There is overwhelming evidence that non-baryonic dark
matter constitutes ~23% of the energy density of the universe. Weakly Interacting Massive Particles (WIMPs)
are promising dark matter candidates that may produce gamma rays via
annihilation or decay detectable by the Fermi Large Area Telescope (Fermi
LAT). A detection of WIMPs would also
indicate the existence of physics beyond the Standard Model. I will present recent results from indirect
WIMP searches by the Fermi LAT Collaboration.
I will focus on our recent search for gamma-ray spectral lines from WIMP
annihilations with 4 years of data.
There has been recent excitement with the report of a line-like feature
localized in the galactic center around 130 GeV. I will be discussing what our search finds
and the systematic checks we've performed on potential signals.
Both AdS/CFT duality and more general reasoning from quantum gravity point to a rich collection of boundary observables that always evolve unitarily. The physical quantum gravity states described by these observables must be solutions of the spatial diffeomorphism and Wheeler-deWitt constraints, which implies that the state space does not factorize into a tensor product of localized degrees of freedom. The "firewall" argument that unitarity of black hole evaporation is incompatible with a regular near horizon region is based on such a factorization, hence is not applicable in quantum gravity. A version of black hole complementarity resolves the apparent conflict. (I will also discuss doubts and questions.)
Gravity
in string theory is a generalized version of Einstein's theory with some
universal features that call for a reformulation
of
the key geometrical concepts. In addition to the metric tensor, for
example, string theory contains an antisymmetric tensor and a dilaton that
allow for extra symmetries. A new branch of mathematics, Generalized Geometry,
suggests a framework that finds a realization in the recent Double Field Theory
formulation of string gravity. I will describe the main ideas, the progress,
and the mysteries that remain in the search for a proper description of string
gravitation.