Massive spin-1/2 fields are studied in the framework of loop quantum gravity by considering a state approximating, at a length scale L much greater than Planck length P = 1.2 × 10 −33 cm, a spin-1/2 field in flat spacetime. The discrete structure of spacetime at P yields corrections to the field propagation at scale L. Next, Neutrino Bursts (p ≈ 10 5 GeV) accompaning Gamma Ray Bursts that have travelled cosmological distances, L ≈ 10 10 l.y., are considered. The dominant correction is helicity independent and leads to a time delay w.r.t. the speed of light, c, of order (p P )L/c ≈ 10 4 s. The fact that some Gamma Ray Bursts (GRB) originate at cosmological distances, (≈ 10 10 light years) [1], together with time resolutions down to submillisecond scale achieved in recent GRB data [2], suggest that it is possible to probe fundamental laws of physics at energy scales near to Planck energy E P = 1.2×10 19 GeV [3,4]. Furthermore, sensitivity will be improved with HEGRA and Whipple air Cerenkov telescopes and by AMS and GLAST spatial experiments. Thus, quantum gravity effects could be at the edge of observability [3,4]. Now, quantum gravity theories imply different spacetime structures [4,5] and it can be expected that what we consider flat spacetime, can actually involve dispersive effects arising from Planck scale lengths. Such tiny effects might become observable upon accumulation over travels through cosmological distances by energetically enough particles like cosmological GRB photons. Now, the most widely accepted model of GRB, so called fireball model, predicts also the generation of 10 14 − 10 19 eV Neutrino Bursts (NB) [7,8]. Yet, another GRB model based on cosmic strings requires neutrino production [9]. Present experiments to observe high energy astrophysical neutrinos like AMANDA, NESTOR, Baikal, ANTARES and Superkamiokande, for example, will detect at best only one or two neutrinos in coincidence with GRB's per year. The planned Neutrino Burster Experiment (NuBE) will measure the flux of ultra high energy neutrinos (> 10 TeV) over a ∼ 1km 2 effective area, in coincidence with satellite measured GRB's [10]. It is expected to detect ≈ 20 events per year, according to the fireball model. Hence, one can study quantum gravity effects on astrophysical neutrinos that might be observed or, the other way around, such observations could be used to restrict quantum gravity theories.In this letter, the loop quantum gravity framework is adopted. In this context, Gambini an Pullin studied light propagation semiclassically [6]. They found, besides departures from perfect non-dispersiveness of ordinary vacuum, helicity depending corrections for propagating waves. In the present work, the case of massive spin-1/2 particles in loop quantum gravity is studied also semiclassically. They could be identified with the neutrinos that would be produced in GRB. Central ideas and results are presented whereas details will appear elsewhere [11].Loop quantum gravity [5] uses a spin networks basis, labelled by graphs embedded in a thr...

Within loop quantum gravity we construct a coarse-grained approximation for the Einstein-Maxwell theory that yields effective Maxwell equations in flat spacetime comprising Planck scale corrections.

A deep survey of the Large Magellanic Cloud at ∼ 0.1−100 TeV photon energies with the Cherenkov Telescope Array is planned. We assess the detection prospects based on a model for the emission of the galaxy, comprising the four known TeV emitters, mock populations of sources, and interstellar emission on galactic scales. We also assess the detectability of 30 Doradus and SN 1987A, and the constraints that can be derived on the nature of dark matter. The survey will allow for fine spectral studies of N 157B, N 132D, LMC P3, and 30 Doradus C, and half a dozen other sources should be revealed, mainly pulsar-powered objects. The remnant from SN 1987A could be detected if it produces cosmic-ray nuclei with a flat power-law spectrum at high energies, or with a steeper index 2.3 − 2.4 pending a flux increase by a factor > 3 − 4 over ∼ 2015 − 2035. Large-scale interstellar emission remains mostly out of reach of the survey if its > 10 GeV spectrum has a soft photon index ∼ 2.7, but degree-scale 0.1 − 10 TeV pion-decay emission could be detected if the cosmic-ray spectrum hardens above >100 GeV. The 30 Doradus star-forming region is detectable if acceleration efficiency is on the order of 1 − 10% of the mechanical luminosity and diffusion is suppressed by two orders of magnitude within < 100 pc. Finally, the survey could probe the canonical velocity-averaged cross section for self-annihilation of weakly interacting massive particles for cuspy Navarro-Frenk-White profiles.

Quantum gravity phenomenology opens up the possibility of probing Planck scale physics. Thus, by exploiting the generic properties that a semiclassical state of the compound system fermions plus gravity should have, an effective dynamics of spin-1/2 particles is obtained within the framework of loop quantum gravity. Namely, at length scales much larger than Planck length ℓ P ∼ 10 −33 cm and below the wave length of the fermion, the spin-1/2 dynamics in flat spacetime includes Planck scale corrections. In particular we obtain modified dispersion relations in vacuo for fermions. These corrections yield a time of arrival delay of the spin 1/2 particles with respect to a light signal and, in the case of neutrinos, a novel flavor oscillation. To detect these effects the corresponding particles must be highly energetic and should travel long distances. Hence Neutrino Bursts accompanying Gamma Ray Bursts or ultra high energy cosmic rays could be considered. Remarkably, future neutrino telescopes may be capable to test such effects. This paper provides a detailed account of the calculations and elaborates on results previously reported in a Letter. These are further amended by introducing a real parameter Υ aimed at encoding our lack of knowledge of scaling properties of the gravitational degrees of freedom.2

The antifields of the Batalin-Vilkovisky Lagrangian quantization are standard antighosts of certain collective fields. These collective fields ensure that SchwingerDyson equations are satisfied as a consequence of the gauge symmetry algebra. The associated antibracket and its canonical structure appear naturally if one integrates out the corresponding ghost fields. An analogous Master Equation for the action involving these ghosts follows from the requirement that the path integral gives rise to the correct Schwinger-Dyson equations.