eintein's equations

In the framework of the algebraic approach to quantum field theory, the existence of Hadamard states allows for a thorough discussion of the regularization and renormalization freedoms of all observables. As a by- product, we can analyse rigorously the semiclassical Einstein?s equations showing that the renormalisation of the stress-energy tensor plays a crucial role. Furthermore, if we consider free scalar matter as well as homogeneous and isotropic solutions of the semiclassical Einstein?s equations, the system displays a de Sitter type behaviour even without a cosmological constant introduced a priori. We will show that, contrary to what often advocated, these solutions turn out to be stable and a comparison with experimental data is possible.

Speaker: Claudio Dappiaggi

Slides 2012-11-16-dappiaggi-2.pdf

12:00 → 14:00 Lunch break

14:00 → 16:00 Discussion

Speakers: Mairi Sakellariadou, Martin Bojowald, Sabine Hossenfelder

Monday 19 November

10:00 → 11:00 Quantum Gravity and Quantum Cosmology: A General Introduction

I start by giving a general introduction to the motivation for and the problems of a theory of quantum gravity. I then briefly describe the main approaches - quantum general relativity (including loop quantum gravity) and string theory - and some of their applications. I then give a general introduction to quantum cosmology, in which I mainly deal with geometrodynamics, but make also remarks on loop quantum cosmology.

Speaker: Claus Kiefer

Slides 2012-11-19-kiefer-1.pdf

11:00 → 12:00 Conceptual Issues in Quantum Cosmology

I start by discussing the issue of boundary conditions in quantum cosmology, which will be deepended by the contributions in the afternoon session. I then discuss at length one of the most important conceptual problems: the quantum-to-classical transition. I give a brief review on the situation in quantum mechanics and then turn to quantum cosmology. The key idea in understanding the quantum-to-classical transition is decoherence. I also discuss the problem of time and attempts to understand the origin of irreversibility in quantum cosmology.

Speaker: Claus Kiefer

Slides 2012-11-19-kiefer-2.pdf

12:00 → 14:00 Lunch break

14:00 → 15:00 Boundary Conditions in Quantum Cosmology

My idea here is to give a short introduction myself (at most half an hour), followed by short presentations of participants and a general discussion. As for the topics of the short presentations, I suggest: "The no-boundary condition", "The tunnelling condition", "Boundary conditions in loop quantum cosmology", as well as other suggestions by participants.

Speaker: Claus Kiefer

Slides 2012-11-19-kiefer-3.pdf

15:00 → 15:30 Effective relational dynamics of a non-integrable cosmological model

We apply the effective approach to evaluating semiclassical relational dynamics to the closed Friedman--Robertson-- Walker cosmological model filled with minimally coupled massive scalar field. This model is interesting for studying relational dynamics in more general setting because (i) it features non--trivial coupling of relational clock to evolving degrees of freedom, (ii) no temporally global clock variable exists, (iii) it is non--integrable which is typical for generic dynamical systems.

Speaker: Emilia Kubalova

Poster Poster

Slides Slides

Tuesday 20 November

10:00 → 11:30 Conformal invariance, dark energy and CMB non-gaussianity, Part I

In addition to simple scale invariance, a universe dominated by dark energy naturally gives rise to correlation functions possessing full conformal invariance. This is due to the mathematical isomorphism between the conformal group of certain three dimensional slices of de Sitter space and the de Sitter isometry group SO(4,1). In the standard homogeneous, isotropic cosmological model in which primordial density perturbations are generated during a long vacuum energy dominated de Sitter phase, the embedding of flat spatial 3-dim sections in de Sitter space induces a conformal invariant perturbation spectrum and definite prediction for the shape of the non-Gaussian CMB bispectrum. This form for the bispectrum is intrinsic to the symmetries of de Sitter space, and in that sense, independent of specific model assumptions. It is different from the predictions of single field slow roll inflation models, which rely on the breaking of de Sitter invariance. We propose a quantum origin for the CMB fluctuations in the scalar gravitational sector from the conformal anomaly that could give rise to these non-Gaussianities without a slow roll inflation field. Moreover we argue that conformal invariance also leads to the expectation for the relation $n_S - 1 = n_T$ between the spectral indices of the scalar and tensor power spectrum. Confirmation of this prediction or detection of non-Gaussian correlations in the CMB of the bispectral shape function predicted by conformal invariance can be used to establish the physical origin of primordial density fluctuations, and distinguish between different dynamical models of cosmological vacuum dark energy. [JCAP09(2012)024, arXiv:1103.4164]

Speaker: Ignatios Antoniadis

12:30 → 14:00 Lunch break

14:00 → 15:00 Conformal invariance, dark energy and CMB non-gaussianity, Part II

Speaker: Ignatios Antoniadis

15:30 → 16:30 Effective field theory of weakly coupled inflationary models

Speaker: Spyridon Sypsas

Slides 2012-11-20-sypsas.pdf

16:30 → 17:00 Two-dimensional quantum dilaton gravity and the quantized cosmological constant

I will discuss the cosmological constant problem in the context of two-dimensional quantum dilaton gravity. Taking advantage of the simplified framework I will show how the quantum constraints can be used to determine the cosmological constant for physical states in a non- perturbatie approach, including quantum fluctuation, dynamical contributions and quantum gravity corrections.

Speaker: Simone Zonetti

18:00 → 20:00 Dinner

Wednesday 21 November

12:00 → 14:00 Lunch break

Thursday 22 November

10:00 → 11:00 Origins of the Universe

I will describe the theory for the dynamic selection of the initial conditions of the universe from the landscape and its observational predictions. This theory allows for the wavefunction of the universe to propagate through the landscape while including decoherence, thereby unifying the many worlds interpretation of quantum mechanics with the landscape of string theory into a single mutliverse. Four of its predictions have been recently succesfully tested.

Speaker: Laura Mersini

Slides 2012-11-22-mersini-01.pdf

11:00 → 12:00 The Gordian Knot of Eternal Inflation

I will briefly review the basis for eternal inflation and make the case of an important ingredient not previously acknowledged - the space time homogeneity . I will describe our proposal for the measure of eternal inflation that includes both essential conditions, large field fluctuations and smooth homogeneous domains, in the self reproducing probability estimate. The new measure is finite and does not violate unitarity. However, due to the increasing inhomogeneities in the background spacetime fractal, self-reproduction stops within a finite time t_f, thus inflation can not be eternal.

Speaker: Laura Mersini

Slides 2012-11-22-mersini-02.pdf

12:00 → 14:00 Lunch break

14:00 → 15:00 Introduction to multifractal spacetimes - part I

We review a recent proposal where spacetime is characterized by a multifractal geometry where dimension changes with the scale. This "anomalous" type of spacetime texture improves the UV behaviour of perturbative quantum field theories, including gravity. After introducing the basic ingredients, we discuss properties of quantum mechanics and field theories living thereon, with applications to gravity and cosmology. The formalism has also connections with noncommutative geometry and other theories of quantum gravity based upon the renormalization group flow.

Speaker: Gianluca Calcagni

Slides 2012-11-21-calcagni_1.pdf

15:00 → 16:00 Introduction to multifractal spacetimes - Part II

We compare observational constraints on LQC and Wheeler-DeWitt quantum corrections to the inflationary spectrum. While the latter are typically negligible, in the former case quantum effects can be large in certain regions of parameter space.

Speaker: Gianluca Calcagni

Slides 2012-11-21-calcagni_2.pdf

Friday 23 November

10:00 → 11:00 Coming of age for Horava gravity: from renormalizability to black holes

After giving an overview of the basic features of Horava gravity, I will focus on the latest developments and argue that, at least for the most general and complete version of the theory, the infrared phenomenology is by now relatively well understood and pathologies have been tamed. This implies that time has come for the theory to face a new series of intriguing challenges, related to quantization, ultraviolet phenomenology, black holes and cosmological singularities etc. I will present some ideas and first results in some of these directions.

Speaker: Thomas Sotiriou

11:00 → 12:00 Black holes in Lorentz-violating gravity

I will consider black hole solutions in gravity theories that exhibit Lorentz invariance violations. I will argue on fairly general grounds that one does not expect to have black hole solutions in such theories. I will then focus for concreteness on two specific Lorentz-violating gravity theories, Einstein-aether theory and Horava-Lifshitz gravity, and I will present two surprising results. First, that in both theories static, spherical black- hole solutions do exist, contrary to previous expectations. Second, that in Horava-Lifshitz gravity slowly-rotating black holes that reduce to these static, spherical black holes at the limit of no rotation do not exist. I will discuss the theoretical and astrophysical implication of these two results.

Speaker: Thomas Sotiriou

12:00 → 14:00 Lunch break

14:30 → 16:00 Discussion

TBA

Speakers: Mairi Sakellariadou, Martin Bojowald, Sabine Hossenfelder

Monday 26 November

10:00 → 11:00 Cosmological production of black hole pairs

In this talk we will review the mechanism of black hole production due to a potential quantum mechanical instability of the deSitter Universe. After recalling the basic formalism in terms of the instanton approach, we will present the foundational results in the field as well some of the latest developments based on non- singular black hole metrics. Possible connections with current astronomical observations will be also discussed.

Speaker: Piero Nicolini

Slides 2012-11-26-nicolini.pdf

11:00 → 12:00 Consistent theories of spin-2 fields interacting with gravity

Speaker: Fawad Hassan

12:00 → 14:00 Lunch break

14:00 → 15:00 Infrared modifications of general relativity

Explaining the acceleration of the universe in a technical natural manner is an outstanding theoretical challenge. Given that the acceleration is triggered by sources of cosmological wavelength, a tempting approach to the problem is to modify the theory of general gravity at those distances. In this talk I will present two different such infrared modifications: Certain theories of massive gravitons on curved backgrounds, and the theory of brane induced gravity in higher codimensions. I will discuss both the consistency and the phenomenological implications of these theories.

Speaker: Felix Berkhahn

Slides 2012-11-26-berkhahn.pdf

Tuesday 27 November

10:00 → 11:00 Non-gaussianity of the primordial perturbation

I discuss the curvature perturbation and the delta-N formalism, with focus on observationally relevant non-gaussianities, which may be generated either during inflation or at the end of inflation. Modelling attempts involve both inflatons and spectators. I emphasize the importance of understanding the decay mechanisms of the inflaton; examples are modulated reheating and preheating. I also discuss briefly isocurvature perturbations.

Speaker: Kari Enqvist

11:00 → 12:00 The curvaton model

Curvaton is a scalar field which during inflation is a spectator but which becomes dynamically important after inflation and generates the primordial perturbation. I present the basic idea and discuss the non-gaussianities. The fact that the curvaton must decay implies radiative corrections to the potential, which can be important for the dynamics. Likewise, non-linearities of the curvaton potential can have a considerable impact on the model prediction for non- gaussianities. I also discuss an attempt at a realistic model, where the Standard Model degrees of freedom are produced by virtue of a higgs- curvaton coupling. In such a case, cosmological evolution of the curvaton gives rise to a fairly complicated pattern of resonant production of higgses, where thermal corrections play an important role.

Speaker: Kari Enqvist

12:00 → 14:00 Lunch break

14:00 → 15:00 Towards Homogeneous Cosmologies from Group Field theories

Group field theories are a class of models that are designed to define a sum over histories approach to quantum gravity. After a brief presentation of the relevant points and features of the theory, I will describe a preliminary attempt to give an effective description of homogeneous cosmologies and their effective dynamics, within an approximation of the full group field theory dynamics that matches closely the Bogoliubov approximation to the dynamics of Bose-Einstein condensates.

Speaker: Lorenzo Sindoni

Slides 2012-11-27-sindoni.pdf

Wednesday 28 November

10:00 → 12:00 Effective Theories, Decoupling and Cosmology: A Bad Cop standing in a Cold Shower, wrapped in a Wet Blanket

This talk briefly reviews effective field theory as applied to gravity and time-dependent systems, with a view to seeing how it constrains thinking about cosmological models. I argue that it limits the scope of reasonable models, and provides useful prejudices when thinking about popular ideas like UV Lorentz violation, inflation, dark matter and dark energy.

Speaker: Cliff Burgess

12:00 → 14:00 Lunch break

14:00 → 16:00 Extra Dimensions, the Cosmological Constant Problem and the LHC: Isn't That Dead Yet?

Two uncertainties define the prevailing attitude toward the LHC: uncertainty about what new physics it may find (if any); together with dissatisfaction with the "technical naturalness" arguments which (when applied to the hierarchy problem) help suggest what it should be looking for. The dissatisfaction arises because of a wide- spread despair about finding a technically natural solution to the cosmological constant problem, despite much effort spent seeking it. In this talk I describe a mechanism within supersymmetric extra-dimensional theories that allows the low-energy effective cosmological constant naturally to be of order the Kaluza-Klein scale. If this is the solution to the cosmological constant problem, then it requires extra dimensions that are both very supersymmetric and large enough to be relevant to the LHC. It in particular implies there must be modifications to gravity on micron distances as well as on cosmological scales. For the LHC it implies in particular three predictions. (1) the (so far - successful) prediction that no supersymmetric partners will be discovered, despite the low-energy supersymmetry; (2) many missing energy channels, with a gravity scale of 10 TeV; and (3) the existence of string excitations of standard model particles, likely below 10 TeV.

Speaker: Cliff Burgess

Thursday 29 November

10:00 → 12:00 Discussion

Speakers: Mairi Sakellariadou, Martin Bojowald, Sabine Hossenfelder

12:00 → 14:00 Lunch break

14:00 → 16:00 Discussion

Speakers: Mairi Sakellariadou, Martin Bojowald, Sabine Hossenfelder

18:00 → 20:00 Dinner

Friday 30 November

12:00 → 14:00 Lunch break