Abstract
Using standard techniques in string/D-brane scattering amplitude computations, we evaluate the scattering of open strings off D-particles in brane world scenarios. The D-particles are viewed as D3 branes wrapped up around three cycles, and their embedding in brane worlds constitutes a case of intersecting branes, among which strings are stretched, representing various types of excitations of the Standard Model (SM) particles in the low-energy limit. Our analysis, reveals interesting and novel selection rules for the resulting causal time delays, proportional to the energy of the incident matter state, from the processes of splitting, capture and re-emission of the latter by the D-particles. There are relatively large time delays only for excitations that belong to the Cartan subalgebra of the SM gauge group, which notably includes photons. We discuss the possible relevance of these results to models of space time foam with non-trivial vacuum refractive index for photons and demonstrate how current astrophysical observations can be used to discriminate low- from high-string-scale models in this context.
Highlights
LORENTZ-INVARIANCE-VIOLATING STRING-FOAM BACKGROUNDSThe advent of the new generation of ground-based Cerenkov or satellite γ-ray telescopes has inaugurated a new era in γ-ray astronomy
Using standard techniques in string/D-brane scattering amplitude computations, we evaluate the scattering of open strings off D-particles in brane world scenarios
The D-particles are viewed as D3 branes wrapped up around three cycles, and their embedding in brane worlds constitutes a case of intersecting branes, among which strings are stretched, representing various types of excitations of the Standard Model (SM) particles in the low-energy limit
Summary
The advent of the new generation of ground-based Cerenkov or satellite γ-ray telescopes has inaugurated a new era in γ-ray astronomy. There are several stringent restrictions coming from other independent tests of Lorentz symmetry that must be taken into account [2] To survive these stringent bounds on Lorentz invariance violation imposed by the plethora of the current astrophysical experiments, any model of quantum-gravity predicting non-trivial refractive indices should be characterised by the following features: (i) Photons are stable (i.e. do not decay) [6] but should exhibit a modified subluminal dispersion relation with Lorentz-violating corrections that should grow linearly with Eγ/MQG where MQG is close to the Planck scale; (ii) The medium should not refract electrons, so as to avoid the synchrotron-radiation constraints [7, 8]; (iii) The coupling of the photons to the medium must be independent of photon polarization, so as to avoid birefringence, avoiding the stringent pertinent constraints [9, 10, 11, 12]; (iv) The formalism of a local effective field theory lagrangian in an effectively flat space-time, including higher-derivative local interaction terms to produce a refractive index [13], breaks down.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
