FIAS Scientific Report 2011 - Frankfurt Institute for Advanced Studies ...

The quest for quantum gravity signals
Collaborators: P. Nicolini 1 , M. Bleicher 1,2 , R. Garattini 3 , M. Rinaldi 4 , M. Sprenger 1,2
1 Frankfurt Institute for Advanced Studies, 2 Institut für Theoretische Physik, Johann Wolfgang Goethe-Universität,
3 Università di Bergamo, Italy, 4 Université de Gèneve, Switzerland.
Research in quantum gravity is often associated to attempts of describing in an efficient and self consistent way
the gravitational field at quantum level. Even if this is certainly true, it is just a narrow view. Before embarking
in the formulation of sophisticated theories, a crucial point is to understand whether quantum gravity signals
might be detected in current experiments or in a near future. This task is mandatory but challenging for two
reasons: first, it is hard to foresee quantum gravity effects without a widely accepted theory of quantum gravity;
second, we conventionally expect quantum gravity effects at a scale, the Planck scale, something like 15 orders
of magnitude higher than the highest energy particle physics experiments.
Despite this background in 2011 we succeeded to determine a detectable signature of quantum gravity effects.
To achieve this, we showed that neutrinos can be the privileged probe to detect the sought signals: even if
neutrino energies do not reach the Planck scale, they propagate without interactions over very large distances
allowing a non-negligible accumulation of small effects. Specifically we showed that the highest-energetic
neutrinos emitted by active galactic nuclei would not oscillate during their propagation towards the Earth, a
fact that opens the possibility of their detection in the original flavor eigenstate at telescopes like IceCube and
ANTARES. A key point of this work has been the implementation of quantum gravity effects in the neutrino
propagation. Along the lines of what already obtained in several other contexts like the Unruh effect and the
quantum vacuum energy, we adopted a string theory induced model of noncommutative geometry to reproduce
the emergence of quantum spacetime graininess in an effective way.
P(νµ → νµ)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Classical oscillations
ML oscillations
0
1 10 100
Energy [GeV]
Distance [km]
10 6
8·10 5
6·10 5
4·10 5
2·10 5
∆p > 0.1
∆p > 0.01
∆p > 0.001
0
0 200 400 600 800 1000
Energy [GeV]
On the left: classical and modified (ML) oscillations for the two-flavour case with baseline L = 5000 km.
On the right: departures from classical oscillations for different values of probability deviation ∆p.
Related publications in 2011:
1) P. Nicolini and M. Rinaldi, A minimal length versus the Unruh effect, Physics Letters B 695 (2011) 303.
2) R. Garattini and P. Nicolini, A Noncommutative approach to the cosmological constant problem, Physical
Review D 83 (2011) 064021.
4) M. Sprenger, P. Nicolini and M. Bleicher, Neutrino oscillations as a novel probe for a minimal length,
Classical and Quantum Gravity 28 (2011) 235019.
5) M. Sprenger, P. Nicolini and M. Bleicher, Quantum Gravity signals in neutrino oscillations, International
Journal of Modern Physics E 20S2 (2011) 1.
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