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We use astrophysical data to shed light on fundamental physics byconstraining parametrized theoretical cosmological and gravitational models.  Gravitational parameters are those constants that parametrize possibledepartures from Einstein's general theory of relativity. We develop a generalframework to describe torsion in the spacetime around the Earth, and show thatcertain observables of the Gravity Probe B experiment can be computed in thisframework. We also search for viable theories of gravity where the Ricci scalarR in the Lagrangian is replaced by an arbitrary function f(R). Making use ofthe equivalence between such theories and scalar-tensor gravity, we find thatmodels can be made consistent with solar system constraints either by givingthe scalar a high mass or by exploiting the so-called Chameleon Effect.  Cosmology can successfully describe the evolution of our universe using sixor more adjustable cosmological parameters. There is growing interest in using3-dimensional neutral hydrogen mapping with the redshifted 21 cm line as acosmological probe. We quantify how the precision with which cosmologicalparameters can be measured depends on a broad range of assumptions. We presentan accurate and robust method for measuring cosmological parameters thatexploits the fact that the ionization power spectra are rather smooth functionsthat can be accurately fit by 7 phenomenological parameters. We find that afuture square kilometer array optimized for 21 cm tomography could have greatpotential, improving the sensitivity to spatial curvature and neutrino massesby up to two orders of magnitude, to Delta-Omega_k ~ 0.0002 and Delta-m_nu ~0.007 eV, and giving a 4 sigma detection of the spectral index runningpredicted by the simplest inflation models.

Constraining Gravitational and Cosmological Parameters with Astrophysical Data