### Quantum gravity phenomenology

**Principal Investigator: ** Stefano Liberati

**Areas: **

- Astrophysical Probes of Fundamental Interactions
- Theory and Phenomenology of Gravity

**Abstract: **The structure of spacetime at the Planck scale may lead to a breakdown (or modification) of Lorentz invariance at high energies in the form of nonlinear dispersion relations for the fundamental particles. In spite of the fact that the extra Lorentz-breaking terms of power higher than 2 in the momentum are suppressed by inverse powers of the Planck scale, it is possible to observe their effect in relatively low energy interactions (w.r.t. the Planck energy) when these involve thresholds, cumulative effects (such as time delay between photons of different frequencies) or are sensitive to the possible existence of a maximal group velocity for the elementary particles (synchrotron effect). An alternative scenario concerns the possibility that Lorentz invariance is conserved but realising the notion of locality. This is what is for example suggested in quantum gravity models such as String Field theory or Causal Set theory where the standard Dâ€™Alambertian appearing in the Klein-Gordon equation for a scalar field is replaced by some function of these operator. Testing this kind of physics is more subtle and requires precision quantum experiments rather than high energies. Finally, quantum gravity effect are supposed to be determinant in resolving singularities at the Big Bang or inside black holes. This resolution can lead to new phenomenology such as bouncing solutions, regular black holes and perhaps even ultra-compact objects. Using multimessanger astrophysics (in particular GW astrophysics) can then open a window to test these deviations from the standard GR scenario.

**Description: **Quantum gravity phenomenology is a recent branch of research aimed at finding low energy tests of physics from quantum gravity scenarios. As such it aims at providing a guideline towards the development of a full fledged theory of quantum gravity.