I review the current status of phenomenological programs inspired by quantum-spacetime research. I stress in particular the significance of results establishing that certain data analyses provide sensitivity to effects introduced genuinely at the Planck scale. My main focus is on phenomenological programs that affect the directions taken by studies of quantum-spacetime theories.

https://link.springer.com/content/pdf/10.12942%2Flrr-2013-5.pdf

Quantum-Spacetime Phenomenology

We present an updated review of Lorentz invariance tests in effective field theories (EFTs) in the matter as well as in the gravity sector. After a general discussion of the role of Lorentz invariance and a derivation of its transformations along the so-called von Ignatovski theorem, we present the dynamical frameworks developed within local EFT and the available constraints on the parameters governing the Lorentz breaking effects. In the end, we discuss two specific examples: the OPERA ‘affaire’ and the case of Hořava–Lifshitz gravity. The first case will serve as an example, and a caveat, of the practical application of the general techniques developed for constraining Lorentz invariance violation to a direct observation potentially showing these effects. The second case will show how the application of the same techniques to a specific quantum gravity scenario has far-reaching implications not foreseeable in a purely phenomenological EFT approach.

http://iopscience.iop.org/article/10.1088/0264-9381/30/13/133001/pdf

Tests of Lorentz invariance: a 2013 update

Hořava’s proposal for non-relativistic quantum gravity introduces a preferred time foliation of space-time which violates the local Lorentz invariance. The foliation is encoded in a dynamical scalar field which we call ‘khronon’. The dynamics of the khronon field is sensitive to the symmetries and other details of the particular implementations of the proposal. In this paper we examine several consistency issues present in three non-relativistic gravity theories: Hořava’s projectable theory, the healthy non-projectable extension, and a new extension related to ghost condensation. We find that the only model which is free from instabilities and strong coupling is the non-projectable one. We elaborate on the phenomenology of the latter model including a discussion of the couplings of the khronon to matter. In particular, we obtain the parameters of the post-Newtonian expansion in this model and show that they are compatible with current observations.

/pdf/models-of-non-relativistic-quantum-gravity-the-good-the-bad-33e16n0zcd.pdf

Models of non-relativistic quantum gravity: The Good, the bad and the healthy

Ground-based gamma-ray astronomy, which provides access to the TeV energy range, is a young and rapidly developing discipline Recent discoveries in this waveband have important consequences for a wide range of topics in astrophysics and astroparticle physics This article is an attempt to review the experimental status of this field and to provide the basic formulae and concepts required to begin the interpretation of TeV observations

Teraelectronvolt Astronomy

If the inflaton is a pseudoscalar, then it naturally interacts with gauge fields through the coupling ∝ Fμν μν. Through this coupling, the rolling inflaton produces quanta of the gauge field, that in their turn source the tensor components of the metric perturbations. Due to the parity-violating nature of the system, the right- and the left-handed tensor modes have different amplitudes. Such an asymmetry manifests itself in the form of non-vanishing TB and EB correlation functions in the Cosmic Microwave Background (CMB). We compute the amplitude of the parity-violating tensor modes and we discuss two scenarios, consistent with the current data, where parity-violating CMB correlation functions will be detectable in future experiments.

https://iopscience.iop.org/article/10.1088/1475-7516/2011/06/003/pdf

Parity violation in the Cosmic Microwave Background from a pseudoscalar inflaton

We discuss the rotation of the linear polarization plane and the production of circular polarization generated by a cosmological pseudoscalar field. We compute analytically and numerically the propagation of the Stokes parameters from the last scattering surface for an oscillating and a monotonic decreasing pseudoscalar field. For the models studied in this paper, we show the comparison between the widely used approximation in which the linear polarization rotation angle is constant in time and the exact result.

Rotation of linear polarization plane and circular polarization from cosmological pseudoscalar fields

The propagation of photons, electrons and positrons at ultrahigh energies above $\ensuremath{\sim}{10}^{19}\text{ }\text{ }\mathrm{eV}$ can be changed considerably if the dispersion relations of these particles are modified by terms suppressed by powers of the Planck scale. We recently pointed out that the current nonobservation of photons in the ultrahigh-energy cosmic ray flux at such energies can put strong constraints on such modified dispersion relations. In the present work we generalize these constraints to all three Lorentz invariance-breaking parameters that can occur in the dispersion relations for photons, electrons and positrons at first- and second-order suppression with the Planck scale. We also show how the excluded regions in these three-dimensional parameter ranges would be extended if ultrahigh-energy photons were detected in the future.

/pdf/lorentz-violation-and-ultrahigh-energy-photons-2dtmui8j0t.pdf

Lorentz violation and ultrahigh-energy photons

We report on an update of the test on the rotation of the plane of linear polarization for light traveling over cosmological distances, using a comparison between the measured direction of the UV polarization in eight radio galaxies at z> 2 and the direction predicted by the model of scattering of anisotropic nuclear radiation, which explains the polarization. No rotation is detected within a few degrees for each galaxy and, if the rotation does not depend on direction, then the all-sky-average rotation is constrained to be θ =− 0. 8 ± 2. 2. We discuss the relevance of this result for constraining cosmological birefringence when this is caused by the interaction with a cosmological pseudo-scalar field or by the presence of a Cherns–Simons term.

Limits on cosmological birefringence from the ultraviolet polarization of distant radio galaxies

Lorentz symmetry breaking at very high energies may lead to photon dispersion relations of the form omega^2=k^2+xi_n k^2(k/M_Pl)^n with new terms suppressed by a power n of the Planck mass M_Pl. We show that first and second order terms of size xi_1 > 10^(-14) and xi_2 < -10^(-6), respectively, would lead to a photon component in cosmic rays above 10^(19) eV that should already have been detected, if corresponding terms for electrons and positrons are significantly smaller. This suggests that Lorentz invariance breakings suppressed up to second order in the Planck scale are unlikely to be phenomenologically viable for photons.

Lorentz Violation in the Photon Sector and Ultra-High Energy Cosmic Rays

We study the bending of light for static spherically symmetric (SSS) space-times which include a dark energy contribution. Geometric dark energy models generically predict a correction to the Einstein angle written in terms of the distance to the closest approach, whereas a cosmological constant $\ensuremath{\Lambda}$ does not. While dark energy is associated with a repulsive force in cosmological context, its effect on null geodesics in SSS space-times can be attractive as for the Newtonian term. This dark energy contribution may not be negligible with respect to the Einstein prediction in lensing involving clusters of galaxies. Strong lensing may therefore be useful to distinguish $\ensuremath{\Lambda}$ from other dark energy models.

Matteo Galaverni

Papers

Rotation of linear polarization plane and circular polarization from cosmological pseudoscalar fields

Lorentz violation and ultrahigh-energy photons

Limits on cosmological birefringence from the ultraviolet polarization of distant radio galaxies

Lorentz Violation in the Photon Sector and Ultra-High Energy Cosmic Rays

Light bending as a probe of the nature of dark energy