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We present a model of inflation based on a racetrack model without flux stabilization. The initial conditions are set automatically through topological inflation. This ensures that the dilaton is not swept to weak coupling through either thermal effects or fast roll. Including the effect of non-dilaton fields we find that moduli provide natural candidates(More)
The recent confirmation that at least some gamma-ray bursters (GRBs) are indeed at cosmological distances [1, 2, 3, 4] raises the possibility that observations of these could provide interesting constraints on the fundamental laws of physics. Here we demonstrate that the fine-scale time structure and hard spectra of GRB emissions are very sensitive to the(More)
When a dark matter halo moves through a background of dark matter particles, self-interactions can lead to both deceleration and evaporation of the halo and thus shift its centroid relative to the collisionless stars and galaxies. We study the magnitude and time evolution of this shift for two classes of dark matter self-interactions, viz. frequent(More)
Received (received date) Revised (revised date) A satisfactory theory of quantum gravity will very likely require modification of our classical perception of space-time, perhaps by giving it a 'foamy' structure at scales of order the Planck length. This is expected to modify the propagation of photons and other relativistic particles such as neutrinos, such(More)
The temperature uctuations in the cosmic microwave background observed by COBE provide strong support for an innationary phase in the early universe, below the GUT scale. We argue that a singlet eld in a hidden sector of an eeective supergravity theory yields the required innationary potential without ne tuning. Reheating occurs to a temperature low enough(More)
We discuss possible signatures of quantum gravity for the propagation of light, including an energy-dependent velocity (refractive index), dispersion in velocity at a given energy, and birefringence. We also compare the sensitivities of different astrophysical observations, including BATSE data on GRB 920229, BeppoSAX data on GRB 980425, the possible HEGRA(More)
We derive constraints on the relic abundance of a generic particle of mass ∼ 1 − 10 14 TeV which decays into neutrinos at cosmological epochs, using data from the Fréjus and IMB nucleon decay detectors and the Fly's Eye air shower array. The lifetime of such unstable particles which may constitute the dark matter today is bounded to be greater than ∼ 10 14(More)