TASI lectures on cosmological observables and string theory
  These lectures provide an updated pedagogical treatment of the theoretical
structure and phenomenology of some basic mechanisms for inflation, along with
an overview of the structure of cosmological uplifts of holographic duality. A
full treatment of the problem requires `ultraviolet completion' because of the
sensitivity of inflation to quantum gravity effects, including back reaction
and non-adiabatic production of heavy degrees of freedom. Cosmological
observations imply accelerated expansion of the late universe, and provide
increasingly precise constraints and discovery potential on the amplitude and
shape of primordial tensor and scalar perturbations, and some of their
correlation functions. Most backgrounds of string theory have positive
potential energy, with a rich but still highly constrained landscape of
solutions. The theory contains novel mechanisms for inflation, some subject to
significant observational tests. Although the detailed ultraviolet completion
is not accessible experimentally, some of these mechanisms directly stimulate a
more systematic analysis of the space of low energy theories and signatures
relevant for analysis of data, which is sensitive to physics orders of
magnitude above the energy scale of inflation as a result of long time
evolution (dangerous irrelevance) and the substantial amount of data. Portions
of these lectures appeared previously in Les Houches 2013, "Post-Planck
Cosmology" .
