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Threshold anomalies in Horava-Lifshitz-type theories
Get PDFRecently the study of threshold kinematic requirements for particle-production processes has played a very significant role in the phenomenology of theories with departures from Poincare symmetry. We here specialize these threshold studies to the case of a class of violations of Poincare symmetry which has been much discussed in the literature on Horava-Lifshitz scenarios. These involve modifications of the energy-momentum ("dispersion") relation that may be different for different types of particles, but always involve even powers of energy-momentum in the correction terms. We establish the requirements for compatibility with the observed cosmic-ray spectrum, which is sensitive to the photopion-production threshold. We find that the implications for the electron-positron pair-production threshold are rather intriguing, in light of some recent studies of TeV emissions by Blazars. Our findings should also provide additional motivation for examining the fate of the law of energy-momentum conservation in Horava-Lifshitz-type theories. (C) 2010 Elsevier B.V. All rights reserved
On the theory and phenomenology of spacetime symmetries at the Planck scale
No full textWe consider some alternative scenarios for the fate of Poincare/Lorentz symmetry at the Planck scale, and we discuss some opportunities to test these scenarios
Discreteness of area in noncommutative spacetime
No full textAbstractWe introduce an area operator for the Moyal noncommutative plane. We find that the spectrum is discrete, but, contrary to the expectation formulated by other authors, not characterized by a “minimum-area principle”. We show that an intuitive analysis of the uncertainty relations obtained from Moyal-plane noncommutativity is fully consistent with our results for the spectrum, and we argue that our area operator should be generalizable to several other noncommutative spaces. We also observe that the properties of distances and areas in the Moyal plane expose some weaknesses in the line of reasoning adopted in some of the heuristic analyses of the measurability of geometric spacetime observables in the quantum-gravity realm
Constraining the Energy-Momentum Dispersion Relation with Planck-Scale Sensitivity Using Cold Atoms
No full textUV AND IR QUANTUM-SPACETIME EFFECTS FOR THE CHANDRASEKHAR MODEL
No full textWe modify the Chandrasekhar model of white dwarfs by introducing some of the momentum-space features which have been considered in the quantum-gravity literature. We find that when the new effects are confined to high energies, one only finds significant corrections to the Chandrasekhar model in regimes where the model anyway lacks any contact with observations. But these high-energy effects could play an important role in cases where ultra-high densities are present, even when the relevant star is still gigantic in Planck-length units. If the effects are not confined to high energies, as a result of "ultraviolet/infrared mixing", there could be significant implications for white dwarfs whose mass is roughly half the mass of the Sun, some of which are described in the literature as "strange white dwarfs"
Taming Nonlocality in Theories with Planck-Scale Deformed Lorentz Symmetry
No full textWe report a general analysis of worldlines for theories with deformed relativistic symmetries and momentum dependence of the speed of photons. Our formalization is faithful to Einstein's program, with spacetime points viewed as an abstraction of physical events. The emerging picture imposes the renunciation of the idealization of absolutely coincident events, but is free from some pathologies which had been previously conjectured
Modifications to Lorentz invariant dispersion in relatively boosted frames
No full textWe investigate the implications of energy dependence of the speed of photons, one of the candidate effects of quantum-gravity theories that has been most studied recently, from the perspective of observations in different reference frames. We examine how a simultaneous burst of photons would be measured by two observers with a relative velocity, establishing some associated conditions for the consistency of theories. For scenarios where the Lorentz transformations remain valid, these consistency conditions allow us to characterize the violations of Lorentz symmetry through an explicit description of the modification of the quantum-gravity scale in boosted frames with respect to its definition in a preferred frame. When applied to relativistic scenarios with a deformation of Lorentz invariance that preserves the equivalence of inertial observers, we find an insightful characterization of the necessity to adopt in such frameworks nonclassical features of spacetime geometry, e.g. events that are at the same spacetime point for one observer cannot be considered at the same spacetime point for other observers. Our findings also suggest that, at least in principle (and perhaps one day even in practice), measurements of the dispersion of photons in relatively boosted frames can be particularly valuable for the purpose of testing these scenarios
GRAVITY IN QUANTUM SPACE-TIME
No full textThe literature on quantum-gravity-inspired scenarios for the quantization of space-time has so far focused on particle-physics-like studies. This is partly justified by the present limitations of our understanding of quantum gravity theories, but we here argue that valuable insight can be gained through semi-heuristic analyses of the implications for gravitational phenomena of some results obtained in the quantum space-time literature. In particular, we show that the types of description of particle propagation that emerged in certain quantum space-time frameworks have striking implications for gravitational collapse and for the behavior of gravity at large distances
OPERA-reassessing data on the energy dependence of the speed of neutrinos
No full textWe offer a preliminary exploration of the two sides of the challenge provided by the recent OPERA data on superluminal neutrinos. On one side we stress that some aspects of this result are puzzling even from the perspective of the wild quantum-gravity literature, where arguments in favor of the possibility of superluminal propagation have been presented, but not considering the possibility of such a sizeable effect for neutrinos of such low energies. We feel this must encourage particularly severe scrutiny of the OPERA result. On the other side, we notice that the OPERA result is reasonably consistent with -neutrino-speed data previously obtained at FERMILAB, reported in papers of 2007 and 1979. And it is intriguing that these FERMILAB79 and FERMILAB07 results, when combined with the new OPERA result, in principle provide a window on -neutrino speeds at different energies broad enough to compare alternative phenomenological models. We test the discriminating power of such an approach by using as illustrative examples the case of special-relativistic tachyons, the case of "Coleman-Glashow-type" momentum-independent violations of the special-relativistic speed law, and the cases of linear and quadratic energy dependence of the speed of ultrarelativistic muon neutrinos. Even just using -neutrino data in the range from 3 GeVs to 200 GeVs the special-relativistic tachyon and the quadratic-dependence case are clearly disfavoured. The linear-dependence case gives a marginally consistent picture and the Coleman-Glashow scenario fits robustly the data. We also comment on Supernova 1987a and its relevance for consideration of other neutrino species, also in relation with some scenarios that appeared in the large-extra-dimension literature
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