# Conference Program

## Schedule of Talks

You can download the program here.

The slides of the summary talk by Stefano Liberati can be downloaded here .

## Conference Talks

**Floyd Stecker** (NASA - Goddard Space Flight Center)

9:15, Mon 1st Sep 2014

*Searching for traces of quantum gravity using high energy astrophisical observations*

High energy astrophysics observations provide the best possibilities to detect a
very small violation of Lorentz invariance, such as may be related to quantum gravity theory and the structure of space-time near the Planck scale of ~10^-35 m. I will discuss some possible signatures of Lorentz invariance violation (LIV) that can be manifested by observing of the spectra, polarization, and timing of gamma-rays from active galactic nuclei and gamma-ray bursts (GRB). Other sensitive tests are provided by observations of the spectra of ultrahigh energy cosmic rays and neutrinos. These results, based on high-energy astrophysical observations, have fundamental implications for space-time physics and quantum gravity models.

**Astrid Eichhorn** (Perimeter Institute, Waterloo)

10:45, Mon 1st Sep 2014

*Testing asymptotically safe quantum gravity through coupling to dynamical matter*

I will discuss the main idea of asymptotically safe quantum gravity.
I will then focus on the effect of dynamical matter degrees of freedom, and discuss the evidence for the consistency of the asymptotic safety scenario for gravity with the Standard Model. Further, I will explain why only some models of "New Physics" seem to be compatible with asymptotic safety, thus providing a possibility to experimentally rule out asymptotic safety at the LHC or future colliders.

**Igor Pikovski** (Vienna Center for Quantum Science and Technology)

11:30, Mon 1st Sep 2014

*Exploring gravitational phenomena in low-energy quantum theory*

We discuss how the ability to manipulate and to control quantum systems to very high precision opens the route for new experiments on the interplay between quantum theory and general relativity. It is shown how quantum optical systems can be used for testing low energy quantum mechanics on a fixed background space-time and quantum gravity phenomenology. We consider gravitational time dilation in low-energy quantum theory and derive the resulting decoherence of composite quantum systems [1]. We also show how pulsed opto-mechanical systems can provide a means to probe possible quantum gravitational modifications of the center-of-mass canonical commutator [2]. The results demonstrate that the interplay between quantum theory and general relativity can affect even low-energy quantum systems and that it offers novel phenomena which can be probed in experiments.
[1] I. Pikovski, M. Zych, F. Costa, and C. Brukner, "Universal decoherence due to gravitational time dilation", arXiv:1311.1095 (2013).
[2] I. Pikovski, M. R. Vanner, M. Aspelmeyer, M. Kim, and C. Brukner, "Probing Planck-scale physics with quantum optics", Nature Physics 8, 393 (2012).

**Francesco Marin** (Universita' di Firenze and INFN)

14:30, Mon 1st Sep 2014

*Tests of quantum gravity with macroscopic mechanical oscillators*

General relativity and quantum physics are expected to merge at the Planck scale, defined by distances of the order of 1.6x10^-35 m and/or extremely high energies of the order of 1.2x10^19 GeV. Since the study of particles collisions around the Planck energy is well beyond the possibilities of current and foreseeable accelerators, high-energy astronomical events (e.g. gamma-ray bursts) have been considered as the privileged natural system to unveil quantum gravitational effects. This common view has been enriched in the last years thanks to a number of studies proposing that signatures of the Planck-scale physics could manifest also at low energies. It is indeed widely accepted that, when gravity is taken into account, deviations from standard quantum mechanics are expected.
In particular, we have recently shown that the very low mechanical energy achieved and measured in a vibration mode of a massive object can set an upper limit to possible modifications of the Heisenberg uncertainty principle, that are expected as an effect of gravity. We have indeed exploited the sub- millikelvin cooling of the normal modes of the ton-scale gravitational wave detector AURIGA at this purpose [1]. Here we will discuss some possible interpretations of our results, including possible consequences on deformed commutators, and an upper limit on the length scale at which quantum fluctuations of the space- time geometry should come into play[2].
We will also describe the preliminary results of a series of experiments devoted to investigate possible modifications to the dynamics of micro-oscillators, due to modified Heisenberg relations.
[1] F. Marin et al., "Gravitational bar detectors set limits to Planck-scale physics on macroscopic variables", Nature Phys. 9, 71 (2013)
[2] F. Marin et al., "Investigation of Planck scale physics by the AURIGA gravitational bar detector", to be published on New J. Phys.

**Dionigi Benincasa** (SISSA)

15:15, Mon 1st Sep 2014

*First steps towards phenomenology of causal sets*

In the first half of this talk I will argue that the coexistence of Lorentz symmetry and fundamental spacetime discreteness comes at a price: one has to give up on locality. This non-locality is manifest in the construction of a causal set d'Alembertian, and I will argue that it survives to length scales much larger than the discreteness/Planck scale itself, thus opening up a window for "low" energy quantum gravity effects. In the low energy, continuum, description of spacetime the effects of the fundamental discreteness show up in non-local, (locally) Lorentz invariant dynamics for matter fields. In the latter half of the talk I will describe how to analyse such non-local dynamics, and how to construct a non-local quantum field theory from it. Finally, time permitting, I will mention a few (basic) phenomenological implications of such theories, and will put forward a suggestion for a non-local modification to the Schrodinger equation, which could be tested in up-coming high precision tests of macroscopic quantum systems.

**Jose Manuel Carmona** (Universidad de Zaragoza)

16:30, Mon 1st Sep 2014

*Thresholds in the presence of Lorentz violating kinematics including modified conservation laws*

We discuss the leading Lorentz violations in the kinematics of particle processes with modified dispersion relations and modified composition law of momenta and some phenomenological implications on thresholds in different reactions.

**Giampiero Esposito** (INFN, Sezione di Napoli)

17:00, Mon 1st Sep 2014

*Three-body problem in effective field theories of gravity*

The quantum corrections to the Newtonian potential obtained in effective field theories of gravity are shown to produce tiny but nonnegligible effects. For example, in the restricted problem of 3 bodies, the coordinates of Lagrangian points are slightly modified, and the planetoid is no longer at equal distance from the two bodies of large mass in the configuration of stable equilibrium. The equations of the full 3-body problem are also under investigation in the presence of quantum corrections.

**Brian Keating** (University of California, San Diego )

9:00, Tue 2nd Sep 2014

*The discovery of primordial B-mode polarization*

The era of Cosmic Microwave Background B-mode polarization cosmology has recently begun. The BICEP2 telescope observed from the South Pole for three seasons (2010–2012) and released results showing an excess of B-modes in the range 30 < ell < 150 with >5 sigma significance. We find that this excess can not be explained by instrumental systematics or foregrounds. The signal was confirmed in cross-correlation with BICEP1 (at 100 and 150 GHz) and preliminary data from the Keck Array. The observed B-mode power spectrum is well-fit by a lensed-LCDM cosmological model with the addition of primordial tensor fluctuations with tensor-to-scalar ratio r=0.20^{+0.07}_{-0.05}. I will discuss the BICEP2 experiment, observations, and data analysis, as well as current and planned efforts to follow up this detection.

**Pawel Bielewicz** (SISSA)

10:30, Tue 2nd Sep 2014

*Planck 2013 cosmological results*

I will present the Planck experiment and review the first cosmological results released in 2013. I will also briefly discuss prospects for the planned this year next release of the cosmological data.

**Paolo Creminelli** (ICTP, Trieste)

11:15, Tue 2nd Sep 2014

*B-mode cosmology*

The experimental sensitivity to B-modes is now in an interesting regime for primordial tensor modes. I will review the robustness of the tensor mode prediction in inflation and speculate about what we can learn if tensor modes are detected.

**Giulio Fabbian** (SISSA)

14:30, Tue 2nd Sep 2014

*POLARBEAR experiment: results from the first observational campaign and the prospects*

I will present the POLARBEAR experiment, an ongoing ground-based CMB polarization experiment located in northern Chile. I will review its latest results obtained from the analysis of the data collected during the first observational campaign and discuss their implication for cosmology and fundamental physics.

**Stephon Alexander** (Dartmouth)

15:15, Tue 2nd Sep 2014

*Parity Violating Gravitational Waves and the Standard Model*

I show how parity violating gravitational waves
can simultaneously generate the observed baryon asymmetry and provide a natural
period of parametric resonance of preheating at the end
of inflation . I discuss how this signal of parity violation may also be observable in
other sectors in theories beyond the standard model.

**Julien Grain** (Institut d'Astrophysique Spatiale)

16:30, Tue 2nd Sep 2014

*A brief overview of loop quantum cosmology and its potential observational signatures*

Loop quantum cosmology (a symmetry-reduced quantum model of the Universe inspired by loop quantum gravity) extends the inflationary paradigm to the Planck era: the big bang singularity is replaced by a quantum bounce naturally followed by inflation. Testing for these models requires to compute the amount of cosmological perturbations produced in this quantum background and subsequently derives their footprints on the cosmic microwave background. I propose to review two theoretical approaches treating for cosmological perturbations in a quantum background (see Barrau et al. 2014 and Agullo et al. 2013), making their respective assumptions and methodology as explicit as possible. I will then show the observational consequences of those treatments focusing on the specific case of the cosmic microwave background anisotropies as a probe of the primordial Universe.

**Agnes Ferte** (Institut d'Astrophysique Spatiale)

17:00, Tue 2nd Sep 2014

*Constraints on chiral gravity through the CMB polarization*

If parity invariance is broken in the primordial universe, the cosmic microwave background TB and EB cross-correlations, usually vanishing, become non zero. Their detection would then constrain the level of parity violation. I propose to present forecasts on the detection of this parameter by realistically estimating the uncertainties on the TB and EB spectra via the pure pseudo spectrum method, which efficiency has been shown. I will present the results of this forecast in the case of two typical experimental setups: a small-scale experiment and a large scale survey. Our results show that no constraints can be put on the level of parity violation in the former case. However a range of model would be accessible with a future CMB satellite-like mission: for instance, a parity violation of at least 50% with r = 0.2 could be detected.

**Mercedes Martin-Benito** (Radboud University Nijmegen)

17:30, Tue 2nd Sep 2014

*Echoes of the early Universe*

By applying quantum informational and optical tools to quantum gravity theories in the very early universe, we show that the fluctuations of quantum fields as seen by late comoving observers are significantly influenced by the history of the early universe, transmitting information about the nature of the universe in timescales when quantum gravitational effects where non-negligible. This might be observable even nowadays thus used to build falsifiability tests of quantum gravity theories.

**Jonathan Granot** (Open University of Israel)

9:00, Wed 3rd Sep 2014

*Experimental Bounds on Quantum Gravity from Fermi Observations of GRBs*

I will discuss recent searches for quantum gravity signatures using high-energy photons from gamma-ray bursts (GRBs), focusing on the search for Lorentz Invariance Violation (LIV) in the form of a dependence of the photon propagation speed on its energy. Fermi gamma-ray space telescope observations of ~8 keV to ~30 GeV photons from the short (< 1 s) GRB 090510 at a cosmological distance (z = 0.903), enabled for the first time to put a direct time of flight limit on a possible linear variation of the speed of light with photon energy that is beyond the Planck scale. Parameterizing |v/c-1| = E/E_{QG}, for deterministic LIV our most conservative limits are E_{QG}/E_{Planck} > 1.2, while less conservative limits are up to 1-2 orders of magnitude stricter. Using the same data, we have now also set Planck-scale limits on stochastic (or fuzzy) LIV - the first of this kind. I will finish by briefly outlining the prospects for future GRB observations by the Cherenkov Telescope Array (CTA) - the next generation ground based very high energy (from ~20-30 GeV to ~300 TeV) observatory.

**Sabine Hossenfelder** (Nordita)

10:30, Wed 3rd Sep 2014

*Space-time Defects*

One of the most important questions in quantum gravity is
whether or not space-time is fundamentally discrete or
continuous. However, directly finding evidence for space-time
discreteness has turned out to be difficult if not impossible.
In my talk I will discuss the possibility to look for defects
in the discrete structure rather than the discrete structure itself.
Interestingly, these space-time defects can be modeled without
violating Lorentz-invariance, and they can become observable by
affecting the propagation of particles.

**Carlo Rovelli** (Aix-Marseille University)

11:15, Wed 3rd Sep 2014

*Planck Stars*

I describe a new suggestion for measurable quantum gravity effects: the bounce of a primordial Planck star.

**Francesca Vidotto** (Radboud University Nijmegen)

14:30, Wed 3rd Sep 2014

*What can we learn from Loop Quantum Cosmology? The case of Planck Stars*

Loop Quantum Cosmology suggests that cosmological singularities are generically resolved by quantum effects. This can be understood at the effective level as the appearance of a repulsive force in the deep quantum-gravity regime. A similar mechanism should take place in the interior of black holes, whose singularity would then be replaced by a core of Planckian energy density. Such “Planck Star” provides a remnant which can help avoid the information paradox. Furthermore, if the evaporation ends with an explosive event, the Planck star could provide a precise astrophysical signal. Using the current models for primordial black holes and the bounds given by dark-matter abundance, this signal could be compatible with a specific kind of gamma rays, that we have already observed.

**Anupam Mazumdar** (Lancaster University)

15:15, Wed 3rd Sep 2014

*Resolution of Cosmological and Blackhole Singularities*

I will discuss how non-local action of higher derivative extension of Einstein's gravity could yield ghost free and devoid of any
space or time like singularities.

**Francesco Cianfrani** (University of Wroclaw)

16:30, Wed 3rd Sep 2014

*Quantum Reduced Loop Gravity: status and perspectives.*

I will present the status and the perspectives of Quantum Reduced Loop Gravity. Instead of discussing in details all the technical issues, I will focus on the relevance of this approach for grounding Loop Quantum Cosmology and for inferring a proper phenomenology for the early Universe.

**Tomasz Trzesniewski** (University of Wroclaw)

17:00, Wed 3rd Sep 2014

*Dimensional Flow in kappa-Minkowski Spacetime*

Running of the spacetime dimension in small scales is predicted by many different approaches to Quantum Gravity, usually using a notion of the spectral dimension. This is also the case for the kappa-Minkowski spacetime, which appears in the Deformed Special Relativity and Relative Locality. The spectral dimension can easily be calculated in the (Euclidean) momentum space representation. Meanwhile, kappa-Minkowski momenta belong to the group AN(n), which can be represented as half of the de Sitter space. A novel prescription shows it can also be mapped to (half of) the Euclidean anti-de Sitter space, which gives the Euclidean version of momentum space. This allows us to calculate the kappa-Minkowski spectral dimension for different possible Laplacians, extending the known results and providing us with a possible hint for the choice of a physical Laplacian.

**Goffredo Chirco** (CPT, Universite' Aix-Marseille)

17:30, Wed 3rd Sep 2014

*Thermally correlated states of Loop Quantum Gravity*

We define a class of states of LQG characterized by thermal correlations at the ultralocal level, which may reproduce the structure of correlations known for the perturbative quantum gravity states, in the appropriate limit. We show that these states have a consistent semiclassical interpretation, being peacked on classical values of the intrinsic geometry; and we study how these correlations propagate non-locally on the spin network. We propose these states as the fundamental quantum bricks defining the architecture of spacetime at the non perturbative level and we elaborate on the possible relevance of this proposal in the definition of a continuum limit for LQG.

**Jonathan Miller** (Universidad Tecnica Federico Santa Maria)

9:00, Thu 4th Sep 2014

*The effect of Quantum Gravity on astrophysical neutrino flavor observables.*

At the quantum level, an interaction of a neutrino with a graviton may trigger the collapse of the neutrino flavor eigenstate to a neutrino mass eigenstate. I will present that such an essentially quantum gravity effect may have strong consequences for neutrino oscillation phenomena in astrophysics due to the relatively large scattering cross section of relativistic neutrinos off massive sources of gravitational fields (the case of gravitational Bethe-Heitler scattering). This results in a new technique for the indirect detection of gravitons by measuring the flavor composition of astrophysical neutrinos.

**Jakub Mielczarek** (Jagiellonian University, Crakow)

10:30, Thu 4th Sep 2014

*Cosmological constraints on quantum gravity*

In this talk, we will discuss a possibility of testing quantum gravity
effects with use of primordial cosmological perturbations. The issue
will be addressed mainly on example of the effective loop quantum
gravity. In this approach, power spectra of primordial perturbations
with quantum gravity corrections can be computed and subsequently
confronted with the CMB data. Advantages and limitations of the method
will be discussed. Some other alternative proposals of constraining
quantum gravity effects through cosmological observations will be
outlined as well.

**Jerzy Kowalski-Glikman** (University of Wroclaw)

11:15, Thu 4th Sep 2014

*Relative locality in 2+1 dimensions*

The relative locality framework is based on two general premises: nontrivial geometry of momentum space and deformed momentum conservation rule. In my talk I will show how these premises take a concrete shape in the case of particles coupled to 2+1 gravity. Then I will briefly discuss the relevance of this construction to the case of physical 3+1 dimensions.

**Giulia Gubitosi** (Sapienza, University of Rome)

14:30, Thu 4th Sep 2014

*Dimensional Reduction in the Early Universe*

In several approaches to quantum-gravity, the spectral dimension of spacetime runs from the standard value of 4 in the infrared (IR) to a smaller value in the ultraviolet (UV).
I discuss results on the relation between deformed dispersion relations, running of spectral dimension and running of momentum space Hausdorff dimension, emphasising the difference between Lorentz breaking scenarios and Lorentz deforming scenarios. I show that a striking cosmological implication is that that UV behavior leading to 2 spectral dimensions results in a scale-invariant spectrum of vacuum scalar and tensor fluctuations.

**Joao Magueijo** (Imperial College, London)

15:15, Thu 4th Sep 2014

*Dimensional reduction in the sky?*

I review the popular idea that at high energies space-time becomes 2 dimensional, thereby simplifying the task of quantum gravity. I then present some recent work on the cosmological implications of this phenomenon.

**Giacomo Rosati** (ITP, University of Wroclaw)

16:30, Thu 4th Sep 2014

*Deformed Lorentz Symmetry and relative locality in FRW spacetime*

An opportunity to test Planck-scale modifications of Lorentz symmetry is represented by propagation of particles from cosmological distances (as from GRBs).
DSR has been investigated so far only for flat (Minkowskian) spacetimes, providing no room for interplay with cosmological redshift. Only recently a generalization to deSitter spacetime has been proposed (Phys.Rev.D86(2012)124035), relying on the recent understanding of relativity of locality in DSR. I here propose a formulation of DSR in FRW spacetimes, discussing some of the differences with the most studied scenario for broken Lorentz symmetries.

**Niccolo' Loret** (Perimeter Institute, Waterloo)

17:00, Thu 4th Sep 2014

*Finsler geometry and deSitter momentum space*

Finsler geometry provides a well studied generalization of Riemannian geometry which allows to account for possibly non-trivial structure of the space of con?gurations of a massive relativistic particle. Another recently developed framework for the description of modi?ed relativistic particle kinematics relies on the description of the particle momentum-space as a curved (pseudo-Riemannian) manifold. We will show that in some cases these two frameworks give equivalent descriptions of the physical properties of a relativistic particle, when its momentum-space is characterized by a deSitter metric and the spacetime is ?at. The generalization of this result could provide a useful mathematical tool to formalize Deformed Special Relativity phenomenology to curved spacetimes.

**Gianluca Castignani** (SISSA)

17:30, Thu 4th Sep 2014

*Gamma-ray bursts as laboratories for quantum effects of gravity*

Gamma-ray bursts (GRBs) are the most powerful explosions in the Universe. Most GRBs detected by the Fermi Gamma-ray Space Telescope exhibit a possible delay of up to about 10 seconds between the trigger time of the hard X-ray signal as measured by the Fermi Gamma-ray Burst Monitor (GBM) and the onset of the MeV-GeV counterpart detected by the Fermi Large Area Telescope (LAT). This delay may hint at important physics, whether it is due to the intrinsic variability of the inner engine or related to quantum dispersion effects (e.g. modified dispersion relations) in the velocity of light propagation from the sources to the observer.
We searched for the presence of time lags between the LAT and GBM light curves for the five brightest GRBs of the 1st Fermi-LAT Catalog by means of cross correlation analysis. Time lags that are significantly different from zero and consistent with those reported in the literature are found for all the GRBs in our sample by mean of cross correlation analysis. Our analysis reveals the complexity of the time behavior of the GBM and LAT light curves and suggests that the delays should be ascribed to intrinsic physical mechanisms. Better sensitivity and a larger sample might put constraints on a possible origin of the delays in the context of modified dispersion relations and will allow to assess whether time lags are universally present in the early GRB emission.

**John Kelley** (Univ. of Wisconsin, Madison)

9:00, Fri 5th Sep 2014

*Observation of High-energy Astrophysical Neutrinos with the IceCube Detector*

The IceCube Neutrino Observatory is a cubic-kilometer-scale neutrino detector built into the ice sheet at the geographic South Pole. IceCube has recently observed a diffuse flux of high-energy astrophysical neutrinos with deposited energies up to 2 PeV. The detection of neutrinos at such energies, as well as features of their energy spectrum and flavor ratios, can be used to constrain potential phenomenological effects of quantum gravity. I will discuss the latest measurements from IceCube of these high-energy neutrinos and the implications for such constraints.

**David Mattingly** (University of New Hampshire)

10:30, Fri 5th Sep 2014

*tba*

Lorentz violating effective field theories

**Daniele Oriti** (Albert Einstein Institute)

11:15, Fri 5th Sep 2014

*The universe as a quantum gravity condensate*

We discuss the geometrogenesis scenario in quantum gravity and the role it may play in the context of loop quantum gravity and group field theory. We also emphasise the connection with other ideas of emergent space-time and with analogue gravity models. We report on recent results, in the group field theory formalism, aiming at realising this scenario and in particular at the derivation of effective cosmological dynamics from group field theory condensates. In light of these results, we suggest several directions to explore to extract testable consequences of this picture of the early universe.