Talk 5: 2pm: Marc Kamionkowski, "Fields, Fossils, Spins and Symmetry: New Physics from Cosmology"
That title is too long. It messes up the formatting on my blog.
This is a seminar, so it's longer and involves more background.
- The CMB is a surface map. One of the basic tools is an expansion in terms of spherical harmonics.
- The power spectrum converts the coefficients of this expansion into rotationally invariant quantities, and so is a true observable.
- Data today is so good that the oscillations in the power spectrum are unambiguous. Even without a theoretical model, we would see their presence.
Marc is emphasising the spectral index. This parameter measures how the primordial power spectrum varies with scale; it is close to, but distinct from, strict scale invariance. The departure has only been confirmed recently, and is expected from inflation.
- A sign of gravity waves/gravitation perturbations
- A direct probe of the very early universe; t ~ t(Big Bang). This is because the universe is effectively transparent to gravity waves.
- Polarisation also sensitive to CP-violation, through E-B cross-correllation. Arises for some generic evolving field coupling to the SM (photon).
- So it's a pity we haven't found them yet.
- A number of ways the inflationary (Gaussian) prediction can be modified.
- Gravitational lensing is one possibility, now observed by correlating with galactic surveys; and more recently just from the CMB itself.
Departures from (Statistical) Isotropy:
- Long an assumption, we can now actually test this hypothesis.
- Models exist which predict this; might be worth looking at some of these.
- Even simplest inflation models do this! Albeit suppressed, of course, from the tensor-scalar-scalar coupling.
- A Power Asymmetry. This seems to be what used to be called the cold spot.
Summary: this is a reasonable seminar, it's just all been a bit away from the stuff I'm really interested in.