Windows on Quantum Gravity: Season 2

28 Oct 2015, 08:00 → 30 Oct 2015, 19:40 Europe/Madrid

Blue room (Instituto de Física Teórica UAM-CSIC)

This the second meeting of the "Windows on quantum gravity" series, held for the first time in 2008. The recent success of WMAP and Planck experiments triggered a new wave of interest in the foundations of primeval cosmology. In particular, since the inflationary process may involve very high energy scales, quantum gravity effects may play an important role in the construction of consistent scenarios. Those experiments also confirmed that the universe is currently undergoing an accelerated expansion. No satisfactory theoretical explanation for he latter is known, which may be a hint towards a mysterious relation to the other aspect of gravitation which is not completely understood: its quantum properties. In the near future, further experiments will hopefully clarify the way in which cosmological observations can help in our understanding of quantum gravity. With the previous motivations in mind, we will devote this workshop to discuss different models of gravity inspired by quantum gravity: GR, dilaton and scalar-tensor gravity, higher-derivative and F(R) gravity, Lorentz-symmetry broken gravity and string-inspired gravity. We aim at presenting an overview of the models and methods to study them. The emphasis will be in their possible role in cosmology - in particular possible quantum effects- to describe the early universe (inflation and alternatives thereof) and late-universe (dark energy).

Poster Windows_QG.jpg

Wednesday, 28 October

09:30 Registration

1 Hermann Nicolai, Comparative Quantum Gravity

I will eview different approaches to quantum gravity from a more `global' perspective, and comment on their respective merits and drawbacks

Nicolai.pdf

Video

11:00 Coffee break

2 Sergei Odintsov: Inflation and quantum gravity

Inflation in modified gravity is investigated. The account of quantum gravity effects is taken into account. Comparison with Planck data is discussed.

Odintsov.pdf

Video

3 Riccardo Moriconi: Chaos Removal in f(R) gravity: the Mixmaster model

We study the asymptotic dynamics of the Mixmaster Universe, near the cosmological singularity, considering $f(R)$ gravity up to a quadratic corrections in the Ricci scalar $R$. The analysis is performed in the scalar-tensor framework and adopting Misner-Chitrè-like variables to describe the Mixmaster Universe, whose dynamics resembles asymptotically a billiard-ball in a given domain of the half-Poincarè space. The form of the potential well depends on the spatial curvature of the model and on the particular form of the self-interacting scalar field potential. We demonstrate that the potential walls determine an open domain in the configuration region, allowing the point-Universe to reach the absolute of the considered Lobachevsky space. In other words, we outline the existence of a stable final Kasner regime in the Mixmaster evolution, implying the chaos removal near the cosmological singularity.

moriconi.pdf

Video

4 Gonzalo J. Olmo: Black holes, geons, and metric-affine gravity.

Using exactly solvable models, it will be shown that black hole singularities in different electrically charged configurations can be cured. Our solutions describe black hole space-times with a wormhole giving structure to the otherwise point-like singularity. This type of solutions can be naturally interpreted as geons in Wheeler's sense. We show that geodesic completeness is satisfied despite the existence of curvature divergences at the wormhole throat.

Video

WQG_Olmo.pdf

Paco Yndurain Colloquium: Supermassive Black Holes and their Galaxies

Guinevere Kauffmann,
Max Planck Institute, Garching.
Sala de Conferencias C-0, Faculty of Science UAM

5 Shin’ichi Nojiri: Dynamical Domain Wall and Localization

Based on arXiv:1202.5375, 1402.1346, and 1510.01099, we give a formulation realizing the dynamical domain wall, where the four dimensional FRW universe is realized on the domain wall in the five dimensional space-time. We also investigate the localization of the fields on the dynamical domain wall and we show that graviton, chiral spinor, and vector field can localize on the domain wall

DDWL_Madrid 3.pdf

Video

6 Raúl Carballo-Rubio: Keeping the cosmological constant small at all scales

The cosmological constant problem can be understood as the failure of the decoupling principle behind effective field theory, so that some quantities in the low-energy theory are extremely sensitive to the high-energy properties. While this reflects the genuine character of the cosmological constant, finding an adequate effective field theory framework which avoids this naturalness problem may represent a step forward to understand nature. We discuss in detail how Weyl transverse gravity helps in doing so.

Carballo-rubio.pdf

Video (until ~37:50)

7 Daniele Colosi: A general boundary approach to quantum gravity

The general boundary formulation (GBF) is a new axiomatic formulation of quantum theory not relying on a spacetime background metric. It has emerged as a viable and effective way to study the dynamics of quantum fields and represent a promising approach to the problem of quantum gravity. The aim of the talk is to give an introduction to the GBF, to present the results obtained so far and to explain the relevance of the GBF for the quantum gravity issue.

Colosi-28-10-15.pdf

Video (from 40:00)

18:30 Welcome cocktail

Thursday, 29 October

8 Sergey Sibiryakov: Semiclassical S-matrix for black holes

Thought experiments with black holes provide an important theoretical tool to uncover the properties of quantum gravity. I will advocate a semiclassical approach to the study of quantum black holes. In particular, I will describe a semiclassical method to calculate S-matrix elements for two-stage gravitational transitions involving matter collapse into a black hole and evaporation of the latter. The method consistently incorporates back-reaction of the collapsing and emitted quanta on the metric. I will illustrate the method in several toy models describing spherical self-gravitating shells.

BHSmatrix_Madrid.pdf

Video

10:30 Coffee break

9 Hermann Nicolai, Maximal (N=8) Supergravity: past, present, future

I will review properties of maximally extended N=8 supergravity, with special emphasis on the finite and infinite dimensional exceptional duality symmetries underlying this theory. I will also discuss the implications of its possible UV finiteness as well as our recent work trying to link the spin-1/2 fermions of this theory to those of the Standard Model.

Nicolai.pdf

Video

10 Tim R. Morris, Asymptotic Safety (the Exact Renormalization Group approach)

I review and critically assess current exact renormalization group research into the asymptotic safety scenario for quantum gravity.

Madrid.pdf

Video

11 Richard Woodard, Quantum Gravity comes of Age

I argue that cosmological data from the epoch of primordial inflation is catalyzing the maturation of quantum gravity from speculation into a hard science. I explain why quantum gravitational effects from primordial inflation are observable. I then review what has been done, both theoretically and observationally, and what the future holds. I also discuss what this tells us about quantum gravity. This talk is based on arXiv:1407.4748.

KU.pdf

Video

16:00 Coffee break

12 Christian Steinwachs: Question of quantum equivalence between Jordan frame and Einstein frame

In the framework of a general scalar-tensor theory, we investigate the equivalence between two different parametrizations of fields that are commonly used in cosmology - the so-called Jordan frame and Einstein frame. While it is clear that both parametrizations are mathematically equivalent at the level of the classical action, the question about their mathematical equivalence at the quantum level as well as their physical equivalence is still a matter of debate in cosmology. We analyze whether the mathematical equivalence still holds when the first quantum corrections are taken into account. We explicitly calculate the one-loop divergences in both parametrizations by using the generalized Schwinger-DeWitt algorithm and compare both results. We find that the quantum corrections do not coincide on shell and hence induce an off shell dependence on the parametrization. According to the equivalence theorem, the one-loop divergences should however coincide on shell. For a cosmological background, we show explicitly that the on shell equivalence is indeed realized by a nontrivial cancellation.

Madrid2015Steinwachs.pdf

Video

13 Miao Shun-Pei: Electrodynamic Effects of Inflationary Gravitons

In this talk I will start with a background Geometry, introduce a motivation of the project, and give an intuitive picture of how this effect could become significant. I will also report a series of study for photons coupled to gravity from flat space-time to de Sitter, point out some misconceptions of gauge issues, and try to address the issues we have encountered in this project.

ElectrodynamicGravitons1.pdf

Video

14 Kevin Falls: Asymptotic safety and gauge independence

The problem of obtaining a gauge independent beta function for Newton's constant is addressed. By a specific parameterisation of metric fluctuations a gauge independent functional integral is constructed for the semiclassical theory around an arbitrary Einstein space. The effective action then has the property that only physical polarisations of the graviton contribute, while all other modes cancel with the functional measure. We are then able to compute a gauge independent beta function for Newton's constant in d-dimensions to one-loop order. Going beyond the one-loop approximation we compute a non-perturbative beta function using functional renormalisation group methods and calculate the critical exponent at an asymptotically safe fixed point. Close to two dimensions the critical exponent is found to be regulator independent. Furthermore close to four dimensions quantitive agreement is found with lattice results for regulators which obey Litim’s optimisation criteria.

talk_Madrid_Falls.pdf

Video

15 Mauro Pieroni: Universality classes for inflationary models

We propose a systematic way to classify inflationary models by using the most basic property of inflation: the approximate scaling invariance. This new framework relies on the possibility of describing inflation in terms of a renormalisation group equation. The slow rolling regime in this context is thus interpreted as the slow evolution close to a fixed point. This explains in part the universality observed in the predictions of a certain number of inflationary models. Our choice of describing inflation with a renormalisation group equation indeed is motivated by theoretical arguments. As suggested by Mc Fadden and Skenderis, it is interesting to provide an holography description for the inflationary universe. In the language of the well known (A)dS/CFT correspondence the departure from (Anti) de Sitter spacetime is mapped into a departure from conformal invariance which is described as usual by a renormalisation group equation.

Madrid_slides.pdf

Video

20:30 Conference Dinner

Friday, 30 October

16 Misao Sasaki, Conformal frames in gravity: frame dependence vs observational equivalence

It seems there is certain degrees of confusion about consequences of a conformal transformation of the metric. In this talk, I clarify what are frame dependent and what are not in the cosmological context. Then we argue that "inflation" should be defined as an accelerated expansion in the Einstein frame assuming it exists. Some interesting examples of thus defined inflationary models are presented.

conformalframe_madrid.pdf

Video

11:30 Coffee break

17 Subodh Patil, Not so hidden fields in Cosmology

Fields that couple to the visible sector only gravitationally remain firmly out of reach of all collider and direct detection experiments for the foreseeable future. Unless these so called hidden fields influence the expansion and clustering history of the universe (i.e. constitute dark matter), the same might seem to be true for cosmological observations as well. In this talk we will review how this is not entirely the case. Hidden fields (even if they are energetically subdominant) can exert a range of effects in the early universe through their influence on the effective strength of gravitational interactions at high energies. In the context of inflationary cosmology, we show how their presence can affect the inferred energy scale of inflation, and if present in large numbers can also generate large non-Gaussianties in the context of single field inflation (away from the so-called squeezed configuration). Thus, one can convert ever more precise bounds on the amount of primordial non-Gaussianity present in the CMB into bounds on the hidden field content of the universe.

IFT_patil.pdf

Video

18 Franco Albareti: Gravitational effects on the Higgs field

In this talk, I will present the scalar 1-loop corrections to the Higgs effective potential in a slowly-varying weak gravitational field. These corrections are finite and do not require further renormalization, i.e. the UV behaviour is the same as in flat spacetime. The computed effective potential with gravitational contributions implies an inhomogeneous Higgs vacuum expectation value and this translates into direct observational probes in the Solar System, e.g. variations on the proton-to-electron mass ratio.

Higgs_Quantum_talk.pdf

Video

19 Cecilia Bejarano: Modified teleparallelism: an alternative approach of modified gravity

The so-called f(T) theories of gravity are a generalization of the well-known teleparallel equivalent of General Relativity in which the dynamical relevant object is the tetrad instead of the metric tensor and the degrees of freedom are encoded in the torsion rather than in the curvature. I will present the principal features of the teleparallel picture and some examples showing how this novel approach works.

cbejarano-madrid2015.pdf

Video

20 Taishi Katsuragawa: Palatini-Born-Infeld Gravity and Bouncing Universe

The Born-Infeld gravity is a modified gravity motivated by the quantum gravity, which has the ability to get rid of the Big Bang and other singularities. The action is highly non-linear, and the ghost mode appears in the metric formalism although we can show that the ghost mode does not appear in the Palatini formalism. We investigate the FLRW universe with dust in this theory, and show that the Big Bang singularity does not always emerge but the scale factor can be bounced. Based on this result, we also discuss the black hole formation for spherical dust collapse.

Madrid_katsuragawa.pdf

Video

16:30 Coffee break

21 Alberto Salvio: Quantum Agravity

I will talk about a theory of all interactions, including gravity, without fundamental scales (agravity). All observed masses, such as the Planck and the weak scales, are generated dynamically. I will discuss in some detail the quantum properties of this scenario.

Quantum Agravity.pdf

Video

22 Pablo Cano: f(Lovelock) theories of gravity

f(Lovelock) gravities are simple generalizations of the usual f(R) and Lovelock theories in which the gravitational action depends on an arbitrary function of the corresponding dimensionally-extended Euler densities. We study several aspects of these theories in general dimensions. We start by identifying the generalized boundary term which makes the gravitational variational problem well-posed. Then, we show that these theories are equivalent to certain scalar-tensor theories and how this relation is crucially characterized by the Hessian of f. We also study the linearized equations of the theory on a general maximally symmetric background. In particular, we show that these theories do not incorporate massive gravitons in their spectrum. Finally, we construct new analytic asymptotically AdS and Lifshitz black hole solutions for a particular Einstein plus f(Lovelock) theory. These generalize previous solutions obtained in R2 gravity and posses interesting thermodynamic properties, such as vanishing mass and entropy.

Presentacion.pdf

Video